JPH02168617A - Method of eliminating thin film at part of laminated substrate where bonding is not completed - Google Patents

Abstract

PURPOSE:To prevent contamination caused by exfoliation in a heat-treating process by a method wherein, after a plurality of semiconductor substrates are stuck, and one substrate is made a thin film of 100mum or less in thickness, the thin film at a part where bonding is not completed is eliminated by applying ultrasonic wave energy in liquid. CONSTITUTION:An oxide film is stuck on the surface of a substrate 1a to be stuck. On the other hand, the surface of a sticking substrate 1b doped with specified impurity is mirror-polished. The polished surface is cleaned, made hydrophilic, and brought into contact with the oxidized surface of the substrate 1a to be stuck, which are unified in a body. After that, by heat treatment in a nitrogen atmosphere at 1100 deg.C, a laminated substrate 1 is obtained which has bonding strength comparable with bulk silicon. The sticking substrate 1b is polished, and turned into a thin film 1c of 100mum or less in thickness. By using an ultrasonic wave applying apparatus, the thin film at a part where bonding is not completed is eliminated. The intensity of the ultrasonic wave may be 0.2W/cm<2>. Thereby, the thin film less than 2mm in thick ness at a part where bonding is not completed can easily be eliminated. Since the exfoliation of the thin film at a part where bonding is not completed is not generated in a heat-treating process, a clean processing can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a bonded substrate of semiconductor substrates, and to a method of removing a thin film in an unbonded portion using ultrasonic energy.

[Summary of the invention]

The present invention involves bonding multiple semiconductor substrates together to form a thin film of 100 microns or less on one substrate, applying ultrasonic energy in a liquid to remove the thin film in the unbonded area, and subsequent heat treatment. This is intended to prevent contamination due to peeling etc. during the process.

(Prior art) Two or more silicon substrates are bonded together to create power devices and SOI (Silicon Insulators).
Prototype production of LSI and memory ICs is being carried out using the Utator.

Techniques for bonding, or gluing, two silicon substrates together include an electrostatic adsorption method, a method using an oxide film, and a method for directly bonding silicon substrates together (Nikkei Micro Device, published March 1, 1988). No. 33). Another method for uniform adhesion is to mirror-polish both sides of the substrate and wrap the element forming surface (Japanese Patent Laid-Open No. 62-1
28112).

Furthermore, efforts have been made to bond different types of semiconductor substrates having different lattice constants (Japanese Patent Application Laid-Open No. 62-36808).

As shown in Fig. 3, a bonded substrate 1b is bonded to the surface of a bonded substrate 1a to form a bonded substrate 1. It is difficult to eliminate it. Air bubbles 4 are present in this unbonded area, and if they come off during the subsequent heat treatment process, they will cause contamination in the furnace.

Therefore, an idea has been devised to remove the large unbonded portion 2 by wrapping one side of the bonded substrates.

[Problem to be solved by the invention]

However, among these unbonded parts, small unbonded parts 3 having a diameter of less than 2 mm+ were often not completely removed and remained.

An object of the present invention is to remove such small unbonded parts in advance so that they do not cause contamination in the subsequent heat treatment process.

[Means to solve the problem]

The present invention achieves the above object by gluing two semiconductor substrates together and forming a thin film of 100 microns or less on the other substrate, and then removing the thin film in the unbonded area by applying ultrasonic energy in a liquid. It is something to be achieved.

[Function] In the bonded substrate of the present invention, one substrate is polished to form a thin film of 100 microns or less, so the diameter is 2f.
A large unbonded portion with an fII of 11 or more is removed by peeling off during the polishing process. Small unbonded parts less than two plates in diameter can be destroyed and removed in a few tens of seconds by applying ultrasonic energy in a liquid in a direction perpendicular to the substrate. The ultrasonic energy at this time was 0.2W/
d is sufficient and has a strength that does not damage the substrate.

