Method of manufacturing a solid state imaging device

Abstract: A solid-state imaging device comprises a color filter formed of a colored transparent material having intended spectral transmissivity characteristics. The color filter possesses plural spectral transmissivity characteristics in one layer. In this constitution, the distance from the color filter to the light sensing part is not extended, and flicker and other image characteristic defects are eliminated. Being not of laminate structure, cracks of color filter due to thermal impact are eliminated, and the reliability is enhanced. In the manufacturing method, by dry-etching of the colored transparent material, the solid-state imaging-device having a color filter is realized. Accordingly, the color filter may be formed without exposure accompanied by pattern formation, development and dyeing process, so that an efficient manufacturing method is realized.

Description: As a method of fabricating a color solid-state imaging device, recently, the method of forming a color filter directly on a substrate on which the solid-state imaging device is in the mainstream. In a small solid-state imaging device, a microlens is formed on a color filter, and the incident light is focused on the light sensing part through the microlens so as to enhance the light sensing sensitivity. A conventional solid-state imaging device and its manufacturing method are described herein while referring to the drawings. Fig. 17 is a partial cross section showing the constitution of a conventional solid-state imaging device. Figs. 18 to 31 are partial cross sections showing the method of manufacturing a conventional solid-state imaging device shown in Fig. 17 in the sequence of processes. First in Fig. 17, the constitution of a conventional solid-state imaging device is explained. Plural (e.g. four in Fig. 17) transparent resin layers 2 are formed in order to planarize the surface asperities of a solid-state imaging device substrate 1. Above a light sensing part 3 , a first color filter layer 4, a second color filter layer 5 and a third color filter layer 6 are formed. Further, a microlens 7 is formed above each light sensing part 3. In other words, the transparent resin layers 2 are formed between the light sensing part 3 and the first color filter layer 4, the second color filter layer 5, the third color filter layer 6 and the microlens 7 respectively so as to prevent mixture of colors and to planarize the first color filter layer 4, second color filter layer 5 and third color filter layer 6. In this constitution, the solid-state imaging device having a color filter is realized. Its operation is as follows. The light entering the microlens 7 in the uppermost layer is focused, and is separated into lights having spectral transmissivity characteristics individually by the first color filter layer 4, second color filter layer 5 and third color filter layer 6. The separated lights enter the light sensing part 3 beneath each color filter layer. The lights entering the light sensing part 3 are converted into electric signals, and therefore the solid-state imaging device functions to present color pictorial images. In Figs. 18 to 31, a manufacturing method of a conventional solid-state imaging device is described. Fig. 18 shows the state of planarizing the surface by forming the transparent resin layer 2 on the solid-state imaging device substrate 1. Fig. 19 shows the state of forming a dye base material layer 8 using a dye base material adding a photosensitizer containing chromium (VI) to gelatin, casein or the like. In succession, Fig. 20 shows the state of forming a patterned dye base layer 9. As shown in Fig. 19, the patterned dye base layer 9 is formed by exposing dye base material layer 8 using a mask and then developing and rinsing the dye base material layer 8. Fig. 21 shows the state of forming the first color filter layer 4 by dyeing the patterned dye base layer 9 by using a first dye solution. Fig. 22 shows the state of forming the transparent resin layer 2 on the first color filter layer 4 for the purpose of planarizing the surface asperities of the first color filter layer 4 and preventing the mixture of colors in the subsequent dye process. Fig. 23 shows the state of forming the dye base material layer 8 similarly as in Fig. 19. Fig. 24 shows the state of forming the patterned dye base layer 9. The patterned dye base layer 9 is also formed by an exposure process using a mask and then developing and rinsing the dye base material layer 8 shown in Fig. 23. Fig. 25 shows the state of forming the second color filter layer 5 by dyeing the patterned dye base layer 9 by using a second dye solution. Fig. 26 shows the state of forming the transparent resin layer 2 on the second color filter layer 5 for the purpose of planarizing the surface asperities of the second color filter layer 5 and preventing the mixture of colors in the subsequent dye process. Fig 27 shows the state of forming. the dye base material layer 8 similarly as in Fig. 23. Fig. 28 shows the state of forming the patterned dye base layer 9. The patterned dye base layer 9 is formed by an exposure process using a mask and then developing and rinsing the dye base material layer 8 shown