ATOMIC LAYER DEPOSITION WITH PLASMA SOURCE
FIELD OF THE INVENTION
5
The present invention generally relates to deposition reactors with a plasma
source. More particularly, but not exclusively, the invention relates to such
deposition reactors in which material is deposited on surfaces by sequential selfsaturating
surface reactions.
10
BACKGROUND OF THE INVENTION
Atomic Layer Epitaxy (ALE) method was invented by Dr. Tuomo Suntola in the
early 1970's. Another generic name for the method is Atomic Layer Deposition
15 (ALD) and it is nowadays used instead of ALE. ALD is a special chemical
deposition method based on the sequential introduction of at least two reactive
precursor species to a substrate. The substrate is located within a reaction space.
The reaction space is typically heated. The basic growth mechanism of ALD relies
on the bond strength differences between chemical adsorption (chemisorption)
20 and physical adsorption (physisorption). ALD utilizes chemisorption and eliminates
physisorption during the deposition process. During chemisorption a strong
chemical bond is formed between atom(s) of a solid phase surface and a molecule
that is arriving from the gas phase. Bonding by physisorption is much weaker
because only van der Waals forces are involved. Physisorption bonds are easily
25 broken by thermal energy when the local temperature is above the condensation
temperature of the molecules.
The reaction space of an ALD reactor comprises all the heated surfaces that can
be exposed alternately and sequentially to each of the ALD precursor used for the
30 deposition of thin films. A basic ALD deposition cycle consists of four sequential
steps: pulse A, purge A, pulse B and purge B. Pulse A typically consists of metal
precursor vapor and pulse B of non-metal precursor vapor, especially nitrogen or
oxygen precursor vapor. Inactive gas, such as nitrogen or argon, and a vacuum
pump are used for purging gaseous reaction by-products and the residual reactant
molecules from the reaction space during purge A and purge B. A deposition
sequence comprises at least one deposition cycle. Deposition cycles are repeated
until the deposition sequence has produced a thin film of desired thickness.
5
Precursor species form through chemisorption a chemical bond to reactive sites of
the heated surfaces. Conditions are typically arranged in such a way that no more
than a molecular monolayer of a solid material forms on the surfaces during one
precursor pulse. The growth process is thus self-terminating or saturative. For
10 example, the first precursor can include ligands that remain attached to the
adsorbed species and saturate the surface, which prevents further chemisorption.
Reaction space temperature is maintained above condensation temperatures and
below thermal decomposition temperatures of the utilized precursors such that the
precursor molecule species chemisorb on the substrate(s) essentially intact.
15 Essentially intact means that volatile ligands may come off the precursor molecule
when the precursor molecules species chemisorb on the surface. The surface
becomes essentially saturated with the first type of reactive sites, i.e. adsorbed
species of the first precursor molecules. This chemisorption step is typically
followed by a first purge step (purge A) wherein the excess first precursor and
20 possible reaction by-products are removed from the reaction space. Second
precursor vapor is then introduced into the reaction space. Second precursor
molecules typically react with the adsorbed species of the first precursor
molecules, thereby forming the desired thin film material. This growth terminates
once the entire amount of the adsorbed first precursor has been consumed and
25 the surface has essentially been saturated with the second type of reactive sites.
The excess of second precursor vapor and possible reaction by-product vapors
are then removed by a second purge step (purge B). The cycle is then repeated
until the film has grown to a desired thickness. Deposition cycles can also be more
complex. For example, the cycles can include three or more reactant vapor pulses
30 separated by purging steps. All these deposition cycles form a timed deposition
sequence that is controlled by a logic unit or a microprocessor.
Thin films grown by ALD are dense, pinhole free and have uniform thickness. For
example, aluminum oxide grown by thermal ALD from trimethylaluminum (CH3)3AI,
also referred to as TMA, and water at 250 - 300 "C has usually about 1% nonuniformity
over the 100 - 200 mm diameter wafer. Metal oxide thin films grown by
ALD are suitable for gate dielectrics, electroluminescent display insulators, fill
5 layers for magnetic read head gaps, capacitor dielectrics and passivation layers.
Metal nitride thin films grown by ALD are suitable for diffusion barriers, e.g., in dual
damascene structures.
Precursors suitable for ALD processes in various ALD reactors are disclosed, for
10 example, in review article R. Puurunen, "Surface chemistry of atomic layer
deposition: A case study for the trimethylaluminium/water process", J. Appl. Phys.,
97 (2005), p. 121301, which is incorporated herein by reference.
The use of radicals in ALD processes may achieve some advantages, such as the
15 possibility to use thermally sensitive substrates at very low deposition
temperatures. In a plasma ALD reactor, radicals are generated by a plasma
source. The use of a plasma source, however, may cause certain requirements or
specific problems for the deposition reactor.
20 SUMMARY
According to a first example aspect of the invention there is provided a method
comprising:
operating a plasma atomic layer deposition reactor configured to deposit material
25 in a reaction chamber on at least one substrate by sequential self-saturating
surface reactions; and
allowing gas from an inactive gas source to flow into a widening radical in-feed
part opening towards the reaction chamber substantially during a whole deposition
cycle.
30
The expression "allowing. ..to flow" may in practice mean "guiding", "conducting" or
"guiding to flow".
