JPH0438148B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical field of the invention] The present invention relates to a photothyristor, a phototriax,
The present invention relates to semiconductor light-receiving devices such as phototransistors and photodiodes, and particularly to planar semiconductor light-receiving devices with high breakdown voltage and high sensitivity. [Technical Background of the Invention] Generally, in a planar semiconductor device, a depletion layer near the surface becomes narrower than an internal depletion layer due to the influence of junction curvature and surface charge; There is a problem in that the breakdown voltage decreases because the electric field strength increases in some parts.
In order to solve this problem, a structure shown in FIG. 1 is adopted in a conventional planar semiconductor device. In FIG. 1, 1 is an N-type silicon substrate. A P ⁺ type diffusion layer 2 is provided on the surface layer of the silicon substrate 1.
is formed, and the surface of the substrate 1 is further covered with a silicon oxide film 3. An aluminum electrode 4 is formed on this silicon oxide film 3 in ohmic contact with the P ⁺ type diffusion layer 2 through a contact hole, and a substrate electrode 5 is also formed on the back surface of the silicon substrate 1 by vapor deposition of aluminum. ing. As shown in the figure, the aluminum electrode 4 is wide and is formed to broadly cover the PN junction. By forming the aluminum electrode 4 so as to overlay the junction as described above, a decrease in the breakdown voltage of the PN junction between the substrate 1 and the diffusion layer 2 is prevented. That is, in a state where a reverse bias is applied to the PN junction as shown in the figure, a depletion layer spreads in the N-type substrate region at the PN junction near the surface under the influence of the negative voltage applied by the aluminum electrode 4. Therefore, a sufficient width of the depletion layer is ensured even at the junction near the surface. The structure shown in FIG. 1 is also applied to semiconductor light receiving devices that require high breakdown voltage. FIG. 2 is a partially cross-sectional perspective view of an example in which the present invention is applied to a photodiode, and numerals 1 to 5 in the figure indicate the same parts as in FIG. 2. In addition, in the same figure, W _d indicates the width of the depletion layer, and L _p and L _o indicate the diffusion length of minority carriers (L _p is the diffusion length of holes, and L _o is the diffusion length of electrons), respectively. . When light enters the PN junction of this photodiode or its vicinity, electron-hole pairs are generated, but in order to separate the electron-hole pairs at the PN junction and convert them into current, there is a As in the case shown in the figure, a reverse bias is applied. Therefore, in this case as well, a reduction in the breakdown breakdown voltage of the junction becomes a problem, and in order to prevent this, the aluminum electrode 4 is formed overlaying the vicinity of the junction. [Problems with the Background Art] As mentioned above, by overlaying and forming a metal electrode such as aluminum on the joint part, it is possible to increase the withstand voltage of the semiconductor light receiving device.
On the other hand, since metal electrodes are opaque or have extremely low light transmittance, the amount of light incident on the junction decreases, resulting in a problem of decreased sensitivity. To explain this problem in more detail with respect to the photodiode shown in FIG. 2, the photosensitive region that can be sensitive to light in the photodiode shown _{in FIG .}
The range is up to However, since a considerable area of this photosensitive region is covered with the non-transparent aluminum electrode 4, the incident light that should originally be effective is blocked, resulting in a decrease in the sensitivity of the light receiving device. It's put away. [Object of the Invention] The present invention has been made in view of the above circumstances, and provides a planar semiconductor light-receiving device that improves the breakdown voltage of the junction by overlaying and forming an electrode near the junction, and has high light-receiving sensitivity. It provides equipment. [Summary of the Invention] A planar semiconductor light receiving device according to the present invention includes:
A semiconductor substrate of a first conductivity type, an impurity diffusion region of a second conductivity type formed on the surface layer of the semiconductor substrate, and an insulating film formed on the boundary and vicinity of the impurity diffusion region on the surface of the semiconductor substrate. and a light-transmitting conductive film electrically connected to the impurity diffusion region, and electrons generated by light incident on the PN junction between the semiconductor substrate and the impurity diffusion region and the vicinity thereof. The hole pair is
It is characterized by separating the PN junction by reverse bias and converting the optical signal into an electrical signal. As the transparent conductive film in the present invention, for example, tin oxide, indium oxide, polycrystalline silicon, etc. can be used. Among these, it is desirable to use polycrystalline silicon doped with impurities such as phosphorus and arsenic to lower the resistance for the following reasons. First, the process of forming and processing polycrystalline silicon films is currently widely used in the manufacturing process of general LSIs and is already technologically mature, so applying it as is will reduce manufacturing costs. becomes possible.
The second reason is that in the manufacturing process of semiconductor devices,
Impurities other than diffusion sources (e.g. indium, tin, etc.)
