JP3085184B2 - SOI substrate and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor substrate having an SOI structure and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, an SOI (Silicon On Insulator) substrate formed by bonding a first semiconductor wafer and a second semiconductor wafer with a dielectric layer interposed therebetween has been known.

[0003] A method of manufacturing this type of semiconductor substrate is as follows. That is, an oxide film (SiO ₂ ) serving as a dielectric layer is formed on at least one of the first semiconductor wafer and the second semiconductor wafer, and the two semiconductor wafers are brought into close contact with each other and subjected to a heat treatment. Then, an adhesive wafer is formed.

[0004] Thereafter, an unbonded portion around the bonded wafer generated by sagging generated during mirror polishing of the wafer is removed by grinding and etching, and a layer to be a device forming layer is ground to a desired thickness and then finished. After mirror polishing, an SOI substrate is obtained.

[0005] The SOI substrate formed by such a conventional bonding method is formed, for example, in the order shown in FIGS.

First, as shown in FIG. 3A, two silicon wafers 1 and 2 are prepared.

[0009] Next, as shown in FIG. 3 (2), an oxide film 5 serving as a dielectric layer is formed on the surface of the silicon wafer 1. Thereafter, a cleaning process is performed on the bonding surfaces of both the silicon wafer 1 and the silicon wafer 2, and the silicon wafers 1 and 2 are brought into close contact at room temperature as shown in FIG. Thereafter, the adhesive strength is increased by performing a heat treatment at a temperature of 800 ° C. or higher.

Next, although not shown in the drawing, sagging occurs around the silicon wafers 1 and 2 at the time of polishing, and unbonded portions occur when both are bonded as they are. This unbonded portion becomes a source of dust when the unbonded portion is peeled off and scattered when cleaning or polishing the bonded wafer, and the wafer surface is contaminated with particles, or a part of the wafer adheres to the surface and is damaged during processing. And others. Therefore, the unbonded portion of the silicon wafer 1 is ground by about 3 mm and removed by etching. 9 is a ground portion after etching.

Then, as shown in FIG. 3D, the silicon wafer 1 is ground from the back surface, and the SOI layer is polished to a desired thickness. As a result, the active layer thickness becomes 2 μm.
Thus, a thick / thin SOI substrate having a uniformity of about ± 1 μm is formed.

Finally, as shown in FIG. 3 (5), the monthly Semiconductor World 199
PACE (Plasma-Assisted) described in No. 4.4
Chemical Etching) processing, and then touch polish (polishing amount is several tens of angstroms to remove etching residue remaining on the processed surface and reduce surface roughness)
(Several hundred angstroms), and the SOI layer thickness is set to 0.1.
An ultra-thin SOI substrate having a thickness of about 1 μm and a tolerance of ± 10% is formed.

[0011]

When the SOI layer of the thick / thin SOI substrate manufactured by the conventional manufacturing method is evaluated for crystal defects by selective etching, crystal defects of OSF and oxygen precipitates are observed. When an OSF nucleus is present in the silicon wafer 1 at the time of forming an oxide film, the OSF is grown by releasing silicon atoms by oxidation. Also,
When oxygen precipitate nuclei exist in the silicon wafer 1, oxygen precipitates are formed during the oxidation heat treatment and the bonding heat treatment. Therefore, in general, a low oxygen semiconductor wafer tends to be used for the silicon wafer 1 (Japanese Unexamined Patent Publication No.
No. 169925).

However, even a thick / thin SOI substrate manufactured using a low-oxygen semiconductor wafer has a temperature of 1000.degree.
After heat treatment for 6 hours in an oxidizing atmosphere, the oxide film is removed and S
When crystal defects of the OI layer were evaluated by light etching, crystal defects of several tens / cm ² level were detected, and crystal defect free could not be achieved. Furthermore, SO
In order to reduce the crystal defects of the I layer, it is necessary to further reduce OSF nuclei, oxygen precipitate nuclei, oxygen precipitates, and the like existing in the step of pulling a silicon single crystal by the CZ method. However, if it is attempted to reduce these crystal defects in the step of pulling a silicon single crystal by the CZ method, there is a disadvantage that the crystal pulling condition is restricted, and the silicon wafer becomes considerably expensive. In addition, it is difficult to completely free crystal defects during the step of pulling a silicon single crystal by the CZ method.

Further, when the SOI layer of the ultra-thin SOI substrate manufactured by the conventional manufacturing method is evaluated for crystal defects by the evaluation method shown in FIG. 4, through pits are observed in the SOI layer.

