JPS633448B2 - - Google Patents

Description

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

Germanium has the property that its crystal structure is easily disturbed by high-temperature heat treatment. Traditionally, arsenic (As), antimony (Sb), and zinc (Zn) have been thermally diffused into germanium substrates, but because these diffusion temperatures are high,
When attempting to form a dissipation layer deep from the surface by long-term heat treatment, there was a problem in that it adversely affected the germanium substrate. For this reason, it has been difficult to form a deep impurity layer, mainly a p-type impurity layer, on the germanium substrate. However, on the other hand, in recent years,
The need for germanium light receiving elements as light receiving elements for 1 μm band optical communication has increased.

As shown in FIG. 1, a conventional germanium light-receiving element includes a p-type germanium substrate 1, a highly impurity-concentrated n ⁺ layer 2 constituting a light-receiving surface, an n-type guard ring layer 3, and a germanium substrate 1. The surface of 1 was covered with a silicon dioxide layer (SiO ₂ ) 4 except for the n ⁺ type layer 2 . When a light-receiving element is constructed using a germanium substrate, the diffusion current generated by minority carriers generated in the substrate diffusing to the depletion layer of the pn junction becomes larger than when silicon is used. Since most of the dark current at room temperature is caused by this diffusion current, germanium light-receiving elements have the disadvantage of large dark current. Furthermore, due to the action of the positive charges in the silicon dioxide layer 4, an n-type inversion layer is formed on the surface of the p-type germanium substrate 1 that is in contact with the silicon dioxide layer 4. Therefore, the depletion layer of the pn junction spreads laterally along the inversion layer, increasing the equivalent junction area and increasing the diffusion current and surface leakage current. However, since there was no suitable method for forming a p-type impurity layer on a germanium substrate at low temperature,
No effective method for preventing the shape inversion layer has been found.

FIG. 2 shows another conventional germanium photodetector, in which boron (B) is ion-implanted into an n-type germanium substrate 5 to form a p ⁺ type layer 6, and zinc (Zn) is ion-implanted into an n-type germanium substrate 5.
The p-type guard ring layer 7 is formed by thermally diffusing. In this conventional example, zinc is heat-treated at a high temperature of 800°C or higher, which adversely affects germanium crystals and increases dark current. Furthermore, since the diffusion coefficient is relatively small in the sub-region, the radius of curvature of the cross section of the guard ring layer 7 is relatively small, causing concentration of the electric field, and the impurity concentration in the sub-region is relatively high, so the depletion layer is made of n-type germanium. Since it mainly only spreads in the direction of the substrate 5, it had the disadvantage of low breakdown voltage.

In view of the above-mentioned conventional drawbacks, an object of the present invention is to provide a method for manufacturing a semiconductor device that reduces dark current by forming a deep p-type channel stopper layer on a p-type germanium substrate at low temperature. shall be.

The purpose of the present invention is to form a p-type channel stopper layer by ion-implanting beryllium (Be) into a p-type germanium substrate, and to form a p-type channel stopper layer on the surface of the p-type germanium substrate by injecting high impurity into the channel stopper layer. This is achieved by forming a high concentration n-type layer.

