JPH0795505B2 - Method for manufacturing bonded wafer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a bonded wafer, which is formed by bonding and integrating two single crystal silicon wafers.

(Prior Art) Conventionally, as a method of forming a single crystal semiconductor thin film on a dielectric substrate, single crystal silicon (S
i) A technique for epitaxially growing a film or the like is well known. However, in this technique, there is a mismatch in the lattice constant between the substrate dielectric and the vapor-grown silicon single crystal. Many crystal defects occur in
For this reason, the technique is not practical.

Further, a thermal oxide film is formed on the surface of the 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 formed on the thermal oxide film, and A well-known technique is to irradiate in one direction to linearly melt, cool, and solidify the silicon film to form a single-crystal thin film as a whole.

By the way, a technique for converting a silicon polycrystalline film on a thermal oxide film into a single crystal film with a laser beam or the like is disclosed in, for example, Japanese Patent Publication No. 62-34716.
It is disclosed in the publication. In this technique, a single crystal projection that is continuous with the single crystal silicon substrate is provided at the end of the single crystal silicon substrate, and an attempt is made to single crystallize the polycrystalline film using this as a nucleus. Although it is possible to partially form a single crystal by interaction, it is difficult to obtain a silicon single crystal film that can withstand practical use.

Therefore, in recent years, a wafer having an SOI (Si On Insulator) structure has been particularly attracting attention. In this bonding wafer, at least one of the two semiconductor wafers is oxidized to form an oxide film on the surface of at least one of the wafers, and these two semiconductor wafers are formed so that the oxide film serves as an intermediate layer. After they are superposed, they are heated to a predetermined temperature to bond them to each other, and an upper layer wafer (hereinafter referred to as a bond wafer) is subjected to polishing to obtain a thin film.

(Problems to be Solved by the Invention) By the way, in a bonded wafer, the bonding strength of both wafers needs to be high over the entire bonding surface, and if the bonding strength is insufficient, it is called a void at the bonding interface. There has been a problem that a non-bonded region is generated and the yield of products is deteriorated. In addition, as a method of detecting a void, an infrared transmission method, an ultrasonic flaw detection method, an X-ray rung method, and the like are known.

In addition, in the manufacturing process of the bonded wafer, etching is performed using, for example, a hydrogen fluoride solution in order to remove the oxide film deposited on the wafer surface. If the erosion resistance to (1) is not high, there is a problem that peeling occurs in the pattern formed on the bond wafer in the device process.

Furthermore, in the case of a silicon wafer, there is a difference in thermal contraction rate (coefficient of thermal expansion) between the single crystal and the oxide film (SiO ₂ ), so if the single crystal surface and the oxide film surface are brought into contact with each other to form a bonded wafer, Since residual stress is accumulated in the bonded wafer, there is a problem that the bonded wafer is bent and deformed (warped).

The present invention has been made in view of the above problems, and the first
It is an object of the present invention to provide a method for producing a bonded wafer, which can obtain a bonded wafer having high bond strength and high erosion resistance of the bonding interface against an etching solution.

A second object of the present invention is to provide a bonded wafer without warpage.

(Means for Solving the Problems) In order to achieve the first object, the method for producing a bonded wafer according to claim 1, wherein a first mirror surface wafer and a second mirror surface wafer each made of single crystal silicon are prepared. Then second
An oxide film is formed on the one-sided mirror surface side of the mirror surface wafer, and the second mirror surface wafer is superposed on the mirror surface of the first mirror surface wafer so that the oxide film serves as an intermediate layer. 1100 ° C ~ in N ₂ atmosphere or oxidizing atmosphere
After heating to 1200 ° C. to bond them, the second mirror-finished wafer is thinned by polishing the surface of the second mirror-finished wafer opposite to the surface bonded to the first mirror-finished wafer.

The method for manufacturing a bonded wafer according to claim 2 for achieving the second object is the method according to claim 1, wherein the heat treatment is carried out in an oxidizing atmosphere. An oxide film is formed on the entire surface of the wafer except the adhesive surface.

(Function) As a pattern for bonding the first and second mirror-finished wafers through the oxide film, the first mirror-finished wafer (a bonded wafer, which is a protective wafer that mainly gives mechanical strength, is referred to as a base wafer hereinafter) (Referred to as "bond wafer"), and an oxide film is formed only on the wafer), and a second mirror surface wafer (a wafer on which a thin film is formed on the bonded wafer to form a device, referred to as a bond wafer) is bonded to the base wafer through the oxide film. On the contrary, the one in which an oxide film is formed only on the bond wafer and both wafers are bonded through this oxide film, and the one in which an oxide film is formed on both wafers and both wafers are bonded through these oxide films , Can be considered.

