JPH03250617A - Manufacture of bonded wafer - Google Patents

Abstract

PURPOSE:To manufacture a bonded wafer formed into a thin film and having high bond strength and erosion resistance by forming an oxide film on the one-sided specular surface side of a second specular wafer, by placing the specular surface with the oxide film formed thereon upon one specular surface of a first wafer, then by heating the first and second wafers to a predetermined temperature to stick them together, and thereafter by grinding the unbonded surface of the second specular wafer. CONSTITUTION:A single-crystal Si bond wafer 1 is oxidized so that SiO2 oxide film 3 is formed on one side of the wafer, the bond wafer 1 is placed upon a base wafer 2 and both wafers are formed into an integral body, and the wafers 1, 2 formed into an integral body are subjected to a thermal oxidation in N2 atmosphere or oxidizing atmosphere so that the SiO2 oxide film 4 is formed on the whole surface. Then, the surface of the bond wafer 1 being the upper layer of the wafers is pre-ground to a specified thickness t1 excepting a specified grinding margin left as it is. At the point of time of the end of pre-grinding, the top and under surfaces of the base wafer 2 are covered with the oxide films 3, 4 of almost the same thickness so that the distribution of the residual stresses in the top and under surfaces of the base wafer 2 is made almost equal and the heat shrinkage in the top and under surfaces is made almost the same to prevent the deflection.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a bonded wafer by bonding two wafers together.

(Prior Art) Conventionally, as a method for forming a single crystal semiconductor thin film on a dielectric substrate, single crystal silicon (
This is a well-known technique for epitaxially growing Si) films, etc., but in this technique, there is a mismatch in lattice constant between the substrate dielectric and the silicon polycrystalline grown in the vapor phase. A large number of crystal defects occur, which makes the technique impractical.

Also, a thermal oxide film is formed on the surface of a silicon substrate, 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 to this film. It is also well known that the silicon film is irradiated in one direction to melt and cool the silicon film in a linear manner, and to form a single crystal thin film as a whole.

By the way, the technique of converting a silicon polycrystalline film on a thermal oxide film into a polycrystalline film using a laser beam, etc.
It is disclosed in Japanese Patent No. 716. In this technology,
A continuous single crystal protrusion is provided at the edge of the single crystal silicon substrate, and the polycrystalline film is attempted to be made into a single crystal by using this as a core, or the polycrystalline film is partially crystallized by interaction with the oxide film of molten silicon. However, the reality is that it is difficult to obtain a silicon single crystal film that can withstand practical use.

Therefore, in recent years, SOI (Si on 1nsulat
ion) structure has attracted particular attention. This bonded wafer is produced by oxidizing at least one of two semiconductor wafers to form an oxide film on the surface of at least one of the wafers, and forming an intermediate layer between the two semiconductor wafers using the oxide film. After stacking them, they are heated to a predetermined temperature to bond them together, and the upper layer wafer (
It is obtained by polishing a bond wafer (hereinafter referred to as a bond wafer) to make it into a thin film.

(Problem to be solved by the invention) However, in bonded wafers, it is necessary that the bonding strength between both wafers be high over the entire bonding surface, and if the bonding strength is insufficient, voids will occur at the bonding interface. This results in unbonded areas, resulting in a problem of poor product yield. Incidentally, known methods for detecting voids include infrared transmission method, ultrasonic damage method, and X-ray Lang method.

In addition, in the manufacturing process of bonded wafers, etching is performed using, for example, a hydrogen fluoride solution to remove the oxide film deposited on the wafer surface, or etching is performed using an etching solution (hydrogen fluoride solution) at the bonding interface. If the corrosion resistance is not high, problems such as peeling or peeling may occur in the pattern formed on the bond wafer in the dehyzing process.

The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a bonded wafer that can obtain a bonded wafer with high bonding strength and corrosion resistance against etching liquid at the bonded interface. There is a particular thing.

Means for Solving Problem 1) In order to achieve the above object, the present invention forms an oxide film on at least one mirror surface side of a second mirror surface wafer of two first and second mirror surface wafers, and The mirror surface of the second mirror wafer on which the oxide film is formed is superimposed on at least one mirror surface of the first wafer so that the oxide film forms an intermediate layer, and then the first and second wafers are heated to a predetermined temperature to separate them. After bonding, a bonded wafer is obtained by polishing the non-bonded surface of the second mirror-finished wafer to make it a thin film.

