JPS62120044A - Bonding method for flat plate - Google Patents

Abstract

PURPOSE:To bond without solvent nor stress by forming the layer of thermoplastic substance film on two Si wafers, and pressurizing and heating the layers in the laminated state. CONSTITUTION:SiO2 films 12, 22 of 0.5mum thick are deposited as an impurity diffusion preventing substance layer on Si wafers 11, 21, and PSG films 13, 23 are similarly deposited in thickness of 2.5mum thereon by an ambient pressure CVD. Thus formed bonding substrates 14, 24 are superposed so that the layers 13, 23 are contacted with each other on two quartz supporting bases 15, filled in an electric furnace 17 in the state placed on a columnar quartz block 16, and bonded by pressurizing and heating. When PSG of 14mol% of P2O5 density is used, the two substrates 14, 24 are completely fusion-bonded by pressurizing with 26g/cm<2> and heating at 950 deg.C with the block 16. When the bonded substrates 14, 24 where pulverized and finely examined, separation of the substrates due to unbonding was not observed.

Description

[Detailed Description of the Invention] [Summary] A layer of thermoplastic material is formed on the surfaces of two flat plates, and the two hand plates are bonded together by applying pressure and heating with the layer surfaces brought together.

[Industrial application field]

The present invention relates to a technique for adhering two flat plates to each other, and more specifically, to a technique for uniformly and firmly bonding high-precision flat plates such as silicon (St) wafers together.

[Conventional technology]

The technique of bonding flat plates, such as Si wafers, to other flat plates is used, for example, in silicon-on-insulator (SOI) variants. SOI is a technology that recrystallizes impure silicon on an insulator using an energy beam such as a laser beam to form a single crystal silicon layer on the insulator. It is also difficult to obtain a complete single crystal silicon layer.

The technology developed to obtain single-crystal silicon with good crystallinity in SOI will be explained with reference to the cross-sectional view in FIG. A layer 32 is formed, silicon is epitaxially grown on it to form a silicon epitaxial layer 33 (hereinafter simply referred to as an epitaxial layer), the surface of the epitaxial layer is oxidized to form a 5i02 film 34, and phosphorus, silicate, glass is formed on top of it. (PSG') is grown to form a PSG film 35.

On the other hand, a substrate 36 (for example, a quartz substrate) is prepared, a PSC film 37 is formed thereon, and PSG films 35 and 37 are adhered thereto.

FIG. 3 is a diagram in which the substrate 36 is inverted compared to the case in FIG. 2. Referring to FIG. 3, the silicon substrate 31 is mechanically ground. Since it is difficult to leave only the epitaxial layer 33 during this grinding, when the remaining material after grinding the silicon substrate 31 is etched using a mixed solution of KOH-IPA-HlO, the etching rate of St is higher than that of highly concentrated boron. Since etching is about 50 times faster, the high concentration boron implanted layer 3 acts as a stopper in the etching described above, and the high concentration boron implanted layer 3 is etched after the silicon substrate 31 is completely removed.
2 remains.

Next, when the high concentration boron injection layer 32 is etched using a mixed solution of HNO3-CH5COOH-HF, the etching rate of the high concentration boron injection layer is about 70 times faster than that of Si, and this etching turns the epitaxial layer into a stopper. , an epitaxial layer 33 remains on the 5i02 film 34, as shown in FIG. This epitaxial layer is formed to a thickness of about 1 μm, but it is made of single crystal silicon with good crystallinity comparable to that of an ideal silicon substrate.
Form the desired device there.

[Problem that the invention seeks to solve]

Conventionally, a polymer adhesive containing a solvent was inserted between two flat plates, and bonding was performed by applying uniform pressure. However, with this method, the solvent is difficult to escape, making it difficult to achieve strong adhesion over the entire surface. In particular, in applications where one of two bonded flat plates (for example, a Si wafer) is made into a thin film by polishing or etching, and a device is created in the thin film (epitaxial layer in the above example),
Cracks may occur in the thin film due to the residual solvent itself and stress caused by uneven adhesion caused by the residual solvent, which may adversely affect the device.

