Photoelectric converting apparatus

Abstract: A photoelectric converting apparatus has a reflection preventing section. The section is formed on at least a peripheral portion of said light receiving section.

Description: The present invention relates to a method of manufacturing a resin sealed photo-electric conversion device and a resin sealed photo-electric conversion device having a light receiving section defined in a substrate, particularly for preventing a malfunction or the like which is caused due to light entering from portions other than a light receiving window and due to internal reflections. Figs. 1 and 2 are schematic arrangement diagrams of first and second examples of conventional photoelectric conversion devices. In Fig. 1, a light shielding layer 3 is formed on the portions of a semiconductor chip 4 having photoelectric converting function excluding a light receiving portion 8. A whole construction is enclosed in a package 6 made of a material such as a plastic, ceramic or the like and sealed by a cover glass 5. The light shielding layer 3 is provided for allowing necessary light 1 to be received by a semiconductor chip 4 and for shielding the unnecessary light. Al, Al-Si, or the like is used as a material of the light shielding film 3. The layer 3 is formed by a vacuum film forming technique such as an electron beam evaporation deposition process, sputtering process, CVD process, or the like. Usually, a sufficient thickness is about 200 nm (2000 Å). However, in the foregoing conventional structure, when unnecessary light flux 2 is incident on the cover glass 5, light is totally internally reflected by the light shielding layer 3 and by the inner surface of the cover glass 5 and reaches the light receiving section 8, as shown in Fig. 1. Therefore, a malfunction of the photoelectric converting device in the semiconductor chip 4 occurs, and there is a problem that the noise figure of the output signal increases. The same problem arises in a case wherein the semiconductor chip 4 is enclosed in a clear mould package 7, the semi-conductor chip 4 having a light receiving element being enclosed within a transparent resin as shown in Fig. 2. There is described in Patent Abstract of Japan, volume 10, No. 244 (E-430) [2300], August 22, 1986 and Japanese Kokai JP-A-61075562 a photo-electric conversion device comprising a substrate with a photo-electric conversion element defined therein, an inner insulating layer of silicon oxide and a layer of polysilicon covering the photoelectric conversion element and remainder major surface of the substrate, and a light shielding layer of aluminium covering the polysilicon layer so as to surround the periphery of the photoelectric conversion element. A reflection preventing layer of aluminium oxide is formed directly on the surface of the aluminium light shielding layer and this and an exposed area of the polysilicon layer are covered by a filter material. Notably, the aluminium oxide reflection preventing layer is produced by sputtering as a means of avoiding contamination of the substrate and deterioration of device characteristics. The present invention is also directed as a solution to the problem of avoiding spurious light incidence upon the photo-electric conversion element. It also provides an alternative approach to solving the problem of avoiding contamination. A method of manufacturing a resin-sealed photoelectric conversion device, and such resin-sealed photoelectric conversion device in accordance with the present invention are defined in claims 1 and 2 respectively. In the accompanying drawings:- Figs. 1 and 2 are schematic arrangement diagrams of first and second examples of conventional photo-electric conversion devices; Fig. 3 is a schematic arrangement diagram of a substantial portion of a semiconductor chip in the first embodiment of a photo-electric conversion device according to the present invention; and Fig. 4 is a schematic arrangement diagram of a second embodiment of the invention. Embodiments of the present invention will be described in detail hereinbelow with reference to the drawings. Fig. 3 is a schematic arrangement diagram of a substantial portion of a semiconductor chip in this the first embodiment of a photoelectric conversion device according to the invention. In Fig. 3, a photo-electric conversion element 10 is formed in a semi-conductor substrate 9. An SiO₂ layer 11 and an insulative layer 12 are formed on and over the semiconductor substrate 9. Further, a light shielding layer 3 is formed on and over the insulative layer 12 excluding a light receiving section 8. An insulative layer 14 is formed on the insulative layer 12. A reflection preventing layer 13 having the same pattern as the light shielding layer 3 is formed on the insulative layer 14. Thus, total internal reflection by the insulative layer 14 can be prevented. In this embodiment, since the reflection preventing layer 13 is formed in the final layer forming step, it can be formed independently of the deposition conditions such as deposition temperature of the insulative layer 14 and a high heat resistance is not necessary. On the other hand, it is possible to avoid pollution of the film forming apparatus used for depositing the insulative layer 14. When the foregoing semiconductor chip 4 of the above embodiment is enclosed in a clear mould package, even if unnecessary light fluxes 2 enter as in the examples shown in Figs. 1 and 2, they are absorbed by the reflection preventing layer 13 and do not reach the photo-sensing element 10. A method of manufacturing this embodiment will now be described. First, a step of forming the photo-sensing element 10 in the semiconductor substrate 9, a step of forming the SiO₂ layer 11, a wiring forming step, and a step of forming the insulative layer 12 are performed. In the wiring forming step, Al or Al-Si is formed on the SiO₂ layer 11 by a sputtering method so as to have a thickness of 0.7 to 1.2 µm. Then, it is patterned to thereby form an aluminium or aluminium silicide wiring. The insulative layer 12 is made of highly insulative material such as silicon nitride or SiO₂. In the case of using silicon nitride, it is formed by a plasma CVD method, using a gas mixture, for example, SiH₄ + NH₃, at a layer forming temperature of 300 to 400°C. A refractive index nf = 2.01 ± 0.05 is achieved. A thickness 400 to 1200 nm (4000 to 12000 Å) of