JPH1092702A - Room-temperature bonding of silicon wafers - Google Patents

Abstract

(57) [Summary] To provide a bonding method for a silicon wafer which has a large bonding strength and does not require pressing or heat treatment by a load. Kind Code: A1 A method for bonding a silicon wafer to a silicon wafer, the bonding surface of both silicon wafers being bonded with an inert gas ion beam or an inert gas fast atom beam in a vacuum at room temperature prior to bonding. Seconds to 1
Irradiate for 800 seconds to perform sputter etching

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 silicon wafers. This technology can be used for assembling and sealing electronic components and mechanical components created by semiconductor fine processing technology.

[0002]

2. Description of the Related Art In the manufacture of integrated circuit chips and parts for micromachines, it is sometimes necessary to bond fine parts made of silicon. In such a case, as a conventional bonding method, as shown in FIG. 7, a bonding surface of a silicon component is subjected to a hydrophilic treatment using a water-soluble chemical such as H ₂ O ₂ + H ₂ SO ₄ to impart a hydroxyl group. Then, bonding is performed based on the bond between the hydroxyl group and water molecule on the bonding surface, and the bonding strength is further increased by heat treatment (direct bonding technology of Si wafer (Applied Physics 60 (1991), 7
90)).

[0003]

However, in this conventional bonding method, the bonding force at the time of contact is obtained by providing a hydroxyl group to the surface of the wafer. It was necessary to change the bond by the hydrogen bond to a stronger bond, which required a heat treatment. However, the application of these heat treatments was sometimes limited because they could damage microfabricated parts. In addition, when joining, it is necessary to promote contact on the joining surface by pressing load or electrostatic attraction, etc.
Similarly, the potential for breakage of micromachined parts limits its application. For this reason, there is a demand for the development of a silicon wafer bonding technique that does not require pressing by a load or heat treatment. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for bonding a silicon wafer having high bonding strength and not requiring pressing or heat treatment by a load. .

[0004]

In response to this object, a room temperature bonding method for a silicon wafer according to the present invention is a method for bonding a silicon wafer to a silicon wafer,
Prior to bonding, the bonding surfaces of both silicon wafers are irradiated with an inert gas ion beam or an inert gas fast atom beam in a vacuum at room temperature to perform sputter etching.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing an embodiment. First, a wafer bonding apparatus used in the wafer bonding method of the present invention will be described. In FIG. 1, reference numeral 1 denotes a wafer bonding apparatus. The wafer bonding apparatus 1 has a vacuum chamber 2. The wafer inlet 3 of the vacuum chamber 2 can be opened and closed by a door 4. A pair of opposed wafer holding members 5 and 6 are arranged in the vacuum chamber 2. One wafer holding member 5 is fixed in the vacuum chamber 2, and the other wafer holding member 6 is a push rod 7.
It is attached to the lower end. The push rod 7 can be moved linearly while keeping the airtightness of the vacuum chamber 2, and the other held wafer 8 b can be held in one of the wafer holding members 5.
Can be brought into contact with the other wafer 8a held in the above.

Further, two beam irradiation devices 11a and 11b are arranged in the vacuum chamber 2. One beam irradiation device 11a is for irradiating one wafer 8a, and the other beam irradiation device 11b is for irradiating the other wafer 8b. The irradiation angle for each wafer is variable. The vacuum in the vacuum chamber 2 is formed by a vacuum pump (not shown) through a vacuum exhaust port 12.

[0007] The wafer bonding method of the present invention using the wafer bonding apparatus 1 configured as described above is performed as follows. First, the bonding surfaces of the wafers 8a and 8b to be bonded are cleaned. The content of the cleaning operation is the same as the processing used in the conventional wafer bonding technology. The washed and dried wafers 8a and 8b are placed in the vacuum chamber 2 and attached to the pair of wafer holding members 5 and 6. Next, the pressure inside the vacuum chamber 2 is reduced. The degree of pressure reduction is 10 ^-3 torr
That is all. Next, the bonding surface of both wafers 8a and 8b is heated at room temperature with an inert gas ion beam or an inert gas fast atom beam for 10 seconds to 1800 seconds, particularly preferably 10 seconds.
Irradiation is performed for 30 seconds to 30 seconds to perform sputter etching. In the present invention, this irradiation time is extremely important. The applied voltage and plasma current of the beam source of this high-pressure inert gas ion beam or inert gas fast atom beam are
Depending considerably on the beam source used, for example from 0.1 to
3.0 kV and 1-50 mA. The etching amount of the sputter etching is 1 nm to 40 nm. Next, after irradiation, the push rod 7 is lowered, and the bonding surfaces of the wafers 8a and 8b are overlapped. In the present invention, pressurizing both superposed wafers is not an important factor. Thereby, the bonding of the silicon wafer is completed.

