JPS5814741B2 - handout - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for selectively and simultaneously forming a low-concentration layer and a high-concentration layer of group Ⅰ, such as boron, aluminum, or gallium, on a semiconductor substrate.

Boron oxide (B203) formed on the silicon substrate surface
, aluminum oxide (Al203), gallium oxide (G
a203) film, or a mixed film of each of these oxides with silicon oxide (Si02-B203 t
Si02-Al203 s Si02-Ga2103)
is used as a source of impurity diffusion into silicon.

For example, for boron, these oxide films have a thickness of 30
Oxidation reaction or thermal decomposition reaction between an organic boron compound or an organic oran at 0 to 700°C, diborane (B2
H6) is formed on the silicon surface by the oxidation reaction of silicon (Si-H4).

For aluminum and gallium, oxide films are similarly formed from their respective organic compounds or halides.

After forming such a film, boron, aluminum, or gallium is diffused into the silicon substrate by leaving the film at 800 to 1200° C. in an oxygen or nitrogen stream, or a mixed gas thereof for an appropriate period of time.

The junction depth and surface concentration due to this diffusion are determined by temperature, time, the temperature of the impurity boron (or aluminum, gallium) in the oxide film, etc. In particular, the surface concentration largely depends on the impurity concentration in the oxide film.

The surface concentration is 10t6~1020/cm3 by this method.
However, in practice it is more than 1018/cm3, and below 1016-17/cm3, the concentration of boron (or aluminum or gallium) in the oxide film must be controlled to be extremely low, making it difficult to reproduce. I can't expect sex.

Therefore, when forming a high concentration layer and a low concentration layer in a silicon substrate, the surface concentration of each layer obtained is 101
8/cm3 or more, which makes it impossible to increase the difference in concentration between the two, and in order to form a high concentration layer and a low concentration layer, film formation and diffusion must be performed separately for each layer.

This is not only a troublesome process, but also repeating the heating process increases defects in the crystal substrate, which is undesirable.

The present invention solves the above-mentioned problems, and includes a material such as boron, aluminum, or gallium on a silicon substrate.
The present invention provides a method for selectively and simultaneously forming diffusion layers with high concentration and low concentration of group impurities.

That is, the present invention provides (1) forming a film containing at least one of boron and boron oxide (or aluminum and aluminum uneven oxide, or gallium and gallium oxide) to serve as an impurity diffusion source on a silicon crystal substrate; One step, a second step of forming a silicon oxide film on a predetermined location on the silicon oxide film, and a third step of performing high-temperature heat treatment in an atmosphere containing ammonia. It is characterized by selectively and simultaneously forming diffusion layers with different surface concentrations and junction depths by heat treatment. Alternatively, (2) a silicon oxide film is formed at a predetermined location on the surface of a silicon crystal substrate, and then a first step is performed.
It is characterized by performing the second and third steps to selectively and simultaneously form diffusion layers with different surface concentrations and junction depths.
Furthermore, (3) a silicon oxide film is formed at a predetermined location on the surface of a silicon crystal substrate, and then the first step described above is performed, and then the third step is performed to selectively form layers with different surface concentrations and junction depths. It is characterized by being formed at the same time.

That is, as in the present invention, a boron oxide silicon monoxide film (
or aluminum oxide, or gallium oxide) 60
A surface concentration of 1016 can be achieved by ammonia treatment in the range 0-1200°C or by diffusion in the presence of ammonia.
Diffusion of ~10l7/CML3 or less is practically possible.

According to the method of the present invention, ammonia replaces oxygen bonded to boron (or aluminum or gallium) in the oxide film with nitrogen, and
N,Ga-N) bonds are formed.

When this bond is formed, diffusion of boron (or aluminum or gallium) in the mixed film is suppressed, and it becomes difficult to introduce into silicon.

This treatment therefore makes it possible to shift the surface concentration two to three orders of magnitude lower than with the conventional doped oxide method.

That is, as mentioned above, 10 obtained by the conventional method
The surface concentration of 18-1020/cIrL3 becomes 1016-1017/cIrL3 by ammonia treatment.

Therefore, if a thick silicon oxide film is used as a mask against ammonia and a window is opened in a part of the film, only the window will be affected by ammonia, resulting in a different diffusion than outside the window, and due to the above reasons, there will be a large concentration difference. That's how you get results.

Next, the method of the present invention will be explained in detail.

Figure 1 A, B, C (1) and (2) above respectively
, (3).

In FIG. 1, 1 is a silicon substrate, 2 is, for example, an S
102 B2 03 film, 3 is SiO2 film, 4 is SiO
2 is a window formed in the film 5, 5 is a low concentration diffusion layer, 6 is a high concentration diffusion layer, and I is a SiO2 film selectively formed on the surface of the silicon substrate 1.

