JPH0474872B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a germanium semiconductor device.

In recent years, the practical application of optical communication has been remarkable, with wavelengths 1 and up.
Germanium is used as a light-receiving material in the 1.6 μm band, and germanium light-receiving elements are being developed, but planarization of these elements is desirable in terms of improving device characteristics and reliability. One of the important techniques for planarization of germanium semiconductor devices, including photodetectors, is the formation of a surface passivation film, but unlike silicon, germanium has a thermal oxide film (GeO ₂ ) has many trap levels, and the interface state density at the interface with the germanium semiconductor is extremely high at 10 ¹² to 10 ¹⁴ cm ^-2 eV ^-1 . In addition, a poor thermal oxide film is water-soluble, which is undesirable in the production of germanium semiconductor devices. Therefore,
Surface passivation of germanium semiconductors has traditionally been carried out using
A heterogeneous insulating film such as a silicon dioxide film has been formed by the CVD method, but the interface state density at the interface between the insulating film and the germanium semiconductor is 10 ¹² to 10 ¹⁴ cm ^- as in the case of a thermal oxide film. ² eV ^-1 , and no significant improvement has been made. Therefore, an object of the present invention is to provide a method for manufacturing a germanium semiconductor device with a low interface state density.

Method for manufacturing a germanium semiconductor device of the present invention After forming a dielectric film on the surface of a germanium semiconductor,
It is characterized by comprising a step of performing heat treatment in an oxygen atmosphere to form germanium oxide at the interface between the dielectric film and the germanium semiconductor.

According to the present invention, since the germanium oxide film does not come into direct contact with the atmosphere, there is no electrical interface instability due to the absorption of moisture from the atmosphere, and the characteristic properties of germanium oxide, such as easy evaporation, can be suppressed. Because of this, there is a significant improvement in interfacial properties compared to conventional thermal oxidation methods. FIG. 1 shows the results of demonstrating the above effect. Figure 1 shows N type 8×
A so-called MIS (Metal ^- Insu ^- lator-
This is the result of deriving the interface state density from the capacitance-voltage characteristics of a diode (Semiconductor). Silicon dioxide film was diluted to 3% with Ar at 450°C.
A thickness of 1200 Å was formed by flowing SiH ₄ at 500 c.c./min, O ₂ at 300 c.c./min, and N ₂ carrier gas at 80 c.c./min.
In FIG. 1, curves 1 and 2 show the results of experiments for comparison with the present invention, and curve 3 shows the case of the present invention.
Curve 1 shows the interface state density distribution not according to the present invention, that is, when only a silicon dioxide film is formed on a germanium semiconductor, but the minimum density distribution is about 3 × 10 ¹² cm ^-2 eV ^-1. . Curve 2 is the case of thermal oxidation for comparison, at 450℃.
It shows the interface state density distribution when a silicon dioxide film is formed under the same conditions as curve 1 above after flowing O ₂ at a flow rate of 2.5 per minute for 5 minutes, and the minimum density is 5 × 10 ¹¹ cm ^- It was reduced to ² eV ^-1 . Curve 3 is
After forming a silicon dioxide film using the method of the present invention, that is, under the same conditions as in curve 1 above,
The graph shows the interface state density distribution when heat treatment was performed by flowing O ₂ at a flow rate of 2.5 per minute for 30 minutes under the conditions, and the density was reduced to a minimum of 8 × 10 ¹⁰ cm ^-2 eV ^-1 .
It is thus clear that the present invention improves the interfacial properties.

