JPH098258A - Manufacture of soi substrate - Google Patents

Abstract

PURPOSE: To reduce the thickness of the active layer of a multilayered SOI substrate with high accuracy by a simple method. CONSTITUTION: After an Si oxide film 20 having a thickness of about 1μm is formed by thermally oxidizing an Si substrate which becomes the origin of an active layer 30, an SOI substrate is manufactured by putting the film 20 on another Si substrate which becomes a supporting substrate 10 and joining the film 20 to the substrate 10 through heat treatment. The thickness of the active layer 30 of the multilayer SOI substrate is reduced by polishing the layer 30 by using a chemimechanical polishing method. Then the active layer 30 is etched by using such an etchant as a mixture of hydrofluoric acid and nitric acid, etc., while the layer 30 is irradiated with light. At the thicker part of the layer 30, more carrier are generated and the etching is accelerated by the carriers. As the layer 30 becomes thinner, the light starts to reach the supporting substrate 10 side through the layer 30 and the produced amount of carriers becomes less, lowering the etching rate. Therefore, the thickness of the layer 30 is uniformized. In addition, the thickness of the layer 30 can be controlled by changing the wavelength of the irradiating light.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an SOI (Sion Insulato) in which a semiconductor layer is formed on a semiconductor substrate via an insulating film.
The present invention relates to a method for manufacturing a substrate, and more particularly, to a technique for thinning an active layer side semiconductor substrate of an SOI substrate by a bonding method.

[0002]

2. Description of the Related Art SOI having a semiconductor active layer on an insulating film
One of the methods for forming a substrate is a bonding method. In this method, at least one of the two silicon substrates is oxidized to form a silicon oxide film which is an insulator, and the silicon oxide films are stacked in an interposed position, and then heat-treated to be bonded. Of the silicon substrate to be thinned. In this method, the silicon substrate, which is originally a single crystal, is thinned, so that the SOI having extremely good crystallinity of the active layer
The structure is obtained.

Conventionally, as a method of thinning the active layer, for example, Journal of Electric Materials, Vol. 21, pp. 669-676, 1992 (Journal)
of Electronic Material, Vol.21, No.7, pp.669-676,
1992), a chemical mechanical polishing method and an etching method using an epitaxial layer as an etch stop are performed.

The former method is a method in which a polishing material (slurry) is dripped onto a rotating polishing table and the substrate is pressed and polished, and the latter is a method in which a high impurity concentration layer / undoped layer or a Si layer / Si.Ge layer / In this method, a plurality of layers having different etching properties, such as a Si layer, are epitaxially grown, and the epitaxial layer is attached to a support substrate with its epitaxial layer side facing up and etched.

[0005] Further, for example, in 1992 I Triple E International SOI Conference Proceedings, pp. 152-153 (1992 IEEE Internat
ional SOI Conference Proceedings, pp.152-153), there is a method to precisely measure the thickness of the active layer after chemical mechanical polishing, and to etch the thicker region longer by local plasma etching than the other regions. By adopting
It is reported that a highly accurate active layer can be formed.

[0006]

Among the above-mentioned prior arts, the one using the chemical mechanical polishing method has difficulty in obtaining a uniform film thickness, and the typical active layer film thickness and uniformity obtained by this method are difficult. Is, for example, 3 μm ± 0.5 μm, and as a result, a thin film (eg, 0.1 μm
m ± 0.01 μm) could not be formed. Further, the method using an epitaxial growth substrate or the method using a local plasma etching method has a drawback that the process becomes complicated and extremely expensive.

Therefore, an object of the present invention is to reduce the thickness of the active layer of a bonded SOI substrate by reducing the thickness of the active layer.
This is to enable high-precision processing without using complicated processes, and this enables a substrate capable of forming a high-performance electronic device by utilizing the characteristics of a bonded SOI substrate having good crystallinity. Try to make it available at low cost

[0008]

According to the present invention, there is provided a method for manufacturing an SOI substrate, comprising the steps of: (1) forming a supporting substrate and a silicon substrate constituting an active layer on any one of substrates; Adhering via an insulating film; and (2) etching the silicon substrate by a wet or dry method while irradiating light to the surface of the silicon substrate to be the active layer to generate carriers in the silicon substrate. Or (1) a step of bonding a supporting substrate and a silicon substrate constituting an active layer via an insulating film formed on any one of the substrates, and (2) a step of bonding the active layer to the silicon substrate. Light is incident on the surface of the silicon substrate to generate a carrier in the silicon substrate and cause a chemical or electrochemical reaction on the silicon substrate to form a reaction product layer on the surface of the silicon substrate. And extent are those comprising, removing etching (3) said reaction product layer.

[0009]

The etching rate of almost all of the solutions for chemically etching semiconductors (for example, fluorinated nitric acid, KOH, and hydrazine solutions, etc.) and a part of the gas (including plasma) is not affected by the etching rate. Depends largely on the presence or concentration of carriers (electrons and holes) in the semiconductor. Also, in many chemical or electrochemical reactions (eg, oxidation and anodization), the amount of the carrier has a large influence on the reaction rate.