〔Example〕

Embodiments of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a cross-sectional view of the bonded substrates after polishing, and there are several bonding methods, but the bonding can be achieved by the following method. First, a bonded substrate 1a and a bonded substrate 1b made of silicon single crystal are prepared. An oxide film is deposited on the surface of the substrate to be adhered 1a. On the other hand, the surface of the bonding substrate 1b doped with a predetermined impurity and to be bonded is mirror-polished. This polished surface is surface-treated with a mixture of ammonia and hydrogen peroxide to make the surface clean and hydrophilic, and the polished surface is brought into contact with the oxidized surface of the bonded substrate 1a in a clean atmosphere and integrated. do. Thereafter, by heat treatment in a nitrogen atmosphere at a temperature of 1100"C, it is possible to obtain a bonded substrate 1 having adhesive strength comparable to that of bulk silicon. However, when viewed locally, as shown in FIG. 1a, A large unbonded part 2 with a diameter of 2 mm or more and a small unbonded part 3 with a diameter of less than 2 mm are generated, and air bubbles 4 are present at the interface of the unbonded part.Therefore, the bonded substrate 1b is polished to a This is a thin film IC of less than a micron.When the film becomes thin like this, the large unbonded parts 2 will peel off during polishing and be removed.However, the small unbonded parts 3 will remain as they are.Therefore, as shown in FIG. The thin film on the unbonded portion 1b is removed using an ultrasonic wave applying device 5 as shown in FIG.

First, a liquid 5c such as water that efficiently transmits ultrasonic energy is placed in a water tank 5a, and the bonded substrate 1 is placed in the liquid 5c.

It is preferable that the vibration direction of the ultrasonic vibrator 5b and the surface of the bonded substrate 1 are perpendicular. Next, when the ultrasonic transducer 5b is activated and ultrasonic energy is applied for several tens of seconds, the thin film in the small unbonded portion 3 is peeled off and removed by the ultrasonic energy, as shown in FIG. The intensity of the ultrasonic energy at this time may be 0.2 W/cffl; if the energy is too strong, the substrate may be damaged, which is not preferable.

In the example, bonding was carried out via an oxide film, but direct bonding or other methods may be used, and liquids other than water may be used when applying ultrasonic energy. Any structure is sufficient as long as it transmits the information efficiently.

In the above embodiment, two silicon substrates were bonded together, but it is also possible to bond two silicon substrates to both sides. Furthermore, it goes without saying that different types of substrates may be used without departing from the spirit of the present invention, as long as the materials of the substrate to be bonded and the bonding substrate do not differ significantly in lattice constant or coefficient of thermal expansion.

〔Effect of the invention〕

By using the method for removing a thin film in an unbonded part of a bonded substrate according to the present invention, even a small thin film in an unbonded part of less than 2 mm can be easily removed by applying ultrasonic energy. Furthermore, since the bonded substrate does not peel off the thin film in the unbonded portion during the subsequent heat treatment process, a clean process can be maintained.

In the cross-sectional views, a is a cross-sectional view of the bonded substrate after polishing, b is a cross-sectional view of the bonded substrate after applying ultrasonic energy, FIG. 2 is the ultrasonic application device used in the present invention, and FIG. 3 is a conventional beam. FIG. 3 is a cross-sectional view of the combined substrate.

1.--...---------1--Glued substrate 1a---Glued substrate 1b------ -Adhesive substrate 1c
m.
−・−Large unbonded area 3−−−−−−−−・−・−
・・・−−−1 Small unbonded part 4・−・・−−−−1−
・・・・・−・−1−−−・−Bubble 5・−・−−−−1−・−・−・・−・−・・−Ultrasonic application device 5a・−
1--------------------- Water tank 5b---1-----Ultrasonic vibrator 5c----Liquid

[Brief explanation of the drawing]

Fig. 1 shows a cross-sectional view of a laminated substrate according to an embodiment of the present invention. Figure 1: Single side view of the conventional 1-gore 8ze board Figure 3: M gold wave εp processing device used in the present invention Figure 2

Claims (1)

[Claims] A method for removing a thin film on an unbonded area of a bonded substrate by polishing one semiconductor substrate to form a thin film of 100 microns or less and applying ultrasonic energy in a liquid to remove the thin film on the unbonded area. .