TWI556283B - A substrate bonding method by polarization through ions absorbed on surfaces - Google Patents

Description

Method for adsorbing ions on a surface to form a dipole to bond substrates

The invention provides a process for low temperature bonding two surfaces, in particular to a method of adsorbing hydrogen ions and plasma bombarding bonding on a surface, and generating dipoles on the surface of the quasi-bonding to strengthen the bonding surfaces of the two substrates. The method of bonding strength.

The conventional technique is to form a covalent bond between the unsaturated bonds of the dangling bonds on the surface of the two substrates by a high-temperature annealing process. However, the high-temperature annealing process limits the application range of the substrate bonding technology. Because the thermal expansion coefficients of the two substrates must be similar to avoid a large thermal stress at the bonding interface at the high temperature, destroying the bonding structure of the two substrates.

In 1990, Duke University's Q.-Y.Tong and others began research on the low-temperature bonding technology of 矽 substrate hydrophilic wafer bonding, and the change of bonding strength during annealing heat treatment. The relationship develops a low temperature bonding technique for long-term low temperature heat treatment. In the conventional direct bonding technique, when the annealing temperature is between 472 and 673 °K, the OH group acts as a bonding species to crosslink between the two surfaces, thereby bringing the bonds closer together to produce bonds. Bonding to each other plays a very important role; the temperature is greater than 1323 °K, the plastic deformation of the ruthenium substrate due to high temperature greatly increases the number of Si-O-Si bonds at the junction, and the grain boundary due to solid diffusion between atoms Re-adjustment, the viscous flow of oxides fills the voids in the unbonded areas. Today's research focuses on reducing the heat treatment temperature required for the process and is compatible with most semiconductor processes (<450 ° C). The surface of the substrate is activated by the plasma bombardment surface technology, and the number of dangling bonds is increased to achieve a low-temperature bonding target for improving the bonding strength between the substrates. A plasma is a partially ionized gas with the same amount of positive and negative charges. Therefore, the effect of the plasma activation treatment depends on the input power of the plasma, the kind of the gas, the volume and collection shape of the reaction chamber, and the flow rate of the gas, and the like. There are many kinds of gases used in plasma, such as O ₂ , CF ₄ , He, Ne, Ar, etc. The premise of using plasma activation is that the plasma used cannot generate a large number of chemical reactions with the surface of the substrate to be bonded to avoid damage. Surface smoothness hinders bonding.

The effect of using plasma on the surface of the substrate can be divided into physical and chemical aspects. Physically, high energy particles bombard the surface of the substrate, and these high energy particles include charged particles and neutrons. Charged particles can be ionized atoms, molecules or electrons. High-speed particles bombard the surface of the substrate causing a broken bond to increase the density of the dangling bonds, but surface defects may also occur. Chemically, mainly charged particles bind to the surface of the substrate.

SUMMARY OF THE INVENTION A primary object of the present invention is to provide a method for adsorbing ions on a surface of a pseudo-bonded two substrate such that the ions do not generate a large amount of chemical reaction with the bonding surface, and form dipoles when in contact with each other to achieve low temperature bonding.

The invention utilizes a segmented surface treatment method to achieve a method of low temperature bonding by adsorbing a dipolar ion group on the surface of the two substrates to be bonded. The present invention generally performs a cleaning process to remove particles and contaminants on the surface of the substrate, and then performs a surface treatment method to attach hydrogen ions to the surface of the pseudo-bonded substrate. Re-application of gas plasma bombardment with nitrogen or oxygen or fluorine or a mixture During the process, since FH, OH, and NH are polarized, they form dipoles with hydrogen ions adsorbed on the surface, and hydrogen bonds are generated between the other pseudo-bonded surfaces to generate strong initial bonding (initial bonding) ).

The two bonded surfaces are then subjected to an annealing process to enable sufficient bonding strength to be obtained. Since the reaction activation required to form the bond is greatly reduced, the time required for the annealing process can also be shortened, resulting in an increase in production efficiency. Further, since the annealing process is performed at a low temperature, the present invention can be applied to a substrate having a large difference in thermal expansion coefficient bonded without generating thermal stress at the bonding interface sufficient to break the bonding structure.

The invention adopts the segmented surface treatment to avoid the damage of the surface of the pseudo-bonded surface due to the direct use of the plasma ion with strong chemical activity and the damage smoothness. For example, direct application of NH ₃ ⁺ plasma gas on the surface of gallium nitride (GaN) (Q.-Y. Tong and U. Gösele, Semiconductor Wafer Bonding: Science and Technology, John Wiley & Sons, Inc., BC Published in 1999) It is expected to produce a chemical reaction with lossy smoothness. For example, the etching rate of H ⁺ to GaN is lower than that of NH ₃ ⁺ . If the GaN substrate is first immersed in a dilute hydrofluoric acid (HF, 0.5-1.0%) solution for 30 s dipping, the surface dangling bonds are passivated by hydrogen ions to cover the hydrogen ions. Nitrogen plasma bombardment is applied to cause nitrogen ions to react with hydrogen ions adsorbed on the surface to produce NH ion clusters, which will have a strengthening effect with NH ₃ ⁺ plasma without eroding surface effects. When bonding GaN/Si substrate pairs, HF wet chemical surface treatment followed by nitrogen plasma treatment can form NxHy ion clusters on the surface and the two pseudo-bonding surfaces generate hydrogen bonds with each other and have strong preliminary bonding. can. The chemical reaction of the covalent bond between the surfaces of the two substrates after annealing is as follows: GaN-(N _x H _y )+(N _x H _y )-Si → GaN-(2N _x )-Si+y H ₂