(Effect) 1st. Second mirror wafer (hereinafter simply referred to as wafer)
The pattern for bonding these through an oxide film is the first wafer (in the bonded wafer, a protective wafer that mainly provides mechanical strength;
An oxide film is formed only on the base wafer (referred to as the base wafer), and the second wafer (the wafer that is thinned and on which devices are formed in the bonded wafer) is connected to the base wafer via this oxide film. A pattern in which an oxide film is formed only on the bond wafer, and a pattern in which both wafers are bonded via this oxide film,
A conceivable pattern is to form oxide films on both wafers, respectively, and then bond both wafers together via these oxide films.

The present inventors discovered that the difference in the pattern described above was due to the difference in the pattern.
As a result of various experiments from the viewpoint of the bonding mechanism of the second wafer, which affects the bonding strength of both wafers and the erosion resistance against etching liquid at the bonding interface, we have found that the method of the present invention is effective only for bonded wafers. It has been found that high bond strength and corrosion resistance can be obtained in thinned bond wafers by forming an oxide film on the bond wafer.

(Example) An example of the present invention will be described below based on the accompanying drawings.

FIGS. 1(a) to 1(e) are explanatory diagrams showing the manufacturing method according to the present invention in the order of the steps, and in the method of the present invention, the first
As shown in Figure (a), the S of the single crystal that should become the element formation surface
An i-bond wafer l is oxidized to form a Si oxide film 3 with a thickness of about 500n+* on one side (lower side), and in addition to this bond wafer l, a single-crystal Si-based wafer is also used as a base material. Prepare.

Next, as shown in FIG. 1(b), the bond wafer 1 is superimposed on the base wafer 2 to integrate them, and the bonded wafers 1 and 2 are placed in an N2 atmosphere or an oxidizing atmosphere. By thermal oxidation treatment at a temperature of 1100°C for about 120 minutes, a 5if film with a thickness of about 500 nm is formed on the entire surface of both wafers 1 and 2, as shown in FIG. 1(c).
A t-oxide film 4 is formed.

Next, the bonded wafers 1 and 2 are cooled, and as shown in FIG. Either pre-polishing (primary polishing) is performed until the thickness t□ (for example, 6 μm), or as mentioned above, the thermal contraction coefficient (thermal expansion coefficient) of the wafer 1.2 made of Si single crystal or SiO
□Because it is larger than that of oxidized M3,4, wafer 1.
After the wafers 2 are cooled, residual stress is accumulated within the wafers 1 and 2.

However, in this embodiment, the upper and lower surfaces of the base wafer 2 have a substantially concave thickness (approximately 500 nm
), the residual stress distributions on the upper and lower surfaces of the base wafer 2 are approximately equal, and the amount of thermal contraction on the upper and lower surfaces becomes a gap, thereby preventing bending deformation of the base wafer 2. .

By the way, the bond wafer l (see FIG. 1(d)), which has been pre-polished as described above and has a thickness tl, is polished to a thickness t2 (for example, 3uLm) by secondary polishing to become a thin film. As a result, a bonded wafer 5 as shown in FIG. 1(e) is obtained.

In order to examine the bonding strength of the bonded wafer 5 obtained as described above, the bonding temperature was 900° C.; 1.
A plurality of bonded wafers obtained by heating at 000° C., 1100° C., and 1200° C. for 2 hours each were prepared, and the tensile strength of each bonded wafer was measured using a tensile tester. The results are shown in FIG. 2(c). In addition, under the same heating conditions, a bonded wafer obtained by directly bonding the wafers without intervening an oxide film, and an oxide film with a thickness of 5001 mm formed on both wafers, and bonding between both wafers through this oxide film. Figures 2 (a) and (b) show the results of measuring the tensile strength obtained by a tensile test conducted on the bonded wafers obtained by bonding the wafers.
are shown respectively. In FIG. 2, the symbol * indicates the value when the bonding interface between both wafers has peeled off, and O indicates the value when the adhesive bonded to the wafer on the tensile testing machine has peeled off. Also, in the same figure, the oxide film is 010 nm, 5001500
nm, 50010n■ means that when there is no oxide film between both wafers, when an oxide film with a thickness of 5000mm is formed on both wafers, and when an oxide film with a thickness of 500n+s is formed only on the bond wafer. (In the case of the present invention)

As is clear from the results shown in FIG. 2(c), if an oxide film is formed only on the bond wafer as in the method of the present invention,
When heated to a temperature of 1100°C or higher, 800kg
A high bonding strength of /cm2 or more can be obtained.