The present invention was created to solve the problems of the prior art as described above, and involves forming a layer of thermoplastic material on two flat plates in advance, applying pressure and heating to the combined state. The object of the present invention is to provide a method that enables fusion bonding by applying a bonding agent to the bonding material, thereby making it possible to bond without using solvents or stress.

[Means for solving problems]

FIG. 1 is a sectional view of an embodiment of the present invention, and in the same figure, 11
is a Si wafer, 12 is a SiO2 film (impurity diffusion prevention material), 13 is a psc film (thermoplastic material), 21 is a Si wafer, 22 is a 5iOz film (impurity diffusion prevention material), , 2
3 is a PSG film (thermoplastic material film), which is a Si wafer,
Adhesion substrate for SiO+ film and PSG film 14.24 respectively
Configure.

The invention comprises a thermoplastic film 13.23, preferably PS
2 layers of G, BSG (boron silicate glass), etc.
It is formed on two Si wafers 11 and 21, and by applying pressure and heat with the layer surfaces aligned, the thermoplastic layer is sufficiently softened or melted to fuse the two St wafers 11 and 21. be.

[Effect]

If a glass-like material is used as the thermoplastic material for the adhesive, the stress applied to the flat plate when solidified will be relatively small. In particular, when the flat plate is a Si wafer, PSG, BSG, etc. are effective as the thermoplastic material. PSG and BSG have been conventionally used for passivation of Si semiconductor devices and planarization of device surfaces, and although they have positive effects (such as gettering of Na) on Si semiconductor devices, they have almost no negative effects.

PSG and BSG each contain P (phosphorus) and B in 5tOz.
(boron) doped, and as the amount of P and B doped increases, the softening temperature decreases and fusion becomes easier.

For example, when two Si wafers are bonded together, one of the wafers is made into a thin film by polishing or etching, and a device is formed in the thin film, the device and the adhesive layer are in close proximity, which may affect the device characteristics. The impact becomes noticeable. When using polymeric adhesives that contain solvents, residual solvents and polymeric materials may have a negative effect on device characteristics, and the effects of stress cannot be ignored because solidification does not occur smoothly. It's something that didn't exist. On the contrary, P
When SG or BSG is used, as mentioned above, there is a sufficient track record of its use in Si semiconductor devices, and there is almost no adverse effect.

Note that B-doped PSG is advantageous for bonding at low temperatures, and if it is used, bonding is possible even at about 800°C.

When applicable to Si semiconductor devices, P'P in PSG and B in BSG are converted to S during high-temperature fusion and device formation processes.
Since there is a risk of diffusion of impurities into the Si wafer, it is desirable to provide an SiO+ film for preventing impurity diffusion on the surface of the Si wafer before depositing PSG or BSG.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

Approximately 5 cm (2 inches) Si wafer 1 as a flat plate
Using 1°21, a 0.5 μl thick layer of 5 was deposited on the surface of the Si wafer 11.21 by atmospheric pressure CVD as an impurity diffusion prevention substance layer.
An i02 film 12.22 was deposited, and a PSG film 13.23 was further deposited thereon to a thickness of 2.5 μm by atmospheric pressure CVD. Adhesive substrate 14 created in this way.
24 on the quartz support 15 and a layer of PSG 13.23
The cylindrical quartz blocks 16 were placed on top of each other so as to be in contact with each other, and the cylindrical quartz blocks 16 were placed on top of the quartz blocks 16, which were placed in an electric furnace 17, and bonded by pressure and heat.

When PSG with h0505 concentration of 4 mo1% is used, two adhesive substrates 14.24 are bonded by applying a pressure of 26 g/cm2 and heating at 950°C using the above-mentioned cylindrical quartz block 16.
was completely fused. When the fused adhesive substrates 14 and 24 were crushed and opened in detail, no peeling of the substrates due to unfused bonding was observed.