The present invention was conducted by ion-implanting various impurities into a germanium substrate, and found that when beryllium was ion-implanted, an impurity concentration distribution as shown in FIG. 3 was obtained. Curves A and B have an acceleration voltage of 100 KeV and a dose of 5×10 ¹⁴ respectively.
cm ^-2 and 2×10 ¹⁴ cm ^-2 , curves C and D have an acceleration voltage of 50 KeV and a dose of 1×10 ¹⁴ cm ^-2 respectively.
The case of 5×10 ¹³ cm ^-2 is shown. In both cases, the wafer impurity concentration was 4×10 ¹⁵ cm ⁻³ and heat treatment was performed at 646° C. for 1 hour. According to this impurity concentration distribution, for example, curve A shows that beryllium exhibits a high carrier concentration of 10 ¹⁸ cm ^-3 or more near the surface, and the concentration decreases rapidly along the depth direction from the surface, but then decreases. It can be seen that the concentration region extends to a depth of about 12 μm. The other curves B, C, and D also show substantially similar impurity concentration distributions. On the other hand, when arsenic is ion-implanted into a germanium substrate, the surface concentration is about 10 ¹⁷ cm ^-3 and the diffusion depth is only about 10 17 cm -3 even after heat treatment at 692°C for 1 hour at an acceleration voltage of 150 KeV and a dose of 5 × 10 ¹³ cm ^-2. The diameter is about 2 μm. In addition, when zinc ions are implanted into a germanium substrate, the acceleration voltage
150KeV, dose 5×10 ¹³ cm ^-2 , surface concentration approximately 10 ¹⁸ cm ^-3 after 4 hours of heat treatment at 695°C, diffusion depth 1.5μ
It is about m.

Therefore, by ion-implanting beryllium into a germanium substrate, it can be achieved at a lower temperature than when ion-implanting arsenic or zinc, as well as when comparing thermally diffusing arsenic or antimony.
It is possible to form an impurity layer with a high surface concentration and a low concentration extending deep from the surface. According to the method of the present invention, the p-type impurity layer can be formed at a temperature of at least 700° C. or lower, so that it is possible to suppress an increase in dark current due to an adverse effect on the crystal structure of the germanium substrate.

FIG. 4 shows an embodiment of the method for manufacturing a germanium light-receiving element according to the present invention. The surface of a p-type germanium substrate 11 (Fig. a) is coated with an oxide film 12 made of silicon dioxide (SiO ₂ ), a window is opened using a normal photoetching technique, and the film is heated at 750°C for 2.5°C.
Timed antimony diffusion is performed to form an n-type guard ring layer 13 (Figure b). Next, after covering the surface again with an oxide film 14, a window is opened in the outer part of the guard ring layer 13, and beryllium is ion-implanted at an acceleration voltage of 100 KeV and a dose of 2×10 ¹⁴ cm ^-2
After implanting it into the substrate 11 (Figure c), the surface is covered with an oxide film, and then heat treatment is applied at 646° C. for 1 hour to activate and diffuse, forming the p-type channel stopper layer 15. (Figure d).
As is clear from the impurity concentration distribution in Figure 2, beryllium has a high concentration near the surface, approximately 10 ¹⁸ cm ^-3
And from the surface to the depths, that is, 10 ¹⁶ cm ^-3
In the case of a germanium substrate with a concentration of , it is diffused to about 6 μm. Next, remove the oxide film inside the guard ring layer 13, diffuse arsenic at 620℃ for 18 minutes,
n ⁺ type layer 1 with a thickness of 4000 Å and a high impurity concentration
form 6. Figure e). The surface of the n ⁺ -type layer 16 acts as a light-receiving surface. Next, aluminum (Al)
An electrode 17 is deposited on the surface of the guard ring layer 13 (Figure f). Note that the guard ring layer 13 is the n ⁺ type layer 1
This is to increase the withstand voltage in the peripheral area of 6. Further, the electrode for the p-type germanium substrate 11 is
It is provided by bonding a gold-plated stem to the back surface of the light-receiving element, and is not shown in the drawings.

The germanium light receiving element manufactured as described above is formed on the p-type germanium substrate 11.
It consists of an n ⁺ type layer 16 and has a channel stopper layer 15 formed by beryllium ion implantation and having a depth at least deeper than the n ⁺ type layer, preferably 5 μm or more.