From the results shown in FIG. 2, when the bonding strength of each type of wafer is judged for each heating temperature, the results shown in FIG. 3 are obtained. In addition, in Figure 3, ○ marks are good and Δ
The mark indicates acceptable, and the x mark indicates disapproval.

Taking all the above results together, it can be concluded that when an oxide film is formed only on the bond wafer as in the method of the present invention, the oxide film is
High bonding strength (800K
g/c■2 or more).

On the other hand, as a result of conducting erosion resistance tests against etching liquid (hydrogen fluoride solution) at the bonding interface on each of the above types of wafers, it was found that the bonded wafers obtained by the method of the present invention have high corrosion resistance. I realized that. In addition, for other bonded wafers (those with no oxide film between both wafers and those with oxide films formed on both wafers),
Satisfactory erosion resistance could not be obtained.

By the way, the bonded wafer 5 obtained by the method of the present invention
In this case, since the bending deformation of the base wafer 2, which accounts for most of the thickness, is prevented as described above, the bonded wafer 5 is free from warp and has a high degree of flatness, and the bonded wafer 5 is Effects such as vacuum suction in step 5 can be achieved reliably.

In order to investigate the durability against etching of the bonding interface,
The aforementioned bonded wafers (shown in FIGS. 2(b) and (c)) are cut with a thin blade, e.g., an 80 gm peripheral diamond slicer, approximately 2 mm from each bonded wafer.
Cut and separate the corner pellets into 20 pieces, and leave them in a concentrated solution of hydrogen fluoride #25% water for 20 minutes at 25°C.
After washing and drying, the bonding condition was examined. That is, when the bond wafer and base wafer sides were pulled in opposite directions using a bin set, about half of the pellets obtained from the bonded wafer shown in Figure 2(b) separated from each other at the bonded portion. The pellet obtained from the bonded wafer shown in FIG. 2(c) according to the present invention was not subjected to such destruction at all. Furthermore, when the interface was examined under a microscope, it was found that the pellet obtained from the bonded wafer 8 according to the present invention shown in FIG. The corrosion had not progressed.

In the bonded wafer having the structure of the present invention, when an integrated circuit element is formed on the bond wafer by a known method, if an oxide film between the peaks is formed by thermal oxidation, the oxide film is formed on the base wafer. Compared to the bond wafer or the dielectric oxide film, the area where the integrated circuit element is formed is completely covered on one side or the other, and the insulation resistance and other electrical properties of the integrated circuit element are lower. or well realized.

(Effects of the Invention) As is clear from the above explanation, according to the present invention, two #!
1. After forming an oxide film on at least one side of the second wafer of the second wafers and stacking the second wafer on the first wafer so that the oxide film becomes an intermediate layer, After heating the second wafer to a predetermined temperature and bonding them together, the surface of the second wafer is polished and made into a thin film to obtain a bonded wafer, and the first and second wafers are bonded together. After that, these first and second wafers were subjected to thermal oxidation treatment to form an oxide film on their entire surface, so the bonding strength and the erosion resistance against etching liquid at the bonding interface were high, making it suitable as a substrate for integrated circuit devices. It is possible to obtain an excellent bonded wafer.

4゜121-sided blind explanation Section 1 (a) to (e) are explanatory diagrams showing the manufacturing method according to the present invention in the order of the steps, and Figures 2 and 3 are diagrams showing the process carried out on various bonded wafers. It is a figure which shows the result of the tensile test carried out.

1... Bond wafer (second wafer), 2... Base wafer (first wafer), 3.4... Oxide film,
5... Bonded wafer.

Claims (1)

[Claims] An oxide film is formed on at least one side of the second wafer of the two first and second wafers, and the second wafer is stacked on the first wafer so that the oxide film becomes an intermediate layer. A method for manufacturing a bonded wafer, which comprises heating the first and second wafers to a predetermined temperature to bond them together, and then polishing the surface of the second wafer to make it a thin film to obtain a bonded wafer.