With development of display technology, a display device with large size, high quality and low cost is the trend. Quality of a color filter which is a major component of a display device (for example, a TFT-LCD display device) determines the display effect of the display device.
At present, a proximity exposure machine optical system is mostly used to perform exposure when fabricating a color filter. Specifically, as shown in FIG. 1, the above mentioned optical system includes an exposure lamp 101, a first planar mirror 102, a fly eye lens 103, a concave mirror 104 and a second planar mirror 105, and further includes a mask plate 106, a substrate 107, an exposure region 108 and a photoresist (not shown in FIG. 1). In this optical system, the exposure lamp 101 is mainly used to emit a light beam to the first planar mirror 102, the first planar mirror 102 is mainly used to reflect an incident light beam onto the fly eye lens 103, the fly eye lens 103 is mainly used to split the received light beam into narrow light beams and then refract the narrow light beams onto the concave mirror 104, the concave mirror 104 is mainly used to reflect the received light beam onto the second planar mirror 105, and the second planar mirror 105 is mainly used to reflect the received light beam onto the mask plate 106. Generally, the concave mirror 104 and the second planar mirror 105 are designed based on a principle that reflectivities of light at respective positions on the mirror are equal so as to guarantee the uniformity of light at different positions in the optical system.
Here, the fly eye lens 103 may include a first lens assembly and a second lens assembly. The first lens assembly includes a plurality of lenses forming a first lens face, and the second lens assembly includes a plurality of lenses forming a second lens face. The first lens face is used to split a broad light beam reflected from the first planar mirror 102 into narrow light beams and then refract the narrow light beams onto the second lens face, and the second lens face is used to dispersively refract the received narrow light beams onto the concave mirror 104. In general, there is positional correspondence existing between the fly eye lens 103 and the concave mirror 104, that is, a lens closer to the center on the second lens face contributes more illuminance to a point closer to the center on a surface of the concave mirror 104 but contributes less illuminance to a point farther from the center on a surface of the concave mirror 104; on the contrary, a lens farther from the center on the second lens face contributes more illuminance to a point farther from the center on the surface of the concave mirror 104 but contributes less illuminance to a point closer to the center on the surface of the concave mirror 104.
When performing the proximity exposure, generally, the illuminance of incident light on the mask plate is evenly distributed, that is, illuminance at any region on the mask plate is identical. In this case, as shown in FIG. 2, when fabricating a color filter using a substrate 201 (for example, a glass substrate), a mask plate 202 and a photoresist 203, a distance between the mask plate 202 before being bent and the substrate 201 ranges from one hundred micrometers to several hundred micrometers. As such, as to the mask plate, it is bent when performing the exposure, which causes the exposure distance in a vertical direction between the substrate 201 and the central region of the mask plate 202 to differ from that between the substrate 201 and an edge region of the mask plate 202. For example, as shown in FIG. 2, the exposure distance G2 between the substrate 201 and the central region of the mask plate 202 is smaller than the exposure distance G1 between the substrate 201 and the edge region of the mask plate 202. During a usual fabricating process, since the proximity exposure machine optical system is influenced by factors such as diffraction angle and light parallelism when performing the exposure, the critical dimension (CD) of the pattern exposed on the substrate 201 is increased as the exposure distance of each region is increased (as shown in FIG. 2). Thus, in a case where the illuminance is fixed, since the exposure distance in the central region is shorter than that in an edge region, the critical dimension of the pattern exposed on the central region is smaller than that of the pattern exposed on an edge region, that is, the critical dimensions of the exposed patterns are not uniform (for example, CD2>CD1, as shown in FIG. 1). In other words, the critical dimensions of the patterns exposed by the above-mentioned optical system have a poor uniformity.
It can be seen from the above fabricating manner that when the proximity exposure machine optical system performs the exposure, the bending of the mask plate causes exposure distances in respective regions to vary so that the critical dimensions of the patterns exposed on the substrate have a poor uniformity and the quality of the color filter is further affected.