the layer is desirable. An SiO₂ layer having a thickness of 30 to 200 nm (300 to 2000 Å) formed by a CVD method may be laid under silicon nitride as will be explained hereinafter. In the case of SiO₂ layer, the insulative layer 12 is formed using a gas mixture, for example, SiH₄ + O₂ at a temperature of 350 to 450°C. so as to have a thickness of 600 to 1200 nm (6000 to 12000 Å) by a CVD method. The insulative layer 14 may be formed under the same conditions and thickness as those of the insulative layer 12. The light shielding film 3 is formed by depositing a light shielding material such as Al or Al-Si or the like, whose thickness is 150 nm (1500 Å) or more by a sputtering method or electron beam evaporation deposition method, and by eliminating the light receiving portion 8 by the patterning. Now the reflection preventing layer 13 will be explained in practical detail. A reflection factor of the reflection preventing layer is chosen to be a small value preferably of 5% or less, more preferably, 1% or less. It is desirable to use a reflection preventing layer which can be easily patterned. Particularly, selecting, as a material of the reflection preventing layer or film, one which can be patterned by light is desirable. As such desirable material, the following can be used: (1) Photosensitive resin: (a) Since a black photosensitive resin has a small reflection factor and can be patterned by light it can be used as a material of the reflection preventing layer. Such a photosensitive resin, for example, can be selected from the resins Nos. PI 2702 and 2703 made by Du Pont Co., Ltd. which are available commercially. (b) Moreover, it is also possible to use as the reflection preventing material a material which is made by mixing the following pigment or dye with a photosensitive resin such as PIQ (photosensitive polyimide, a trade name, made by Hitachi Chemical Co., Ltd.) As an organic pigment suitable for use, one or two kinds or more are selected from a group of azo system pigments of the soluble azo system, insoluble azo system, condensed azo system, or the like, a phthalocyanine system pigment, and condensed polycyclic system pigments including the indigo system, anthraquinone system, perylene system, perynone system, dioxazine system, quinacridone system, isoindolinone system, phthalone system, methine·azomethine system, and other metal complex system and mixed. On the other hand, it is also possible to use inorganic pigment such as a carbon black, iron black, graphite, or a compound oxide black pigment of the copper chromium system, copper, iron, and manganese system. As a dye, one, two, or three kinds or more can be selected from the dyes of various systems such as azo, anthraquinone, phthalocyanine, carbonium, quinonimine, methine, benzoquinone, naphthoquinone, and the like and mixed. In the case of the semiconductor chip 4 shown in Fig. 3, after the insulative layer 14 has been formed, the photosensitive resin material of (a) or (b) compound is coated over the whole surface by a spin coater and exposed to ultraviolet rays using the same mask as used previously for defining the light shielding layer 3. The reflection preventing layer 13 is then formed by developing and rinsing steps. A thickness of 100 to 1000 nm (1000 to 10000 Å) of the layer is desirable. The photosensitive resin material also has the light shielding effect because it is black and can be also used as the material of the reflection preventing layer 15 in the third embodiment. (2) Heat resisting binder system: A mixture is made by mixing any of the above-mentioned pigments or dyes with OCD (Trade name: made by Tokyo Applied Chemical Co., Ltd.; OCD is obtained by binding SiO₂ in ethanol and has a concentration of 10% or less). This mixture is coated onto the whole surface by using, for example, a spin coater and it is baked at temperatures of about 100 to 200°C in an atmosphere of N₂, thereby forming an inorganic silica film containing dye or pigment. Subsequently, the inorganic silica film is patterned by a photographic etching technique using the same mask as used for defining the light shielding layer 3, thereby forming the reflection preventing layer 13. The reflection preventing film can be also similarly formed by mixing the foregoing pigment or dye into a heat resisting resin such as polyamide or the like. (3) Inorganic film: An inorganic film of a low reflectivity made of an inorganic material such as PbS, SnS, CuS, FeO, CuO, or the like is formed by a vacuum depositing method and patterned, so that the reflection preventing layer 13 can be formed. On the other hand, a film consisting of Ti or Ti compound is formed and this film is left under the conditions of oxygen flow rate of 5 to 200 cc/min and a pressure of 1x10 to 4.0x10² Pa (0.1 to 3.0 Torr) and in the plasma of discharge power, 100 to 1000 kW. Thus, a black reflection preventing layer 13 having fine concave and convex surfaces can be formed. In addition it is also possible to use a method of reducing the reflectivity by the interfering effect. A good result was obtained by depositing a film consisting of Si, TiO, Ge, Cr, Ti. The present invention is not limited to the semiconductor chip 4 configuration in which the reflection preventing layer has been formed as in the foregoing embodiment. A similar effect can be derived even when the light shielding layer is formed on the outside of a resin mould package as will be explained hereinbelow. Fig. 4 is a schematic arrangement diagram of a second embodiment of the invention. In the second embodiment shown in Fig. 4, a reflection preventing layer 17 is formed on the upper surface of a clear mould package 7, so that unnecessary light can be absorbed (refer to Fig. 2). As described in detail above, in both the photoelectric conversion devices, by forming a reflection preventing layer surrounding the periphery of the light receiving section, even if the unnecessary light flux enters it can be absorbed before reaching the light receiving section and adverse influence on the photoelectric converting operation can be prevented. Consequently, a malfunction of the photoelectric conversion device due to the entrance of light from portions other than the light receiving window and a fluctuation of the output can be eliminated. The noise figure of the output is reduced. The reliability of the photoelectric conversion device can be improved.

