JP3272908B2 - Method for manufacturing semiconductor multilayer material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor multilayer material having a top silicon layer.

[0002]

2. Description of the Related Art SOI materials are Semiconductor On Insulat.
or material, meaning a semiconductor with a multilayer structure. In recent years, as a semiconductor device raw material, an SOI material having a thin and high-purity top silicon layer has been demanded.

Conventionally, the control of the boron concentration in a silicon wafer has been performed by a boron ion implantation method or an epitaxial growth method. In addition, thinning of the top silicon layer has been performed by utilizing the property that the etching rate of silicon depends on the boron concentration.

[0004]

However, in the conventional method, it is impossible to prevent the generation of defects due to the implantation of boron ions and the occurrence of misfit transition from the high-concentration boron substrate during the epitaxial process.

[0005] Such a phenomenon is likely to induce device defects, and is a major cause of lowering the yield.

[0006] In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a method capable of producing a high quality semiconductor multilayer material with high yield.

[0007]

An embodiment of the present invention will be described.
As shown, in a method for manufacturing a semiconductor multilayer material having a top silicon layer, a silicon wafer (11) containing boron at a concentration of 10 ¹⁹ cm ⁻³ or more is subjected to a heat treatment at a temperature of 1000 ° C. or more in a hydrogen atmosphere. Boron near the surface of the wafer is diffused outward, and the boron low concentration layer (1
1a) is formed, and thereafter, the top silicon layer (11b) is thinned by etching using an alkaline solution.
Der Ru.

The semiconductor multilayer material manufactured by the method of the present invention has a top silicon layer (11b) having a boron concentration of 10 ¹⁹ cm ^-3 or more and a thickness (X (f)) of 5 μm or less.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of diligent research, the present inventors have found that the outward diffusion of boron in a silicon wafer depends on the processing atmosphere. That is, even though the boron-containing silicon wafer is heat-treated in an argon gas atmosphere, boron hardly diffuses outward. However, by heat-treating the wafer in a hydrogen gas atmosphere, boron is diffused outward to reduce the boron concentration near the surface. I found what I could do. The present invention is based on such findings.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing a method for manufacturing a semiconductor multilayer material according to the present invention.

First, two Cs of the top 11 and the base 12
Prepare a Z silicon wafer. Among them, the top CZ silicon wafer 11 is a wafer containing boron at a concentration of 10 ¹⁹ cm ⁻³ or more.

The top and base silicon wafers 11 and 12 are dried in an oxidizing atmosphere at 850-10.
A thermal oxidation treatment is performed in a temperature range of 50 ° C. for 10 to 60 minutes. By this heat treatment, thermal oxide layers 13 and 14 are formed on the surface of each wafer. The thickness of the thermal oxide layers 13 and 14 is, for example, about 5 to 100 nm.

Next, the top 11 and the base are bonded together so that the thermal oxide layers 13 and 14 are joined together. The bonding method is
After direct bonding, 10 minutes to 1 hour, 800 to 1100
A method of performing a bonding heat treatment in an Ar atmosphere at a temperature of, for example, can be employed.

After bonding, the wafer on the top 11 side is subjected to ordinary mechanical polishing treatment to reduce the thickness of the top 11 to X (m). X (m) is, for example, about 7 to 15 μm.

Next, the bonded silicon wafer is placed in a hydrogen gas atmosphere at a temperature of 1000 to 1200 ° C. for 10 to 100 hours.
By heating for 0 minutes, boron on the surface of the top 11 is diffused outward to form a low boron concentration layer 11a there. The low boron concentration layer 11a is a Boron Denuded Zone (Boron DZ). The boron concentration of the low boron concentration layer 11a is at least 10 ¹⁸ cm ⁻³ or less.

[0016] In addition, mechanical polishing is performed in the pre-process and the top 1 is obtained.
The reason why the thickness of 1 is reduced is to shorten the time required for the boron outward diffusion step and to suppress the cost.

