JPH04263932A - Method for bonding substrate - Google Patents

Abstract

PURPOSE:To bond substrates so as to have uniform bonding strength as a whole without leaving air bubbles between the substrates. CONSTITUTION:A substrate pair 20 wherein substrates 23,25 are bonded by an adhesive 24 is placed on a pressure head 55b and a curved plate 10 is placed thereon so as to come into contact with the substrate pair 20 on the protruding side thereof. The curved plate 10 is formed by laminating a low expansion metal plate 12 and a high expansion metal plate 11 and protrudes on the side of the low expansion metal plate 11 at room temp. but deforms by raising temp. and becomes a flat shape at adhesion temp. A pressure head 55a is lowered to press the center of the substrate pair 20 to push out air bubbles in the vicinity of the center to the outside. Continuously, when the whole is heated, the curved plate 10 is deformed to become flat to further push out air bubbles to the outside. The curved plate 10 becomes flat at adhesion temp. and air bubbles are removed from the adhesive between the substrates and bonding strength also becomes uniform.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bonding substrates, which prevents air bubbles from remaining between the substrates and applies uniform bonding pressure to the entire substrate at the bonding temperature.

0002

[Prior Art] Conventionally, bonding technology by thermocompression bonding of semiconductor substrates or insulating substrates using adhesives has been used to manufacture SOI substrates (Atsushi Yamada, Toshio Kawasaki, "Method of Bonding Semiconductor Substrates Using Adhesives", 1988). Proceedings of the 47th Japan Society of Applied Physics Conference (Autumn 1988, pp 495), device transfer method (Shinsuke Endo, Tsuneo Hamaguchi, Naoki Kasai "Transfer of 1/2 μm thick device layer and its characteristics" 47th Applied Physics Conference, Autumn 1986) It has been applied to academic conference proceedings, pp. 495). However, since the substrate surface is not completely flat, when trying to bond two substrates with adhesive, air bubbles inevitably remain between the substrate and the adhesive or between the adhesives, and during thermocompression bonding, air bubbles are left in the adhesive layer. I get into it.

[0003] On the other hand, in direct bonding of substrates without using adhesive, the supporting stand is equipped with a mechanism that can hold the substrate in two states: a state in which the board is bent and a state in which it is not bent. A method is known in which one of the substrates is brought into contact with the other, and then the vacuum suction of the support is released to bond the two substrates together (Japanese Patent Publication No. 182239/1983, ``Semiconductor Substrate Bonding Apparatus''). The adhesion method described in this publication is shown in FIG. Semiconductor wafers 91 and 92 are held on the support stand 94 and holder 93 as shown in (a) and (b), and relative positioning is performed with the two brought close together as shown in (c). d) As shown in the figure, bend the semiconductor wafer held on the support stand, bring the semiconductor wafers held on the holder into contact (Figure (e)), release the vacuum suction on the support stand, and separate the two wafers. The semiconductor wafer is bonded (Figure (f)).

0004

[Problems to be Solved by the Invention] However, since the method shown in FIG. 7 only releases adsorption, high pressure cannot be applied, and the method has a complicated structure such as a variable support stage, so it cannot withstand high temperatures. Therefore, this method cannot be applied to bonding substrates using adhesives that require high temperature and high pressure.

[0005] An object of the present invention is to provide a method for bonding substrates for thermocompression bonding that ultimately provides uniform pressure distribution over the entire substrate while removing the above-mentioned air bubbles.

[0006]

[Means for Solving the Problems] In the substrate bonding method of the present invention, a low-expansion metal plate and a high-expansion metal plate are pasted together, and the low-expansion metal plate side is convex at room temperature, and deforms as the temperature rises. A curved plate that becomes flat at the bonding temperature is sandwiched between the pressure head and the pair of substrates to be bonded so that the convex portion is in contact with the opposite side of the substrate, and then pressure and heat are applied. It is characterized by applying uniform adhesive pressure to the entire substrate while removing air bubbles existing between the substrates.

[0007]

[Operation] In the present invention, when bonding semiconductor substrates, insulating substrates, etc., a curved plate is inserted between the part that applies pressure to the substrate and the substrate so that the convex side is in contact with the substrate. By doing this, pressure is applied only to the center area at the initial stage of pressurization, and air bubbles existing near the center between the substrates are first pushed out. Subsequently, by applying heat, the curved plate transforms from a convex shape to a flat shape due to the difference in thermal expansion coefficient, and as a result, the air bubbles between the substrates are further pushed outward, and at the bonding temperature, it becomes a parallel plate shape. Air bubbles are removed from between the substrates and uniform pressure is applied across the substrates.

[0008]

Embodiments Next, embodiments of the present invention will be described with reference to FIGS. 1 to 6. FIG. 1 is a cross-sectional view of the curved plate 10 (a).
is a cross-sectional view at room temperature Tr °C, and (b) is a cross-sectional view at adhesion temperature Ta
FIG. 3 is a cross-sectional view when the temperature is raised to ℃. High expansion alloy plate 1
1 and a low expansion alloy plate 12 are pasted together so that the low expansion alloy side is convex at room temperature Tr ℃. When heat is applied to this, the high expansion alloy plate expands more than the low expansion alloy plate, and the bonding occurs. It deforms into a flat shape at a temperature of Ta °C. Note that the appropriate size of the curved plate 10 is approximately the same size as the substrate to be bonded or slightly larger.