In view of the fact that the difference in the above patterns affects the bonding mechanism of both wafers in the bonded wafer, by extension the bonding strength of both wafers, and the erosion resistance of the bonding interface to the etching liquid. As a result of various experiments,
As in the method of the present invention (claim 1), if an oxide film is formed only on the one-sided mirror surface side of the bond wafer, and the two are bonded 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 erosion resistance can be obtained in the bonded wafer.

Further, it has been found that the warp 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 the bonding surface (claim 2). It was

(Example) Below, one Example of this invention is described based on an accompanying drawing. 1 (a) to 1 (e) 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. 1 (a), a bond wafer 1 made of single crystal silicon to be an element formation surface and a base wafer 2 made of the same single crystal silicon to be a base material.
And prepare. Then, the bond wafer 1 is subjected to an oxidation treatment, and a mirror surface on one side thereof (the surface on the lower side of the drawing) has a thickness of about 500 nm.
SiO ₂ oxide film 3 is formed.

Next, as shown in FIG. 1 (b), the bond wafer 1 is superposed on the base wafer 2 to be integrated.

Next, as shown in FIG. 1 (c), these integrated wafers 1 and 2 are heated in an oxidizing atmosphere at a temperature of about 1100 ° C. for about 120 ° C.
The wafers 1 and 2 are adhered to each other by thermal oxidation treatment for a minute, and the SiO ₂ oxide film 4 having a thickness of about 500 nm is formed on the entire surfaces of the wafers 1 and 2 (excluding the adhering surface).

Next, after cooling the bonded and integrated wafers 1 and 2, as shown in FIG. 1 (d), the surface of the upper bond wafer 1 is subjected to a predetermined polishing allowance (for example, 3 μm) to a predetermined value. To a thickness t ₁ (for example, 6 μm) of pre-polishing (1
Next polishing).

In this case, since the thermal contraction rate (coefficient of thermal expansion) of the wafers 1 and 2 made of single crystal silicon is larger than that of the SiO ₂ oxide films 3 and 4 as described above, the integrated bonding after the oxide film 4 is formed. Residual stress accumulates on wafers 1 and 2 when the synthetic wafer is cooled.

However, in this embodiment, since 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 base wafer 2
The residual stress distributions on the upper and lower surfaces are substantially equal, and the heat shrinkage amounts on the upper and lower surfaces are substantially the same, so that the bending deformation of the bonded integrated wafer is prevented.

Next, the bond wafer 1 (see FIG. 1 (d)) having the thickness t ₁ pre-polished as described above is subjected to the secondary polishing to obtain the thickness.
It is thinned by polishing to t ₂ (for example, 3 μm) to obtain a bonded wafer 5 as shown in FIG. 1 (e).

In order to investigate the bonding strength of the bonded wafer 5 obtained as described above, the heating temperature at the time of bonding 900 ° C, 1000 ° C, 1100
Prepare a plurality of bonded wafers obtained by heat treatment at ℃ and 1200 ℃ for 2 hours each, and measure the tensile adhesive strength of each bonded wafer.
It was measured with a tensile tester. In this case, bond wafer 1
And the lower surface of the base wafer 2 were fixed to the pulling member of the tester with an adhesive. The results are shown in FIG. 2 (c).

Further, as a comparative example to the above-mentioned embodiment of the present invention, under the same heating conditions, a bonded wafer obtained by directly bonding without interposing an oxide film between the wafers, and an oxide film with a thickness of 500 nm respectively on both wafers. Prepare a bonded wafer obtained by forming and bonding both wafers through this oxide film,
These bonded wafers were similarly tested for tensile adhesive strength. The results are shown in FIGS. 2 (a) and 2 (b). In addition, in FIG. 2, a ● mark indicates a value when both wafer bonding interfaces are peeled off, and a ○ mark indicates a value when the bonded wafer is peeled from the pulling member of the tensile testing machine (peeling of the adhesive). .

Furthermore, in FIG. 2, “oxide film 0/0 nm” is the case where no oxide film exists between both wafers, and “oxide film 500/500 nm” is the case where an oxide film with a thickness of 500 nm is formed on both wafers. “500/0 nm” indicates the case where an oxide film having a thickness of 500 nm is formed only on the bond wafer (Example of the present invention).

As is clear from FIG. 2 (c), according to the method of the present invention,
An oxide film is formed only on the bond wafer, and the temperature is 1100 ° C-12
When heated to 00 ° C, a high bond strength of 600 kg / cm ² or more can be obtained.

Then, based on the results shown in FIG. 2, when the bonding strength of the bonded wafers of each type is evaluated for each heating temperature,
The result is as shown in FIG. In FIG. 3, ◯ indicates good, Δ indicates good, and X indicates bad.

