JPS6058683A - Manufacture of light receiving element - Google Patents

Abstract

PURPOSE:To manufacture the titled element so as to reduce the surface leakage current by a method wherein a guard ring and a channel stopper are formed at a time of process of heat treatment by the use of a double-layer or a three-layer dielectric film as a selective mask in the formation of the guared ring by the thermal diffusion of impurity. CONSTITUTION:The dielectric film of the first layer is patterned so as to serve as a selective mask for a channel stopper, and the dielectric film of the second layer adhesion-formed thereon uses a film containing an impurity which cannot penetrated through the first layer at a diffusion temperature for guard ring formation and has the same conductivity type as that of a substrate. Further, in some case, the third layer to prevent the evaporation of the second layer impurity is adhered and then made as a selective diffusion mask for an impurity to form the guard ring as a whole of the double layer or the three layers. Thereby, the number of the process of heat treatment during the manufacturing process and that of the process wherein the exposed part of the P-N junction loses a film are made as small as possible, and accordingly the surface leakage current can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor light-receiving device, and particularly to a diffusion mask used when forming a guard ring.

In conductor light receiving elements used in optical receivers, etc., especially in high-speed, high-sensitivity avalanche photodiodes, the light-receiving area is located on the surface of a semiconductor substrate that exhibits a single conductivity type. In order to prevent local breakdown at the outer periphery, a deep low concentration impurity region of the same conductivity type as the light-receiving region is formed to include the outer periphery of the light-receiving region. Many devices have a structure in which a guard ring is formed, and an impurity of the same conductivity type as the substrate is introduced outside the guard ring to reduce surface leakage current to form a channel stopper.

Conventionally, to form this channel stopper, a special method has been used in which impurities having the same conductivity type as the substrate are selectively diffused or ion implantation is performed followed by heat treatment. One heat treatment step was required for formation.

In general, in a light receiving element, crystal defects are likely to occur on the wafer surface due to thermal strain at the interface between the mask material and the wafer surface during heat treatment, and this is often a factor that causes an increase in surface leakage current. To reduce these crystal defects, select a mask material and slow the heat treatment rate.40. There are methods such as capless heat treatment, and methods such as etching the crystal surface after heat treatment to remove crystal defects.
At present, it is difficult to avoid all defects, and it can be considered that increasing the number of heat treatment steps will worsen the interface condition. In particular, if the substrate material is Ge, -? In the case of N-V group compounds, no suitable surface protective film has been found, so the increase in surface leakage current, that is, the increase in dark current due to crystal defects on the surface generated in this heat treatment process is significant [7]. There is something.

On the other hand, in the manufacturing process of a photodetector, various functional regions such as a photodetection region, a guard ring, and a channel stopper are sequentially formed by selective thermal diffusion or ion implantation of impurities. In addition, in the case of Ge and JI[-V group compounds, the method of forming a protective film by thermal oxidation of the wafer is not used, so the selection mask for each impurity introduction process needs to be deposited each time and removed in the next process. I have to give it back. In other words, is the surface of the Geg plate between processes? There are many opportunities for mushrooms to appear. The point where surface leakage current flows is p
If adhesion formation and etching removal are repeated at the surface exposed portion of the n-junction, the interface condition deteriorates, that is,
This results in an increase in the number of interface units, leading to an increase in surface leakage current.

In short, in the manufacturing process of a photodetector using a Ge or N-V group substrate, minimizing the heat treatment process and the process in which the exposed pn junction loses its coating reduces surface leakage current. In other words, this leads to keeping the dark current low.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a light-receiving element that overcomes the process problems described above and reduces dark current compared to conventional methods.

According to the manufacturing method of the present invention, a two-layer or three-layer dielectric film is used as a selective mask when forming a guard ring by thermal diffusion of impurities, and each layer is formed so as to satisfy the following requirements. Particularly, both the guard ring and the channel stopper can be formed in one heat treatment process, and the above object can be satisfied. That is, the first layer dielectric film is patterned to serve as a selective mask for the channel stopper, and the second layer dielectric film deposited thereon is patterned at the diffusion temperature for guard ring formation. Using a material containing impurities of the same conductivity type as the substrate that cannot pass through the layer,
Further, in some cases, a third layer M is deposited to prevent evaporation of impurities in the second layer, and these two or three layers as a whole can serve as a selective diffusion mask for impurities for forming a guard ring.

An example of a process for manufacturing a germanium (Ge) light receiving element will be described below with reference to the drawings.

When a guard ring is formed by thermal diffusion of zinc (Zn) to form a Ge p+n type light receiving element,
A non-doped silicon oxide film (8i02 film) does not function as a mask and allows Zn to pass through, so a silicon oxide film (PSG film) containing 5 mo1% or more of phosphorus must be used as a diffusion mask. Must be. However, since this P acts as an n-type impurity for Ge, it is necessary to use 5f02 J[ti as an underlay to prevent P diffusion. In addition, since the PSG film is highly deliquescent,
The adhesion of the photoresist on the surface is poor, and a 5I02 film must be deposited as a cap layer.