That is, FIG. 4 (1) corresponds to FIG. 3 (5)
Is an ultra-thin SOI substrate, and 6 is a crystal defect. This is performed by diluting selective etching (for example, by volume ratio of 5).
wt% K ₂ Cr ₂ O ₇ : 48 wt% HF: H ₂ O = 1: 2:
5 through the crystal defect (see FIG. 4 (2)). 7 is a through pit. Then, 25wt
% HF solution to transfer the through pits to the buried oxide film. As a result, the through pits 8 become apparent.

A silicon single crystal pulled up by the CZ method is processed into a wafer, and SC1 cleaning is performed to obtain a COP (Crystal or Crystal).
A pit having a depth of about 0.1 μm, which is called “iginated particle”, is detected. It has been reported that this is caused by crystal defects formed during single crystal growth.

The penetrating pits are considered to have crystal defects. However, normal wafer SC1
More pits are detected than the amount of pits observed after repeated washing. This is thought to be because crystal defects were selectively etched in the thin film process of plasma etching, and some of the remaining pits became through pits according to the evaluation. On the other hand, the SOI layer on the bonding surface side had Since a COP having a depth of about 0.1 μm already exists and remains after forming an oxide film, SOP is exposed or not exposed in a thin film process in plasma etching.
It exists in the I layer, which is considered to have become a penetration pit according to the evaluation. Therefore, it is necessary to prevent crystal defects that become pits due to repetition of SC1 cleaning before processing the ultrathin film. However, at present,
It is difficult to make this crystal defect free in the step of pulling a silicon single crystal by the CZ method.

Therefore, the present invention uses a first semiconductor wafer that has been heat-treated or epitaxially grown to provide an SOI layer having no crystal defects and low manufacturing cost.
It is an object to provide an OI substrate and a method for manufacturing the OI substrate.

[0018]

According to a first aspect of the present invention, there is provided an SOI substrate formed by bonding a first semiconductor wafer and a second semiconductor wafer.
The semiconductor wafer includes a layer having an interstitial oxygen concentration of 1 × 10 ¹⁸ atoms / cm ³ (old ASTM, the same applies hereinafter) or less on at least the main surface side, the main surface is a mirror surface, and the second The semiconductor wafer has at least a main surface which is a mirror surface, an oxide film is formed on a main surface of at least one of the first and second semiconductor wafers, and both main surfaces are in close contact with each other. Heat treatment and bonding, wherein the SOI layer is the first semiconductor
Newly formed interstitial oxygen concentration of that in a in those with it is and SOI layer thickness at 1 × 10 ¹⁸ atoms / cm ³ or less in the wafer is a SOI substrate structure is 5μm or less.

According to a second aspect of the present invention, in a method for manufacturing an SOI substrate formed by bonding a first semiconductor wafer and a second semiconductor wafer, the first semiconductor wafer has at least a main surface. On the side, a layer having an interstitial oxygen concentration of 1 × 10 ¹⁸ atoms / cm ³ or less is provided on the first semiconductor wafer.
A main surface is a mirror surface, and the second semiconductor wafer has at least a main surface being a mirror surface, and at least one of the first and second semiconductor wafers is provided. After forming an oxide film on the main surface of the semiconductor wafer, the two main surfaces are brought into close contact with each other and heat-treated for bonding, and the first semiconductor wafer is made thinner from the back side, and the interstitial oxygen concentration becomes 1 × 10 ¹⁸ at
and a step of mirror-finishing the surface while leaving only a layer of oms / cm ³ or less.

According to a third aspect of the present invention, in the second aspect, the interstitial oxygen concentration is 1 × 1.
The layer having a thickness of 0 ¹⁸ atoms / cm ³ or less has an SO structure of a structure formed by epitaxial growth at a temperature of 800 ° C. or more.
This is a method for manufacturing an I substrate.

According to a fourth aspect of the present invention, in the second aspect, the interstitial oxygen concentration is 1 × 1.
The layer having a thickness of 0 ¹⁸ atoms / cm ³ or less is a method for manufacturing an SOI substrate in which a layer is formed by heat treatment at 800 ° C. or more in a reducing gas atmosphere.

According to a fifth aspect of the present invention, in the second aspect, the interstitial oxygen concentration is 1 × 1.
This is a method for manufacturing an SOI substrate in which a layer having a thickness of 0 ¹⁸ atoms / cm ³ or less is formed by heat treatment at 800 ° C. or more in an inert gas atmosphere.

Therefore, according to the present invention, the first semiconductor wafer is subjected to a high-temperature heat treatment in an atmosphere of a reducing or inert gas by epitaxial growth or CZ.
A layer having no crystal defects lower than the oxygen concentration achievable by pulling a silicon single crystal by the method can be formed as a surface layer of the wafer, and by forming the layer as an SOI layer,
An SOI substrate having no crystal defects in the OI layer can be obtained.

