JPH07201690A - Junction method for substrate - Google Patents

Abstract

PURPOSE:To uniformize a pressurizing force applied to a wafer surface by a method wherein sealing is performed in an outer peripheral part of a laminated substrate from either one of uppermost and lowermost layers of the laminated substrate or the both, and the laminated substrate is pressurized by pressure of a pressurizing material containing gas or liquid within this seal. CONSTITUTION:A pressurizing container 2 is arranged on one side of a laminated silicon wafer 1 and fixed by an upper rod 4 and a lower rod 5. Further, an optional rod load W is applied to the upper rod 4 and lower rod 5. A pressurizing material 3 containing gas or liquid is guided into the pressurizing container 2, and optional pressurizing pressure P is applied. The rod load W and pressurizing pressure P applied to the pressure container 2 are set in good balance, whereby the leakage of the pressurizing material containing gas or liquid from the pressurizing container 2 can be prevented, and also a uniform pressure distribution can be caused on the entire wafer surface containing a sealed part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a complex three-dimensional microstructure related to a micromachine, and more particularly to a method for bonding a plurality of substrates and a silicon structure in a wafer size.

[0002]

2. Description of the Related Art Conventionally, there are various techniques for joining substrates, but for example, a technique relating to joining of silicon wafers is a method of joining without applying pressure or a technique of applying pressure. There is a way.

As an example of the former, there is a dielectric isolation type substrate (silicon on insulator substrate) forming technique described in Applied Physics Vol. 60 No. 8 (1991) P790 to P793. In this technique, OH groups are formed on the surfaces of two mirror-finished silicon wafers, and bonding is performed at room temperature. At this time, the two wafers are bonded with a bonding force of ^{3 to 5} kgf / cm ² by hydrogen bonding between OH groups on the surface. When you want to obtain a larger joining force, 100 with no load
1700kgf / cm by performing high temperature heat treatment above 0 ℃
A bonding force of ² or more can be obtained. With the above technique, it is possible to directly bond silicon surfaces to each other, silicon oxide films to each other, or a silicon surface and a silicon oxide film. In any of the above cases, there is no locally etched recess on the surface of the silicon wafer to be bonded, and the flatness facilitates bonding on the entire surface of the wafer.

When bonding is performed without applying a pressing force, Nikkei Microdevice March 1988 issue P85-P91 describes that the surface roughness of the wafer is not 13 nm or more. That is, in the direct bonding of silicon in the above method, the surface roughness of the wafer must be processed to 13 nm or less. Further, it is described that in that case, the warp of the wafer is 50 μm or less, and it is possible to bond up to a 6-inch wafer.

On the other hand, as a technique for bonding the latter wafer by pressing, there is, for example, Japanese Patent Application Laid-Open No. 4-373118 as a jig for uniformly bonding silicon wafers. In this method, when a silicon wafer is sandwiched between carbon and quartz holding plates and heated, a large pressing force is applied to the silicon wafer by utilizing the difference in thermal expansion between carbon and quartz in the thickness direction.

[0006]

When attempting to bond a plurality of silicon wafers each having a fine structure processed in a wafer size, the following problems occur in the conventional technique.
That is, when bonding the wafers without applying pressure, there is a problem that the wafer surface must be processed until it becomes a mirror surface because the surface roughness of the wafer size is 13 nm or more. For example, in a processing process of forming a structure on a silicon wafer using a semiconductor process, a silicon surface is rough because steps such as wet etching are always performed. Therefore, it is possible to polish the wafer surface for each process.
The polishing process is technically difficult and the cost is high.

Further, when the wafers are pressed and bonded together, the prior art does not consider the variation in the thickness of the silicon wafer. In general, 1 of a silicon wafer that has been polished on both sides
Thickness variation within a wafer is at least ± 3 μm
There is a degree. Therefore, it is difficult to uniformly pressurize and bond the entire surface of the silicon wafer. A more detailed description is shown in FIG.
Refer to. FIG. 5 shows an explanatory view of a conventional mechanism for pressing the bonding between the wafers on a plane. Even if two wafers are pressed flat as shown in the figure, only a part of the wafer surface is pressed, and it is difficult to uniformly bond the entire surface of the silicon wafer. Further, if a large pressure is applied forcibly, it will cause a strain to remain on the silicon wafer.

