JPH1070054A - Manufacture of junction wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a junction wafer which is high in its bonding strength and the corrosion resistance of a junction interface to an etching solution. SOLUTION: The junction wafer 5 is obtained by forming an SiO2 , oxide film 3 one mirror surface side of a bond wafer 1, integrally overlapping the bond wafer 1 on a base wafer 2 (mirror surface wafer) so that the oxide film 3 becomes an intermediate layer, thermally oxidizing the integrated wafer in an oxidizing atmosphere for about 2 hours at temperatures of 900, 1000, 1100 and 1200'C to join the wafers 1 and 2 together, and polishing the bond wafer 1 into a thin film. The junction wafer can exhibit a bonding strength higher than 600kg/cm<2> , since the oxide film is formed only to the bond wafer and the integrated wafer is heated and joined at temperatures of 1100 to 1200 deg.C in an oxidizing atmosphere.

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 bonded wafer obtained by bonding and integrating two single crystal silicon wafers.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a single crystal semiconductor thin film on a dielectric substrate, a technique of epitaxially growing a single crystal silicon (Si) film or the like on a single crystal sapphire substrate is well known. In the technology, since there is a mismatch in lattice constant between the substrate dielectric and the silicon single crystal to be vapor-grown, a large number of crystal defects are generated in the silicon vapor-grown layer. Poor.

A thermal oxide film is formed on the surface of a silicon substrate, and a polycrystalline or amorphous silicon film is deposited on the thermal oxide film, and an energy beam such as an electron beam or a laser beam is linearly applied thereto. A technique is known in which the silicon film is linearly melted, cooled and solidified by irradiating the silicon film in one direction and forming a single-crystal thin film as a whole.

A technique for converting a polycrystalline silicon film on a thermal oxide film into a single crystal film using a laser beam or the like is disclosed in, for example, Japanese Patent Publication No. 62-34716. In this technique, a single-crystal projection is provided integrally with an end of a single-crystal silicon substrate, and a single-crystal projection is attempted using the projection as a nucleus. Although the single crystallization can be partially performed by the interaction, it is difficult to obtain a silicon single crystal film that can withstand practical use.

Therefore, in recent years, SOI (Si On Insulator)
Structured wafers have received particular attention. In this bonding wafer, at least one of the two semiconductor wafers is oxidized to form an oxide film on at least one surface of the wafer, and the two semiconductor wafers are formed such that the oxide film becomes an intermediate layer. After overlapping, the two are bonded by heating to a predetermined temperature, and a wafer on the upper layer (hereinafter, referred to as a bond wafer) is polished and thinned.

[0006]

By the way, in the bonding wafer, it is necessary that the bonding strength between the two wafers is high over the entire bonding surface. If the bonding strength is insufficient, a void is formed at the bonding interface. This causes a problem that a non-bonded region is generated and the product yield is deteriorated. In addition, as a method of detecting a void, an infrared transmission method, an ultrasonic inspection method, X
The line rung method and the like are known.

In the process of manufacturing a bonded wafer,
In order to remove the oxide film deposited on the wafer surface, for example, etching using a hydrogen fluoride solution is performed,
Unless the erosion resistance of the bonding interface to the etchant (hydrogen fluoride solution) is high, there is a problem that a pattern formed on the bond wafer is peeled off in the device process.

Further, in the case of a silicon wafer, since there is a difference in the thermal shrinkage (thermal expansion coefficient) between the single crystal and the oxide film (SiO ₂ ), the single crystal surface and the oxide film surface are brought into contact with each other to join the wafer. Then, since residual stress is accumulated in the bonding wafer, there is also a problem that the bonding wafer is deformed (warped).

The present invention has been made in view of the above problems, and an object of the present invention is to provide a bonding wafer having high bonding strength and high erosion resistance to a bonding interface etching solution.

[0010]

In order to achieve the above object, a method for manufacturing a bonding wafer according to the present invention is a method for manufacturing a bonding wafer used in a device manufacturing step including a step of immersing the wafer in a hydrofluoric acid aqueous solution. In each case, a first mirrored wafer and a second mirrored wafer made of single crystal silicon are prepared, an oxide film is formed on at least one side of the second mirrored wafer, and the second mirrored wafer is used as an intermediate layer. After being superposed on the mirror surface of the first mirror surface wafer, the first and second mirror surface wafers are heated to 1100 ° C. to 1200 ° C. in an oxidizing atmosphere to bond them,
The second mirror-finished wafer is characterized in that a surface of the second mirror-polished wafer opposite to the bonding surface with the first mirror-polished wafer is polished to make the second mirror-polished wafer thin.