In certain embodiments, the deposition reactor is a plasma enhanced atomic layer
deposition reactor, a PEALD reactor. In certain embodiments, the deposition
reactor comprises a plasma source on the top side of the reactor chamber. In
certain embodiments, the plasma source is an inductively coupled plasma source.
5 In certain embodiments, the plasma source produces radicals used as reactants in
the deposition reactor. In certain embodiments, the activated species output of the
plasma source consists of radicals. In these embodiments, the activated species
output is radicals without substantially containing ions.
10 In certain embodiments, the plasma atomic layer deposition reactor (plasma ALD
reactor) may be used for both plasma ALD and thermal ALD. The in-feed lines for
thermal ALD may be separate from the plasma ALD source line via which radicals
are guided into the reaction chamber.
15 A deposition process consists of one or more consecutive deposition cycles. Each
deposition cycle may consist of a thermal ALD period followed by a plasma ALD
period or a plasma ALD period followed by a thermal ALD period. Each plasma
ALD period may substantially consist of a plasma ALD pulse period (radical
generation period) and a subsequent plasma ALD purge period. Similarly, each
20 thermal ALD period may substantially consist of a thermal ALD pulse period and a
subsequent thermal ALD purge period. In certain embodiment, each ALD cycle
may comprise more than two pulse periods (which may be followed by respective
purge periods).
25 In certain embodiments, the method comprises:
allowing gas from the inactive gas source to flow into the radical in-feed part via a
plasma source during a plasma precursor pulse period of a plasma atomic layer
deposition period, the gas during that pulse period functioning as carrier gas for
generated radicals.
30
In certain embodiments, the method comprises:
allowing gas from the inactive gas source to flow into the radical in-feed part via
the plasma source during a purge period of a plasma atomic layer deposition
period, the gas during that purge period functioning as purge and inert shield gas.
In certain embodiments, the method comprises:
allowing gas from the inactive gas source to flow into the radical in-feed part via
5 the plasma source both during a plasma atomic layer deposition period and during
a thermal atomic layer deposition period.
In certain embodiments, the method comprises:
allowing gas from an inactive gas source to flow into the radical in-feed part via a
10 route that bypasses the plasma source.
In certain embodiments, the method comprises:
allowing gas from the inactive gas source to flow into the radical in-feed part via
both a route travelling via the plasma source and via another route bypassing the
15 plasma source during the plasma atomic layer deposition period.
In certain embodiments, the method comprises:
allowing gas from the inactive gas source to flow into the radical in-feed part only
via the route bypassing the plasma source during the thermal atomic layer
20 deposition period, and
guiding gas from the inactive gas source that flows via the plasma source into an
evacuation line during that period.
In certain embodiments, the method comprises:
25 guiding inert gas towards the reaction chamber via thermal atomic layer deposition
in-feed line(s) during the plasma atomic layer deposition period, the thermal
atomic layer deposition in-feed line(s) being separate from plasma source line(s)
via which radicals are guided into the reaction chamber during the plasma atomic
layer deposition period.
30
Accordingly, in certain embodiments the deposition reactor may comprise two
routes from an inactive gas source to the in-feed part, while in some other
embodiments only a singly route is implemented. In certain embodiments, the
plasma source may be separated from the reaction chamber by a gate valve or a
comparable closing member closing the route via the plasma source when needed
so that then the route does not continue via the in-feed part into the reaction
chamber, but bypasses the reaction chamber altogether.
5
In certain embodiments, the method comprises using a deformable in-feed part
which is deformable between a contracted shape and an extended shape by at
least one mechanical actuator.
10 In certain embodiments, a substrate holder carrying at least one substrate is
mechanically coupled to the deformable in-feed part, and the method comprises:
causing by deforming said deformable in-feed part said substrate holder carrying
at least one substrate to lift into an upper position for loading or unloading.
15 According to a second example aspect of the invention there is provided a plasma
atomic layer apparatus, comprising:
a gas line from an inactive gas source to a widening radical in-feed part opening
towards a reaction chamber; and
a control system configured to allow gas from the inactive gas source to flow into
20 in-feed part substantially during a whole deposition cycle, and
the plasma atomic layer deposition reactor being configured to deposit material in
the reaction chamber on at least one substrate by sequential self-saturating
surface reactions.
25 In certain embodiments, the apparatus or control system is configured to allow gas
from the inactive gas source to flow into the radical in-feed part via a plasma
source during a plasma precursor pulse period of a plasma atomic layer deposition
period, the gas during that pulse period functioning as carrier gas for generated
radicals.
30
In certain embodiments, the apparatus or control system is configured to allow gas
from the inactive gas source to flow into the radical in-feed part via the plasma
source during a purge period of a plasma atomic layer deposition period, the gas
during that purge period functioning as purge and inert shield gas.
In certain embodiments, the apparatus or control system is configured to allow gas
from the inactive gas source to flow into the radical in-feed part via the plasma
5 source both during a plasma atomic layer deposition period and during a thermal
atomic layer deposition period.
In certain embodiments, the apparatus or control system is configured to allow gas
from an inactive gas source to flow into the radical in-feed part via a route that
10 bypasses the plasma source.
In certain embodiments, the apparatus or control system is configured to allow gas
from the inactive gas source to flow into the radical in-feed part via both a route
travelling via the plasma source and via another route bypassing the plasma
15 source during the plasma atomic layer deposition period.