Thus, when the above results are summed up, if an oxide film is formed only on one side mirror surface of the bond wafer as in the method of the present invention and heated to 1100 ° C. to 1200 ° C. at the time of bonding, high bond strength (600 k
g / cm ² or more) was obtained.

On the other hand, as a result of performing an erosion resistance test on the bonding interface etching liquid (hydrogen fluoride solution) for each of the above-mentioned bonded wafers, it is confirmed that the bonded wafers obtained by the method of the present invention have high erosion resistance. I understood. In addition, other bonded wafers (with no oxide film between both wafers,
And an oxide film formed on both wafers),
Satisfactory erosion resistance was not obtained.

By the way, the bonded wafer 5 obtained by the method of the present invention
In this case, since the flexural deformation of the base wafer 2 which occupies most of the thickness is prevented as described above, the bonded wafer 5 has no warp and has a high degree of flatness. It is possible to obtain the effect that the vacuum suction of the bonding wafer 5 is reliably performed.

In order to examine the durability of the bonding interface against an etching solution, the above-mentioned bonding wafer (shown in FIGS. 2 (b) and (c)) was cut with a thin blade, for example, a peripheral diamond slicer of 80 μm, and each bonding was performed. About 2m from Waha
Twenty pieces of m-square pellets were prepared, and these pellets were allowed to stand in a hydrofluoric acid aqueous solution at a temperature of 25 ° C at a concentration of 25% for 20 minutes, washed with water, dried, and then examined the bonding state. That is, when lightly pulling the bond wafer side and the base wafer side in opposite directions with tweezers, about half of the pellets from the bonded wafer shown in FIG. 2 (b) were separated into the bond wafer and the base wafer at the bonding interface. . On the other hand, in the pellet from the bonded wafer shown in FIG. 2 (c) according to the present invention, the above breakage did not occur at all.

Further, when the joint interface of the joint wafer after being washed with water and dried was observed with a microscope, in the pellet from the joint wafer shown in FIG. 2 (c), even at the joint interface between the base wafer and the oxide film, the central portion thereof was observed. Then, the corrosion by the etching solution did not proceed.

The bonding wafer obtained by the method of the present invention is formed on a bond wafer by, for example, an integrated circuit element formed by a known method, and if the intermediate oxide film is formed by thermal oxidation, the oxide film is formed on the base wafer. On the other hand, since one surface of the area where the integrated circuit element is formed in the bond wafer is completely covered with the oxide film as the dielectric, the insulation resistance of the integrated circuit element and other electrical Good characteristics can be realized.

(Effects of the Invention) As is apparent from the above description, according to the method for manufacturing a bonded wafer according to claim 1, the bonding strength and the erosion resistance of the bonding interface with respect to the etching solution are high, and the substrate for an integrated circuit element is high. As a result, an excellent bonded wafer can be obtained.

Further, according to the method for producing a bonded wafer according to the second aspect, there is an effect that a warped bonded wafer can be obtained.

[Brief description of drawings]

1 (a) to 1 (e) are explanatory views showing a method of manufacturing a bonded wafer according to an embodiment of the present invention in the order of steps, and FIGS. 2 and 3 show the wafer obtained in the above embodiment and It is a figure which shows the test result of the tensile adhesive strength about the joining wafer obtained in the comparative example. 1 ... Bond wafer (second mirror surface wafer), 2 ... Base wafer (first mirror surface wafer), 3, 4 ... Oxide film,
5 ... Bonding wafer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuo Yoshizawa 1393 Yashiro Odaira, Sarahaku-shi, Nagano Nagano Electronics Co., Ltd. 72) Inventor Masao Fukami, 1393 Yashiro, Ojiro, Saranomiya-shi, Nagano Nagano Electronics Co., Ltd. (56) Reference JP-A-3-62511 (JP, A)

Claims (2)

[Claims] 1. A first mirror surface wafer and a second mirror surface wafer both made of single crystal silicon are prepared, an oxide film is formed on one side of the second mirror surface wafer, and the second mirror surface wafer is formed by the oxide film. Are laminated on the mirror surface of the first mirror surface wafer so as to be an intermediate layer, and then these first and second mirror surface wafers are heated to 1100 ° C to 1200 ° C in an N ₂ atmosphere or an oxidizing atmosphere to bond them. After that, the second mirror-finished wafer is thinned by polishing the surface of the second mirror-finished wafer opposite to the surface bonded to the first mirror-finished wafer to thin the second mirror-finished wafer. 2. The bonding according to claim 1, wherein the heat treatment is performed in an oxidizing atmosphere to form an oxide film on all surfaces of the first and second mirror-finished wafers except the bonding surface. Wafer manufacturing method.