JPH03214615A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To execute a highly accurate pasting operation by a method wherein a metal whose melting point is lower than that of semiconductor substrates is used as a pasting medium and the medium metal itself is diffused into the semiconductor substrates. CONSTITUTION:A metal thin film 2 whose melting point is lower than that of both semiconductor substrates 1, 3 to be pasted is sandwiched between the semiconductor substrates 1, 3 to be pasted; an alloying process with the metal is executed; after that, nearly all of metal atoms of it are diffused into at least one of the semiconductor substrates. That is to say, when the low-melting metal 2 is used as a pasting medium, the semiconductor substrates 1, 3 are pasted, and the medium metal 2 itself is diffused and absorbed as part of the semiconductor substrates 1, 3. Thereby, the substrates can be pasted with good accuracy irrespective of the material, crystal plane orientation and flatness of the substrates to be pasted; a crystal defect is hard to produce in the pasted substrates and a highly accurate bonding operation can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, which includes a technique for bonding semiconductor substrates of the same type or different types.

[Conventional technology]

FIG. 2 is an example of the prior art direct bonding of Si wafers published in the March 1988 issue of Nikkei MicroDehys. Also, Figure 3 is from the Journal of the Institute of Electronics, Information and Communication Engineers Vol. 1.70, No.
6, pp. 593-595. '87. It is a diagram showing the detailed mechanism of the same technology published in the June issue.

The conventional technology will be explained below using these two figures. First, in Figure 2, 1.3 is the two types of Si wafers to be bonded, and 6 is hydrogen peroxide to clean the wafer surface prior to bonding and at the same time convert the surface into silanol (-Si-OH). (H202) and sulfuric acid (H2 S 04
), 7 is an infrared light transmitting light source (most semiconductors, including Si, transmit infrared light) to observe defects such as poids on stacked wafers, and 8 is a light source for observing the infrared transmitted light. It is a TV camera for 9
Is this a heat treatment furnace that heats the bonded wafers? .

Next, the process shown in FIG. 2 will be explained. First, Figure 2 (
As mentioned above in al., the wafer 1.3 to be bonded
At the same time as cleaning the surfaces of the wafers 1 and 3, the wafers 1 and 3 are converted into silanol. Thereafter, the dried wafers are stacked together in the air at room temperature (FIG. 2(b)). At this time, a void inspection is performed using infrared transmitted light to check whether the bonding is successful (Fig. 2 (C)). Items that have passed this inspection are placed in a normal heat treatment furnace 9 and heat treated (see Figure 2).
d)). For example, 1) Heat treatment is performed at 00° C. for about 2 hours in an atmosphere with a mixing ratio of 0:0 and nitrogen (N2) of 1:5. Thereafter, one or both surfaces of the wafers, which have been bonded through heat treatment, are polished to a desired thickness (FIG. 2 {e}).

FIG. 3 shows detailed reactions occurring during the heat treatment process shown in FIG. 2 Fdl. In the figure, 13' is the St atom on the outermost surface of the Si substrates 1 and 3 to be bonded, and the oxygen atom 10 and hydrogen atom 1) when silanolized in the step of FIG. 2(a) are -Bonded in OHO form. Furthermore, when bonded together in Figure 2 (bl), two hydroxyl groups (-
OH) are in a chemically equivalent state, so Figure 3 (a
1, a hydrogen bond is formed in the form H/\Si-00-SiH, and the outermost Si atoms 1' and 3' are bonded via two hydroxyl groups. 1000 from this state
In the process of gradually heating up to near °C, the temperature in Figure 3 (bl
Water molecule H2012 separates from the two hydroxyl groups \ / H that are hydrogen bonded as shown in the figure, dehydration condensation occurs to the bond -Si-0-Si-, and the 1' and 3' Si atoms become oxygen atoms. A state is reached in which only 10' is used as an intermediary. Furthermore, as shown in Fig. 3 (for Cl, during the heating step of 10 o'c or more, the aforementioned 10' oxygen source? even diffuses into the 1 or 3 Si substrate as interstitial oxygen 10' or into the atmosphere of the furnace). Eventually, the atoms 1' and 3' on the outermost Si surface are directly bonded to each other by their own bonds 13.