In certain embodiments, the apparatus or control system is configured to:
allow gas from the inactive gas source to flow into the radical in-feed part only via
the route bypassing the plasma source during the thermal atomic layer deposition
20 period; and
guide gas from the inactive gas source that flows via the plasma source into an
evacuation line during that period.
In certain embodiments, the apparatus or control system is configured to guide
25 inert gas towards the reaction chamber via thermal atomic layer deposition in-feed
line(s) during the plasma atomic layer deposition period, the thermal atomic layer
deposition in-feed line(s) being separate from plasma source line(s) via which
radicals are guided into the reaction chamber during the plasma atomic layer
deposition period.
30
In certain embodiments, said in-feed part defining or forming the expansion space
is variable in its dimensions or its shape or size. In certain embodiments, said
lifting mechanism is configured to change the dimensions of said in-feed part.
In certain embodiments, said in-feed part is a part via which radicals enter the
reaction chamber. In certain embodiments, said in-feed part has a contracted
shape and an extended shape, the transition between these shapes being
5 operated by a lifting mechanism (an elevator or similar). The elevator may be
configured to push or pull said in-feed part from said extended shape to said
contracted shape allowing said loading of said at least one substrate when said infeed
part is in its contracted shape. In certain embodiments, said in-feed part is
configured to deform vertically.
10
In certain embodiments, said in-feed part comprises a set of nested sub-parts or
ring-like members movable to fit within each other. The sub-parts may be hollow
from inside. The number of nested sub-parts may be two or more to form a
telescopic structure. The form of the nested sub-parts may be a truncated cone. In
15 an embodiment, where said in-feed part practically consists of two or more subparts,
at least the sub-part that is closest to the reaction space may be a truncated
cone. In certain embodiments, said in-feed part consists of two nested sub-parts.
In certain embodiments, the in-feed part is deformable, and the apparatus
20 comprises at least one mechanical actuator to deform the in-feed part between a
contracted shape and an extended shape.
In certain embodiments, a substrate holder carrying at least one substrate is
mechanically coupled to the deformable in-feed part, and wherein deforming said
25 deformable in-feed part causes said substrate holder carrying at least one
substrate to lift into an upper position for loading or unloading.
According to a third example aspect of the invention there is provided a plasma
atomic layer apparatus, comprising:
30 means for operating a plasma atomic layer deposition reactor configured to
deposit material in a reaction chamber on at least one substrate by sequential selfsaturating
surface reactions; and
means for allowing gas from an inactive gas source to flow into a widening radical
in-feed part opening towards the reaction chamber substantially during a whole
deposition cycle.
Different non-binding example aspects and embodiments of the present invention
5 have been illustrated in the foregoing. The above embodiments are used merely to
explain selected aspects or steps that may be utilized in implementations of the
present invention. Some embodiments may be presented only with reference to
certain example aspects of the invention. It should be appreciated that
corresponding embodiments may apply to other example aspects as well. Any
10 appropriate combinations of the embodiments may be formed.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example only, with reference to the
15 accompanying drawings, in which:
Figure 1
Figure 2
20
Figure 3
Figure 4
25 Figure 5
Figure 6
Figure 7
30
Figure 8
shows a general framework of a deposition reactor in accordance with
an example embodiment;
shows certain details of the deposition reactor in accordance with an
example embodiment;
shows a reaction chamber and certain related parts of the deposition
reactor in accordance with an example embodiment;
shows process instrumentation of the deposition reactor in
accordance with an example embodiment;
shows an example of a timing diagram in the example embodiment of
Fig. 4;
shows process instrumentation of a deposition reactor in accordance
with another example embodiment;
shows an example of a timing diagram in the example embodiment of
Fig. 6; and
shows a rough block diagram of a deposition reactor control system in
accordance with an example embodiment.
DETAILED DESCRIPTION
In the following description, Atomic Layer Deposition (ALD) technology is used as
an example. The purpose, however, is not to strictly limit to that technology but it
5 has to be recognized that certain embodiments may be applicable also in methods
and apparatus utilizing other comparable atomic-scale deposition technologies.
The basics of an ALD growth mechanism are known to a skilled person. Details of
ALD methods have also been described in the introductory portion of this patent
10 application. These details are not repeated here but a reference is made to the
introductory portion with that respect.
Figure 1 shows a deposition reactor (a plasma ALD reactor or similar) in a side
view. The deposition reactor comprises a reaction chamber (not shown in Fig. 1)
15 below a substrate transfer chamber inside an ALD reactor module 130. Source
gas flows via a carrier and purge gas line 101 into a plasma source 11 0 on the top
side of the reaction chamber. Radicals generated by the plasma source 110 from
the source gas flow via a reaction chamber in-feed line or plasma source line 102
towards the reaction chamber. In between the plasma source 11 0 and the reaction
20 chamber there is the substrate transfer chamber 120. At least one substrate is
loaded into the reaction chamber via the transfer chamber 120. The substrate
transfer chamber 120 comprises an interface for a load lock or similar for loading
said at least one substrate. In an example embodiment, the interface may be a
load lock flange 122, or similar, to which a load lock having a gate valve can be
25 attached. In an example embodiment, loading of the at least one substrate into the
transfer chamber may be an automated procedure. Alternatively, the at least one
substrate may be loaded manually. A larger hatch 123 integrated to the transfer
chamber is particularly suitable for manual loading and unloading in the room
pressure.