[0008]

In order to solve the above-mentioned problems, the present invention uses a substrate, for example, a silicon wafer, in which a structure is formed at room temperature to form a silicon wafer or a structure. A desired number of unbonded silicon wafers are combined and laminated in a clean room of class 100 or less, and then the outermost wafers stacked in the electric furnace are treated with gas or liquid from one side. Bonding is performed by applying the pressure of the pressure material.

According to the above method, it is possible to apply a pressure uniformly to the silicon wafer surface, and even if there is a variation in the thickness of the silicon wafer, it is possible to obtain a good pressure without locally applying a pressure on the wafer surface. Bonding can be realized.

As another solution, instead of pressurizing with a pressurizing material containing gas or liquid, a plurality of pressurizing rods are applied uniformly from one side of the laminated substrate to bond them. It is achieved by performing. More specifically,
In the method using a plurality of pressure rods, the laminated silicon wafers are pressurized by the pressure rods as they are, or the pressure rods through a plurality of springs are used, or a plurality of screws are used. The method of applying pressure is used. It should be noted that it is preferable to use ceramics as the material of the portion that comes into contact with the laminated wafer in order to suppress reaction with silicon.

The joining form in each of the above-mentioned methods can be applied to either a direct joining method at a high temperature, a joining method via solder at a low temperature, or a joining method by sandwiching a low melting point glass. That is, the temperature range to be used can be selected over a wide range depending on the joining method.

As an additional solution, the alignment between the stacked wafers is performed by directly processing the alignment grooves or protrusions on each wafer by utilizing anisotropic etching. .

[0013]

According to the present invention, since the pressure is applied by using the pressure of the pressure material containing the gas or the liquid, the pressing force is uniformly applied to the wafer surface. As a result, even if there are variations in wafer thickness and waviness, pressure is applied uniformly to the entire surface of the wafer, causing local deformation and cracking due to local pressure, local residual stress, and occurrence of unbonded portions. To be prevented.

Similarly, when the pressure rod system is used,
Pressure is uniformly applied to the wafer surface. This is to evenly distribute the pressing force.

Further, since the groove or protrusion for alignment is directly processed on each wafer, it is not necessary to perform alignment using an optical system from the outside, and moreover, it is possible to stack multiple layers. The time required for alignment before joining can be shortened.

[0016]

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

FIG. 1 is a cross-sectional view showing a pressure mechanism of a silicon lamination bonding apparatus according to an embodiment of the present invention. Reference numeral 1 is a laminated silicon wafer composed of five layers of wafers, each having a structure formed thereon. For example, fine processing represented by a semiconductor process is applied to the formation of the structure. In addition to this structure, each wafer is provided with alignment grooves or protrusions by utilizing anisotropic etching.

The bonding interface of the silicon wafer can be appropriately selected according to the application of the device to be manufactured. For example, silicon may be directly bonded to silicon, or a silicon oxide film, aluminum, gold, gold-tin eutectic, or the like formed on the surface of silicon may be used.

FIG. 1 shows a mechanism for pressurizing the pressurizing surface of the laminated substrate by utilizing the pressure of a pressurizing material containing gas or liquid. In the mechanism of FIG. 1, the pressure vessel 2 is arranged on one surface of the laminated silicon wafer 1 and is fixed by the upper rod 4 and the lower rod 5. Further, an arbitrary pressing force W (hereinafter, referred to as a rod load W) is applied to the upper rod 4 and the lower rod 5. A pressure material 3 containing gas or liquid is introduced into the pressure container 2 and an arbitrary pressure P is applied. Further, the surface of the upper rod 4 in contact with the wafer is processed with high accuracy so as to have sufficiently high flatness and smoothness.