That is, C is obtained by epitaxial growth.
A defect-free layer that cannot be achieved by pulling a silicon single crystal by the Z method can be formed. By using this layer as an SOI layer, an SOI substrate free of crystal defects can be obtained.

Further, by subjecting the first semiconductor wafer to a high-temperature heat treatment in a reducing or inert gas atmosphere, the outward diffusion and reduction of oxygen can be achieved without growing crystal defects in the surface layer of the first semiconductor wafer. The crystal defects can be shrunk and eliminated by the action. The layer is SO
By using the I layer, an SOI substrate having no crystal defect can be obtained.

In general, when heat treatment or epitaxial growth is performed, the production cost of the wafer is increased because a prime product is used for the substrate. In the production of an SOI substrate by bonding, only the very surface layer of the first semiconductor wafer is used, so that a wafer of a dummy product level can be used for the substrate, and the first semiconductor wafer is inexpensive as compared with a newly pulled wafer and processed. And a low-cost SOI substrate can be manufactured. Here, the dummy product level is a defective product derived in the process of manufacturing a prime product, such as a defective product in shape (warpage, flatness, etc.), a defective crystal defect, a defective rear surface,
A wafer having a defective thickness or the like and having a mirror surface state in which voids are not generated by bonding, that is, a wafer having no foreign matter on its surface and no local unevenness.

As described above, according to the present invention, an SOI substrate having no crystal defects in the SOI layer and having a low manufacturing cost can be provided.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to specific examples. FIG. 1 is a sectional view showing a manufacturing process of an SOI substrate according to the present invention.

First, as shown in FIG. 1A, a first semiconductor wafer 1 having at least one surface mirror-polished is prepared. For example, in order to reduce the manufacturing cost, a 6-inch dummy product level semiconductor wafer having a crystal plane (100), a P-type, and a specific resistance of 5 Ω · cm is prepared.

Next, as shown in FIG. 1 (2), the surface of the semiconductor wafer is etched with hydrogen or hydrochloric acid gas in an epitaxial furnace, and silane gas is heated in a hydrogen gas atmosphere at 800 ° C. or more (eg, 1100 ° C.). Causing the decomposition or hydrogen reduction reaction to occur at 800 ° C. or higher (eg, 1100 ° C.),
Epitaxial growth of 0.1 μm or more, for example, 5 μm, is performed, and the interstitial oxygen concentration is 1 × 10 ¹⁸ on the semiconductor wafer.
A layer 4 having no crystal defects is formed at a density of atoms / cm ³ (old ASTM, the same applies hereinafter). As for the reaction temperature, the higher the temperature, the faster the growth rate is, which is advantageous in production, but there is a problem that slip is likely to occur,
It is necessary to perform epitaxial growth under the optimum conditions suitable for the epitaxial furnace. The semiconductor wafer to be used preferably has the same impurity as the impurity to be doped. In order to prevent autodoping during epitaxial growth and to set the resistance of the epitaxial layer to a predetermined value, it is better to use a semiconductor wafer having a specific resistance of 1 Ω · cm or more. If a mound or the like is generated on the epitaxial growth surface, it is removed by polishing.

Next, as shown in FIG. 1 (3), the epitaxial surface is oxidized in an oxidizing atmosphere at a temperature of 500.degree.
Heat treatment is performed at 100 ° C. to form an oxide film 5 of 100 Å or more, for example, 2,000 Å on the surface of the first semiconductor wafer. The oxidizing atmosphere is an atmosphere containing oxygen or water vapor.

Further, as shown in FIG. 1D, the first semiconductor wafer 1 and the second semiconductor wafer 2 are cleaned,
After adsorbed moisture and silanol groups are formed on the surface, they are adhered at room temperature by a method that does not generate voids. An oxide film may be formed on the surface of the second semiconductor wafer 2. The material of the wafer used for the second semiconductor wafer 2 is not only single crystal silicon or polysilicon, but also quartz, quartz,
Sapphire may be used. In addition, TTV (Total Thicknes
(S Variation) is better if it is small, and if possible, 1 μm or less is optimal. TTV can be reduced by processing with a double-side polishing machine, so a double-side polished product may be used.