When the same experiment as above was carried out using PSG (BL03 concentration: 3moj!%, PL03 concentration: 9mo1%) in which B was substituted for the above-mentioned psc, the temperature of two adhesive substrates at 850°C was 14.24%. Completely fused.

Furthermore, we conducted the same experiment as above for BSG,
In the case of BSG with a B103 concentration of 11 mo/%, 1000°C
It was confirmed that complete board adhesion was possible.

In this example, we have introduced the case where psc, BSG, etc. are used as the thermoplastic material, but it is not limited to these, and it has been confirmed that adding Ge to other materials lowers the softening point of PSG. This Ge-containing PSG can also be used as an adhesive.

In addition, in the above embodiment, 5i0 is used as an impurity diffusion prevention substance.
2 was adopted, but it is not limited to this, and for example, 5iJN1 etc. can also have a sufficient effect of preventing impurity diffusion.

In addition, various impurity diffusion prevention substances can be used depending on the type of thermoplastic material.

Furthermore, as thermoplastic substances, B, Ge, A
s.

AN, Na, K, Mg, Ca, Pb+
Mn, W, Tit Zr, Hf.

Scales are made of glass containing one or more elements of Ta, Cr, NAl, and Nb, and in addition to PSG and BSG, silica glass (S
It was confirmed that 1Oz) can also be used. Furthermore, if this fusion is performed in a vacuum, there will be no air bubbles, so
It was confirmed that there was no occurrence of cranking due to stress, etc., and that stronger adhesion was possible.

The above bonding method is effective in the SOI modification example explained with reference to FIGS. 2 and 3, and in that case the Si wafer is thinned, but even in that case, the single crystal silicon layer may be cracked due to stress etc. It was confirmed that this was prevented.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to bond two flat plates such as Si wafers uniformly and firmly, which improves the manufacturing yield of semiconductor devices in, for example, modified SOI. Effective in increasing device reliability. In addition, in the method of the present invention, the solid phase←
Since we use a thermoplastic material whose state changes widely from softened state to liquid phase, there is no need for strict heating conditions.
There is an advantage that a simple method of heating in an electric furnace as shown above can be used.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention. FIGS. 2 and 3 are cross-sectional views showing modified examples of the sor. In Figure 1, 11 and 21 are Si wafers, 12, 22 is 5i02 M smell, 13 and 23 are psc layers, 14 and 24 are adhesive substrates; 15 is a quartz support stand; 16 is a quartz block. Book record 1 work case front prisoner Figure 1 # view of Sol variant Figure 2 So1 sentence pattern example O illustration Figure 3

Claims (9)

[Claims] (1) A thermoplastic layer (13, 23) is formed on the surface of a pair of flat plates (11, 21), and the pair of flat plates (11, 21) A flat plate bonding method characterized in that the pair of flat plates (11, 21) are fused together by stacking them and applying pressure and heat. (2) The method according to claim 1, wherein the thermoplastic material is phosphorus-silicate glass. (3) The thermoplastic substance is silica glass (SiO_2)
The method according to claim 1, characterized in that: (4) The thermoplastic substance is B, Ge, As, Al, N
a, Mg, Ca, Mn, W, Ti, Zr, Hf, T
2. The method according to claim 1, wherein the glass is a glass containing one or more of the following elements: a, Cr, Ni, and Nb. (5) The flat plate (11, 21) is a semiconductor substrate, and an impurity diffusion prevention material layer (12, 22) is provided between the substrate and the thermoplastic material layer (13, 23). A method according to claim 1. (6) The method according to claim 1, wherein the impurity diffusion preventing substance is SiO_2. (7) The method according to claim 1, wherein the impurity diffusion preventing substance is Si_3N_4. (8) The method according to claim 1, characterized in that the bonded semiconductor substrate is thinned. (9) The method according to claim 1, wherein the bonding is performed under reduced pressure.