in Fig. 27. Fig. 29 shows the state of forming the third color filter layer 6 by dyeing the patterned dye base layer 9 by using a third dye solution. Fig. 30 shows the state of forming the transparent resin layer 2 on the third color filter layer 6 for the purpose of planarizing the surface asperities of the third color filter layer 6. Fig. 31 finally shows the state of forming the microlens 7 by patterning the photosensitive material and treating the material by heating or the like. In the conventional manufacturing method of the solid-state imaging device, the dye base material adding a photosensitizer containing chromium (VI) to gelatin, casein or the like is used, which causes the problem of contamination by chromium. By repeating, still further, the steps of forming and dyeing the dye base layer by using the dye base material to form the first color filter layer 4, second color filter layer 5 and third color filter layer 6, many process steps are desirable to form the solid-state imaging device. Further, although the conventional manufacturing method includes the dyeing process, the conventional method causes the problems of swelling of the color filter layer pattern. As a result, the pattern dimensions are changed before and after dyeing. In the dyeing process, the dyeing occurs while a plurality of significant dyeing conditions are strictly controlled. These dyeing conditions include dye solution temperature, concentration, pH, dyeing time and dyeing fluctuations. Furthermore, from JP-A-57-4012 a color separating filter for a color television camera is known wherein a plurality of colored polymer layers is formed successively in a single layer. The colored polymer layers are coated by a photoresistor layer to form a mask having a prescribed pattern. A filter element is formed by removing the colored polymer layer except the part masked and the mask is then removed. After forming all filter elements an overcoat layer is provided as a protective layer. The object underlying the present invention is to provide a method which facilitates manufacturing of a solid state imaging device having excellent imaging characteristics. This object is solved by a method having the steps as set forth in claim 1. Referring now to the drawings the invention is described in detail below. Fig. 1 is a partial cross section showing the constitution of a solid-state imaging device. Figs. 2 to 16 are partial cross sections showing, first to fifteenth step of the manufacturing method of a solid-state imaging device of the invention in a sequence of processes. Fig. 1, the constitution of the solid-state imaging device is explained below. To planarize the surface asperities of the solid-state imaging device substrate 1, a first etching resistant material layer 10a is formed on the light sensing part 3. On the first etching resistant material layer 10a of a desired light sensing part 3, a first color filter layer 11, a second color filter layer 12 and a third color filter layer 13 are formed respectively in a same layer, being composed of a colored transparent material mainly made of an acrylic material. On the first color filter layer 11, second color filter layer 12 and third color filter layer 13, a second etching resistant material layer 10b is formed for the purpose of planarizing the surface and adjusting the focal length. A microlens 7 is formed thereon. The sectional shad of the microlens 7 is formed in a radius of curvature suited to the focal length up to the light sensing part 3 in a semicircular shape. In other words, each microlens 7 has substantially hemispheric shape. In such a structure, the solid-state imaging device having a color filter is realized. In this constitution, since the first color filter layer 11, second color-filter layer 12 and third color filter layer 13 are formed in a same layer, the distance between the light sensing part 3 and each color filter layer is uniform and not long. As a result, flicker and other image defects are eliminated. In addition, by the function of microlens 7 and an appropriate focal length, the incident light is focused efficiently on the light sensing part 3, and the light sensitivity of the light sensing part 3 is high, and the solid-state imaging device of excellent image characteristics is realized. Besides, the overall thickness of the color filter is not great, and the constitution is not of multiple layers as in the prior art, and cracks and other breakages due to external thermal impact are extremely reduced. Since the colored transparent material for forming the color filter is mainly made of an acrylic material, and a color filter layer which is excellent in hardening properties is realized, a solid-state imaging device with a high reliability is realized. Incidentally, when the first color filter layer 11 is composed of a colored transparent material layer having a spectral transmissivity characteristic of red, the second color filter layer 12 of green, and the third color filter 13 of blue, a solid-state imaging device having R, G, B color filters is obtained. Instead of red, green and blue, a colored transparent material having spectral transmission characteristics of complementary colors of magenta, yellow and cyan may be