Thereafter, a temperature of 200 ° C. or more, for example, 11
The heat treatment is performed at 00 ° C. for a time during which the adhesive strength is stabilized, for example, for 2 hours. This heat treatment may be performed after the film is thinned if there is no problem such as peeling in the thinning step. In order to prevent the back surface / chamfered portion from being scratched or stained in a later step, it is preferable to form an oxide film on the back surface. Therefore, the heat treatment atmosphere is preferably an oxidizing atmosphere.

In the oxidation and bonding heat treatment, the first
Since the interstitial oxygen on the bulk side of the semiconductor wafer may diffuse into the epitaxial layer to generate defects, it is optimal to use a semiconductor wafer having a low interstitial oxygen concentration of the first semiconductor wafer. Note that it is desirable to form the oxide film at a low temperature in a short time.

As shown in FIG. 1 (5), after the peripheral unbonded portion is removed by grinding and etching, the back surface of the first semiconductor wafer 1 is ground and polished so that there is no damage layer on the surface. Mirrored thin film SOI with SOI layer thickness of 3 ± 1μm
Form a substrate. In particular, when peripheral peeling is not a problem, it is not necessary to remove peripheral unbonded portions by grinding and etching.

Finally, as shown in FIG.
E processing and touch polishing, SOI layer thickness is 0.1
An ultra-thin SOI substrate of μm ± 10% is manufactured.

FIG. 2 is a sectional view showing a manufacturing process of an SOI substrate according to another embodiment of the present invention.

First, as shown in FIG. 2A, as the first semiconductor wafer 1, a semiconductor wafer as used in the above-described embodiment is prepared. That is, a first semiconductor wafer having at least one surface mirror-polished, for example, a crystal surface (10
0) A P-type, 6-inch dummy semiconductor level semiconductor wafer having a specific resistance of 5 Ω · cm is prepared.

Next, as shown in FIG. 2B, the first semiconductor wafer 1 is heat-treated in a hydrogen atmosphere of 800 ° C. or more for 10 minutes or more, for example, at 1150 ° C. for 1 hour. The flow rate at this time is 0.001 × 10 ⁻³ Nm ³ / min or more, for example, 90
Perform at × 10 ⁻³ Nm ³ / min. A mixed gas of hydrogen gas and inert gas may be used. By this process, a layer 4 having an interstitial oxygen concentration of 1 × 10 ¹⁸ atoms / cm ³ or less and having no crystal defects is formed. Since the oxygen concentration in the surface layer is determined by the heat treatment temperature, it is desirable to perform the heat treatment at a higher temperature. However, even in this case, it is necessary to optimize the heat treatment because of problems such as slip and metal contamination. If the surface is rough and voids are generated, polishing may be performed.

As shown in FIG. 2C, the surface is subjected to a heat treatment in an oxidizing atmosphere at 500 ° C. or more, for example, at 1100 ° C., and the surface of the first semiconductor wafer 1 is made 100 Å or more, for example, 2,000 Å. Oxide film 5 is formed. The oxidizing atmosphere is an atmosphere containing oxygen or water vapor. If this oxide film forming process is continuously performed in the same heat treatment furnace under the hydrogen atmosphere, productivity can be improved and manufacturing cost can be reduced.

Thereafter, in the steps shown in FIGS. 2 (4) to 2 (6), an ultra-thin SOI substrate having an SOI layer thickness of 0.1 μm ± 10% is manufactured by the same processing as in the first embodiment. .

That is, as shown in FIG.
After cleaning the semiconductor wafer 1 and the second semiconductor wafer 2 to form adsorbed moisture and silanol groups on the surface, the semiconductor wafer 1 and the second semiconductor wafer 2 are adhered at room temperature by a method that does not generate voids. An oxide film may be formed on the surface of the second semiconductor wafer 2.

Thereafter, a temperature of 200 ° C. or more, for example, 11
The heat treatment is performed at 00 ° C. for a time during which the adhesive strength is stabilized, for example, for 2 hours. This heat treatment may be performed after the film is thinned if there is no problem such as peeling in the thinning step. In order to prevent the back surface / chamfered portion from being scratched or stained in the subsequent process, a method of forming an oxide film on the back surface is preferable. Therefore, the atmosphere for the heat treatment is preferably an oxidizing atmosphere.

In the oxidation and bonding heat treatment, the first
Since the interstitial oxygen on the bulk side of the semiconductor wafer described above may diffuse into the low oxygen layer to generate defects, it is optimal to use a semiconductor wafer having a low interstitial oxygen concentration of the first semiconductor wafer. Note that it is desirable to form the oxide film at a low temperature in a short time.