[0009] It is important to manufacture the film so that it has an exactly flat shape when the bonding temperature is Ta° C. as shown in FIG. 1(b). Figure 2 shows an example of the design. The expansion coefficient of the high expansion alloy is Mh, the expansion coefficient of the low expansion alloy is Ml,
The curved plate 10 has a spherical shape with a radius of curvature r and an opening angle θ at room temperature Tr °C, as shown in Fig. 2(a), and the distance between the alloy plates is d.
shall be. However, the value of the distance d between the alloy plates is represented by the distance between the centers of the respective alloy plates, ignoring the thickness of the alloy plates. In such a case, if a curved plate is manufactured to satisfy the following equation (1), it will become a flat plate as shown in FIG. 2(b) when the bonding temperature is Ta°C.

0010

[0011] If the characteristic values of the bimetal are known from the catalogs of various companies, the design may be made as follows, for example. JIS method (Japan) (Reference: Metal materials No. 12
Volume No. 1 p. 70), the curvature constant K is defined as in the following equation (2).

0012

In FIG. 3(a), 31 is the shape at T1°C, 32 is the shape at T2°C, and D is the temperature at T1°C.
This is the amount of deformation when changing from T2 °C to T2 °C. however,
T2 > T1. Therefore, if it is deformed by D expressed by the following equation (3) at room temperature Tr ℃ as shown at 33 in FIG. .

[0014]

[0015] Since the amount of deformation D is difficult to use for machining,
As shown in FIG. 3(c), the radius of curvature r and the opening angle θ are converted as shown in the following equations (4) and (5), and processing can be performed using these r and θ.

[0016]

As an example, the low expansion metal is 42% Ni-F.
e, the high expansion metal is 25%Ni-8.5%Cr-Fe. Let's calculate the case when using bimetal. The curvature constant K is K=11.3×10-6/℃ (temperature range 20~3
50℃) (Reference: Metal Materials Vol. 12 No. 1
p. 68 (see Table 1). The thickness d of the bimetal plate is 0.5 cm, and the diameter of the wafer and bimetal plate is 10 cm.
For example, polyimide with a bonding temperature of about 300° C. is used to bond the wafers. These values are expressed as equation (4), (
5) and calculate the radius of curvature r and opening angle θ,
r≈79 cm, θ≈7.3°, and if the bimetal plate is processed in this way, it will become flat at the bonding temperature, making it possible to bond wafers from which air bubbles have been removed.

Other than the method shown in FIG. 3, ATM method (Europe), ASTM method (USA) (Reference: Metal Materials Vol. 12, No. 1, p. 70, see FIG. 1)
Even if the measured curvature ratio is known, a design method tailored to each case can be easily devised in the same manner as the method shown in FIG. Alternatively, a curved plate manufactured using the above-mentioned design method is actually heated to the bonding temperature, and if it deviates from the flat surface, external force is applied to deform it into a flat shape, and then it is returned to room temperature. It is also possible to create a more accurate shape by applying

FIGS. 4 to 6 show a method for bonding silicon substrates using a polyimide adhesive as an example of the method for bonding substrates using the curved plate of the present invention. First, as shown in FIG. 4, a pair of substrates 20 to which silicon substrates 23 and 25 are bonded with polyimide adhesive 24 is placed on a pressure head 55b, and a curved plate 10 is placed on top of the pair of substrates 20, with the low expansion alloy 12 side facing the pair of substrates 20. Place it on the side. At this time, the centers of the curved plate 10 and the substrate pair 20 are made to coincide. Next, the pressure head 55a is pushed down and the silicon substrate 23 - polyimide adhesive 24 - silicon substrate 2 is pressed down.
Apply pressure to step 5. Since the convex side of the curved plate 10 is in contact with the substrate, high pressure is applied near the center of the substrate, and air bubbles 67 existing near the center are pushed out (Figure 5).
. Subsequently, when the heater 56 is turned on and heat is applied, the curved plate 10 gradually deforms toward a flat shape, and accordingly, the air bubbles 67 existing between the substrates are further pushed out. And the adhesive temperature of polyimide adhesive is about 400℃
At this point, the curved plate assumes a flat shape as shown in FIG. 6, the air bubbles 67 are removed from between the substrates, uniform pressure is applied to the entire substrate, and at the same time the polyimide adhesive is cured. This makes it possible to bond the substrates without any air bubbles between the substrates and with uniform adhesive strength over the entire substrate.

[0020]

As described in detail above, according to the present invention, it is possible to bond the substrates so that no air bubbles are present between the substrates and the bonding strength is uniform throughout the substrates.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a curved plate used in an embodiment of the present invention.

FIG. 2 is a diagram for explaining a design example of a curved plate.

FIG. 3 is a diagram for explaining a design example of a curved plate.

FIG. 4 is a diagram showing the bonding method of the present invention.

FIG. 5 is a diagram showing the bonding method of the present invention.

FIG. 6 is a diagram showing the bonding method of the present invention.

FIG. 7 is a diagram for explaining a conventional method of directly bonding substrates.

[Explanation of symbols]

10 Curved plate 11 High expansion alloy 12 Low expansion alloy 20 Board pair Shape at 31　T1　℃ Shape at 32　T2　℃ Shape at 33 Tr °C Shape at 34 Ta °C 23, 25 Silicon substrate 24 Polyimide adhesive 55 Pressure head 56 Heater 67 Bubbles 91,92 Semiconductor wafer 93 Holder 94 Support stand

Claims (1)

[Claims] 1. A curved plate in which a low-expansion metal plate and a high-expansion metal plate are pasted together, and the low-expansion metal plate side is convex at room temperature, but deforms as the temperature rises and becomes flat at the bonding temperature, A method for bonding substrates, which comprises sandwiching between a pressure head and a pair of substrates to be bonded so that a convex portion is in contact with the opposite side of the substrates, and applying pressure and heat.