JPS5946111B2 - Photodetection semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photodetection semiconductor device, and particularly to a highly stable and reliable silicon photodetector that exhibits high photoelectric conversion efficiency in a wide wavelength range from ultraviolet to near infrared.

Conventionally proposed diffusion bonding type silicon photodetectors are stable and reliable elements suitable for detecting mainly visible light, but have the drawback that they do not respond well to light in the ultraviolet region.

One reason for this is that silicon has an extremely large absorption coefficient for ultraviolet wavelength light, so that most of the incident light is absorbed within about 1000λ from the light-receiving surface. Since the electron-hole pairs photoexcited near the light-receiving surface have a high surface recombination speed, most of them disappear due to recombination before reaching the pn junction. Therefore, a typical silicon photodetector in which a diffused pn junction is formed at a depth of about 1 μm or more from the light-receiving surface has to suffer from a decrease in its ultraviolet sensitivity. On the other hand, apart from such a diffusion bonding type photodetector, photodetectors with high ultraviolet sensitivity that utilize an inversion layer formed at the 5102-51 interface and a Schottky barrier have been proposed, but these types of devices are , which utilizes phenomena on the surface or interface of a semiconductor, has the problem of lacking stability and reliability.

An object of the present invention is to provide a highly stable and highly reliable silicon photodetector that maintains the advantages of the prior art described above while eliminating its disadvantages, and exhibits high photosensitivity over a wide range including the ultraviolet region.

The present invention is based on the knowledge that high ultraviolet sensitivity exceeding that of conventional inverted layer photodetectors can be achieved by specifying the pn junction formation depth and the sheet resistance of the diffusion layer in diffusion bonding silicon photodetectors. be. According to the research conducted by the inventors, as shown in Figure 1, in order to exceed the ultraviolet sensitivity level B reached by the conventional inverted layer photodetector, the depth of the p-n junction must be
In Figure 1, the sensitivity measurement wavelength is 220 nm, and curves A and C respectively represent the relationship between the sheet resistance of the diffusion layer in a diffusion bonded photodetector with a junction depth of 0.05 to 0.2 μm, and the relationship between the depth of the Pn junction and the ultraviolet sensitivity. The sheet resistance value of the zero diffusion layer shown and the depth of the Pn junction are generally related to the impurity concentration, and the sheet resistance value is 500 to 50.
00Ω/mouth is approximately 1x1017~1x1020CTL'''
This corresponds to an impurity concentration of 3.

In this way, the diffusion layer according to the present invention has an impurity concentration of 1×1
017 to 1×1020c7n-3, and has a diffusion depth of 0.05 to 0.2 μm,
It has a characteristic that the sheet resistance is 500 to 5000Ω/mouth.

When a diffusion layer with these characteristics is formed, fewer defects occur in the diffusion layer, which reduces the recombination rate, and also reduces current limitation due to layer resistance, resulting in improved ultraviolet sensitivity. Significantly improved. In addition, as shown in Figure 2, by forming a distribution of impurity concentration that gradually decreases in the depth direction within the diffusion layer of thickness t, the electrostatic potential within the diffusion layer differs depending on the position. In other words, the band tilts and a drift effect comes into play, and the electric field effect caused by the diffusion potential of the junction combine to generate a drift electric field within the diffusion layer, which increases the optically excited carrier. It is thought that this also contributes to the improvement of ultraviolet sensitivity, such as the fact that the particles move quickly due to drift and are captured by the junction within a short time after generation, so the rate of recombination is extremely small. In addition, in Figure 2, CB, EF, and VB indicate the conduction band, Fermi level, and valence band, respectively. However, if the surface impurity concentration is higher than the above value, a gap will occur. , the disadvantage is that the recombination speed becomes faster. On the other hand, if the impurity concentration is too low, the resistance of the diffusion layer increases, so the photocurrent is limited by the resistance. In addition, if the diffusion depth is too deep, the distance for the carriers to reach the junction becomes long, and as a result, the electric field effect does not work effectively near the surface of the diffusion layer, and the recombination rate of the carriers decreases. increases. On the other hand, if the diffusion depth is too shallow, the layer resistance increases and it becomes susceptible to surface effects, so the photocurrent is limited by the resistance and changes depending on the state of the light-receiving surface, making the photocurrent unstable. becomes.

The invention will now be described in detail with reference to embodiments shown in the accompanying drawings.

FIG. 3 is a cross-sectional view of a silicon photodiode according to an embodiment of the present invention.

1 is an n+ type silicon base branch with a high impurity concentration of about 102r-3.

2 has an impurity concentration of 1×1014? -3 high resistivity n-type layer with a thickness of 10 μm.0 This was formed by epitaxial growth.