When the SOI substrate active layer is irradiated with light having a wavelength corresponding to a desired film thickness, electron-hole pairs are generated in the active layer. Irradiation light is not absorbed by the active layer but penetrates to the support substrate side in a region of the active layer which has reached a desired thickness as etching proceeds, and does not contribute to generation of electron-hole pairs.
Therefore, the etching rate decreases in the region where the desired film thickness is reached, and a uniform ultrathin film active layer can be obtained. Also, when a reaction product is formed by a chemical or electrochemical reaction, similarly, in a region where the remaining active layer thickness has reached a predetermined value, irradiation light penetrates to the support substrate side, and electron-hole No pairs are generated.

As an example, a fluorinated nitric acid solution (HF / H
The mechanism by which the presence of carriers affects the etching rate in chemical etching using a mixed solution of NO ₃ / CH ₃ COOH) will be described more specifically. When etching Si using an HF / HNO ₃ solution using CH ₃ COOH as a buffer, the etching proceeds by a series of reactions represented by the following equations (1) to (3). Si + 2h ⁺ → Si ²⁺ (1) Si ²⁺ + 2OH ⁻ → SiO ₂ + H ₂ (2) SiO ₂ + 6HF → H ₂ SiF ₆ (water-soluble) + 2H ₂ O (3)

As shown in equation (1), the presence of carriers (holes in this case) plays a large role in the progress of etching. Therefore, when the etching proceeds and reaches a film thickness through which the irradiated light can penetrate, the etching rate is automatically reduced due to the shortage of holes, and an etch stop mechanism operates. Thereby, an active layer having a desired film thickness can be formed with high accuracy.

[0013]

Next, embodiments of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIGS. 1A and 1B show a first embodiment of the present invention.
FIG. 9 is a process order cross-sectional view for explaining the third to third embodiments. The bonded SOI substrate has p
A silicon oxide film 20 having a thickness of about 1 μm is formed by thermally oxidizing a Si-type Si substrate (specific resistance: 1 to 3 Ω · cm), and this is then converted to a p-type Si substrate (specific resistance: 1 to 3 Ω · cm) serving as a support substrate 10. , 625 μm in thickness) and heat treatment for superposition was applied to produce a laminate. After the production of the bonded substrate, the active layer 30 is subjected to ordinary chemical mechanical polishing (Chemical Mechanical Polishing:
The thickness was reduced to 3 to 5 μm with a thickness accuracy of ± 0.5 μm by CMP). FIG. 1A is a sectional view showing a state of an SOI substrate obtained by this method, which is equivalent to a conventional bonded SOI substrate formed by a chemical mechanical polishing method.

Next, while irradiating the W lamp light, etching was performed with a HF / HNO ₃ / CH ₃ COOH mixed solution having a mixing ratio of 1: 3: 10. The etching was automatically stopped after proceeding for about 10 to 30 minutes, and an active layer 40 having a uniform thickness was obtained [FIG. 1 (b)]. The thickness of the semiconductor active layer measured by an optical film thickness measuring device is about 0.5 μm, and the accuracy is ± 0.0
It was 1 μm. Also, pure CH in the above mixed solution is used.
₃ COOH CH ₃ COOH to the iodine saturated instead of
Etching with a mixed solution using was also performed. In this case, the flatness of the sample surface after the completion of etching was superior to the case where a solution to which pure CH ₃ COOH was added was used.

[Second Embodiment] A bonded SOI substrate shown in FIG. 1A is manufactured in the same manner as in the first embodiment, and etching is performed while irradiating the active layer surface with a W lamp. Etching was performed using a 30% KOH solution. When etching was performed while maintaining the solution temperature at 50 to 80 ° C., the etching was automatically stopped in about 5 to 10 minutes. With respect to the thickness of the semiconductor active layer after etching and the distribution thereof, the same results as in the first embodiment were obtained.

In the etching of the semiconductor active layer, the same effect can be expected because the etching rate differs depending on the presence or absence and concentration of carriers in most etching solutions such as a hydrazine solution in addition to a hydrofluoric acid or KOH solution. Also,
Solution and active layer 3 proposed in Japanese Patent Application No. 7-97338.
By using a method of giving a potential difference between any two of the 0 and the support substrate 10 or between the three, the etch stop can be made more reliable.

[Third Embodiment] After the bonded SOI substrate shown in FIG. 1A was manufactured, the active layer was irradiated with light from a W lamp, and plasma etching was performed using CCl ₄ gas. In this case, the rate of decrease in the etching rate at a film thickness through which light penetrates and only a small number of carriers are present is smaller than in the first and second embodiments using the wet method, so that the film is obtained after thinning. Although the thickness of the active layer was about 0.5 μm, the distribution was ± 0.1 μm and the uniformity was poor. However, this uniformity is superior to the conventional example by the chemical mechanical polishing method, and other advantages of the gas etching, such as being capable of processing by the dry method and being excellent in compatibility with other processes, are provided. Can be utilized. In addition to CCl _4, a similar effect can be expected with a gas capable of etching a semiconductor. In addition, a vapor phase etching method using an etching gas can be similarly applied without using plasma etching.

