JPH05217972A - Manufacture of soi substrate - Google Patents

Abstract

PURPOSE:To provide a method of forming a thin film Silicon On Insulator(SOI) having a uniform thickness without grinding flagging and grinding inclination in improvements in a method of manufacturing the thin-film SOI. CONSTITUTION:This embodiment comprises a process by which an epitaxial layer 2 having lower impurity concentration of a substrate is grown on a Si substrate 1 which will be an element substrate to form a field oxide film 3 on the epitaxial layer, a process by which the element substrate is adhered to a supporting substrate 6 in which a SiO2 film is formed on the other Si substrates, and a process by which the Si substrate of the element substrate and a part of the epitaxial layer are selectively removed by etching to perform a chemical mechanical grinding.

Description

Detailed Description of the Invention

[0001]

The present invention relates to thin film SOI (Silicon On Ins
ulator) improvement method. In recent years, the thickness of SOI films required for higher speed semiconductor devices is becoming thinner and thinner. As a result, grinding and polishing technology for SOI fabrication is becoming more and more important.

[0002]

2. Description of the Related Art FIG. 4 is a diagram for explaining a conventional method of manufacturing a thin film SOI. As shown in Fig. 4 (a), the Si substrate
After forming the field oxide film 32 on 31 and the element substrate on which the CVD SiO ₂ film 33 was formed, and the supporting substrate on which the SiO ₂ film 35 was formed on the Si substrate 34, as shown in FIG. 4 (b), Laminate at 950 ° C. Then, as shown in Fig. 4 (c), the Si substrate
31 is selectively polished by a chemical mechanical method and SO
Form I 31 '.

[0003]

[Problems to be Solved by the Invention] However, this Si substrate 31
In the polishing process, polishing sag (the surface of SOI 31 'becomes concave) and polishing inclination (the surface of SOI 31' inclines in one direction) are likely to occur, and SOI 31 'of uniform thickness is formed. It was not easy to form. This was even more difficult when trying to obtain a thin SOI.

Therefore, an object of the present invention is to provide a method for forming a thin SOI having a uniform thickness without polishing dripping or polishing inclination.

[0005]

[Means for Solving the Problems] The above-mentioned problems include a step of growing an epitaxial layer having an impurity concentration lower than that of an Si substrate to be an element substrate and forming a field oxide film on the epitaxial layer, A step of bonding the element substrate to a support substrate on which another SiO ₂ substrate is formed with a SiO ₂ film, and a step of selectively removing the Si substrate and a part of the epitaxial layer of the element substrate by etching and then performing chemical mechanical polishing. The method of manufacturing an SOI has the following steps.

FIG. 1 is a diagram for explaining the principle of the present invention. In order to form the element substrate, as shown in Fig. 1 (a),
After forming a Si nitride film 4 on an epitaxial layer 2 with a B concentration of 10 ¹⁵ cm ^-3 formed on a p ⁺ Si substrate 1 doped with boron (B) of 10 ¹⁹ cm ^-3 , a normal LOCOS film is formed. (Local Oxidat
The field oxide film 3 is formed by the ion of silicon) method. LOCOS measures the substrate temperature to 95% in a wet oxygen atmosphere.
Hold at 0 ° C for 20 minutes. As is well known in this process, under field oxide 3, p
⁺ B diffusion occurs from the Si substrate 1 to the epitaxial layer 2, while B diffusion does not occur in the activation region (the portion of the epitaxial layer 2 below the nitride film 4) as well.

FIG. 1 (b) shows that the element substrate shown in FIG. 1 (a) is bonded to another support substrate 6 by a well-known bonding process, and then the p ⁺ Si substrate 1 and the epitaxial layer are 2
As a result of carrying out the chemical etching of, the case where the epitaxial layer 2 having a convex portion in the activated region remains is shown.

[0008]

[Operation] In the epitaxial layer 2 and the Si substrate 1 of FIG.
The concentration distribution of B 2 along the depth direction from the interface between the epitaxial layer 2 and the field oxide film 3 is shown in FIG. 1 (c). The curve (1) shows the distribution in the active region, and the curve (2) shows the distribution under the field oxide film 3. curve
As shown in (1), inside the epitaxial layer 2, B
The concentration is constant at about 1x10 ¹⁵ cm ^-3 , and about 1x10 ¹⁹ cm ^-3 inside the p ⁺ Si substrate 1. In curve (2), B is p
As a result of diffusion from the ⁺ Si substrate 1 to the epitaxial layer 2, it is shown that the B concentration below the field oxide film 3 inside the epitaxial layer 2 is higher than that in the active region.

Depending on the oxidation conditions (temperature, time, etc.) in the LOCOS process, as shown by the curve (3),
It is also possible to create a B concentration distribution such that the diffusion layer reaches the field oxide film 3.

When Si is etched by a mixed solution of acetic acid as a moderator in a solution in which the volume ratio of hydrofluoric acid and nitric acid is 1: 3, the etch rate of Si depends on the impurity concentration in Si. For a mixed solution with a volume ratio of acetic acid of 2 or more, Si with a high impurity concentration has a lower impurity concentration.
It is known to have a higher etch rate than Si.
(See, for example, VLSI Process Data Handbook (Science Forum), page 441, 1983)
By chemically etching the Si substrate 1 and the epitaxial layer 2, as shown in Fig. 1 (b), the Si substrate 1 and the B diffusion layer are removed, and a convex portion (plateau) is formed in the activation region of the epitaxial layer 2. Can be formed.