also used. The operation of the solid-state imaging device is described below. The light entering the microlens 7 is focused, and is separated into lights having individual spectral transmissivity characteristics by the first color filter layer 11, second color filter layer 12 and third color filter layer 13. These separated lights efficiently enter the light sensing part 3 beneath each color filter layer. In this constitution, the distance from the light sensing part 3 to the microlens 7 is equal to the focal length; and therefore as compared with the prior art, the focus is not deviated. Thus, the light enters at a higher focal density. The light entering the light sensing part 3 is converted into an electric signal, thereby operating as a solid-state imaging device for presenting a color pictorial image. Referring then to Figs. 2 to 16, the manufacturing method of a solid-state imaging device of the invention is described below. Fig. 2 shows the state of forming a first etching resistant material layer 10a for planarizing the surface asperities of the solid-state imaging device substrate 1. Here, the thickness of the first etching resistant material layer 10a is a minimum thickness necessary for planarizing the surface asperities of the solid-state imaging device substrate 1. Fig. 3 shows the state of forming a first colored material layer 14 by coating the first etching resistant material layer 10a with an acrylic material having a characteristic of, for example, red as the intended spectral transmissivity characteristic. The first colored material layer 14 is thermally cured at this step. Fig. 4 shows the state of forming a second etching resistant material layer 10b on the first colored material layer 14 and only above the intended light sensing part 3 to be used as the resist mask. The second etching resistant material layer 10b is formed by selective exposure, development and rinsing. In succession, Fig. 5 shows the state of forming a first color filter layer 11 by removing the first colored material layer 14 of other than masked by the second etching resistant material layer 10b, by dry etching using oxygen plasma as etching means. Fig. 6 shows the state of forming a second colored material layer 15 by applying an acrylic material having a characteristic of, for example, green as the spectral transmissivity characteristic on the whole surface of the first and second etching resistant material layer 10a and 10b. The second colored material layer 15 is formed, for example, by so called "short-spin coating". The short-spin coating is executed by the following steps. A resist is dropped on a wafer, and the wafer is rotated by high speed rotation in a very short time. The time is a few seconds. Then, the wafer rotation is stopped. As a result, the second colored material layer 15 on the first etching resistant material layer 10a becomes thick, and the second colored material layer 15 on the second etching resistant material layer 10b becomes thin, as shown in Fig. 6. Here, the second color material layer 15 is thermally cured. Fig. 7 shows the state of forming the second etching resistant material layer 10b on the second colored material layer 15 only above the intended light sensing part 3 to be used as the resist mask. The method of patterning on the desired position is as mentioned above. Fig. 8 shows the state of forming a second color filter layer 12 by removing the second colored material layer 15 other than the part masked by the second etching resistant material layer 10b, by dry etching as in Fig. 5, in the state in Fig. 7. Fig. 9 shows the state of forming a third colored material layer 16, by applying an acrylic material having a characteristic of, for example, yellow, as the intended spectral transmissivity characteristic on the whole surface of the first and second etching resistant material layers 10a and 10b. The third colored material layer 16 is formed by the same short-spin coating used for the second colored material layer 15. Here, the third colored material layer 16 is thermally cured. Fig. 10 shows the state of forming the second etching resistant material layer 10b on the third colored material layer 16 and above only the intended light sensing part 3 to be used as resist mask. The method of patterning on the desired area is as shown above. Fig. 11 shows the state of forming a third color filter 13 by removing the third colored material layer 16 other than the part masked by the second etching resistant material layer 10b similarly as in Fig. 5 and Fig. 8, in the state of Fig. 10. Fig. 12 shows the state of forming the final second etching resistant material layer 10b on a single color filter layer in order to planarize the surface asperities of the first color filter layer 11, second color filter layer 12 and third color filter layer 13. Fig. 13 shows the state of forming a photosensitive material layer 17 by using a material having a thermal softening property which is cured after being softened. Fig. 14 shows the state of forming a photosensitive material pattern 18 by selectively exposing the photosensitive material layer 17 with light (i-rays) of wavelength of 365 nm by using a mask, and developing and rinsing. The wavelength of the light for