JPH04349636A - Impurity diffusion method - Google Patents

Abstract

PURPOSE:To obtain a smoothed high concentration As diffused layer which is free from crystal defects and fine defects by a method wherein a very thin SiO2 film is provided between an Si single crystal substrate and an amorphous Si layer deposited on it and an SiO2 film having a specific thickness is formed on the deposited amorphous Si film under a low temperature, etc. CONSTITUTION:As ions are implanted into an amorphous Si film 3 deposited on an Si single crystal substrate 1. The amorphous Si layer 3 doped with As ions are oxidized in, for instance, a wet oxygen atmosphere under a high temperature about 1150 deg.C and, further, in that state, As ions are diffused into the Si single crystal substrate 1. After oxide films such as the oxidized amorphous Si layer 3 doped with As ions are removed, as ions are diffused to a required depth to form a diffused layer 6. In such an impurity diffusion method, a very thin SiO2 7 is provided between the Si single crystal substrate 1 and the amorphous Si film 3 deposited on it and, further, an SiO2 film 8 having a thickness about 200Angstrom is formed on the deposited amorphous Si film 3 and then a process described above is performed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a method for removing an arsenic ion-implanted amorphous silicon layer formed on a silicon single crystal substrate from the silicon single crystal substrate by oxidizing the surface of the silicon single crystal substrate after removal. The present invention relates to an impurity diffusion method characterized by smoothing the surface and making it free from defects.

0002

[Prior Art] Conventionally, a polycrystalline silicon layer deposited on a silicon single crystal substrate or an arsenic ion-implanted polycrystalline silicon layer is
When oxidized in a moist oxygen gas atmosphere at a temperature of about 950°C to 1050°C, the oxidation rate near the grain boundaries increases, resulting in a deposited silicon film on the silicon single crystal substrate surface after the oxide film is removed. Irregularities are more likely to occur. In particular, when an arsenic ion-implanted polycrystalline silicon layer is oxidized, the segregation of arsenic to the grain boundaries increases, resulting in larger unevenness on the surface of the silicon single crystal substrate after oxidation, which is undesirable. For this purpose, attempts have been made to use an amorphous silicon layer instead of polycrystalline silicon to improve the unevenness of the silicon single crystal substrate surface after oxidation removal, but when using an arsenic ion implantation deposited silicon layer, In the case of an oxidation temperature of 950° C. to 1050° C., there is a limit to the extent to which unevenness on the silicon surface after oxidation removal can be reduced due to the segregation phenomenon of arsenic to grain boundaries.

For example, when a deposited polycrystalline silicon film is oxidized in humid oxygen gas at an oxidation temperature of 950° C. to 1050° C., the surface of the silicon single crystal substrate after the oxide film is removed becomes noticeably uneven due to grain boundary effects. It is formed. If a deposited amorphous silicon layer is used instead of a polycrystalline silicon layer, the grain boundary effect is alleviated and the surface of the silicon single crystal substrate after oxidation becomes extremely smooth. For example, when a silicon layer is oxidized in moist oxygen gas at an oxidation temperature of 950°C to 1050°C, arsenic segregation occurs at grain boundaries during the oxidation process, so the silicon single crystal substrate surface after oxide film removal There are still some unevenness left. The height of this unevenness is 1 nm or more. However, when the oxidation temperature is set to a high temperature of, for example, 1150° C., arsenic segregation at grain boundaries decreases and approaches the silicon single crystal surface state (1 nm or less) after oxidation removal without arsenic ion implantation.

However, crystal defects tend to occur on the surface of a silicon single crystal substrate after the arsenic ion implantation deposited amorphous silicon layer is oxidized at a high temperature of, for example, 1150° C. and the oxide film is removed.

[0005]

SUMMARY OF THE INVENTION In order to improve these drawbacks, the present invention aims to process an arsenic ion-implanted amorphous silicon layer deposited on a silicon single crystal substrate by heating it with moist oxygen gas at a high temperature of, for example, 1150°C. By oxidizing the silicon inside, the amount of arsenic that tends to segregate at grain boundaries is reduced, the increase in oxidation rate at grain boundaries is alleviated, and a smooth silicon single crystal surface is obtained. In addition, to prevent crystal defects that tend to occur during high-temperature oxidation, we have introduced a thin silicon oxide film on the silicon single crystal substrate boundary and the deposited silicon film on it, creating a smooth surface without micro defects. This is where the diffusion layer is formed.

[0006]

[Means for Solving the Problems] In order to prevent the occurrence of crystal defects, a thin silicon dioxide film of, for example, about 30 Å is interposed between a silicon single crystal substrate and an amorphous silicon layer deposited thereon, and arsenic ions are also provided. In order to prevent micro defects that are likely to occur when the implantation layer is oxidized, a silicon dioxide film of about 200 Å was deposited at a temperature of, for example, 600° C. on the amorphous silicon film deposited before arsenic ion implantation. After ion implantation, an oxidation treatment is performed, and a further diffusion treatment is performed to remove the oxide film, and then a second drive diffusion is performed to obtain the desired surface concentration and diffusion depth.

[0007] By taking such a process,
A smooth, highly concentrated arsenic diffusion layer free of crystal defects, micro defects, etc. can be obtained.