The boron distribution C in this boron diffusion process
(X, t) can be represented by the following outward diffusion equation.

[0018]

(Equation 1) In Equation 1, x is the depth from the surface, t is a heat treatment time, D is a boron concentration of the diffusion coefficient, C ^B and C ^S, respectively bulk and surface of the boron. The value of C ^S is 120
In the case of 0 ° C., it can be estimated to be 10 ¹⁶ cm ⁻³ or less. Also,
The diffusion coefficient D of boron is the same as the diffusion coefficient in a general P-type silicon crystal, and is about 5 × 10 ^{−13 at} 1200 ° C.
cm ² s ⁻¹ .

Now, as generally known, silicon
The etching rate of wafers in alkaline solution is
Strongly depends on the concentration of Especially the etching rate r and boron
The concentration C (x, t) can satisfy the following empirical relational expression.
It has been reported. H. Seidel, J. Electrochem. Soc.137
 , (1990) 3626.

[0020]

(Equation 2) In Equation 2, C ₀ is called a critical concentration, and r ₀ is an etching rate of a silicon wafer having a boron concentration C (x, t) << C ₀ . The parameters r ₀ and C ₀ are also determined by the type, concentration, temperature, etc. of the alkaline solution. For example, in the case of 60 ° C. and 10% KOH, each is about 10 μm / h.
r and about 4 × 10 ¹⁹ cm ⁻³ . Therefore, boron concentration 4
When the boron concentration increases around × 10 ¹⁹ cm ⁻³ , the etching rate of the silicon crystal sharply decreases.

That is, boron DZ formed by outward diffusion of boron in a hydrogen atmosphere is removed by chemical etching in an alkaline solution, so that the top silicon layer can be thinned. Here, the size of the boron DZ or the thickness of the silicon layer to be removed can be defined by an outward diffusion equation (Equation 1) and a relational equation between the etching rate and the boron concentration (Equation 2).

That is, the time and temperature of the heat treatment in the hydrogen atmosphere in Equation 1 can be set from the etching rate in the alkaline solution of Equation 2, and based on this, the final thickness of the top silicon layer can be determined. .

Specifically, the thickness of the top silicon after mechanical polishing is x (m), and the target final thickness is x (f).
Then, the required etching time τ can be estimated by the following Expression 3.

[0024]

(Equation 3) The etching rate r in Equation 3 is represented by Equations 1 and 2, and the etching time τ can be obtained from Equations 1 to 3 above.

When the alkali etching is performed with the estimated etching time τ estimated as described above, the entire boron low concentration layer can be removed by etching, and the thickness x
The top silicon layer (f) can be obtained.

The reason why the boron concentration of the top silicon wafer is set to 1 × 10 ¹⁹ cm ⁻³ is as follows. This is because when the boron concentration is less than 1 × 10 ¹⁹ cm ⁻³ , the etching rate is high as can be seen from Expression 2, and a steep change in the boron concentration cannot be obtained. The out-diffusion defined in Equation 1 makes it impossible to control the final thickness of the top silicon layer.

Hereinafter, Embodiment 1 of the present invention will be described.

15 Ω as a base silicon wafer
−cm, boron doped P type, (100), 6 inch, CZ wafer was used. The top silicon wafer has a boron concentration of 1.2 × 10 ²⁰ cm ⁻³ (1 mΩ-c
m), (100), 6 inch, CZ wafer.

Both the base and top silicon wafers are oxidized in a dry atmosphere at 950 ° C.
Was formed on the surface of each wafer.

Next, after both wafers are directly bonded, 3
Bonding was performed by performing heat treatment in an Ar atmosphere at 950 ° C. for 0 minutes, and the surface layer of the top silicon wafer was polished to X (m) = about 10 μm by ordinary mechanical polishing. Then, after standard cleaning, 1 hour in a hydrogen atmosphere.
The treatment was performed at 200 ° C. for 10 hours.