Embodiment 1

Use two Si wafers. A standard stoichiometric Si ₃ N ₄ substrate was formed on the surface of the Si wafer by LPCVD (Low-Pressure Chemical Vapor Deposition) process technology. The surface of the Si ₃ N ₄ substrate was then washed with an RCA solution (H ₂ O ₂ :NH ₄ OH:H ₂ O=1:0.2:5). Next, the Si ₃ N ₄ substrate was rinsed with deionized water and immersed in a hydrofluoric acid solution (1% HF, CMOS grade) for 30 sec. Immediately thereafter, the two Si ₃ N ₄ substrates were subjected to Nitrogen-Plasma Activation. Then, two Si ₃ N ₄ substrates were subjected to direct bonding in the atmosphere, and subjected to annealing treatment at 200 ° C.

Embodiment 2

Use two Si wafers. The surface of the two Si substrates was washed with an RCA solution (H ₂ O ₂ :NH ₄ OH:H ₂ O=1:0.2:5). Next, the two Si substrate pairs were rinsed with deionized water and immersed in a hydrofluoric acid solution (1% HF, CMOS grade) for 30 sec. Immediately thereafter, the two Si substrates were subjected to Nitrogen-Plasma Activation. Then, the two Si substrates were subjected to direct bonding in the atmosphere, and subjected to annealing treatment at 100 °C.

Embodiment 3

A Si wafer and an Al ₂ O ₃ substrate are used. A standard stoichiometric Ga.N substrate was formed on the surface of the Al ₂ O ₃ wafer by MOCVD process technology. The surface of the GaN substrate was then washed with acetone. Next, the Si and GaN substrates were rinsed with deionized water and immersed in a hydrofluoric acid solution (1% HF, CMOS grade) for 30 sec. The GaN and Si substrates were subjected to Nitrogen-Plasma Activation immediately. Then, the bonded substrate was subjected to direct bonding in the atmosphere and subjected to annealing at 250 ° C.

Embodiment 4

A two Si wafer substrate is used. A 2 μm thick, standard stoichiometric GaN substrate was formed on the surface of a Si wafer by MOCVD, lateral epitaxy, and buffer layer processing techniques. The surface of the GaN substrate was then washed with acetone. Next, the Si and GaN substrates were rinsed with deionized water and immersed in a hydrofluoric acid solution (1% HF, CMOS grade) for 30 sec. The GaN and Si substrates were subjected to Nitrogen-Plasma Activation immediately. Then, the bonded substrate was subjected to direct bonding in the atmosphere and subjected to annealing at 250 ° C.

Embodiment 5

A Si wafer and an Al ₂ O ₃ substrate are used. The surface of the Si and Al ₂ O ₃ substrates was washed with an RCA solution (H ₂ O ₂ :NH ₄ OH:H ₂ O=1:0.2:5). Next, the Si and Al ₂ O ₃ substrates were rinsed with deionized water and immersed in a hydrofluoric acid solution (1% HF, CMOS grade) for 30 sec. The Al ₂ O ₃ and Si substrate were subjected to Nitrogen-Plasma Activation immediately. Then, the bonded substrate was subjected to direct bonding in the atmosphere and subjected to annealing at 200 ° C.

The above-mentioned preferred embodiments of the present invention are intended to be equivalent to variations and modifications of the scope of the present invention.

Claims (10)

A method of bonding a two substrate surface, the method comprising the steps of: providing two substrates; performing an ion adhesion surface treatment process on at least one of the two substrates to adhere a first ion to the surface; Applying at least a subsequent ion attachment surface treatment process to form a dipole with the first ions; and contacting the two substrate surfaces with each other for bonding. The method of claim 1, wherein the substrate surface comprises one or more thin film layers. The method of claim 2, wherein the substrate surface comprises a nitride substrate film layer. The method of claim 2, wherein the substrate surface comprises an oxide substrate film layer. The method of claim 2, wherein the substrate surface comprises a film layer of a tri-five (III-V) substrate. The method of claim 1, wherein the first ion is a hydrogen-containing ion. The method of claim 1, wherein the subsequent surface treatment process is a nitrogen-containing plasma bombardment process. The method of claim 1, wherein the subsequent surface treatment process is an oxygenation Plasma bombardment process. The method of claim 1, wherein the subsequent surface treatment process is a fluorine-containing plasma bombardment process. A method for bonding the surfaces of two substrates, the method comprising the steps of: providing a first substrate and a second substrate; performing a wet surface treatment process of a hydrofluoric acid solution to make the surface of the first substrate and the second substrate Absorbing hydrogen ions on the surface; performing a nitrogen plasma bombardment process to adsorb nitrogen ions on the surface of the first substrate and the surface of the second substrate; and bonding the surface of the first substrate and the surface of the second substrate to each other to bond the a first substrate and the second substrate.