Generally, the impurity concentration of the n-type layer 2 is 1X1016cTr
It is desirable that the thickness be about L-3 or less, and if it is necessary to increase the sensitivity on the long wavelength side, it is necessary to increase the thickness. Next, the n+ type layer 3 and the p type layer 4 are formed into a ring shape using a known diffusion method. The ml type layer 3 is formed to prevent surface leakage current due to channels, and can be removed if there is no risk of channel generation. The p-type layer 4 is a region from which one electrode is taken out. Next, an oxide film is formed, and the oxide film in the portion where the p-type layer 5 is to be formed is removed by a known hot etching method. This oxide film acts as a master for subsequent boron diffusion. After that, an oxide film containing boron is formed on the surface of the wafer by vapor phase growth, and then heat treated for a short time.
As a result, a p-type diffusion layer 5 is formed. The diffusion layer formed in this example has a surface concentration of 1×1019? -3, diffusion depth 0.15μ sheet resistance 2000Ω/? It was hot. After a surface protection film 6 made of SiO2 is formed by a known method, an antireflection film 7 is formed. 8} and 9 are electrode layers.

In addition, J is a shallow Pn formed by region 2 and region 5.
Indicates joining. The photodiode manufactured by the above method has high sensitivity to ultraviolet light (for example, the quantum efficiency for light with a wavelength of 250 nm is about 40%) because of the considerations described above.

In addition, light with visible} and near-infrared wavelengths has a high resistance and is absorbed in region 2 where the carrier life is long, so the carriers generated there are not annihilated by recombination and are absorbed by the junction J.
It can be captured by Therefore, high sensitivity is achieved. Also,
In the junction formed according to the present invention, since there are fewer defects near the junction, noise caused by such defects is reduced, and the S/N ratio of the light receiving element is improved. According to the sheet resistance is 6000Ω/? Or 200Ω/? In this case, it was confirmed that the ultraviolet sensitivity was approximately 1/2 that in the case of the present invention.

Another method for obtaining the thin diffusion layer 5 in the silicon photodiode according to the present invention is to use the following doped silicon diffusion method.

A silicon wafer as a diffusion source doped with boron at a concentration of about 8 x 1018 is sealed in a vacuum quartz tube together with the silicon wafer on which the diffusion layer 5 is to be formed, and
After heat treatment at 000°C for 120 minutes, the sheet resistance ρs was approximately 1.
A thin diffusion layer 5 having a resistance of 100Ω/hole is formed.

Such a doped silicon diffusion method has good reproducibility and yield, and is therefore effective for practical use. Further, it is also possible to form by an open tube diffusion method at a low temperature (for example, 750 to 800° C.) using boron nitride (BN) as a diffusion source.

As detailed above, by adopting the present invention, the following advantageous effects can be obtained.

(1) Sensitivity in the ultraviolet wavelength region is significantly improved. (4) A highly sensitive light receiving element can be obtained over a wide wavelength band from ultraviolet to near infrared. (111) Since there are fewer defects near the junction, noise is reduced and the S/N ratio is improved.

In the above-described specific embodiment of the present invention, the diffusion layer 5 is formed by boron diffusion, but it is also possible to use an ion implantation method, an ion beam method, an ion plating method, etc. The essence of the present invention will not be changed even if it is formed as follows.

Further, in the embodiment, the case where an n+ substrate is used has been described, but the essence of the present invention does not change even when a p+ substrate is used, which is changed from n+ to p+, n-+P, or p-+n1.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between sheet resistance and Pn junction depth and ultraviolet sensitivity in a silicon photodetector. FIG. 2 is a graph showing the band structure of a photodetector according to the present invention. FIG. FIG. 1 is a cross-sectional view of a photodiode according to an embodiment of the present invention. 1... N+ type silicon layer, 2... N type silicon layer, 3... N+ type channel prevention layer,
4... p+ type diffusion layer, 5... p type diffusion layer, 6... surface protective film, 7... antireflection film, 8, 9. ...Electrode layer.

Claims (1)

[Claims] 1. A semiconductor region of a conductivity type opposite to the above-mentioned conductivity type is formed in the light-receiving surface region of a silicon semiconductor layer of one conductivity type so that its impurity concentration gradually decreases in the depth direction, and is substantially parallel to the light-receiving surface of the semiconductor layer. In the photodetecting semiconductor device in which a light-receiving pn junction is defined between the semiconductor layer and the semiconductor region, the depth of the light-receiving pn junction is approximately 0.05 to 0.2μ.
m, and the sheet resistance of the semiconductor region is set in a range of about 500 to 5000 Ω/□.