This is because polycrystalline silicon does not have to worry about contamination with polycrystalline silicon. A third reason is that polycrystalline silicon has a high light transmittance, particularly for long wavelength (near infrared) light. In the planar semiconductor light-receiving device of the present invention, the electrode provided to cover the junction interface in order to increase the breakdown voltage of the PN junction is transparent and does not block incident light. Therefore, almost all the light incident on the effective area reaches the photosensitive area and is converted into electric current, making it possible to obtain high light-receiving sensitivity. The light-transmitting isoelectric film pattern may be formed by forming a film using an existing method suitable for the material used, such as a vapor deposition method, a sputtering method, or a vapor phase growth method, and then patterning the film. Further, as shown in the Examples described later, the semiconductor light receiving device of the present invention can be easily manufactured by simply adding a step of forming a transparent isoelectric film pattern to the conventional planar process. [Embodiments of the Invention] Hereinafter, embodiments of the present invention will be described with reference to FIGS. 3 to 5. FIG. 1 is a sectional view showing an embodiment in which the present invention is applied to a photodiode. In the same figure, 11
is an N-type silicon substrate. The silicon substrate 11
A P ⁺ type impurity diffusion region 12 is formed in the surface layer of the substrate, and the substrate surface is covered with a silicon oxide film 13. An aluminum electrode 14 is formed on this silicon oxide film 13 in ohmic contact with the P ⁺ type impurity diffusion region 12 through a contact hole, and furthermore, the aluminum electrode 14
A polycrystalline silicon film pattern 15 connected to is formed. Polycrystalline silicon film pattern 15
is formed in a ring shape covering the boundary and the vicinity of the P ⁺ type impurity diffusion region 12, and is doped with arsenic to reduce the resistance. and,
These electrodes 14 and 15 are further covered with a protective film 16 made of silicon oxide or the like. On the other hand,
An N ⁺ type layer 17 is formed on the back side of the N type silicon substrate 11 for making ohmic contact with the substrate electrode, and a substrate electrode 18 is formed on the surface of the N ⁺ type layer 17. In order to specifically verify the effects of the present invention on the photodiode of the above embodiment, a photodiode having the structure shown in FIG. 3 was manufactured in the following manner. First, antimony-doped resistivity 0.01Ω・
cm N ⁺ type silicon wafer as the base wafer,
An N-type silicon layer 1 with a specific resistance of 10 Ω·cm and a film thickness of 40 μm is formed on the base wafer by a vapor phase epitaxial method.
Grow 1. Next, this N-type silicon layer 1
One surface is thermally oxidized to form a silicon oxide film 13 with a thickness of 1 μm covering the entire surface. Next, after opening a diffusion window of 300 μm (R30 μm at the corner) in the silicon oxide film, boron is thermally diffused using BSG as a diffusion source to form a P ⁺ type impurity diffusion region 12 with a junction depth of 5 μm. Form. Next, add 1x arsenic
After depositing a polycrystalline silicon layer doped at a concentration of 10 ¹⁹ atoms/cm ³ over the entire surface, this is patterned to form a junction with a width of 10μ inward and 40μ outward from the boundary of the P ⁺ type impurity diffusion region 12. A ring-shaped polycrystalline silicon film pattern 15 is formed to cover the portion. Thereafter, a contact hole is formed on the silicon oxide film 13 on the P ⁺ type impurity diffusion region 12, and aluminum is vapor-deposited and patterned to make ohmic contact with the P ⁺ type impurity diffusion region 12. Aluminum electrode 1 connected to polycrystalline silicon film pattern 15
form 4. After lapping the back surface of the base wafer, vanadium and nickel were deposited on the remaining N ⁺ type layer 17 surface to form a substrate electrode 18. The withstand voltage and light receiving sensitivity of the thus manufactured photodiode shown in the example shown in FIG. was gotten. The following two types of conventional photodiodes were used for comparison. (A) A photodiode (hereinafter referred to as conventional product A) having the same dimensions as the example product and the structure shown in FIG. (B) A photodiode (hereinafter referred to as conventional product B) having the same dimensions as the example product and the same structure as that shown in FIG. 2 except that the aluminum electrode 4 does not cover the joint portion. In addition, to compare the light sensitivity, we used a silicon-doped GaAs light-emitting diode with a center emission wavelength of 940 nm manufactured by liquid phase growth as a light source, and compared the photocurrents measured for each photodiode in relative values. I did it.

〔Effect of the invention〕

As described in detail above, according to the present invention, it is possible to improve the breakdown voltage by overlaying and forming an electrode near the junction, and to provide a semiconductor light receiving device having high light receiving sensitivity.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing a structure adopted in a conventional planar semiconductor device to prevent electric field concentration at the junction curvature and improve breakdown voltage.
The figure is a sectional view of a conventional photodiode adopting the structure shown in Fig. 1, Fig. 3 is a sectional view showing an embodiment in which the present invention is applied to a photodiode, and Fig. 4 is a sectional view showing another embodiment in which the present invention is applied to a phototransistor. FIG. 5 is a sectional view showing still another embodiment in which the present invention is applied to a photothyristor. 11... N-type silicon substrate, 12... P ⁺ type impurity diffusion region, 13... silicon oxide film, 14...
... Aluminum electrode, 15 ... Polycrystalline silicon film pattern, 16 ... Protective film, 17 ... N ⁺ type layer,
18...Substrate electrode, 19...N ⁺ type emitter region,
20...Guard ring.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate of a first conductivity type, an impurity diffusion region of a second conductivity type formed on the surface layer of the semiconductor substrate, and a boundary of the impurity diffusion region on the surface of the semiconductor substrate and the vicinity thereof. a transparent conductive film formed on the semiconductor substrate and the impurity diffusion region via an insulating film and electrically connected to the impurity diffusion region; What is claimed is: 1. A planar type semiconductor light receiving device, characterized in that electron-hole pairs generated by the light are separated by a reverse bias between the PN junctions, and an optical signal is converted into an electrical signal. 2. The planar semiconductor light receiving device according to claim 1, wherein the transparent conductive film is a polycrystalline silicon film.