The following is a detailed explanation of the application to the production of a germanium avalanche photodiode (hereinafter referred to as Ge-APD) as an example, but it should be easily understood that the invention is not limited only to the example. It won't happen. First, an experimental example for comparison with the present invention will be described. FIG. 2 shows an example from the middle of the manufacturing process. The prepared germanium substrate 21 is n-type and has a carrier concentration of 8×10 ¹⁵
cm ^-3 . On the germanium substrate 21, a p conductive type guard ring portion 22 provided to improve multiplication characteristics and a p ⁺ conductive layer 23 serving as a light receiving portion were formed by ion implantation of beryllium and boron, respectively (Fig. 2). a). The accelerating voltage and dose for beryllium ion implantation were 100keV and 100keV, respectively.
1×10 ¹⁴ cm ^-2 was chosen. In addition, the acceleration voltage and dose amount for boron ion implantation are 40keV, 2×
10 ¹³ cm ^-2 was chosen. After ion implantation, 650℃
The implanted ions were activated by heating in a nitrogen atmosphere for 45 minutes. At this time, the junction depth of the guard ring portion 22 is approximately 3 μm, and the junction depth of the p ⁺ light receiving portion 23 is approximately 0.3 μm. Next, 450℃
After forming a thin germanium oxide layer 24 on the germanium surface by flowing O ₂ at a flow rate of 2.5 per minute for 5 minutes under
was formed under the conditions described above to give a total thickness of 2300 Å (Figure 2b). Next, a window for electrode formation is made using a well-known exposure technique, and the Al electrode 26 is
was formed to complete Ge-APD (Figure 2c).

Next, as an example of the present invention, Ge-APD will be described as an example. FIG. 3 shows the manufacturing process from the middle. FIG. 3a shows exactly the same process as FIG. 2a. Next, after forming the silicon dioxide derivative film 25 under the above-mentioned conditions (FIG. 3b), O ₂ was flowed at a flow rate of 2.5 per minute at 600° C. for 30 minutes to form a layer between the silicon dioxide film 25 and the germanium substrate 21. forming a germanium oxide layer 24 (FIG. 3c);
The total passivation film thickness was 2300 Å. Next, Figure 2c
Similarly, an Al electrode 26 was formed to complete the Ge-APD. (Figure 3d). FIG. 4 shows an avalanche manufactured by simply forming a silicon dioxide film not according to the present invention, by the process shown in FIG. 2, and by the process shown in FIG. 3 according to the present invention. It shows the dark current-voltage characteristics of a photodiode. From Figure 4, breakdown voltage of Ge-APD
V _B is approximately -30V. Curve 41 is a dark current-voltage curve of Ge-APD manufactured by a conventional method not according to the present invention, and the dark current is 0.5 to 0.5 at 0.9V _B.
0.6μA, which is extremely high. The dark current of the comparative thermal oxidation-produced Ge-APD shown in FIG. 2 is shown in curve 42 and was reduced to 0.3-0.4 μA at 0.9 V _B. Furthermore, in the Ge-APD manufactured by applying the method according to the present invention, the dark current was reduced to 0.1 to 0.2 μA at 0.9 V _B, as shown in curve 43, and results consistent with the results shown in Figure 1 were obtained. Ge−
The characteristics of APD were improved.

In the above embodiment, the case of using silicon dioxide film as the dielectric was explained, but other dielectrics such as silicon nitride film (Si ₃ N ₄ ), germanium nitride film (Ge ₃ N ₄ ), and aluminum oxide (Al ₂ O ₃ ) can also be used. Exactly the same effect was obtained.

As described above, according to the present invention, it is possible to form a germanium oxide layer at the interface between a dielectric and a germanium semiconductor without exposing it to the outside air, so it has the advantage that good interface characteristics with a small interface state density can be obtained. have

[Brief explanation of the drawing]

Figure 1 shows the interface state density distribution curve.
2 shows the case where a silicon dioxide film was simply formed, which is not according to the present invention, 2 shows the case where thermal oxidation was used for comparison, and 3 shows the case according to the present invention. FIG. 2 is a diagram illustrating the manufacturing process of Ge-APD using thermal oxidation for comparison. Figure 3 Ge according to the present invention
- It is a figure explaining the manufacturing process of APD. Figure 2,
In FIG. 3, 21 is a germanium substrate, 22
23 is a guard ring layer, 23 is a light receiving part, 24 is a germanium oxide layer, 25 is a silicon dioxide film, and 26 is a
It is an Al electrode. Figure 4 shows the dark current of Ge-APD.
It is a voltage characteristic diagram. 41 shows the case where a silicon dioxide film is simply formed, 42 shows the case where thermal oxidation is used for comparison, and 43 shows the case according to the present invention.

Claims (1)

[Claims] 1. Manufacture of a germanium semiconductor device, comprising the step of forming a dielectric film on the surface of a germanium semiconductor and then performing heat treatment in an oxygen atmosphere to form germanium oxide at the interface between the dielectric film and the germanium semiconductor. Method.