Although the two wafers bonded together in this way were initially physically separate, it was reported that they could eventually be handled as one wafer both mechanically and electrically. This method is said to be effective for power devices in which the current path is formed from the back to the front of the Si wafer, that is, it passes through the bonding surface.

On the other hand, simple mechanical bonding of Si wafers includes a method using a SiO film and an electrostatic bonding method. Pages 1325-1327 "High Voltage, New Driver IC Technisoku Wafer Direct Ponding J (PESC')
88 RECOl? D (.^pri1 198B)p
p. 1325~pp. 1327 u old gh Volta
ge, Neu DriverIC Technique
e on Silicon Wafer Direct
-Bor++1ing (SDB)”) and I-E-E Electron Deheys Letters E
D L Volume 8 No. 10 October 1987 454~
Page 456 [Electrical Isolate Photodiode Array by Silicon Wafer Direct Bonding
n Device Letters. Vol EDL
-8+ No. 10, Oct. '8L pp. 45
4-456 “A Dielectrically
Isolated Photodiode Array
by Silicon-Wafer Direct B
However, as mentioned above, the feature of these methods in terms of electrical properties between the bonded wafers is rather insulation, which is completely different from the purpose of this invention. Therefore, I will not go into details here.

In addition, there is a known technology for bonding anode metal plates (Mo, W, etc.) of high power devices such as Cyrisk and Si wafers using the A42 alloy method, but this is also a bonding process of metal and semiconductor. Since this is completely different from the present invention, explanation thereof will be omitted.

[Problem to be solved by the invention]

Since the conventional direct bonding method for semiconductor substrates is configured as described above, it has the following problems.

First, microscopically, bonding progresses by the mechanism shown in Figure 3, so the moment the two wafers are superimposed (Figure 2 (b)
), there was a problem that if the orientations of the crystal axes of both materials did not match accurately enough, not only would many crystal defects and distortions occur at the bonding interface after bonding, but also the bonding itself would not be successful.

Second, when overlapping mirror surfaces of wafers, care must be taken to ensure that no air bubbles remain at the wafer interface, and if the wafers themselves are not sufficiently flat, the bonding mechanism may cause
Since there is no process of "training", there was a problem that "hang" could easily occur.

Thirdly, although it has been reported that this bonding mechanism is based on "a treatment that imparts hydrophilicity to the surface of the semiconductor substrate," it is actually a phenomenon unique to the conversion of Si to silanol (-Si-OH) and its dehydration condensation reaction. Therefore, bonding using this mechanism is limited to Si substrates only.

Fourth, as the wafer diameter increases, it becomes difficult for ice molecules to easily detach from the center of the wafer as shown in Figure 3(b), and various compounds of Si, O, and H atoms cause crystal defects. There was a problem of inducing

Fifth, because the oxygen atom concentration increases at the bonding interface, kV
Even when using an S1 wafer manufactured by the FZ method with a low oxygen concentration, which is suitable for high-voltage power devices, the same properties as Si substrates obtained by the CZ method with a locally high oxygen concentration (for example, oxygen precipitation, etc.) ).

This invention was made to solve the above-mentioned problems, and is a method for bonding semiconductor substrates that is insensitive to the material, crystal plane orientation, and flatness of the bonded substrates. An object of the present invention is to provide a method for manufacturing a semiconductor device using a bonding technique in which crystal defects are less likely to occur.

[Means to solve the problem]

A method for manufacturing a semiconductor device according to the present invention includes, as a method for bonding semiconductor substrates, a metal thin film having a lower melting point than the semiconductor bases of both substrates to be bonded is sandwiched between the semiconductor substrates to be bonded, and an alloying process with the metal is performed. After that, the method includes a step of diffusing substantially all of the metal atoms into at least one of the semiconductor substrates.

