Special receptacle or package – Holder for a removable electrical component – For a semiconductor wafer
Reexamination Certificate
2001-06-28
2002-10-22
Ghyka, Alexander (Department: 2812)
Special receptacle or package
Holder for a removable electrical component
For a semiconductor wafer
C206S213100, C206S583000, C438S758000, C438S800000, C414S217000
Reexamination Certificate
active
06467626
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of housing wafers mirror-polished, cleaned, dried of their surfaces and a container for housing the wafers, and a transfer process for housing the wafers into the container. Specifically, it relates to a method for housing wafers, a container for housing the wafers, and a transfer process for housing the wafers into the container, for the sake of decreasing the adhesion of particles generated in the process of transport and so forth on the surfaces of the mirror-polished silicon wafers.
TECHNICAL BACKGROUND
The manufacturing process of semiconductor devices, for example, memory chips and LSI chips, is largely divided into following process steps: the single crystal producing step in which a single crystal silicon ingot is obtained from polycrystalline silicon; the wafer processing step in which the ingot is sliced and the thin plate-like wafers are mirror-polished; and the device manufacturing step in which various devices are fabricated on the mirror polished wafers. The each process step has various batch treatment divisions. Each of the treatments and steps is processed in batches or in other places, and with time intervals. Therefore, there is a case where the wafers are housed in containers to be stored or transported between the treatment divisions or steps.
Particularly, in almost all cases, process steps until mirror polishing step and the device manufacturing step in which various ICs are produced on the mirror polished wafers, are performed in different companies. In that case, the wafers processed until mirror polishing are housed in a container in a large number and shipped to a device manufacturing company. The container is often called shipping box.
As non-existence is required of particles, organic substances and ions on the surface of wafer in the device manufacturing step, cleaning for removal of the particles is performed at the last of the wafer processing step, that is, before housing the wafers into the container for shipment.
The influence of the shipping box was also examined. The result was that the chlorine and organic substances coming out from the box becomes problem, and improvements in the material, etc. of the box have been done. There is also disclosed a method in which the atmosphere in the box is substituted by nitrogen gas for the sake of preventing the generation of so-called “Kasumi” (cludiness) on the wafer(for example, Japanese Unexamined Patent Publication No. Hei 10-92918).
As described above, when wafers are shipped to a device manufacturing company, extreme cautions must be paid as to the protection of the surfaces of the wafers from contamination. But there has been no effective method for preventing the adhesion of particles to the surfaces of the wafers.
For example, an art is disclosed in Japanese Unexamined Patent Publication No. Hei 8-64666, in which wafers are housed in a gas-tight container filled with high purity steam obtained from a pure water bubbling section prepared at some midpoint in the supply route of dry gas, for the sake of removing the influence of particle and gas contamination.
The art is effective in the case where hydrofluoric acid treatment, which is referred to as hydrofluoric anhydride treatment in the Japanese Unexamined Patent Publication No. Hei 8-64666, is prepared at the next step. Also, the art is effective in reducing the quantity of high purity nitrogen gas for purging to increase atmosphere purity in the container.
However, according to the test result by the inventor of the present invention, it was proved that the art is not much useful in the prevention of adhesion of the particles generated from the container, and that it is not suitable as a housing method and transfer method for housing in the case the mirror-polished wafers are transported to a device manufacturing process.
When a number on thin plate-like wafers are housed and supported in a container for storage or transport, the container(shipping box) is subjected to various vibrations during transport. Scrubbing between the contacting parts of the box and falling off of the dust depositing on the inner surface of the box caused by the friction due to the vibrations, allow particles to be generated: these particles adhere to the wafers by the action of vibration and static electricity. Here particle is a collective name of fine grains of substance floating in space or adhering to the surface of a thing, and is composed of metals, inorganic substances, and organic substances.
The generation of particles in a container during transport has not been so problematic while the degree of integration of LSI is low and required design rules in LSI manufacturing process is not so minute. But the degree of integration has become higher, and for manufacturing LSI of 1 G level, particle size to be controlled has become small, making the increase of particles during transport not negligible problem. Finer design rules of sub-micron with increasing degree of integration has lowered the size of particle to be controlled from 0.16 &mgr;m to 0.10 &mgr;m. In the future generation of 0.13 &mgr;m design rules, the particle size to be controlled will be 0.08 &mgr;m.
Adherence of particles to the wafer in the device process causes not only a short or damage in the fine circuit, but the particle of metal and organic substance cause the degradation of device characteristics, inducing to low yields.
Therefore, these particles is listed in the inspection items, and the wafer transferred from the wafer processing step is inspected in the device process, in which acception or rejection check is done based on the size and number of particles.
Although the wafer is cleaned in the wafer processing step to remove the particles, many of device makers clean the wafer at receiving step of device process. Higher level of cleaning is necessary to clean the particles down to those of smaller size, and man-hour increases.
It is difficult to completely prevent the adhesion of particles generated during transport on wafers. Particularly, when the wafers are transported by a truck or air plane, the vibrations the wafers being subjected to are different according to the construction of the vehicle, road condition, handling of the container, etc., and so there are various methods for preventing the adhesion of particles on the wafers. But there has been no effective means for preventing the generation of particles in the container.
SUMMARY OF THE INVENTION
The object of the present invention is, in the light of the problems mentioned above, to provide a wafer housing method and container and transfer process for housing the wafer into the container, which allow the adhesion of particles to the minimum even if the particles are generated during transport.
The process of reaching the present invention will be described hereinbelow.
The inventor of the present invention found that, the adhesion of particles on the mirror polished wafers which are vacuum-dried after cleaning their surfaces and housed in a hermetically sealed container, is largely reduced in the case where the inside space of the container is kept dry(for example, relative humidity is 10% or lower, or 2 ppm or lower, preferably 1 ppm or lower in absolute humidity) and the container is vibrated, comparing to the case where the inside space of the container is kept highly wet(for example, relative humidity is 40%, or 6.5~8 ppm in absolute humidity) and the container is vibrated.
The reason that particles are reluctant to adhere to the surface of wafer in the air of low water content can be explained as follows: in the case the surface of wafer is dry without water, even if a particle accelerated by the vibration collides against the wafer, the particle is simply repelled at the surface and not adheres to the wafer, but in the case the air in the container is highly wet, the surface of the wafer is damped and the particle adheres to the surface by the action of the water on the surface.
The present invention was made based on the fact mentioned above. The waf
Crowell & Moring LLP
Ghyka Alexander
Shin-Etsu Handotai Co, Ltd.
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