A pattern for bonding the first and second mirror-surface wafers through an oxide film includes a first mirror-surface wafer (a protection wafer that mainly provides mechanical strength in a bonded wafer; hereinafter, a base wafer and a base wafer). An oxide film is formed only on the wafer, and a second mirror surface wafer (a wafer on which a device is to be formed into a thin film in a bonding wafer, which is called a bond wafer) is bonded to the base wafer via the oxide film. Conversely, an oxide film is formed only on the bond wafer and both wafers are bonded via this oxide film. An oxide film is formed on both wafers and both wafers are bonded via these oxide films. , Can be considered.

The present inventors consider that the difference in the pattern affects the bonding mechanism of the two wafers in the bonding wafer, and furthermore, the bonding strength of the two wafers, and the erosion resistance of the bonding interface to the etchant. As a result of various experiments while standing, as in the method of the present invention, an oxide film is formed only on one mirror surface of the bond wafer, and the two are joined by heating to a predetermined temperature in an N ₂ atmosphere or an oxidizing atmosphere. ,
It has been found that high bonding strength and the above-mentioned erosion resistance can be obtained in the bonded wafer.

Further, it has been found that warping of the bonded wafer can be prevented by performing the heat treatment in an oxidizing atmosphere and forming an oxide film on all surfaces of the bond wafer and the base wafer except for the bonding surface.

[0014]

Embodiments of the present invention and comparative examples will be described below with reference to the accompanying drawings. Example 1 FIGS. 1A to 1E are explanatory views showing a method for manufacturing a bonded wafer according to the present invention in the order of steps. As shown in FIG. 1A, a bond wafer 1 made of single-crystal silicon to be a device forming surface and a base wafer 2 made of the same single-crystal silicon to be a base material are prepared. Then, the bond wafer 1 is oxidized to form an SiO ₂ oxide film 3 having a thickness of about 500 nm on one mirror surface (the lower surface in the drawing).

Next, as shown in FIG. 1B, the bond wafer 1 is overlaid on the base wafer 2 and integrated. Next, as shown in FIG. 1 (c), these integrated wafers 1 and 2 are thermally oxidized in an oxidizing atmosphere at a temperature of about 1100 ° C. for about 120 minutes, so that the wafers 1 and 2 are processed. At the same time as bonding, the entire surface of each of the wafers 1 and 2 (excluding the bonding surface) has a thickness of
An O ₂ oxide film 4 is formed.

Next, the bonded wafers 1
After cooling, the surface of the upper bond wafer 1 is pre-pressed to a predetermined thickness t ₁ (for example, 6 μm) with a predetermined polishing allowance (for example, 3 μm) as shown in FIG. Polish (primary polishing). In this case, as described above, the thermal shrinkage (thermal expansion coefficient) of the wafers 1 and 2 made of single-crystal silicon is larger than that of the SiO ₂ oxide films 3 and 4, so that the joint after the formation of the oxide film 4 is formed. Residual stress accumulates on the wafers 1 and 2 at the time of cooling the oxidized wafer.

However, in this embodiment, the upper and lower surfaces of the base wafer 2 are covered with the oxide films 3 and 4 having substantially the same thickness (about 500 nm) at the time when the pre-polishing is completed. The distribution of residual stress on the lower surface is substantially equal, and the heat shrinkage on the upper and lower surfaces is substantially the same, so that the bending deformation of the integrated wafer is prevented.

Next, the thickness t pre-polished as described above is used.
_{The first} bond wafer 1 (see FIG. 1 (d)) is polished to a thickness t ₂ (for example, 3 μm) by secondary polishing to make it thinner, thereby forming the bonding wafer 5 as shown in FIG. 1 (e). obtain.

The bonding wafer 5 obtained as described above
To determine the bonding strength of
A plurality of bonding wafers obtained by heat treatment at 2 ° C., 1000 ° C., 1100 ° C., and 1200 ° C. for 2 hours were prepared, and the tensile adhesive strength of each bonding wafer was measured by a tensile tester. In this case, the upper surface of the bond wafer 1 and the lower surface of the base wafer 2 were fixed to the tensile member of the testing machine with an adhesive. The result is shown in FIG. 2 (c).

COMPARATIVE EXAMPLE 1 As a comparative example with respect to the embodiment of the present invention, a bonded wafer obtained by directly bonding under the same heating conditions without interposing an oxide film between the wafers, and a 500 nm-thick film on both wafers. An oxide film is formed, and a bonded wafer obtained by bonding both wafers via the oxide film is prepared.
These bonded wafers were similarly tested for tensile adhesive strength. The results are shown in FIGS. 2 (a) and 2 (b). In FIG. 2, the mark ● indicates the value when the bonded interface of both wafers peeled off, and the mark を indicates the value when the bonded wafer was peeled (adhesive peeled) from the tensile member of the tensile tester. .

Further, in FIG. 2, “Oxide film 0/0 nm” means that the oxide film does not exist between the two wafers.
0/500 nm "means that each wafer has a thickness of 500 n
When the oxide film of m is formed, “500/0 nm” is
The case where an oxide film having a thickness of 500 nm is formed only on the bond wafer (Example of the present invention) is shown.