Next, FIG. 6 shows a wafer pressure control diagram in the first embodiment of the present invention. The horizontal axis represents the pressure P applied to the pressure vessel 2, and the vertical axis represents the rod load W. In the initial state, it is necessary to apply a constant minute load to the outer peripheral portion in order to maintain the laminated state of the laminated silicon wafers regardless of the presence or absence of the pressurizing pressure. In this case, when a load larger than the minute load is applied, the outer peripheral portion of the wafer is constrained during the heat treatment, so that strain is left when the warp of the wafer is corrected. After that, the pressurizing pressure P is set high in order to suppress the bending of the wafer, but in that case, the leakage of the pressurizing material containing the gas or the liquid introduced into the pressure container from the outer peripheral portion of the silicon wafer is prevented. In order to achieve this and to apply a uniform pressing force over the entire surface of the wafer, it is necessary to increase the rod load W in proportion to the pressing pressure P.

By the way, when the silicon wafer has a warp, the value of the pressurizing pressure P required to correct the warp can be expressed by Equation 1 (Cited document; Official Journal of the Mechanics of Materials, Corona Publishing Company, 1978).

[0022]

[Equation 1]

For example, when the outer radius of the bent portion of the wafer plate before bonding is 2 cm and the initial amount of warp is 20 μm, the pressure applied is about 3.5 × 10 ⁴ Pa.

Specifically, by setting the rod load W and the pressure P applied to the pressure vessel 2 in a well-balanced manner,
It is possible to prevent the pressure material containing gas or liquid from leaking from the pressure vessel 2 and to generate a uniform pressure distribution over the entire surface of the wafer including the seal portion. That is, without applying unnecessary pressure to the laminated silicon wafer 1,
Deformation due to local pressure and cracking due to excessive strain,
Generation of local residual stress and unbonded portions is prevented.

Further, in the present invention, as a mechanism different from the above-mentioned method, there is a method of applying pressure from one side of the laminated silicon wafer 1 using a plurality of pressure rods. More specifically, a method of directly applying pressure with a plurality of pressure rods, using a pressure rod through a plurality of springs, or using a method of using a plurality of screws is used. These methods will be described with reference to FIGS.

FIG. 2 shows a sectional view of a pressing mechanism of a joining apparatus showing a second embodiment of the present invention. The laminated silicon wafer 1 inserted in the support base 6 is pressed from one side by using several pressing rods 8. The pressure bar 8 is supported by the support jig 10.

FIG. 3 shows a sectional view of a pressing mechanism of a joining apparatus showing a third embodiment of the present invention. This is a system in which the laminated silicon wafer 1 is placed on the support base 6 and pressure is applied from one side of the laminated silicon wafer by using several pressure rods 8 via several springs 9. The pressure rod 8 is a supporting jig 10.
Is supported by and is pressed by an arbitrary weight 11 thereon. In this case, a pressing force is uniformly applied to the wafer surface. This is because the spring 9 evenly distributes the pressing force.

FIG. 4 is a sectional view of a pressing mechanism of a joining apparatus showing a fourth embodiment of the present invention. The laminated silicon wafer 1 is inserted into the support table 6, and the laminated silicon wafer is uniformly pressed by using several push screws 12 from one side of the wafer.
Further, the support jig 10 fixes the pressing force of the push screw 12, and is fixed to the support base 6. The pressing force is controlled by utilizing the tightening force of the push screw 12. At this time, in order to uniformly press the laminated silicon wafer, the pressing screw 1 is used with a torque wrench in consideration of the thermal expansion coefficient of each jig.
Adjusted 2. As a result, the pressure can be adjusted freely. Further, the number or size of push screws can be freely set depending on the size of the wafer to be pressed.

Further, as the material of various jigs in the embodiments shown in FIGS. 1 to 4, it is preferable to select a material which does not react with silicon at a target bonding temperature. For example, when joining at low temperature, metal can be used, but when joining at high temperature, it is desirable to use ceramics. In addition, a heater is installed around the pressurizing mechanism in each system, and the temperature can be freely set by the controller.
Further, the joining form can be applied to either a direct joining method at a high temperature, a joining method at a low temperature via solder, or a joining method with a low melting point glass sandwiched. That is, the temperature range to be used can be selected over a wide range depending on the joining method.

In the assembly of the substrate in the present invention, for example, when a silicon wafer is used, a silicon wafer on which a structure is formed or a silicon wafer on which a structure is not formed is used in a clean room of class 100 or less at room temperature. It suffices to attach and stack the same number of layers.

As an additional solution, the alignment between the stacked silicon wafers is performed by using anisotropic etching on the silicon wafer 7 as shown in FIG. 15 or the projection 16 is directly machined. In this case, the alignment accuracy between the wafers was within ± 5 μm.

FIG. 8 shows the relationship between the surface roughness of the silicon joint and the joint strength when the static pressure application method of the present invention is used and when the conventional pressure application method is not used. The joining method used was high temperature joining. The surface roughness of the test piece was measured after the formation of the structure was completed.

If there is no conventional pressing force, the surface roughness is 10
When it exceeds nm, the bonding strength is extremely reduced. However, when the static pressure method of the present invention is used, the surface roughness is 10 nm.
Even if the value exceeded, the bonding strength did not decrease and good bonding was performed.

Although the substrate applied in this embodiment is a silicon wafer, the present invention can also be applied to substrates other than silicon wafers. For example, it can be applied to a glass substrate or a metal substrate. The various substrates may be used individually or in combination.

[0035]

According to the present invention, a laminated silicon wafer is not subjected to excessive strain or deformation due to local pressure during bonding, and can be applied under a wide bonding range from low temperature to high temperature. In addition, it is possible to bond silicon structures in a wafer size.

Further, the substrate applicable to the present invention is not limited to a silicon wafer, but may be a glass substrate or a metal substrate.

[Brief description of drawings]

FIG. 1 is an explanatory view of a pressure mechanism of a joining device that represents a first embodiment of the present invention.

FIG. 2 is an explanatory view of a pressurizing mechanism of a joining device showing a second embodiment of the present invention.

FIG. 3 is an explanatory view of a pressurizing mechanism of a joining device showing a third embodiment of the present invention.

FIG. 4 is an explanatory view of a pressurizing mechanism of a joining device showing a fourth embodiment of the present invention.

FIG. 5 is a cross-sectional view of a pressure mechanism of a conventional joining device.

FIG. 6 is a control diagram according to the first embodiment of the present invention.

FIG. 7 is an explanatory view of a positioning mechanism.

FIG. 8 is a pragmatic view of the relationship between surface roughness and bonding strength.

[Explanation of symbols]

1 ... Laminated substrate, 2 ... Pressure vessel, 3 ... Pressurizing material containing gas or liquid, 4, 5 ... Rod.

Claims (6)

[Claims] 1. A joining method for laminating and joining a plurality of substrates, wherein sealing is performed at an outer peripheral portion of the laminated substrate from either or both of an uppermost layer and a lowermost layer of the laminated substrate,
A method of joining substrates, wherein a pressure is applied to a laminated substrate by a pressure material containing a gas or a liquid in the seal. 2. The pressurizing material containing a gas or a liquid, which is in contact with the pressurizing surface of the laminated substrate, contacts the laminated substrate from either one or both of the uppermost layer and the lowermost layer of the laminated substrates. A method for joining substrates which are pressurized in a pressure vessel. 3. A method for joining substrates, wherein a plurality of substrates are laminated and joined together by applying pressure from one side of the laminated substrate using a plurality of pressure rods. 4. The method for joining substrates according to claim 3, wherein any one of a spring, a screw, a weight, or a combination thereof is used as a method for applying a pressing force to the pressure bar. 5. The method for joining substrates according to claim 1, 2, 3 or 4, wherein a portion in contact with the laminated substrate is made of ceramics. 6. The method according to claim 1, 2, 3, 4 or 5.
At least one of the laminated substrates is a silicon wafer, and the silicon wafer has a structure formed by beam processing, etching processing, or the like.