[Effect]

In the method of bonding semiconductor substrates according to the present invention, semiconductor substrates are bonded together by using a low melting point metal as a bonding medium, and the medium metal itself is absorbed as a part of these semiconductor substrates by diffusion.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a method for manufacturing a semiconductor device according to an embodiment of the present invention.
Wafer 2 is an Affi film formed on a P-type Si wafer, and 3 is an N-type St wafer, which, like 1, has an All thin film 2 on its surface. The figure (b) is A4
This shows a heating process for alloying Si and Si.

The same figure (4 in Cl is the Si-Aj2 alloy layer. The same figure (di again shows the heating process to sufficiently diffuse Aβ atoms into the Si substrate from the Si-AA alloy layer.
Then 5 is AI! ．． It shows a P-type high concentration impurity region generated by diffusion of .

Next, the procedure will be explained.

First, clean and flat P-type and N-type Si substrates 1.3 from which heavy metals, organic substances, etc. have been sufficiently removed are prepared, and an Al thin film 2 is formed on one surface of each (see Fig. 1).
a)).

Next, align the sides of the two substrates with the Ap thin film attached,
Heat in an inert or reducing atmosphere at 600°C or higher (No. IIFFb)).

By leaving it at this temperature for several tens of minutes to several hours, the S
An alloy layer 4 of t-Aρ is formed, and the two wafers are bonded together (FIG. 1(C)).

However, at this point, although the two wafers 10 are mechanically bonded, they have a semiconductor/metal/semiconductor structure electrically and cannot be considered as one semiconductor substrate. Therefore, for example, N2. When heated to about 1200°C in an inert atmosphere such as Ar and left for several hours (Fig. 1(d)), Al atoms change to P-type 1, N-type, as shown in Fig. 1(e). fully diffused into each St substrate of type 3, originally A! Since 2 is a P-type impurity dopant for the Si substrate, a P'' impurity region is formed, and electrically and physically it can be regarded as one semiconductor substrate.

As a more specific example, consider the case where 300 people deposit A-ρ2. Aj! -SiO azeotrope is 1 at 577℃
2.2 Since it is atXin Si, if Aρ-Si alloying is performed at a practical alloying temperature of about 660°C, AN
Approximately 3,000 Aβ-Si alloy layers 4 are formed, which is approximately 10 times as many as the 300-layer film. The surface impurity concentration considered to be a high-concentration P゛spreading layer 1 is 10'9 to 1020 particles/cm2, and on the other hand, the Al2-
There are 8β atoms in the Si alloy layer at an atomic concentration of approximately 1022 atoms/cm2, and in order for the surface concentration after diffusion to be 3X10'' to 3X].020 atoms/cm2, this Al2-Si Layer width is 03
μm×1022/3×1019~1020-100~1
It is necessary to spread the damage until it reaches 0 μm. On the other hand, 1200
A at °C! The diffusion coefficient D,, is 1.6X 1 0-
1) cm2/sec. and the diffusion coefficient Dl of the B atom] (-1
．． 3 X 1 0-"'cm"/sec. ) compared to DA. -/DB'M12.3 Confucian 6χ3.
5, indicating that /l diffuses approximately 3.5 times faster than B atoms. According to experimental data, B atoms diffuse by about 35 μm in about 24 hours at 1200°C, so in the case of An, the diffusion rate is also 12
00℃, 24. 35μm x 3.5-122μm for hr
Spread. Therefore, in the case of 300 people in the An film, 1200
C. for several hours to several tens of hours in the process shown in FIG. 1(d).

Here, the MBE (molecular beam epitaxial) method is actually used. By using techniques such as MOCVD (metal organic CVD) and rcB (ion cluster beam), it is possible to form an An thin film with a thickness of several (-atomic level) to several tens of people, as shown in Figure 1 ( d)-12 The heat treatment process is performed at a low temperature of several hundred degrees or several tens of minutes. It is also possible to shorten the time.