exposure above may be also other than i-rays, such as grays of 436 nm, h-rays of 405 nm, or light including all these wavelengths. For forming fine patterns, the i-rays of short wavelengths is desired. Fig. 15 shows the state of forming a photosensitive material layer pattern 19 made transparent by enhancing the transmissivity of the visible ray region by over 90% by fully exposing the photosensitive material layer pattern 18 with light in the wavelength of the ultraviolet region. Fig. 16 shows the state of forming the microlens 7 by heating and melting the transparent photosensitive material layer pattern 19 at 150 to 200°C so as to form a hemispheric shape by the surface tension. To form the etching resistant material layers 10a and 10b used in planarizing the surface asperities or as a resist mask, a material having resistance to, for example, O 2 ashing may be used as dry etching using oxygen plasma. As the colored transparent material of the first colored material layer 14, second colored material layer 15 and third colored material layer 16 for forming the first color filter layer 11, second color filter layer 12 and third color filter layer 13, an acrylic material blended with a pigment with a desired spectral transmissivity characteristic is preferably used. Examples of such acrylic material may include organic high polymer transparent material containing polymethyl methacrylate (PMMA), polyglycidyl methacrylate (PGMA) or their copolymer. Besides, any other material may be used which possesses hardening properties and is removable by dry etching means such as 0 2 ashing using oxygen plasma, whether possessing photosensitivity or not. As the material of photosensitive material layer 17 for forming the microlens 7, for example, ultraviolet photosensitive positive resist of phenol compound using naphthoquinone diazide as the photosensitive group may be used, but any other material may be used which is superior in adhesion and affinity for the first etching resistant material layer 10a in the lower layer, and is capable of forming a fine pattern by selective exposure. Any other material may be used as far as enhancing the transmissivity of the visible ray region by over 90% by the light in the wavelength in the ultraviolet region. Thus, in the solid-state imaging device, a color filter layer of plural colors is formed in a same layer by a colored transparent material possessing intended spectral transmissivity characteristics. Accordingly, the color filter layers are not different in steps, transparent material is not present between color filters, and the color filter is thinner on the whole. Accordingly, the distance from the color filter to the light sensing part is not long, and the distance is uniform in each color filter, so that flicker and other defects in image characteristics may be eliminated. On the whole, the color filter thickness is thin, and the microlens is formed in an adequate focal length, so that the focusing performance is improved, and the light sensitivity of the light sensing part is enhanced. The color filter is not formed in multiple layers, and cracks or damages of the filter due to external thermal impact are eliminated, so that the reliability is enhanced. In the manufacturing method, using colored transparent material, the color filter can be formed without a dyeing process, and the manufacturing process is shortened. Besides, the colored transparent material is not required to have photosensitivity, and does not contain harmful substances such as chromium (VI), so that a contamination-free manufacturing method is realized.

Claims: A method of manufacturing a solid-state imaging device comprising the following steps: (a) forming a plurality of light sensing parts (3) on a substrate (1) ; (b) forming a first etching resistant material layer (10a) on the substrate (1) ; (c) forming a colored transparent material layer (14, 15, 16) on the first etching resistant material layer (10a) ; (d) selectively forming a second etching resistant material layer (10b) on the colored transparent material layer (14,15, 16) ; (e) forming a color filter (11,12,13) by etching the colored material layer (14,15,16) using the second etching resistant material layer (10b) as a mask. (f) repeating steps (c) to (e) to form a plurality of color filters (11,12,13) in juxtaposition in a single layer having different special transmissivity characteristics, wherein the portions of said second etching resistant material serving as a mask remain on the formed color filters during subsequent processing; (g) forming a plurality of microlens (7) on the second etching resistant material layer (10b). The method according to claim 1, characterized in that the steps of forming the first and second etching resistant material layer (10a,10b) employs a material having resistance to dry etching using oxygen plasma. The method according to claim 1 or 2, wherein the step of forming the colored transparent material layer (14,15,16) employs an organic high molecular transparent material layer.

Inventors: NONURA TORU, NONURA, TORU
Applicants: MATSUSHITA ELECTRONICS CORP, MATSUSHITA ELECTRONICS CORPORATION, LTD.
Application year: 1992
Main classification: H01L31
IPC codes: H01L31, H01L27