[0008]

[Experimental example]

(Experimental equipment) A sample as shown in FIG. 3 was cut out from a 4-inch N-type silicon wafer of about 20 Ωcm with a diamond saw and used. The sample was shaped into a stepped platform to eliminate edge effects on adhesion. This shape was formed by KOH etching using the thermal oxygen film as a mask. After etching, the sample was cleaned prior to bonding. The content of the cleaning operation is the same as the hydrophilic treatment used in the conventional wafer bonding technology. The sample was placed in the vacuum device shown in FIG. 2, and the inside of the vacuum device was 1 × 10 ^−8.
Torr, and then FAB110 (Ion
Tech Ltd. (UK) was used as a two-beam source to generate an argon fast atom beam to irradiate the joint surface of the sample. The applied voltage and plasma current of each beam source were 1.2 kV and 20 mA. Beam irradiation angle is 45 °, irradiation time is 10 seconds to 1
Changed up to 800 seconds.

(Experimental Results) FIG. 4 is a table showing the results of a tensile test. Even if the sample is kept in a vacuum atmosphere for several hours, the two are not joined by themselves, but when the argon beam is irradiated for only 10 seconds, the two are joined.
Those with the maximum adhesive strength were those irradiated for 30 seconds.
Regarding the relationship between the irradiation time and the adhesive strength, if the irradiation time exceeds 30 seconds, there is no significant difference in the adhesive strength up to the irradiation of 300 seconds. If it exceeds 300 seconds, the bonding strength is rather lowered.
This bonding strength is almost the same as the bonding strength in the wet method which requires heating at 900 to 1100 ° C. in the conventional method. No additional load is required for joining. FIG. 5 shows the relationship between the applied load and the joining strength. As is clear from FIG. 5, the bonding strength hardly changes in the range of the load of 0.025 Mpa to 1.8 Mpa, and this value is almost the same as the bonding strength obtained by the wet method which requires heating at 1100 ° C. in the conventional method. It is. It is clear from this that the addition of load is not a major factor in the joining strength of the present method.

[0010]

According to the silicon wafer bonding method of the present invention, an adsorbed gas or a natural oxide film present on the wafer surface is removed by etching the wafer surface with an inert gas beam such as argon in a vacuum. Applying bonding force for bonding to the surface, utilizing the fact that the surface of the wafer is extremely smooth, and superimposing them in a vacuum to bond the wafers without heating and without pressure Can be done. In the method of bonding a wafer according to the present invention,
As shown in FIG. 6, since the bonding surface of the silicon wafer is etched with an inert gas beam such as argon, there is no water molecule or oxide film on the surface, and the bonding between the atoms of the wafer is formed. A strong bond can be formed. Therefore, the present invention can be applied to the joining of microfabricated parts that can be damaged by pressing or heat treatment by a load. As is clear from the above description, according to the present invention, it is possible to obtain a method for bonding silicon wafers having high bonding strength and not requiring pressing or heat treatment by a load.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing a silicon wafer bonding apparatus.

FIG. 2 is a configuration explanatory view showing an experimental apparatus for bonding silicon wafers.

FIG. 3 shows a sample.

FIG. 4 is a table showing results of a tensile test.

FIG. 5 is a table showing a relationship between an applied load and a joining strength.

FIG. 6 is an explanatory view showing the principle of bonding silicon wafers of the present invention.

FIG. 7 is an explanatory view showing the principle of bonding of a conventional silicon wafer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wafer bonding apparatus 2 Vacuum chamber 3 Wafer insertion / removal port 4 Door 5, 6 A pair of wafer holding pair members 7 Push rod 8a, 8b Wafer 11a, 11b Beam irradiation apparatus 12 Vacuum exhaust port

Continuation of the front page (72) Inventor Yuichi Suga 4-6-1 Komaba, Meguro-ku, Tokyo Inside the Research Center for Advanced Science and Technology, University of Tokyo (72) Inventor Zheng Sawalong 4-6-1 Komaba, Meguro-ku, Tokyo No. Research Center for Advanced Science and Technology, University of Tokyo

Claims (7)

[Claims] 1. A method for bonding a silicon wafer to a silicon wafer, wherein a bonding surface of both silicon wafers is irradiated with an inert gas ion beam or an inert gas fast atom beam in a vacuum at room temperature prior to bonding. Temperature bonding method for silicon wafers, characterized by performing sputter etching by sputtering 2. The irradiation time of the irradiation is from 10 seconds to 1800.
2. The room temperature bonding method for a silicon wafer according to claim 1, wherein 3. The method for bonding silicon wafers at room temperature according to claim 1, wherein the irradiation time of the irradiation is 10 seconds to 30 seconds. 4. An applied voltage of a beam source of the inert gas ion beam or the inert gas fast atom beam is 0.1.
2. The method for bonding silicon wafers at room temperature according to claim 1, wherein the voltage is 3 kV. 5. The method for bonding silicon wafers at room temperature according to claim 1, wherein the amount of said sputter etching is 1 nm to 40 nm. 6. The method for bonding silicon wafers at room temperature according to claim 1, wherein said vacuum is 10 ^-3 torr or more. 7. A method for bonding a silicon wafer to a silicon wafer, wherein a bonding surface of both silicon wafers is applied at a room temperature of 10 ⁻³ torr or more under vacuum and the applied voltage of each beam source and the plasma current are reduced by 1%. Irradiation with an inert gas ion beam or an inert gas fast atom beam of 2 kV and 20 mA for an irradiation time of 10 seconds to 1800 seconds,
Room-temperature bonding of silicon wafers characterized by overlapping