30
The plasma source line 102 from the plasma source may be closed prior to the
transfer chamber 120 by a closing member or valve 11 5, such as a gate valve or
similar (hereinafter referred to the gate valve 115), attached to the plasma source
line 102. When the valve 115 is open, radicals generated by the plasma source
11 0 from the source gas flow via the plasma source line 102 towards the reaction
chamber. The radicals flow through the transfer chamber upper flange 121 into an
expansion space (not shown in Fig. 1) that widens towards the reaction chamber.
5 This, and other additional details, is shown in more detail in Fig. 2. In an
embodiment as shown in more detail in Fig. 6 and related description, the closing
member or valve 115 may be omitted from the construction and there is a
protective inert gas (such as argon) flow from the source gas line 101 through the
plasma generator 110 towards the reaction space (331, Fig. 3) during the
10 deposition process.
The expansion space is defined or formed by an in-feed part or an assembly
comprising a set of nested sub-parts or ring-like members which are movable to fit
within each other. In the embodiment shown in Fig. 2, the number of sub-parts is
15 two. The sub-parts 241 and 242 form a telescopic structure. In the example
embodiment shown in Fig. 2 the upper sub-part 241 is attached to the transfer
chamber upper flange 121. The flange 121 may also be denoted as a vacuum
chamber flange, since a vacuum or almost a vacuum can typically be generated
into the portion of the transfer chamber that surrounds the in-feed part. In the
20 example embodiment shown in Fig. 2 the lower sub-part 242 is attached to an
expansion space flange 224 which, during deposition, is substantially leak-tightly
fitted against a reaction chamber flange 234 preventing gas leaks between the
reaction space (331, Fig. 3) and the gas space surrounding the reaction chamber
(335, Fig. 3).
25
In the embodiment shown in Fig. 2, a retractable shaft of an elevator 250 is
attached to the expansion space flange 224, or directly to the in-feed part. The
body of the elevator 250 may also be attached to the transfer chamber upper
flange 121 or to another suitable counterpart in the deposition reactor. The
30 elevator 250 may be for example an elevator which operates by means of a rigid
retractable shaft at least partially covered with bellows 251 or similar. In an
embodiment, this arrangement forms a leak-tight vertically flexible cover between
a pneumatic or a linear actuator and the expansion space flange 224 or the in-feed
part. In an embodiment, a linear feedthrough for moving the in-feed part and
expansion space flange together with the substrate holder in vacuum and
controlled from atmosphere side is used.
5 The deposition reactor shown in Fig. 2 has an optional evacuation line 207 in fluid
communication with the plasma source line 102. The evacuation line 207 is joined
to the plasma source line 102 on the portion of the plasma source line 102
between the plasma source 11 0 and the gate valve 11 5.
10 Further, the deposition reactor shown in Fig. 2 has an optional shield gas line 204
in fluid communication with the plasma source line 102. Inactive shield gas flowing
in the shield gas line prevents particle or gas flow in the upstream direction. The
shield gas line 204 is joined to the plasma source line 102 on the portion of the
plasma source line 102 after the gate valve 11 5, in an embodiment immediately
15 next to the gate valve 11 5 in the downstream direction.
In an alternative embodiment, the expansion space flange 224 is not separate
from the in-feed part but forms part of the in-feed part thus forming a bottom part
of the in-feed part. The bottom part in that embodiment functions as a rim seal
20 against the reaction chamber. On the other hand, it functions as a fixing point for
the elevator 250 (elevator shaft).
In a reaction space 331 of reaction chamber 335, as shown by Fig. 3, at least one
horizontally placed substrate 360 is supported by or lies on a substrate holder 361.
25 In an embodiment, the substrate holder comprises two separate sections with an
open gap wide enough for allowing free movement of a substrate fork between the
sections. The substrate holder 361 is attached to the expansion space flange 224
by holder supports 362. In an example embodiment, the substrate holder 361 is
configured to move together with the expansion space flange 224. In an
30 embodiment, the bottom end of the elevator bellows 251 is leak-tightly coupled up
with the shaft. Pulling the shaft within the elevator bellows 251 with the actuator
contracts the elevator bellows 251, and the at least one substrate 360 or the
substrate holder 361 can be pulled up for loading or unloading while keeping the
substrate handling area and its surroundings in vacuum. The in-feed part
comprising the sub-parts 241 and 242 contracts vertically when the sub-part 242
slides onto the smaller sub-part 241 leaving a space for loading and unloading via
the transfer chamber 120 (Fig. 1). There can be more than one elevator, such as
5 two elevators. The elevator bellows 351 of a second elevator has been shown in
Fig. 3 with dotted lines.
In an embodiment, the substrate holder 361 is detachably attachable to the
expansion space flange 224. In that way the substrate holder 361 together with the
10 at least one substrate 360 can be loaded or unloaded when pulled up. Similarly, a
batch of substrates vertically placed in a substrate holder can be loaded into and
unloaded from the deposition reactor.