In the germanium light receiving element according to the above embodiment of the present invention, the channel stopper layer 15 is formed by the oxide film 14.
Since the p-type carrier concentration due to beryllium is high in the portion in contact with the n-type inversion layer, no n-type inversion layer is formed. Because of this, the depletion layer does not spread laterally,
Diffusion current and surface leakage current can be reduced. Further, since the p-type channel stopper layer 15 extends deep from the surface, the region having a higher impurity concentration than the p-type germanium substrate 11 becomes larger. In a high impurity concentration region, the diffusion current due to minority carriers, that is, electrons here, decreases, so the p-type channel stopper layer 15 can reduce the diffusion current of the p-type germanium substrate 11. While a conventional photodetector without a channel stopper layer has a dark current of about 10 ^-7 A, the photodetector manufactured according to the present invention can reduce the dark current to about 10 ^-6 A. Therefore, the minimum light reception level of the light receiving element can be lowered.

In addition, in the manufacturing process shown in Figure 4, the heat treatment process for ion-implanted beryllium (Figure d)
This and the step of forming the n ⁺ -type layer 16 by thermal diffusion of arsenic (Fig. e) may be performed simultaneously.

Next, FIG. 5 shows another embodiment of the method for manufacturing a light receiving element according to the present invention.

The surface of an n-type germanium substrate 21 (Figure a) is coated with an oxide film 22 made of silicon dioxide, and a window is opened in this using a normal photoetching technique, and beryllium is deposited at an acceleration voltage of 50 KeV and a dose of 1×10 ¹⁴ cm.
^-2 ion implantation (Figure b) to form a p-type guard ring layer 23, open a window in the oxide film 22, and indium (In) at an acceleration voltage of 90 KeV and a dose of 2×
Ion implantation is performed at 10 ¹³ cm ^-2 (figure c) to form a p ⁺ type layer 24 (figure d). Then, the surface is covered with an oxide film 22 and heat treated at 646° C. for 1 hour to form a p-type guard ring layer 23 to a depth of about 6 μm. At the same time, the p ⁺ type layer 24 has a thickness of about 1000 Å and a thickness of 10 ¹⁸ cm.
Formed at a high concentration of ^-3 . Next, the oxide film on the surface of the p ⁺ -type layer 24 is removed (Fig. e) to serve as a light-receiving surface, and the electrode 25 is attached by vapor depositing aluminum on the surface of the guard ring layer 23.

The germanium light-receiving element manufactured as described above includes an n-type germanium substrate 21, a p ⁺ type layer 24, and a p-type guard ring layer 23.

The germanium photodetector according to this example has p
Since the depth of the guard ring layer 23 can be as deep as 5 μm or more, the radius of curvature of the cross section of the p guard ring layer 13 can be large, and the carrier concentration of the p guard ring layer 23 is 10 ¹⁶ cm ^-3. Since it is relatively low, the depletion layer spreads toward both the p-type guard ring layer 23 and the n-type germanium substrate 21. Therefore, the withstand voltage becomes high. Furthermore, since the p-type guard ring layer and the p ⁺ -type layer are formed on the n-type germanium substrate, noise can be lowered than when a p-type germanium substrate is used.

As described above, according to the present invention, a p-type channel stopper layer can be formed at a low temperature of 700° C. or less by ion-implanting beryllium into a p-type germanium substrate, thereby providing a method for manufacturing a semiconductor device.

[Brief explanation of the drawing]

FIGS. 1 and 2 are cross-sectional views of conventional light-receiving elements, and FIG. 3 is a diagram showing impurity concentration distribution when beryllium is ion-implanted into a germanium substrate.
FIG. 4 is a process diagram showing one embodiment of the manufacturing method of the present invention, and FIG. 5 is a process diagram showing another embodiment of the manufacturing method of the present invention. 11...p-type germanium substrate, 13...n-type guard ring layer, 15...p-type channel stopper layer, 16...n ⁺ -type layer, 21...n-type germanium substrate, 23...p-type guard ring Layer, 24...
…p ⁺ shape layer.

Claims (1)

[Claims] 1. A step of ion-implanting beryllium into a p-type germanium substrate to form a p-type channel stopper layer, and forming an n-type layer with a high impurity concentration inside the channel stopper layer on the surface of the p-type germanium substrate. A method for manufacturing a semiconductor device, comprising the steps of: