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Under the guidance by Professor Tadatomo Suga of Tokyo University who has leaded the surface activated room temperature bonding technology, which is the key technology to semiconductor three-dimensional multilayer method, we developed the bonding process system at the wafer-level with surface activation technology. By this technology, it can be realized that mass-production of three-dimensional LSI, low temperature (around 150 degree Celsius) wafer or chip bonding in low vacuum or in the air. Its bonding technology helps to make MEMS hybrid devise. We select better surface activation bonding techniques most suitable to bond different semiconductor materials such as Au and Cu by Ar etching in low vacuum plasma, Si and glass by plasma hydrophilic treatment in atmosphere. By conventional anodic bonding with the electrostatic force and the plasma surface activation combined, we achieved a void-less low temperature bonding.



First of all, the advantage of SAB is directly bond a different kind of materials at room temperature. This will create new field of different materials , like a solar battery and a SAW filter. In the field, a mass production has already started. And this will create a breakthrough for 3D integration. And the production starts in form of the improvement of the current process in the field of the 3D integration and MEMS.

①Ar Ion bombardment SAB in UHV|different materials such as compound semiconductor etc.
Firstly, traditional room temperature bonding method is Ar bombardment in an ultra-high vacuum. This method is to remove the oxide film and contaminants on the bonding surface by Ar ions or atoms bombardment in an ultra-high vacuum, then to create dangling bond on bonding interface for the connection atoms. After performing that on both side of bonding interface, atomic level bonding among dangling bonds is carried out by having the bonding interface contacted each other in an ultra-high vacuum. By this process, room temperature bonding of different materials is achieved, such as chemical compound semiconductors and the like which are normally hard to bond. In order to avoid recontamination of the molecules, 10-10torr ultra-high vacuum is required, and it is an obstacle to shift to mass production. Bondtech made possible to do large area uniform bonding with lower vacuum level by our unique treatment even in this ultra-high vacuum process.




②Oxide bonding by Si nano adhesive layer
Secondly, there is a point that the ion crystalline material cannot be bonded in SAB. They are such as an oxide film or a nitride film that are wanted to bond material in the semiconductor, so this is a cause applicable to the semiconductor has been delayed. One solution for this issue is the application to the above-described hydrophilic bonding and another is a system of Si sputtering as an intermediate layer between the activation treatment alternatively. Si atoms to the extent that less than 1 layer in this manner made it possible to bond in ionic crystal material by the interposition of the interface. The application can be applied to any material.

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For example, in the currently used process, by activating the surface, it can be bonded in low temperature and in a short time. Furthermore, it can obtain improvement of the alignment accuracy, the throughput and the ideal bonded interface. In this field, it is not necessarily room temperature and expand the bonding field by permitting low temperature around 150-200 degrees C.


①Solder bonding by SAB for Semiconductor Packaging
Firstly, this can be applied to conventional solder bonding. In this field, it is necessary to be diffused with an oxidation layer in a high temperature than a melting point with high pressure for breaking it. However it can be boned in a vacuum after removing oxidation layer. Therefore it can do the ideal solder fusion at low temperature, in the short time are enabled.
In addition, it can improve mass productivity because the solid-phase temporary bonding is enabled by SAB. And it can improve the productivity by dividing temporary bonding and main-bonding using the solid-state bonding..



②Metal electrode low temperature bonding in atmosphere by Ar Plasma (Optical component , memory)

Secondly, this method enables to use plasma-level surface activation with low vacuum (10-2torr) by limiting bonding material only in Au and Cu, those do not oxide or adhere easily. In addition bonding by this method can be performed even in atmosphere in case having done within one hour. This method is the bonding under small amount of re-contamination like a bonding in atmosphere. Therefore the conditions in bonding is to be improved by adding a little pressure and heating at a low temperature. As a result, the process was established enough to withstand for mass production.




③Anodic Bonding by SAB for MEMS
Thirdly, this can be applied to conventional anodic bonding. Alkali in the glass is taken apart in high temperature of 400 degrees C. And it attracts an oxygen ion by applying the anode voltage and do covalent bond to Si. For this high temperature, it needs two hours for one wafer of bonding, including heating, cooling.
Modify by SAB, It can bond at low temperature for a short time without supplying oxygen to the bonding interface by handling surface activation with the plasma in advance, and temperature at the alkali decomposition is not needed It succeed in the bonding at 200 degrees C for 15 minutes and can get throughput of 4 times. In addition, it enable the anodic bonding without getter materials because the out gas in the cavity decreases.





④Hydrophilic bonding for CIS
Fourthly, this can be applied to conventional hydrophilic bonding in the atmosphere. In this field, it is activated with RIE plasma, but cannot produce the enough OH group. Therefore it can secure a bond strength only in the atmosphere, which water is used. The bonding in the atmosphere usually makes some voids. Therefore it prevent involution of the air by letting a wafer bend, and extending the bonding from the center to circumference by the center push. However, the process that make a surface state better and CMP is needed to remove a void to be greatly influenced by a particle and wet speed.
Modify by SAB, It can find a bond strength in vacuum by increasing the quantity of the OH group of the bonding interface by irradiating with Ar beam containing Si atoms processing.
In addition, even a method to give radical processing after RIE processing called the sequential plasma activation can increase OH groups and becomes able to improve the bond strength in the vacuum. The generous particle removal becomes needless without involution of the air in vacuum bonding. In addition, the bonding accuracy improves because it does not bend a wafer.
If connected to the activated processing → vacuum bonding in the vacuum, the throughput can improve the throughput and the simplify the equipment.




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I introduce High Accuracy Alignment System for UHV
So far, wafer is aligned in the atmosphere and clamped a wafer by a jig, and is transferred to chamber, and a spacer is taken off, and to bond in a vacuum chamber. However, there was a problem to produce a position slip when it is heated or when a spacer is pulled in vacuum chamber. However our method can bond without a position error by IR camera and recognize it just before the bonding in vacuum chamber. In addition, the function to correct a position error at the contact can keep accuracy after the bonding of +-0.2μm in the 300mm wafer. Piezo is used in UHV as the actuator and image processing is used to recognize alignment with an infrared transmission camera from the outside of the chamber. This is constructed by the software called MagicVision that even the image with bad contrast can highly recognized by the infrared transmission and the piezo actuator having the system to align of 6 axial directions. Different from X,Y,θ, 3 axis alignment such as the exposure machine, 6 axis alining that each blast direction included becomes important not to misalign even if the pressure is applied to two surfaces.



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①Equipment for mass production in UHV
Firstly, a disadvantage of the SAB is that a vacuum degree UHV is necessary. In the environment UHV, there was the problem that it was hard to use in the mass production equipment. It is used in R&D because it needs baking and time for a vacuum.
However, by arranging the road lock chamber to a bonding chamber, it do wafer handling in the atmosphere now and succeed in the throughput improvement of 6 minutes per wafer.


②Ar Beam Source for Scanning Large Area up to 12'
Secondly, Even if the small sample could work in the Ar beam source, it was not able to handle the wafer level. 3 inches of wafers are limits, therefore it cannot go from the area of R&D. Then we developed Line type Ar beam source. It can be scanned to a large are. To the mass-produced equipment can apply it to 12 “ wafers.


③Special Beam Source for Si Nano-adhesion Layes
Thirdly, we developed Special Beam Source for Si Nano-adhesion Layer. In this method, it can apply to any materials and application, bonding by sputtering a Si atom among the interface. In addition,. It succeeds by scanning it while changing the direction of the Ar beam source with the activated processing by the Ar beam source for a device, and irradiating a Si target.
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