Deposition of material on the at least one substrate 360 occurs by alternating
15 sequential self-saturating surface reactions in the reaction space 331 of the
reaction chamber 335. Alternately, radicals from the plasma source 110 (Figs. 1
and 2) and other precursor vapor flow to the reaction space 331 of the reaction
chamber 335. Radicals from the plasma source 110 flow as a top to bottom flow
301 via the expansion space to the reaction space 331. The other precursor vapor
20 flow either via in-feed line 371 via an example tube fitting 381 and channel 373
within the reaction chamber flange 234 or via in-feed line 372 an example tube
fitting 382 and channel 374 within the reaction chamber flange 234. In a typical
reactor construction the number of in-feed lines is for example 4 or 6. Alternatively,
the other precursor may also flow into the reaction chamber 335 via the plasma
25 source line 102 with the plasma generation shut off. Exhaust gases are removed
via an exhaust guide on the bottom to an exhaust line as indicated with the flow
direction arrow 305.
In an embodiment, the gas space between the plasma generator (plasma source
30 I 10) and the substrate holder 361 substantially consists of an open gas space so
that the majority of radicals generated by the plasma generator is capable of
arriving essentially intact to the substrate 360 without hitting any surfaces before
the substrate.
Figure 4 shows process instrumentation of the deposition reactor in accordance
with an example embodiment. An inert gas flow from an inert (or inactive) gas
source is divided into a carrier and purge gas flow that flows via the carrier and
5 purge gas line 101 and a shield gas flow that flows via the shield gas line 204. In
an embodiment, argon or helium, or similar, is used as the inert gas. The carrier
and purge gas line 101 can be opened and closed by a carrier and purge valve
410. During operation, the default position of the valve 410 is 'open'. The shield
gas line 204 can be opened and closed by a shield gas valve 416. During
10 operation, the default position of the valve 416 is 'open'. The flow rate in the carrier
and purge gas line 101 is controlled by a mass flow controller (MFC) 431, and the
flow rate in the shield gas line 204 is controlled by a mass flow controller 432. The
shield gas line 204 joins to the plasma source line 102 downstream the gate valve
115. During operation, the default position of the gate valve is 'open'. The
15 combined flow flows via the plasma source line 102 and enters the reaction
chamber 335 via the expansion space 425. A vacuum pump 438 is used for
purging exhaust gases from the reaction space 331 into the exhaust line. The
pressure transducer PT is used for verifying that the plasma source line pressure
is in a suitable range for operating the remote plasma generator.
20
Downstream the carrier and purge valve 410 before entering the plasma source
110, the carrier and purge gas flows through plasma source precursor pulsing
valves 41 1-414. In an embodiment, the valves are three-way valves. The carrier
and purge gas flows into a first input of a pulsing valve and outputs via an output.
25 In this context a precursor that can flow via a pulsing valve 41 1-414 into the carrier
and purge gas line 101 and can subsequently be used to generate radicals in the
plasma source 110 is denoted as plasma source precursor. The desired plasma
source precursor, depending on the applied deposition cycle, is guided via an
MFM (Mass Flow Meter) and through a capillary or a needle valve into a second
30 input of a corresponding pulsing valve. During operation, the default position of
valves 41 1-414 is that the first input and output are 'open', the second input is
'closed' and will be opened only during plasma precursor pulse periods of a
selected plasma source precursor.
In the embodiment shown in Fig. 4, nitrogen gas, hydrogen gas, ammonia gas and
oxygen gas serve as examples of plasma source precursors. The mass flow meter
MFM 441 measures the flow rate of nitrogen gas from a nitrogen gas source
5 through a capillary or needle valve 451 to the nitrogen pulsing valve 41 1. Similarly,
the MFM 442 measures the flow rate of hydrogen gas from a hydrogen gas source
through a capillary or needle valve 452 to the hydrogen pulsing valve 412, the
MFM 443 measures the flow rate of ammonia gas from an ammonia gas source
through a capillary or needle valve 453 to the ammonia pulsing valve 413, and the
10 MFM 444 measures the flow rate of oxygen gas from an oxygen gas source
through a capillary or needle valve 454 to the oxygen pulsing valve 414. MFMs
441 - 444 are used for verifying that the mass flow rate of the plasma source
precursor settles to a desired value controlled with the pressure of the plasma
source precursor to the upstream of the capillary or needle valve 451 - 454 and
15 with the orifice size of the capillary or with the adjustment of needle valve 451 -
454. When the second input of a pulsing valve is open, the corresponding plasma
source precursor is mixed with the carrier gas flow and flows further towards the
plasma source 11 0 for radical generation.
20 The evacuation line 207 joined to the plasma source line 101 downstream of the
plasma source 11 0 and upstream of the gate valve 11 5 is not used during normal
operation. Accordingly, the default position of an evacuation valve 417 (by which
the evacuation line 207 can be opened and closed) is 'closed'.
25 In Figure 4 there are also shown the other in-feed lines 371 and 372 visible in Fig.
3 via which other precursor vapor may flow into the reaction chamber 335 during,
for example, a thermal ALD period.