Claims: A method of manufacturing a resin sealed photoelectric conversion device comprising the steps of: providing a substrate (9); defining a photo-electric conversion element (10) in a major surface of said substrate (9); covering said major surface of said substrate (9), including said photo-electric conversion element (10), with an inner insulating layer (12); forming a patterned light shielding layer (3) on said inner insulating layer (12), which light shielding layer (3) surrounds the periphery of said photo-electric conversion element (10); and covering said light shielding layer (3) and that part of said inner insulating layer (12) left exposed by said light shielding layer (3) with an outer insulating layer (14); which method is characterised by: surrounding said substrate (9) with a resin seal (7) and providing a reflection preventing layer (13,17) surrounding at least the periphery of said photoelectric conversion element (10) over said outer insulating layer (14) either directly on said outer insulating layer (14) in contact with said resin seal (7) or alternatively on the outer surface of said resin seal (7). A resin sealed photoelectric conversion device comprising: a substrate (9); a photoelectric conversion element (10) defined in a major surface of said substrate (9); an inner insulating layer (12) covering the major surface of said substrate (9); a light shielding layer (3) for preventing incidence of unnecessary light on said photoelectric conversion element (10) located on said inner insulating layer (12) surrounding the periphery of said photoelectric conversion element (10); an outer insulating layer (14) covering of said said light shielding layer (3) and that part of the inner insulating layer (12) left exposed by said light shielding layer (3); and a resin seal (7) surrounding said substrate (9) wherein said device further comprises a reflection preventing layer (13, 17) at least surrounding the periphery of said photoelectric conversion element (10) and provided over said outer insulating layer (14), either directly on said outer insulating layer in contact with said resin seal (7) or alternatively on the outer surface of said resin seal (7). A device according to claim 2, wherein said reflection preventing layer (13) is of resin material. A device according to claim 3, wherein said resin is a developed photosensitive resin. A device according to claim 3 or 4, wherein said resin contains a pigment. A device according to claim 5, wherein said pigment is (a) at least one organic pigment selected from azo system, phthalocyanine system, and condensed polycyclic system pigments including indigo system, anthraquinone system, perylene system, perynone system, dioxazine system, quinacridone system, isoindolinone system, phthalone system, methine·azomethine system, and metal complex system and/or (b) at least one inorganic pigment selected from carbon black, iron black, graphite, and compound oxide black pigment of the copper chromium system, copper, iron and manganese system. A device according to claim 3, wherein said resin contains a dye. A device according to claim 7, wherein said dye comprises at least one selected from azo, anthraquinone, phthalocyanine, carbonium, quinonimime, methine, benzoquinone, naphthoquinone. A device according to any of claims 3 to 8, wherein said resin contains SiO₂. A device according to any of claims 4 to 9, wherein said resin is of polyamide. A device according to claim 2, wherein said reflection preventing layer (13) is an inorganic film or layer. A device according to claim 11, wherein said inorganic film or layer comprises a material selected from PbS, SnS, CuS, FeO, CuO, Ti, TiO, Ti-compound, Si, Ge and Cr. A device according to any of claims 2 to 12, wherein said reflection preventing layer (13) has a reflectivity lower than 5%. A device according to claim 2, wherein said light shielding layer (3) and said reflection preventing layer (13) have substantially the same configuration.

Inventors: MATSUMOTO SHIGEYUKI, MATSUMOTO, SHIGEYUKI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H01L31
IPC codes: G01J1, H01L31