The surface of this convex portion is a smooth surface because it is close to the interface between the Si substrate 1 and the Si epitaxial layer 2. When the chemical mechanical polishing of the epitaxial layer 2 in this state is further performed, the region that becomes the SOI as shown in Fig. 4 (c) is not excessively polished and therefore the surface does not become a concave surface. A uniform thickness SOI layer with no "tilt" is obtained.

[0012]

EXAMPLES Examples of the present invention will be described below with reference to the drawings. FIG. 2 is a diagram for explaining a method of manufacturing a thin film SOI according to the present invention.

As shown in FIG. 2 (a), the B concentration is 10 ¹⁹ cm.
A Si epitaxial layer 2 having a B concentration of about 10 ¹⁵ cm ^-3 and a thickness of 1 to 1.5 μm is formed on a ^-3 p-type substrate 1 by the CVD method.

As shown in FIG. 2 (b), Si is formed by the CVD method.
A Si nitride film 4 is deposited on the epitaxial layer 2 and
The LOCOS method (for example, exposing to a wet oxygen atmosphere for 20 minutes at 950 ° C) was applied to a 220 nm thick field oxide film.
To form.

As shown in FIG. 2 (c), further, on the entire surface,
A CVD SiO ₂ film 5 is formed. (Si nitride film 4 is not shown.) As shown in Fig. 2 (d), BPSG (BoroPhosphoSilicate Glass) film 7 is formed on another Si substrate to be Si supporting substrate 6 Fig. 2 (e) As shown in Fig. 2 (d), the BPSG film 7 and Fig. 2 (c)
The CVD SiO ₂ film 5 is attached. The bonding condition is temperature
900 ° C, holding time 15 minutes. In this case, p-type substrate 1
The B diffusion region 8 to the Si epitaxial layer 2 is shown by a dotted line. This is the impurity concentration distribution in Fig. 1 (c).
Corresponds to (2).

As shown in FIG. 2F, the Si substrate 1 and the epitaxial layer 2 are chemically etched. As the etching solution, a mixed solution of hydrofluoric acid, nitric acid and acetic acid in a volume ratio of 1: 3: 8 is used. This etching removes the Si substrate 1 and the epitaxial layer 2 by removing the B diffusion region 8.
It has a shape that leaves a convex portion (plateau) in the activated area.

As shown in FIG. 2 (g), the remaining portion of the epitaxial layer 2 is chemically mechanically polished. This chemical mechanical polishing is performed with a foamed polyurethane pad using an abrasive containing colloidal silica. As a result, a portion of the epitaxial layer 2 (that is, thin SOI) having a uniform thickness and no "sloping" or "tilt" is obtained in a form bordered by the field oxide film 3.

Depending on the bonding condition or the LOCOS condition, the B diffusion region 8'becomes the region shown by the dotted line in FIG. 3 (e '). (Corresponding to (3) in Fig. 1 (c)) As shown in Fig. 3 (f '), the Si substrate 1 on the field oxide film 3 and the Layer 2 is removed, and a shape in which epitaxial layer 2 remains in a plateau shape only in the activated region is obtained.

By performing the same chemical mechanical polishing as in the case of FIG. 2G, as shown in FIG.
(Same as (g)) Thickness is uniform and there is no "who" or "tilt",
A thin SOI is obtained bordered by field oxide 3.

In the above embodiments, the case of the B-doped p-type substrate has been described, but the same method can be applied to the case of the phosphorus (P) -doped n-type substrate, for example.

[0021]

According to the present invention, there is provided a method for obtaining a thin SOI having a uniform thickness without polishing dripping or polishing inclination. As a result, it greatly contributes to the speedup of semiconductor devices.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a diagram for explaining a method for manufacturing a thin film SOI according to the present invention (No. 1)

FIG. 3 is a view for explaining the method of manufacturing a thin film SOI according to the present invention (No. 2)

FIG. 4 is a diagram for explaining a conventional method for manufacturing a thin film SOI.

[Explanation of symbols]

1, 31 Si substrate 2, epitaxial layer 3, 32 Field oxide film 4 Si nitride film 5, 33, 35 CVD SiO ₂ film 6, 34 Si support substrate 7 BPSG film 31 'SOI part 8, 8'B diffusion region

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Tanaka, Toru Tanaka, 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Yamasaki, Hiroshi, 1015, Kamedotachu, Nakahara-ku, Kawasaki, Kanagawa Prefecture Fujitsu Stock In the company

Claims (3)

[Claims] 1. A method for manufacturing an SOI substrate, which comprises bonding an element substrate having an insulator layer formed on a first Si substrate and a support substrate having an insulator layer formed on a second Si substrate to each other.
A step of growing a Si epitaxial layer having a lower impurity concentration than that of the substrate on the Si substrate and forming a field oxide film on the epitaxial layer, and bonding the element substrate and the insulating layer of the supporting substrate so as to face each other. And a step of chemically removing the remaining portion of the epitaxial layer after selectively removing the Si substrate of the element substrate and a portion of the epitaxial layer by chemical etching. Manufacturing method of SOI substrate. 2. The thickness of the impurity diffusion layer formed in the Si epitaxial layer when the field oxide film is formed is
The method for manufacturing an SOI substrate according to claim 1, wherein the method is controlled by a condition for forming a field oxide film. 3. The chemical etching of the epitaxial layer is carried out in a solution of hydrofluoric acid and nitric acid at a volume ratio of 1 to 3,
The method for manufacturing an SOI substrate according to claim 1, wherein the method is performed using a mixed solution containing two or more acetic acids.