Figure 5 shows the operation of the deposition reactor of Figure 4 by means of a
30 timing diagram in accordance with an example embodiment. The deposition
process is basically formed by repeated deposition cycles. At time instant tl, the
gate valve 115 of the plasma source line 102 is opened. The gate valve 11 5
remains opened during the whole deposition process. At time instant t2, the
isolation valve (carrier and purge valve 410) of the carrier and purge gas line 101
is opened. The MFC 431 of the carrier and purge gas line 101 is set to a
processing value, e.g., 50 sccm. At time instant t3, the MFC 432 of the shield gas
line 204 is set from a high value to a low value, e.g., 20 sccm. The time between t3
5 and t4 can be used for purging the reaction chamber 335. At time instant t4, the
pulsing valve of a (non-metal) plasma source precursor is opened. In the example
shown in Figure 5, hydrogen gas is used as the plasma source precursor, so at
time instant t4 it is the pulsing valve 412 that is opened. At time instant t5, the
power of the plasma generator (plasma source 110) is increased to the radical
10 generation level, e.g., 2000 W. In an embodiment, the power herein mentioned is
radio frequency (RF) power. Radicals are generated during the time between t5
and t6. In other words, between time instants t5 and t6 a plasma ALD phase is
carried out. At time instant t6, the power of the plasma generator (plasma source
11 0) is lowered to a level where radicals are not generated, e.g., to a power that is
15 less than 100 W. At time instant t7, the pulsing valve (here: valve 412) of the
plasma source precursor is closed. At time instant t8, the MFC 432 of the shield
gas line 204 is set from a low value to a high value. The time between t7 and tg can
be used for purging the reactor chamber 335. At time instant tg, second precursor
vapor is guided into the reaction chamber 335. In the present embodiment, the
20 second precursor is a metal precursor. Between tg and tlo the second precursor
pulse phase is carried out. The time between tg and tlo may consist of the second
precursor pulse and the third purge period for removing surplus second precursor
molecules and reaction byproducts from the reaction space 331 while the mass
flow rate of the shield gas through the shield gas line 204 is at the high value for
25 preventing the backstreaming of reactive molecules towards the gate valve 115
and the remote plasma generator 110. This can be carried out as the as-such
known conventional thermal ALD method. The deposition cycle formed by the
purge period between t3 and t4, the plasma ALD phase between t5 and t6, the
second purge period between t7 and tg, and the thermal ALD phase between tg
30 and tlo is repeated until a desired thickness of material has grown onto the at least
one substrate in the reaction chamber 335. In the end, at time instant tll, the
carrier and purge valve 410 is closed, and the MFC 431 of the carrier and purge
gas line 101 is set to a zero value. Finally, the gate valve 115 is closed at time
instant tI2.
An alternative embodiment concerns, for example, situations in which for a certain
reason the plasma source line 102 is desired to be closed by the gate valve 115
5 during a deposition process. This can occur, for example, during the thermal ALD
phase, or if the reactor is desired to carry out a deposition process with thermal
ALD phases only. In these embodiments, the route via the pulsing valves 41 1-414
and the plasma source 110 to the reaction space 331 is closed. Since a constant
pressure should preferably be maintained in the plasma source 110, the
10 evacuation line valve 417 is opened and a gas flow through the plasma source
110 is guided via the evacuation line 207 directly to the exhaust line to maintain a
constant pressure. Shield gas flowing from the shield gas line 204 forms a
shielding buffer preventing particle and gas flow from rising from the direction of
the reaction chamber 335 into the direction of the gate valve 11 5.
15
Figure 6 shows process instrumentation of the deposition reactor in accordance
with another example embodiment. The embodiment shown in Figure 6 otherwise
corresponds to the embodiment shown in Figure 4 except that it does not contain
the gate valve 11 5, the related evacuation line 207, the shield gas line 204 and the
20 carrier and purge valve 41 0.
In certain embodiments, oxygen radicals generated from oxygen gas are used for
growing metal oxides, such as oxides of group 3 metals (e.g. yttrium oxide), oxides
of group 4 metals (e.g. hafnium dioxide), oxides of group 5 metals (e.g. tantalum
25 pentoxide) and oxides of group 13 metals (e.g. aluminum oxide). Ammonia
radicals generated from ammonia gas and nitrogen radicals generated from
nitrogen gas are used for growing metal nitrides, such as nitrides of group 4
metals (e.g. titanium nitride), nitrides of group 5 metals (e.g. tantalum nitride and
superconducting niobium nitride) and nitrides of group 14 elements (e.g. silicon
30 nitride). Hydrogen radicals generated from hydrogen gas are used as a reducing
agent for growing elemental thin films, such as group 4 metals (e.g. titanium),
group 5 metals (e.g. tantalum), group 6 metals (e.g. tungsten) and group 11
metals (e.g. silver). Volatile hydrocarbons are utilized for generating hydrocarbon
radicals for growing metal carbides, such as carbides of group 4 metals (e.g.
titanium carbide).
Figure 7 shows the operation of the deposition reactor of Figure 6 by means of a
5 timing diagram in accordance with an example embodiment. At time instant tA the
MFC 431 of the carrier and purge gas line 101 is set to a processing value,
preferably in the range of 10 - 200 sccm, more preferably in the range of 20 - 100
sccm, e.g., 50 sccm. The time between t~ and tc is used for pulsing metal
precursor vapor, e.g. trimethylaluminum (TMA), in thermal ALD mode to the
10 reaction space 331 heated to a temperature selected from a range of
approximately 50 - 500 "C, e.g. 200 "C in case of TMA used as a metal precursor.
The time between tc and tD is used for purging the reaction space 331 with inert
gas that consists of argon or helium gas from the plasma source line 102 and
nitrogen gas from the in-feed lines 371, 372. At time instant tD, the pulsing valve of
15 a (non-metal) plasma source precursor is opened. Oxygen gas is selected from
the available plasma source gases in Figure 6, so at time instant tD it is the pulsing
valve 414 that is opened. At time instant tE, the power of the plasma generator
(plasma source 110) is increased to the radical generation level, to the RF power
selected from a range of 100 - 3000 W, e.g., 2000 W in case of oxygen radical
20 generation. Radicals are generated during the time between tE and tF. In other
words, between time instants tE and tF a plasma ALD phase is carried out. At time
instant t ~th, e power of the plasma generator (plasma source 110) is lowered to a
level where radicals are not generated, preferably to a power that is less than 100
W, e.g. 0 W. At time instant tG, the pulsing valve (here: oxygen gas valve 414) of
25 the plasma source precursor is closed. The time between t~ and t~ is used for
purging the system with inert gas. The deposition cycle from the time instant tB to
the time instant t~ consisting of the metal precursor pulse, purge, radical precursor
pulse and purge is repeated until a thin film of desired thickness is grown on the
substrate 360.
30
It is to be noted that several variants of the embodiments presented herein may be
implemented. In a construction shown in Fig. 4 the deposition cycle may be
implemented in the order shown in Fig. 5, or for example, in the order shown in
Fig. 7.
In certain embodiments, gas is guided to flow from the inactive gas source into the
radical in-feed part (or expansion space 425) via the plasma generator (plasma
5 source 110) during the plasma precursor pulse period of the plasma ALD period,
the gas during that pulse period functioning as carrier gas for generated radicals,
and in certain embodiments, gas is guided to flow from the inactive gas source into
the expansion space 425 via the plasma generator during the purge period of the
plasma ALD period, the gas during that purge period functioning as inert or purge
10 gas. In certain embodiments, gas is guided in this way during both of these
periods. During both of these periods, gas from the inactive gas source is
additionally guided in certain embodiments into the expansion space 425 via the
shield gas line 204. During, for example, a thermal ALD period, gas from the
inactive gas source is guided in certain embodiments into the expansion space
15 425 via both routes, or via the shield gas line 204 only (in the event, the route from
the plasma generator to the expansion space 425 is, for example, closed). Also,
whenever the route from the plasma generator to the expansion space 425 is
otherwise closed, gas from the inactive gas source is guided in certain
embodiments during these periods into the expansion space 425 via the shield
20 gas line 204 causing a continuous inert gas flow into the expansion space 425 and
preventing the backstreaming effect. If the route from the plasma generator to the
expansion space 425 is closed, gas from the inactive gas source that flows via the
plasma generator is guided in certain embodiments into an evacuation line during
that period so as to maintain a constant pressure in the plasma generator.
25
The following experimental example further demonstrates the operation of
selected example embodiments.
Example 1
30
A 100-mm silicon wafer was loaded to the reaction chamber 335 with the dual
elevator shown in Figure 3. The instrumentation of the deposition reactor
according to Figure 6 and the timing diagram of Figure 7 were used for growing
aluminum oxide A1203 from trimethyl aluminum TMA and water H20 on the silicon
wafer at 200 "C. The flow rate of argon gas was 30 sccm through the carrier and
purge gas line 101. The TMA pulse length was 0.1 s followed by the 6 s purge.
Oxygen gas pulsing valve 414 was opened and 50 sccm of oxygen gas was
5 flowing through the pulsing valve 414 to the remote plasma generator 11 0. The RF
power was increased from 0 W to 2500 W to switch on the plasma and kept at the
2500 W level for 6 s. After that the RF power was lowered from 2500 W to 0 W to
switch off the plasma. Next the oxygen gas valve was closed and the system was
purged with inert gas for 10 s. The deposition cycle was repeated until a 36-nm
10 A1203 thin film was grown. As a result, the I-sigma non-uniformity of the thin film
thickness measured with an ellipsometer from 49 points was only 1.3 %.
In an example embodiment, the deposition reactor described herein is a computercontrolled
system. A computer program stored into a memory of the system
15 comprises instructions, which upon execution by at least one processor of the
system cause the deposition reactor to operate as instructed. The instructions may
be in the form of computer-readable program code. Fig. 8 shows a rough block
diagram of a deposition reactor control system 800. In a basic system setup
process parameters are programmed with the aid of software and instructions are
20 executed with a human machine interface (HMI) terminal 806 and downloaded via
Ethernet bus 804 to a control box 802. In an embodiment, the control box 802
comprises a general purpose programmable logic control (PLC) unit. The control
box 802 comprises at least one microprocessor for executing control box software
comprising program code stored in a memory, dynamic and static memories, I10
25 modules, AID and DIA converters and power relays. The control box 802 sends
electrical power to pneumatic controllers of the valves of the deposition reactor,
and has two-way communication with mass flow controllers, and controls the
operation of the plasma source and radical generation and the elevator, as well as
otherwise controls the operation of the deposition reactor. The control box 802
30 may measure and relay probe readings from the deposition reactor to the HMI
terminal 806. A dotted line 816 indicates an interface line between the deposition
reactor parts and the control box 802.
The foregoing description has provided by way of non-limiting examples of
particular implementations and embodiments of the invention a full and informative
description of the best mode presently contemplated by the inventors for carrying
out the invention. It is however clear to a person skilled in the art that the invention
5 is not restricted to details of the embodiments presented above, but that it can be
implemented in other embodiments using equivalent means without deviating from
the characteristics of the invention.
Furthermore, some of the features of the above-disclosed embodiments of this
10 invention may be used to advantage without the corresponding use of other
features. As such, the foregoing description should be considered as merely
illustrative of the principles of the present invention, and not in limitation thereof.