In the conventional process, the concentration of through-cinene blunt material is 1×10”/
5 of 1500λ on an n-type Ge substrate 1 of about cm3
An in2 film 4 is deposited on the entire surface as shown in (a).

Next, the three-layer film 2, 3.4 is patterned as shown in (b), and Zn is diffused in a sealed tube to form a Zn guard ring.
A diffusion region 5 is formed. Next, the three-layer films 2, 3 and 4 are removed by etching), and a new SiO2 film 6 for a channel stopper selection mask is deposited (FIG. (C)). 8402
After patterning the film 6, an n-type region 7 in the dJ diagram is formed by ion implantation or thermal diffusion of arsenic (As).Then, the 8i02 film 6 is removed and a photoresist 8 for forming a light-receiving region is formed using Ge. Apply directly to the surface (e)
), this is patterned by lithography and boron (III) ions are implanted to form a P+m region 9 (
(f) Figure). Photoresist 8 is removed to activate the ion implantation region.

A 5io2 film 10 is deposited and heat treated using this as a cap (Figure (g)). 8i02 with heat treated cap
Since impurities are mixed into the film 10, a 5in2 film 11 for a contact mask is newly formed by removing the film 10 which was a cap (FIG. (h)). This 8i02 film 11 is patterned to form an aluminum (Al) electrode 12 in contact with a part of the P-type region 9, and the surface processing of the light receiving element is completed ((ill). In the process, the surface exposed part of the final pn junction, that is, the outer periphery of the guard link 5, is coated five times and removed four times throughout the entire process, resulting in Asd diffusion. If it were to be introduced, it would have to undergo heat treatment three times.

As mentioned earlier, the number of times of heat treatment and the number of times that the pn junction is exposed to the surface lead to an increase in dark current, and in order to reduce dark current, these times must be reduced as much as possible. Must be.

A second example of implementing the present invention in the manufacturing process of a Ge photodetector is shown in the second example.
As shown in the figure. That is, in this embodiment, unlike the conventional method, the VC
5in2 film 2 without growing 3 layers 1i2, 3.4 at once
After forming only on the n-type Ge substrate 1 (Figure (a)),
This is patterned into a channel stopper selection mask ((b) figure), and the PEG film 3, 5io2 film 4 is deposited on the entire surface ((CJ figure)).

When the three-layer film 2, 3.4 in this state is turned and sealed and diffused with Zn as shown in (d), it becomes p-type Znwli.
At the same time as region 5 is formed in the same manner as before, 5io22
By this patterning, P contained in PSGSaO2 is thermally diffused at the locations where the P8G film 3 is in contact with the Ge substrate 1, and an n-type P diffusion region 21 is formed. The following three-layer film 2, 3.4 is removed and photoresist 8'5r:
The coating process (Figure (e)) is completely the same as the conventional method, so the guard ring 5 is
The outer periphery of the film is coated 4 times and removed 3 times in the entire process.
Only two heat treatments are required. This is one fewer number of times than the conventional method.
Furthermore, since the guard ring and channel stopper image areas are formed simultaneously, the process can be simplified and dark current can be reduced.

In the above example, the manufacturing process for creating a p+-n type element on a Ge n-type substrate was explained, but even if a p-type substrate is used, it is also possible to Needless to say, the same effect can be obtained in both cases.

[Brief explanation of the drawing]

FIGS. 1(a) to 0) are cross-sectional views showing an example of the conventional manufacturing process of a Ge photodetector, and FIGS. 2(a) to (e) show the present invention in the manufacturing process of a Ge photodetector. This is an example of application. In addition, from FIG. 2(e) onward, from FIG. 1(e), (i
) up to area 7 becomes area 21, and the rest are the same, so they are omitted. In the figure, 1 is n[Ge substrate, 2 is 5i02jli)
, 3 is a PSG film, 4 is a 5in2 film, 5 is a Zn diffusion region indicating p-type, 6 is an 8i02 film, 7 is an As implantation region indicating n-type, 8 is photoresist, and the opening is B implantation indicating p+ type. area, 10 is SiO2 film, 11 is 5in2 film, 12 is AJ
The electrode 21 represents a P diffusion region exhibiting n-type. Figure 1 Figure 1 Figure 2 “-” “□--

Claims (1)

[Claims] 1. A crystal surface exhibiting a first conductivity type has a second conductivity type opposite to the first conductivity type.
In a method for manufacturing a light receiving element in which a PN junction is formed by introducing an impurity of a conductivity type, a first dielectric material containing no impurity is used as a selection mask when forming a guard ring by diffusing an impurity of a second conductivity type. A two-layer film of a film and a second dielectric film containing an impurity exhibiting the first conductivity type is used, and prior to depositing the second dielectric film, the first dielectric film is placed outside the outer edge of the guard ring. A desired portion of the film is removed by etching, and in the final diffusion step for forming the guard ring, the impurity of the first conductivity type in the second dielectric film is simultaneously selectively diffused onto the crystal surface of the etched portion. A method of manufacturing a light receiving element, characterized in that: 2. In the manufacturing method according to claim 1, a third dielectric film containing no impurities is deposited on the two-layer dielectric film to form a three-layer film. Method.