DESCRIPTION TITLE OF THE INVENTION: EXPOSURE METHOD AND EXPOSURE DEVICE TECHNICAL FIELD [0001] The present invention relates to an exposure method and an exposure device for producing color filter substrates for use in liquid crystal display devices and the like. BACKGROUND ART [0002] In recent years, increase in size of liquid crystal display devices leads to increase in size of color filters for use in the liquid crystal display devices. In a process of producing a color filter, patterning is performed by using a photolithography method to form colored layers. However, since a large exposure mask is very expensive, a problem arises that production cost for the color filters may be increased. Thus, novel exposure methods using small masks have been variously suggested. CITATION LIST PATENT LITERATURE [0003] Patent Literature 1: Japanese Laid-Open Patent Publication No. 2008-216593 Patent Literature 2: Japanese Laid-Open Patent Publication No. 2007-121344 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [0004] As an exposure method using a small mask, a method (hereinafter, referred to as a "small mask continuous exposure mode") for repeatedly performing an exposure of the entire surface of a substrate to be exposed to light while conveying the substrate, by using an exposure machine in which a photomask having a size smaller than a size of a display pixel area of a color filter substrate is mounted to an exposure head, is known. [0005] FIG. 13 illustrates a substrate exposure method using the small mask continuous exposure mode. In the following description, a direction in which the substrate is conveyed is the Y-axis forward direction. [0006] Firstly, a substrate 920 having a resist applied thereto is positioned below a blinking light source (not shown) and a photomask 910. In the photomask 910, a plurality of openings 911 are aligned in the X-axis direction and the Y-axis direction so as to form a matrix. Each opening 911 corresponds to one colored pixel on the color filter substrate. Further, the plurality of openings corresponding to colored pixels of the same color are formed in the X-axis direction. Subsequently, the substrate 920 is conveyed in the Y-axis forward direction (a direction indicated by an arrow in the drawing), and the resist on the substrate 920 is exposed to light through the openings 911 at a position shown in FIG. 13(a). Next, the substrate 920 is conveyed to a position (FIG. 13(b)) at which none of the openings 911 are located above exposed patterns 921. In this position, the resist on the substrate 920 is exposed to light through the openings 911, and the exposed patterns 921 formed as a plurality of dots aligned in the X-axis direction are provided at regular intervals in the Y-axis direction. [0007] In each exposure to light, alignment between the photomask 910 and the substrate 920 is performed based on images which are taken by a camera and represent the photomask and a pattern on the substrate 920. More specifically, the photomask 910 has formed therein a pattern following opening 912 used for detecting a position of the substrate 920, and a position of the substrate 920 is detected based on an image pattern of the substrate 920, which is taken through the pattern following opening 912. The position of the photomask 910 is adjusted in the X-axis direction based on the position of the substrate 920 having been detected. As a result, a misalignment in relative position between the photomask and the substrate in the X-axis direction is corrected with a high accuracy. Further, a time at which light is to be emitted from the blinking light source is determined based on the position of the substrate 920 having been detected. [0008] As a cause of the misalignment between the photomask and the substrate, a distortion of a conveyor shaft of a substrate conveyor device, a rotation of the substrate caused by yawing of the substrate, or a rotation of the photomask mounted to an exposure head, may be considered. Hereinafter, problems caused when a misalignment in relative position between the photomask and the substrate occurs will be sequentially described for each cause of the misalignment. [0009] FIG. 14 illustrates deviation in position of a substrate, and FIG. 15 illustrates a direction in which the position of the substrate deviates. [0010] As shown in FIG. 14(a), in a substrate conveyor device 930, one side of the substrate 920 along the Y-axis direction is secured to a conveyor shaft 931a by a fixing component 932, and the other side thereof is supported by a conveyor shaft 931b. The substrate conveyor device 930 conveys the substrate 920 in the Y-axis forward direction shown in FIG. 14 in a state where the substrate 920 is held at one side thereof. [0011] When the substrate conveyor device 930 that holds only one side of the substrate 920 is used, a deviation in position of the substrate 920 is caused as indicated by dashed lines due to a distortion of the conveyor shaft 931a (FIG. 14(b)) or yawing of the substrate 920 which is being conveyed (FIG. 14(c)). The substrate 920 is secured only by the conveyor shaft 931a. Therefore, the deviation in position of the substrate 920 is caused by, for example, rotation of the substrate 920 about a point m near the conveyor shaft 93 la. When the rotation center of the substrate 920 is near the conveyor shaft 931a, the greater a distance from the point m corresponding to the rotation center is, the greater the deviation in position in the X-axis direction and the Y-axis direction is, as shown in FIG. 15. For example, at a point d which is furthest from the point m, a deviation 994 in position in the X-axis direction, and a deviation 995 in position in the Y-axis direction occur. The deviation in position in the X-axis direction can be corrected by the photomask being moved during exposure to light as described above. However, the deviation in position in the Y-axis direction cannot be corrected only by adjustment during exposure time, and the deviation may remain uncorrected. [0012] FIG. 16 is a plan view illustrating a relationship between a rotation of the substrate and deviation in position of colored layers. FIG 17 is a cross-sectional view taken along a line XVII-XVII shown in FIG 16. FIG 18 is a cross-sectional view taken along a line XVIII-XVIII shown in FIG. 16. [0013] When the substrate 920 rotates, the greater a distance from the rotation center of the substrate 920 is, the greater a misalignment between the substrate 920 and the photomask is. Thus, for example, from a portion A toward a portion B, as shown in the drawing, in a region in which exposure to light is performed by using a photomask 910a, colored layers 980 are deviated in the Y-axis backward direction. Also from the left end portions toward the right end portions in regions in which exposure to light is performed by using photomasks 910b and 910c, the colored layers 980 are similarly deviated in the Y-axis backward direction. As a result, amounts of the deviation of the colored layers 980 may be greatly changed near ajoint (dashed line) between the photomasks adjacent to each other, so that non-uniformity may occur in display. [0014] As shown in FIGS. 17 and 18, in a case where widths with which the colored layer 980 and a black matrix 960 overlap each other are different (as indicated as Wl and W2), maximal heights (height from the surface of the substrate. Indicated as HI and H2) of portions in which the colored layer and the black matrix overlap each other are different. Specifically, the greater a width with which the colored layer 980 and the black matrix 960 overlap each other is, the greater is the maximal height of the colored layer 980. In comparison between the colored layer as indicated by a solid line shown in FIG. 17 and the colored layer as indicated by a solid line shown in FIG. 18, W1