As shown in FIG. 2 (5), after removing the peripheral unbonded portion by grinding and etching, the back surface of the first semiconductor wafer 1 is ground and polished so that there is no damage layer on the surface. Mirrored thin film SOI with SOI layer thickness of 3 ± 1μm
Form a substrate. In particular, when peripheral peeling is not a problem, it is not necessary to remove peripheral unbonded portions by grinding and etching.

Finally, as shown in FIG.
E processing and touch polishing, SOI layer thickness is 0.1
An ultra-thin SOI substrate of μm ± 10% is manufactured.

In this embodiment, annealing in a hydrogen atmosphere is described, but an inert gas atmosphere, for example, an argon gas atmosphere may be used.

By the above processing, for example, SO
An ultra-thin SOI wafer having an I layer thickness of about 0.1 μm ± 10% is manufactured.

Actually, when the SOI layer of the SOI substrate obtained by the present invention was evaluated by the above two types of defect evaluation, crystal defect free and through pit free which could not be achieved by the conventional method could be achieved.

[0050]

As described above, according to the present invention,
Since a layer with few crystal defects is used as the SOI layer, an SOI substrate with few crystal defects in the SOI layer can be obtained. In addition, since a low-cost wafer can be used as a substrate for forming a layer with few crystal defects, a low-cost SOI substrate can be obtained.

As described above, according to the manufacturing method of the present invention and the SOI substrate obtained by the method, an SOI substrate having few crystal defects in the SOI layer and low manufacturing cost can be obtained. A wide range of device applications is possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of an SOI substrate according to the present invention.

FIG. 2 is a cross-sectional view illustrating a manufacturing process of an SOI substrate according to another specific example of the present invention.

FIG. 3 is a cross-sectional view showing a manufacturing process of an SOI substrate by a conventional bonding method.

FIG. 4 is a cross-sectional view showing a method for evaluating crystal defects of an ultra-thin SOI substrate manufactured by a conventional manufacturing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st semiconductor wafer 2 2nd semiconductor wafer 4 layer 5 oxide film 6 crystal defect 7 penetrating pit 8 exposed penetrating pit 9 grinding part

Continuation of front page (56) References JP-A-7-263652 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 27/12 H01L 21/02 H01L 21/304

Claims (5)

(57) [Claims] 1. An SOI substrate formed by bonding a first semiconductor wafer and a second semiconductor wafer, wherein the first semiconductor wafer has an interstitial oxygen concentration of 1 × 10 ¹⁸ at least on the main surface side. A layer of atoms / cm ³ (old ASTM, same hereafter) is newly formed on the first semiconductor wafer.
A main surface mirror with provided form, and the second semiconductor wafer, at least the main surface is a mirror, one of the first and second semiconductor wafer, the main surface of the at least one semiconductor wafer An oxide film is formed on the first semiconductor wafer, and the two main surfaces are brought into close contact with each other and heat treated and bonded. The SOI layer is newly formed on the first semiconductor wafer.
Be those having been interstitial oxygen concentration of that is 1 × 10 ¹⁸ at
OMs / cm ³ or less and an SOI layer thickness of 5 μm or less. 2. A method for manufacturing an SOI substrate formed by bonding a first semiconductor wafer and a second semiconductor wafer, wherein the first semiconductor wafer has an interstitial oxygen concentration of at least 1 on a main surface side. The second semiconductor wafer has a layer of not more than × 10 ¹⁸ atoms / cm ³ , has a main surface which is a mirror surface, and at least the main surface has a mirror surface, and of the first and second semiconductor wafers, Forming an oxide film on at least one of the main surfaces of the semiconductor wafer, and then adhering the two main surfaces together with heat treatment to form a thin film from the back surface side of the first semiconductor wafer; A method of mirror-finishing the surface while leaving only a layer having a concentration of 1 × 10 ¹⁸ atoms / cm ³ or less, a method for manufacturing an SOI substrate. 3. An interstitial oxygen concentration of 1 × 10 ¹⁸ atoms.
^{3. The} method for manufacturing an SOI substrate according to claim 2, wherein the layer having a thickness of / cm ³ or less is formed by epitaxial growth at a temperature of 800 ° C. or more. 4. An interstitial oxygen concentration of 1 × 10 ¹⁸ atoms.
/ Cm ³ or less in a reducing gas atmosphere.
3. The method for manufacturing an SOI substrate according to claim 2, wherein the SOI substrate is formed by a heat treatment at a temperature of not less than ° C. 5. The method according to claim 1, wherein the interstitial oxygen concentration is 1 × 10 ¹⁸ atoms.
^{3. The} method for manufacturing an SOI substrate according to claim 2, wherein the layer having a thickness of / cm ³ or less is formed by a heat treatment at 800 ° C. or more in an inert gas atmosphere.