As is apparent from FIG. 2C, when an oxide film is formed only on the bond wafer by the method of the present invention and heated to a temperature of 1100 ° C. to 1200 ° C., 600 kg is applied.
/ Cm ² or higher bonding strength. And FIG.
When the evaluation of the bonding strength of the bonding wafer of each type is made for each heating temperature from the results shown in FIG. 3, the results shown in FIG. 3 are obtained. In FIG. 3, the mark 良 indicates good, the mark △ indicates acceptable, and the mark × indicates unacceptable. Thus, taking the above results into consideration, if an oxide film is formed only on one mirror surface of the bond wafer as in the method of the present invention and heated to 1100 ° C. to 1200 ° C. during bonding, a high bond strength (600 kg / cm ^{2) is obtained.} that's all)
Was obtained.

On the other hand, as a result of an erosion resistance test of the bonding wafers of the above-mentioned respective types with respect to an etching solution (hydrogen fluoride solution) at the bonding interface, a high erosion resistance is secured to the bonding wafer obtained by the method of the present invention. It turned out to be. In the other bonded wafers (the wafers having no oxide film between them and the wafers having the oxide films formed), satisfactory erosion resistance was not obtained.

In the bonding wafer 5 obtained by the method of the present invention, since the base wafer 2 occupying most of the thickness is prevented from being deformed as described above, the bonding wafer 5 is warped. There is no effect, and the degree of flatness is high, and an effect is obtained such that the vacuum suction of the bonding wafer 5 is surely performed in the next and subsequent steps.

In order to examine the durability of the bonding interface to the etchant, the above-described bonding wafer (shown in FIGS. 2B and 2C) was cut with a thin blade, for example, an 80 μm outer peripheral diamond slicer, and each was cut. 20 pieces of about 2 mm square pellets were prepared from each of the bonding wafers described above, left in a hydrofluoric acid aqueous solution at a concentration of 25% and a temperature of 25 ° C. for 20 minutes, washed with water, dried, and the bonding state was examined. That is, when the bond wafer side and the base wafer side were lightly pulled in the opposite directions with tweezers, FIG. 2 (b)
In the pellets from the bonded wafer shown in (1), about half of them were separated into a bond wafer and a base wafer at the bonded interface. On the other hand, in the pellet from the bonded wafer shown in FIG. 2C according to the present invention, the above-described destruction did not occur at all.

Further, when the bonding interface of the bonded wafer after washing with water and drying was observed with a microscope, it was found that the pellets from the bonded wafer shown in FIG. At the center, corrosion by the etchant did not progress.

The bonded wafer obtained by the method of the present invention may be applied to a base wafer if an intermediate oxide film is formed by thermal oxidation when, for example, an integrated circuit element is formed on the bond wafer by a known method. As compared with the case where one side of the region where the integrated circuit element is formed in the bond wafer is completely covered with the oxide film which is a dielectric, the insulating property of the integrated circuit element, Other electrical characteristics can be realized well.

[0028]

As is apparent from the above description, according to the method for manufacturing a bonded wafer according to the present invention, the bonding strength and the erosion resistance of the bonded interface to the etching solution are high, and the substrate is excellent as a substrate for an integrated circuit device. There is an effect that a bonded wafer can be obtained. Further, by performing the heat treatment in an oxidizing atmosphere and forming an oxide film on all surfaces of the bond wafer and the base wafer except for the bonding surface, there is an effect of obtaining a bonded wafer without warpage.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a method for manufacturing a bonded wafer according to an embodiment of the present invention in the order of steps.

FIG. 2 is a view showing test results of tensile adhesive strength of the wafer obtained in the above example and the bonded wafer obtained in the comparative example.

FIG. 3 is a diagram showing the results of evaluating the bonding strength of each bonding wafer for each heating temperature based on the results of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bond wafer (2nd mirror wafer) 2 Base wafer (1st mirror wafer) 3, 4 Oxide film 5 Bonding wafer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Katsuo Yoshizawa, inventor 1393, Yashiro Yashiro, Nagano Pref., Nagano Electronics Co., Ltd. 72) Inventor Masao Fukami Nagano Pref.

Claims (1)

[Claims] 1. A method for producing a bonded wafer used in a device producing step having a step of immersing in a hydrofluoric acid aqueous solution, wherein a first mirror-finished wafer and a second mirror-finished wafer, both made of single-crystal silicon, are prepared. An oxide film is formed on at least one mirror surface of the second mirror wafer, and the second mirror wafer is superimposed on the mirror surface of the first mirror wafer so that the oxide film becomes an intermediate layer. The mirror-polished wafer is heated to 1100 ° C. to 1200 ° C. in an oxidizing atmosphere to bond the two, and then the second mirror-polished wafer is polished on the side opposite to the surface to be bonded to the first mirror-polished wafer to form the second mirror-polished wafer. A method for producing a bonded wafer, characterized in that the wafer is thinned.