First, according to FIG. 1A, the ammonia acts only through the window 4, and the diffusion of boron in the SiO2-B203 film 2 under this window is suppressed, and the silicon substrate 1 has a low surface concentration.
A diffusion layer 5 with a shallow junction depth is formed, while a SiO2 film 3
Since the SiO2-B2O3 film covered with ammonia is not treated with ammonia, a diffusion layer 6 having a high surface concentration and a deep junction is formed.

This prevents the diffusion of impurities directly under the SiO2 film 7, and in this case as well, different diffusion layers 5 and 6 can be formed in areas other than directly under the SiO2 film.

C is the same as B in which the SiO2 film 3 is not formed and a low concentration diffusion layer 5 is selectively formed.

Next, examples of the present invention will be shown.

4 on N-type silicone substrate 1 (specific resistance 6 to 10 Ωcrn)
At 00°C, the flow rate of a mixed gas of 7ran and nitrogen (silane concentration 5%) is 270 ml/min, and the flow rate of a mixed gas of diborane and nitrogen (diborane concentration 0.5%) is 150 ml/min.
The silicon oxide/boron monoxide mixed film 2 was formed to a thickness of 1000 people under the conditions of 4017 min of nitrogen and 100 ml/min of oxygen.

Next, diborane is stopped at step i, and a silicon oxide film 3 of 10,000 Å is formed thereon under the above conditions.

A part of this silicon oxide film 3 was etched into a film with a width of 30μ by photolithography.
Remove it in a grid pattern.

After this, in an ammonia air flow (flow rate 2 l/min 1000
Heat treatment is performed at ℃ for 30 minutes.

Diffusion is carried out at 1150° C. for 30 minutes in a nitrogen stream (flow rate 1 l/min).

As a result, in the part where the oxide film 3 has been removed, the surface concentration of the diffusion layer 5 is 3 x 10l7/cm3, and the junction depth is 0.8μ-, and the surface concentration of the diffusion layer 6 in the other part is 2 x 1020/cm3.
m3, and the bonding depth was 2.3μ.

FIG. 2 shows a cross-sectional photograph of the diffusion layer enlarged 20 times by angle polishing.

Note that in this photo, the oxide film has been removed by stain etching with hydrofluoric acid.

In this way, the area where the oxide film has been removed is affected by the ammonia treatment, which suppresses diffusion and reduces the surface concentration, and directly below the silicon oxide film, ammonia is prevented from entering the silicon oxide boron monoxide film. High concentration diffusion takes place.

In the case of aluminum or gallium, similar results can be obtained by forming an aluminum oxide silicon monoxide film or a gallium oxide silicon monoxide film on the silicon surface and performing the same treatment as in the previous description.

As described above, the present invention facilitates selective and simultaneous diffusion of impurities, which is particularly useful for devices that require high breakdown voltage and low-concentration and high-concentration diffusion such as photoavalanche diodes. .

[Brief explanation of drawings]

FIGS. 1A, B, and C are explanatory diagrams of the method according to the present invention. FIG. 2 is a cross-sectional photograph of a diffusion layer formed by the method of the present invention. 1... Silicon substrate, 2... SiO2
-B203 film, 3... SiO2 film, 4...
...Window, 5...Low concentration diffusion layer, 6...
High concentration diffusion layer, 7...S102 film.

Claims (1)

[Claims] 1. A step of forming a film containing at least one of a group (III) element and an oxide of a group (III) element serving as an impurity diffusion source on a semiconductor crystal substrate, and forming an oxide (9) at a predetermined location on this film. It consists of a step of forming an elementary film and a step of performing high-temperature heat treatment in an atmosphere containing ammonia, and simultaneously or at the same time as this step, diffusion layers with different surface concentrations and junction depths are selectively formed at the same time by a necessary high-temperature heat treatment. 1. A method for diffusing impurities into a semiconductor, characterized by forming. 2. A silicon oxide film is formed at a predetermined location on the surface of a semiconductor crystal substrate, and then a film containing at least one of a group (III) element and an oxide of a group (III) element, which serves as an impurity diffusion source for the substrate, is formed. A method for diffusing impurities into a semiconductor according to claim 1. 3. A step of forming a silicon oxide film at a predetermined location on the surface of a semiconductor crystal substrate, and a film containing at least one of a group III element and a compound of a group III element, which serves as an impurity diffusion source, on the substrate and the silicon oxide film. 1. A method for diffusing impurities into a semiconductor, comprising the steps of forming a semiconductor crystal substrate and then performing high-temperature treatment in an atmosphere containing ammonia, and selectively diffusing the group (I) element into the semiconductor crystal substrate.