Hence, the scope of the invention is only restricted by the appended patent claims.
Claims
1. A method comprising:
operating a plasma atomic layer deposition reactor configured to deposit
5 material in a reaction chamber on at least one substrate by sequential selfsaturating
surface reactions; and
allowing gas from an inactive gas source to flow into a widening radical infeed
part opening towards the reaction chamber substantially during a whole
deposition cycle.
10
2. The method of claim 1, comprising:
allowing gas from the inactive gas source to flow into the radical in-feed part
via a plasma source during a plasma precursor pulse period of a plasma
atomic layer deposition period, the gas during that pulse period functioning as
15 carrier gas for generated radicals.
3. The method of claim 1 or 2, comprising:
allowing gas from the inactive gas source to flow into the radical in-feed part
via the plasma source during a purge period of a plasma atomic layer
20 deposition period, the gas during that purge period functioning as purge and
inert shield gas.
4. The method of any preceding claim, comprising:
allowing gas from the inactive gas source to flow into the radical in-feed part
25 via the plasma source both during a plasma atomic layer deposition period
and during a thermal atomic layer deposition period.
5. The method of any preceding claim, comprising:
allowing gas from an inactive gas source to flow into the radical in-feed part
30 via a route that bypasses the plasma source.
6. The method of claim 1, comprising:
allowing gas from the inactive gas source to flow into the radical in-feed part
via both a route travelling via the plasma source and via another route
bypassing the plasma source during the plasma atomic layer deposition
period.
5 7. The method of claim 1 or 6, comprising:
allowing gas from the inactive gas source to flow into the radical in-feed part
only via the route bypassing the plasma source during the thermal atomic
layer deposition period, and
guiding gas from the inactive gas source that flows via the plasma source
10 into an evacuation line during that period.
8. The method of any preceding claim, comprising:
guiding inert gas towards the reaction chamber via thermal atomic layer
deposition in-feed line(s) during the plasma atomic layer deposition period, the
15 thermal atomic layer deposition in-feed line(s) being separate from plasma
source line(s) via which radicals are guided into the reaction chamber during
the plasma atomic layer deposition period.
9. The method of any preceding claim, comprising:
20 using a deformable in-feed part which is deformable between a contracted
shape and an extended shape by at least one mechanical actuator.
10.The method of claim 9, wherein a substrate holder carrying at least one
substrate is mechanically coupled to the deformable in-feed part, the method
25 comprising:
causing by deforming said deformable in-feed part said substrate holder
carrying at least one substrate to lift into an upper position for loading or
unloading.
30 11 .A plasma atomic layer apparatus, comprising:
a gas line from an inactive gas source to a widening radical in-feed part
opening towards a reaction chamber; and
a control system configured to allow gas from the inactive gas source to
flow into in-feed part substantially during a whole deposition cycle, and
the plasma atomic layer deposition reactor being configured to deposit
material in the reaction chamber on at least one substrate by sequential selfsaturating
surface reactions.
5
12.The apparatus of claim 11, wherein the control system is configured to allow
gas from the inactive gas source to flow into the radical in-feed part via a
plasma source during a plasma precursor pulse period of a plasma atomic
layer deposition period, the gas during that pulse period functioning as carrier
10 gas for generated radicals.
13.The apparatus of claim 11 or 12, wherein the control system is configured to
allow gas from the inactive gas source to flow into the radical in-feed part via
the plasma source during a purge period of a plasma atomic layer deposition
15 period, the gas during that purge period functioning as purge and inert shield
gas.
14.The apparatus of any preceding claim 11 - 13, wherein the control system is
configured to allow gas from the inactive gas source to flow into the radical in-
20 feed part via the plasma source both during a plasma atomic layer deposition
period and during a thermal atomic layer deposition period.
15.The apparatus of any preceding claim 11 - 14, wherein the control system is
configured to allow gas from an inactive gas source to flow into the radical in-
25 feed part via a route that bypasses the plasma source.
16.The apparatus of claim 11, wherein the control system is configured to allow
gas from the inactive gas source to flow into the radical in-feed part via both a
route travelling via the plasma source and via another route bypassing the
30 plasma source during the plasma atomic layer deposition period.
17.The apparatus of claim 1 1 or 16, wherein the control system is configured to:
allow gas from the inactive gas source to flow into the radical in-feed part
only via the route bypassing the plasma source during the thermal atomic
layer deposition period; and
guide gas from the inactive gas source that flows via the plasma source into
an evacuation line during that period.
5
18.The apparatus of any preceding claim 1 1 - 17, wherein the control system is
configured to guide inert gas towards the reaction chamber via thermal atomic
layer deposition in-feed line(s) during the plasma atomic layer deposition
period, the thermal atomic layer deposition in-feed line(s) being separate from
10 plasma source line(s) via which radicals are guided into the reaction chamber
during the plasma atomic layer deposition period.
19.The apparatus of any preceding claim 11-18, wherein said in-feed part is
deformable, and the apparatus comprises at least one mechanical actuator to
15 deform the in-feed part between a contracted shape and an extended shape.
20.The apparatus of claim 19, wherein a substrate holder carrying at least one
substrate is mechanically coupled to the deformable in-feed part, and wherein
deforming said deformable in-feed part causes said substrate holder carrying
20 at least one substrate to lift into an upper position for loading or unloading.