[Fourth Embodiment] FIGS. 2 (a) to 2 (d)
FIG. 14 is a process order sectional view for explaining a fourth embodiment of the present invention. After a bonded SOI substrate is manufactured by the same method as in the first embodiment [FIG. 2 (a)], a W lamp light is irradiated in an ethylene glycol solution while the solution and the active layer are interposed therebetween. A voltage was applied so that the active layer side became positive so that the flowing current value became constant. This method is known as anodic oxidation, in which the semiconductor active layer is oxidized from the front side. The current density was kept constant at 20 mA / cm ^2, and when the voltage was increased by 50 V, a Si oxide film 50 having a thickness of 100 to 300 ° was formed (FIG. 2B).

The formed Si oxide film 50 was removed by etching using an HF solution (FIG. 2C). Subsequently, the anodic oxidation and the etching of the oxide film by HF were repeated in the same manner to make the active layer thinner. The oxidation reaction was stopped halfway, and the same film thickness and thickness as those in the first and second embodiments were obtained. An active layer 40 having a uniform film thickness with a film thickness distribution was obtained [FIG.
(D)]. In order to perform anodic oxidation, a mixed solution of sodium tetraborate and boric acid or an N-methylacetimide solution may be used in addition to ethylene glycol.

[Fifth Embodiment] FIGS. 3 (a) to 3 (c)
FIG. 14 is a process order sectional view for explaining a fourth embodiment of the present invention. After a bonded SOI substrate was manufactured by the same method as in the first embodiment (FIG. 3A), the solution was irradiated with W lamp light in a solution of HF / ethyl alcohol = 2: 3. Between the active layer and the active layer, the active layer side being positive 5
A voltage of １５15 V was applied. This method is known as anodization, and the current value during the anodization is approximately 20 to 80 mA /
cm ² . The reaction was stopped in 5 to 15 minutes, and a porous Si film 60 was formed from the surface of the semiconductor active layer.
(B)]. After removing only the porous Si film 60 with a hydrofluoric acid solution [FIG. 3 (c)], the thickness of the active layer and its distribution were measured and found to be the same as in the first embodiment.

Not only in the reactions described in the third and fourth embodiments, but also in other reactant producing methods utilizing a chemical reaction or an electrochemical reaction on the semiconductor surface, the reaction rate is determined by the presence or absence of the carrier and the concentration thereof. And any of those reactions can be used according to the present invention.

While the preferred embodiment has been described above,
The present invention is not limited to these embodiments, and various changes can be made without departing from the gist of the present invention described in the claims. For example, in the above embodiment, a W lamp, which is relatively easy to handle, was used as a light source of the light to be irradiated. The layer thickness is obtained. Further, if the irradiation angle of the irradiation light to the sample is adjusted and the total reflection condition or the multiple reflection condition is used, more advanced film thickness control can be expected. Also, in order to accelerate the reaction at the beginning of the reaction and increase the productivity, the irradiation light intensity is set high first and then gradually decreased, or irradiation is first performed using two light sources of short wavelength and long wavelength. At the final stage of the reaction, only long-wavelength light may be irradiated. Further, the conductivity type and the resistivity of the support substrate, the active layer, and the like used in the above embodiment are not limited to the above examples.

[0023]

As described above, the SO according to the present invention can be used.
Since the method of manufacturing the I-substrate involves etching while irradiating the active layer with light or forming a reaction product and removing the reaction product, it is necessary to obtain a thin and uniform active layer with a simple process. This makes it possible to provide a high-quality SOI substrate at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in a process order for describing first to third embodiments of the present invention.

FIG. 2 is a cross-sectional view in a process order for explaining a fourth embodiment of the present invention.

FIG. 3 is a cross-sectional view in a process order for explaining a fifth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Support substrate 20, 50 Si oxide film 30 Active layer 40 Active layer of uniform thickness 60 Porous Si film

Claims (5)

[Claims] (1) a step of bonding a supporting substrate and a silicon substrate constituting an active layer via an insulating film formed on any one of the substrates; and (2) a step of adhering to a surface of the silicon substrate to be the active layer. Etching the silicon substrate by a wet or dry method while irradiating light to generate carriers in the silicon substrate. 2. A step of: (1) adhering a supporting substrate and a silicon substrate constituting an active layer via an insulating film formed on any one of the substrates; and (2) a step of adhering to a surface of the silicon substrate to be an active layer. Forming a reaction product layer on the surface of the silicon substrate by causing a chemical or electrochemical reaction on the silicon substrate while receiving light to generate carriers in the silicon substrate; (3) the reaction Etching away the product layer;
A method for manufacturing an SOI substrate, comprising: 3. The method for manufacturing an SOI substrate according to claim 1, wherein in the initial stage, the step (2) is performed while setting the intensity of the illumination light high and gradually decreasing the intensity. 4. The method according to claim 1, wherein a step of polishing the surface of the silicon substrate is inserted between the step (1) and the step (2). S
A method for manufacturing an OI substrate. 5. The method according to claim 3, wherein the polishing is performed by a chemical mechanical polishing method.