The structure of the present invention is as shown below. That is, the present invention includes a first step of implanting arsenic ions into an amorphous silicon film deposited on a silicon single crystal substrate, and a step of implanting the arsenic ion-implanted amorphous silicon layer at, for example, 1150°C.
A second step of oxidizing in a humid oxygen atmosphere at a relatively high temperature, and further diffusing arsenic into the silicon single crystal substrate in this state, and then implanting the oxidized arsenic ions into the amorphous silicon layer, etc. In the impurity diffusion method, which consists of the third step of removing the oxide layer and then diffusing to a predetermined diffusion depth to form a diffusion layer, there is a By performing the first, second, and third steps after the step of interposing a thin silicon dioxide film and the step of forming a silicon dioxide film of about 200 Å on the deposited amorphous silicon film at a low temperature, This is an impurity diffusion method characterized by forming a highly concentrated arsenic diffusion layer with almost no crystal defects or micro defects.

[0009]

[Embodiment] This embodiment will be explained below with reference to the drawings. Figure 2
1 shows an example based on a conventional method. For example, silicon P type (111) single crystal substrate 1, boron addition 1
A silicon dioxide film 2 for selective diffusion with a thickness of about 0.6 μm is formed on a 0Ω·cm layer by photolithography, and the silicon dioxide film portion 2 on the buried diffusion region 6 is removed. Next, for example, an amorphous silicon film 3 is deposited at a deposition temperature of 520° C. by, for example, reduced pressure vapor phase growth.
is deposited to a thickness of approximately 1000 Å. Next, arsenic ion 4 was applied at 30kV.
After injection of 3×10 15 cm −2 at 3×10 15 cm −2 , it was completely oxidized at an oxidation temperature of 950° C. to 1050° C. in humid oxygen gas. This was followed by diffusion at 1150°C for 10 min with N2 (4):
The process is carried out as it is in an atmosphere with a capacity ratio of O2(1), the oxide is removed, and a second drive diffusion is performed until the target surface concentration and diffusion depth are achieved. After embedding arsenic and diffusion, silicon was epitaxially grown to 1.5 μm and the morphology of the growth surface and crystal defects were examined.
Unevenness 5 due to micro defects and grain boundary effects can be seen.

FIG. 1 shows an example of an embodiment according to the method of the present invention. First, a thin silicon dioxide film 7 of about 30 Å is interposed between the silicon single crystal substrate 1 and the deposited amorphous silicon film 3. Furthermore, due to the chemical reaction of keisane ethyl, the temperature at 600℃
An oxide film of about 200 Å was deposited on the deposited amorphous silicon layer 3 for 5 minutes. Arsenic ions were injected at 3 × 1015 cm-2 at 30 kV into this, and 1
Oxidize at 150°C for about 15 minutes, and then diffuse in an atmosphere with a capacitance ratio of N2 (4):O2 (1) for about 10 minutes. After removing the oxide films 2, 3, 7, and 8, the N2 (4) )
:O2 at 1150℃ in an atmosphere with a capacity ratio of (1).
Time 2nd drive spread. The layer resistance at this time is approximately 33Ω
/It was a mouth. As in the case of the conventional method shown in FIG. 2, silicon was epitaxially grown on this arsenic buried diffusion layer, and surface morphology and crystal defects were examined. By high temperature oxidation,
The state of the silicon surface after oxidation is extremely smooth.
The occurrence of crystal defects (dislocations, stacking faults) and micro defects was significantly reduced and improved.

[0011]

Effects of the Invention As explained above, by oxidizing the arsenic ion-implanted amorphous silicon layer in moist oxygen gas at a high temperature of about 1150°C, the oxidized arsenic ion-implanted amorphous silicon layer After the oxide film is removed, not only can a smooth silicon single crystal surface be obtained, but it is also possible to reduce crystal defects and micro defects that tend to occur on the silicon surface after the oxide film has been removed. This method involves implanting ions inside, oxidizing them, and using them as a diffusion source.
It is effective for forming a high concentration arsenic diffusion layer, and its practicality will be remarkable if it is used for forming a buried diffusion layer of a bipolar LSI system.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing a high concentration arsenic diffusion layer formed by the method of the present invention.

FIG. 2 is a cross-sectional view showing a high concentration diffusion layer formed using a conventional arsenic ion implantation method.

[Explanation of symbols]

1 Silicon single crystal substrate 2 Silicon dioxide film for selective diffusion mask 3 Deposited amorphous silicon film 4 Beam for arsenic ion implantation 5 Silicon surface after oxidation and diffusion 6 Arsenic embedded diffusion region

Claims (1)

[Claims] 1. A first step of implanting arsenic ions into an amorphous silicon film deposited on a silicon single crystal substrate;
The arsenic ion-implanted amorphous silicon layer is, for example, 1150
A second process in which arsenic is oxidized in a humid oxygen atmosphere at a high temperature of about °C, and then diffused into the silicon single crystal substrate in this state.
In an impurity diffusion method, the impurity diffusion method comprises a third step of removing the oxidized arsenic ion-implanted amorphous silicon layer or the like and then diffusing to a predetermined diffusion depth to form a diffusion layer. , a process of interposing an extremely thin silicon dioxide film between a silicon single crystal substrate and an amorphous silicon film deposited on it, and a process of forming a silicon dioxide film of about 200 Å on the deposited amorphous silicon film at low temperature. An impurity diffusion method characterized in that a high concentration arsenic diffusion layer with almost no crystal defects and micro defects is formed by performing the first, second, and third steps.