In the above embodiment, the first and second semiconductor substrates 1.3 are a P-type high impurity concentration Si substrate and an N-type low impurity concentration S substrate.
Taking the t-substrate as an example, Al, which serves as a P-type impurity dopant I for the Si base, was selected as the low melting point metal for these intermediate layers, but the materials are not limited to these. That is, 1st. The second substrates 1 and 3 may be P type, N type, or intrinsic (neutral), and the impurity concentration may be any combination of high concentration and low concentration, and it is also necessary that the plane orientations of the crystal axes of the substrates match. The material is not limited to S3, but also GaAs. Any combination of any compound semiconductor such as InP, CdTe, or SiC, or a single material semiconductor such as Si may be used.

In addition, the low melting point metal thin film that acts as an intermediary also serves as a P-type dopant for Si, such as Aβ, Ga. ．． In addition to As and Sb, which serve as N-type dopants, neutral metals such as Sn and Ti or their compounds may also be used, and any type of elemental metal such as 13 Se, Te, etc. may be used depending on the type of substrate other than Si. and compounds thereof may also be used.

In addition, in FIG. 1 of the above embodiment, the process of alloying Si-AI (FIG. 1(b)) and the process of diffusing Al by high-temperature heat treatment (FIG. 1(d)) were explained separately, but the atmospheric gas By devising the type, heating device, and its jigs and tools, the processes from alloying (FIG. 1(b)) to heating expansion (FIG. 1(e)) can be performed at the same time.

Further, the metal 2 sandwiched between the semiconductor substrates 1 and 3 may be formed on either one of the semiconductor substrates 1 and 3 depending on the thickness and type, or may be formed on both as in this embodiment. .

According to this embodiment, the semiconductor substrates are bonded together by using a low melting point metal as the bonding medium, and the bonding medium metal itself is absorbed as part of the semiconductor substrate by diffusion, so that the bonded substrates are bonded together. They can be bonded together with high precision regardless of the material, crystal plane orientation, or flatness of the substrates, and crystal defects are less likely to occur in the bonded substrates, making it possible to achieve high-precision bonding.

14 [Effects of the Invention] As described above, according to the present invention, the method for bonding semiconductor substrates to each other uses a metal with a lower melting point than these semiconductor substrates as a bonding medium, and most of the medium metal itself is contained in these semiconductor substrates. Since it is configured to diffuse, it can be formed more easily and with a higher yield than conventional techniques, and has the effect of providing a wide range of applications.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing a method for bonding semiconductor substrates in a method for manufacturing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a schematic cross-sectional view showing a conventional method for bonding semiconductor substrates, and FIG. 2 is a schematic cross-sectional view showing in detail a part of the mechanism shown in FIG. 2. FIG. In the figure, 1.3 is a semiconductor substrate, 2 is a low melting point metal thin film, 4 is an alloy layer of the semiconductor substrate material and the low melting point metal thin film, 5 is a diffusion region of low melting point metal thin film atoms, and 6 is sulfuric acid, hydrogen peroxide. Mixed liquid, 7 is an infrared transmission light source, 8 is a television camera for infrared observation, 9 is a heat treatment furnace, 10 is 15 oxygen atoms bonded between Si atoms and H atoms, and 10' is bonded between Si atoms. Oxygen atoms, 10″ are oxygen atoms that escape from the semiconductor substrate interface, 1
) is a hydrogen atom bonded to an oxygen atom, 12 is an ice molecule that escapes from the semiconductor substrate interface, and 13 is a bond between Si atoms at the semiconductor substrate interface. Procedural amendment (voluntary) ■. Incident display patent application No. 10189/1992 2. Title of invention: Method for manufacturing semiconductor devices 34 4. Relationship to the case of a person who cheats on amendments Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Moriya Shiki

Claims (1)

[Claims] (1) In a method for manufacturing a semiconductor device including a substrate bonding step of bonding a first semiconductor substrate and a second semiconductor substrate, in the substrate bonding step, out of the first and second semiconductor substrates, forming a metal thin film having a lower melting point than both the first and second semiconductor substrates on the surface of at least one semiconductor substrate; bonding the first and second semiconductor substrates together using the metal thin film as an intermediary; A method for manufacturing a semiconductor device, comprising: a step of combining; and a step of diffusing nearly all of the atoms in the metal thin film into at least one of the first and second semiconductor substrates by heating. .