Now, in order to set the target final thickness to X (f) = 1 μm, the etching time τ when a solution of 10% KOH is used at 60 ° C. is calculated by using the above formula 3 (and 1, 2). Estimated, the required time τ is about 90 minutes.

Therefore, when the etching was actually performed for 90 minutes, the thickness of the top silicon was 1.5 ± 0.5 μm.
Became.

As a result, the boron concentration is 1.2 × 10 ²⁰ cm ^-3 and the thickness is 1.5
A semiconductor multilayer material having a top silicon layer of ± 0.5 μm was obtained. When the top silicon layer was observed with an electron microscope, no crystal defects were observed.

[0034]

According to the method of the present invention, a semiconductor multilayer material having a high quality top silicon layer free from crystal defects such as bulk crystals can be manufactured with a high yield.

More specifically, defects inevitable in the manufacturing process of the semiconductor multilayer material, that is, generation of defects due to implantation of boron ions and misfit transition from a high-concentration boron substrate generated during epitaxial processing are considered. It can be reliably prevented.

The semiconductor multilayer material of the present invention has a high-quality top silicon layer and can realize a sharp change in boron concentration, and is therefore useful as a raw material for semiconductor devices.

The present invention is not limited to the above embodiment. For example, if the thickness of the top silicon wafer is reduced in advance, the mechanical polishing can be made very small or omitted.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of a method for producing a semiconductor multilayer material according to the present invention.

[Explanation of symbols]

 11 Silicon wafer for top 11a Boron DZ layer 12 Silicon wafer for base 13, 14, 15 Oxide film

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nariwazu Suzuki 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. (72) Inventor Kenro Hayashi 30 Soya, Hadano-shi, Kanagawa Toshiba Ceramics Co., Ltd. In the laboratory (56) References JP-A-7-111321 (JP, A) JP-A-2-278766 (JP, A) JP-A-61-182241 (JP, A) JP-A-6-338604 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 27/12 H01L 21/02 H01L 21/22-21/24 H01L 21/306-21/3063 H01L 21/308 H01L 21/33- 21/331 H01L 29/68-29/737

Claims (3)

(57) [Claims] In a method of manufacturing a semiconductor multilayer material having a top silicon layer, a silicon wafer (11) containing boron at a concentration of 10 ¹⁹ cm ⁻³ or more is subjected to a heat treatment at a temperature of 1000 ° C. or more in a hydrogen atmosphere. Then, boron near the wafer surface layer is diffused outward to form a low-concentration boron layer (11a) thereon, and thereafter, an etching process is performed using an alkaline solution to form a top silicon layer (11b).
A method for producing a semiconductor multilayer material, comprising: 2. A semiconductor multilayer material having a top silicon layer.
In the method of manufacturing the material, the silicon wafer for base (1
2) and boron containing boron at a concentration of 10 ¹⁹ cm ^-3 or more.
Silicon wafer for polishing (11) via an oxide film.
Silicon wafers (11, 12) are bonded together,
Thereafter, heat treatment is performed at a temperature of 1000 ° C. or more in a hydrogen atmosphere.
And diffuse boron in the vicinity of the wafer surface to the outside.
Forming a low-concentration layer (11a), followed by alkali
Top silicon layer by etching using solution
(11b) a semiconductor multilayer characterized by thinning treatment
Material manufacturing method. 3. A base silicon wafer (12);
10 ¹⁹ cm ^-3 or more to form an oxide film (13, 14) on one side of the silicon wafer of each oxidation treatment is performed on both silicon wafer between the top silicon wafer containing boron (11) at a concentration of oxide The two silicon wafers (11, 12) are bonded together with the films (13, 14) facing each other, and thereafter, the silicon wafer for top (11)
The method of manufacturing a semiconductor multilayer material of claim 1 or 2, characterized in that to form a surface layer on the boron lightly doped layer (11a).