Wafer aligning apparatus for semiconductor device fabrication

A wafer aligning apparatus for semiconductor device fabrication includes a cassette support on which is mounted a cassette holding wafers immersed in a non-conducting fluid. A guide roller is composed of carbon fiber reinforced polyether and rotates in contact with circumferential edges of the wafers. A wafer support holds the wafers apart from the roller when flat zones of the wafers are aligned with the wafer support

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a wafer aligning apparatus for 
semiconductor device fabrication, and more particularly, to a wafer 
aligning apparatus having an anti-static guide roller. 
2. Description of the Related Art 
Generally, semiconductor devices are manufactured by repeatedly carrying 
out various kinds of processes such as photolithography, diffusion, 
etching, ion-implantation and metallization on semiconductor wafers. In 
order to carry out these processes, the wafers are placed in various kinds 
of equipment, each designed for a certain processing step. 
When the wafers are inserted in such equipment, the wafers often must be 
aligned according to a certain specific direction because of crystal 
orientations in the wafer. Production problems can occur if an orientation 
dependent process is performed on wafers which are not aligned. When the 
wafers are misaligned in such a process, the process may not be performed 
accurately, thereby the yield of semiconductor devices produced by the 
equipment is decreased, and in some cases subsequent processing of the 
semiconductor device must be discontinued. 
Conventional wafer aligning apparatus make use of the flat zone formed on 
one part of the perimeter of the wafer which is otherwise circular. The 
flat zone is formed by cutting the edge of a circular wafer (or one side 
of a cylindrical ingot from which individual wafers are subsequently 
sliced) along a straight line in a direction that designates one of the 
standard crystal directions. The conventional apparatus aligns wafers for 
a certain process by aligning the flat zones of all the wafers in a 
cassette of wafers undergoing that process. 
The conventional wafer aligning apparatus includes a guide roller which 
contacts the circular edges of the wafers in the cassette with sufficient 
friction to rotate the wafers. But since the flat zones do not extend as 
far from the center of the circular portion of the wafer edge, the middles 
of the flat zones do not contact the guide roller with sufficient friction 
to rotate the wafers. The wafers are aligned when the guide roller no 
longer rotates the wafers. 
Typically the roller is located below the wafers in the cassette so that 
gravity helps to maintain frictional contact between the circular, i.e. 
circumferential, edges of the wafers and the guide roller. In addition, a 
wafer support placed at the same height as the guide roller holds the flat 
zones of the wafers out of contact with the guide roller. As a result, all 
the wafers inside the cassette are aligned with the flat zones along the 
downward direction within a specific time after the guide roller begins 
rotating. 
However, the conventional wafer aligning apparatus has a problem with 
static electricity. The conventional guide roller has a shaft that is made 
of metal, and a roller coat that encloses the shaft and is made of 
nonconducting synthetic resins, such as rubber or TEFLON. The friction 
between the wafers and the coat of the guide roller generates static 
electricity charges that accumulate on the surface of the nonconducting 
roller coat and on the wafers. If the wafers are immersed in a 
nonconducting fluid, such as air, the accumulated charges remain on the 
surfaces of the wafers and roller. Particles around the apparatus with 
slight charges of opposite sign are attracted to and are also accumulated 
on the charged wafers and guide roller. These particles contaminate the 
wafers. In addition, the particles cause corrosion damage on the wafer 
surface when the accumulated static electricity is suddenly discharged 
after building to a sufficiently large voltage. 
Furthermore, the rubber-made guide roller surface is easily worn down by 
the friction with the wafers, and produces additional particles that 
contaminate the wafers. 
Since, these friction and the discharge problems have not been solved, 
there is a need to prevent the generation of static electricity on the 
guide roller, or to prevent the accumulation of the static electricity and 
the attracted particles. 
SUMMARY OF THE INVENTION 
The present invention is directed to a wafer aligning apparatus having a 
guide roller that can discharge the generated static electricity, which 
substantially overcomes one or more of the problems due to the limitations 
and the disadvantages of the related art. 
To achieve this and other objects and advantages of the present invention, 
the wafer aligning apparatus for semiconductor device fabrication includes 
a cassette support on which is mounted a cassette holding wafers immersed 
in a substantially non-conducting fluid. A guide roller composed of carbon 
fiber reinforced polyether rotates in contact with circumferential edges 
of the wafers. A wafer support holds the wafers apart from the roller when 
flat zones of the wafers are aligned with the wafer support. 
It is understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory and are not 
limiting. The invention is broader than these descriptions and is intended 
to encompass all embodiments that fall within the scope of the appended 
claims and their equivalents.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the preferred embodiment of the 
present invention, examples of which are illustrated in the accompanying 
drawings. 
As shown in FIG. 1, the wafer aligning apparatus for semiconductor device 
fabrication includes a cassette support 1 on which a cassette for wafers 2 
is mounted. An anti-static guide roller 4, that rotates in frictional 
contact with the arcuate circumferential edges of the wafers 2 inside the 
cassette, is made of carbon fiber-reinforced polyether. A wafer support 3 
holds the aligned wafers 2, after rotation, away from frictional contact 
with the guide roller 4. 
The carbon fiber of the carbon fiber reinforced polyether is preferably 
about 10 micrometers (.mu.m) to about 20 .mu.m long, having diameters from 
about 7 .mu.m to about 9 .mu.m, and constituting about 10 to about 20 
percent by weight of the polyether. 
The polyether contains an ether (--C.dbd.O--) linkage among the back bone 
of the polymer. It is normally formed by the reaction of aldehyde and 
epoxide or similar functional group. The polymer is widely used for 
various kinds of chemical devices, or containers and valves for chemical 
materials because of its good chemical-resistance and mechanical 
characteristics. In the preferred embodiment, the polyether is 
polyetheretherketone. 
The carbon fiber in the polyether functions to reinforce the mechanical 
characteristics of the polyether of the guide roller 4, and also, because 
it provides some enhanced electrical conductivity, i.e. lowered electrical 
resistivity, it functions to prevent static electricity from being 
accumulated. That is, since the carbon fiber itself has good electrical 
conductivity, it allows the generated static electricity to flow away from 
the wafers and roller surface before a large charge accumulates on the 
wafers or roller surface. 
Though experimentation it was determined that if the amount of the carbon 
fiber in the polyether is above 20% by weight, the physical properties of 
the polyether are degraded. If the amount of the carbon fiber in the 
polyether is less than 5% by weight, the discharge of the static 
electricity is not sufficient. 
According to the present invention, carbon fiber is added to the polyether 
such that the surface resistivity of the polyether is decreased to about 
10.sup.-5 to 10.sup.-9 Ohms per square centimeter (.OMEGA./cm.sup.2). As a 
result, the flow of the static electricity charge away from the wafer is 
allowed with the passage of time at a faster rate. The resistivity is 
chosen so that the static electricity lasts on the surface for a static 
decay time less time than the time the roller is operated, and the 
accumulation of excessive charge on the wafers during alignment is 
prevented. Therefore, the particles attracted due to the accumulation of 
static electricity and the surface corrosion of the wafers due to the 
discharge of the static electricity are both prevented. 
The static decay time is 0.01 to 1 seconds when using material having 
10.sup.-5 to 10.sup.-9 .OMEGA./cm.sup.2 of surface resistivity for the 
guide roller 4. With this static decay time, static electricity is not 
accumulated excessively on the surface of the roller during roller 
operation and is discharged smoothly when the frictional contact between 
of the roller and wafer is substantially ended. 
The guide roller 4 illustrated in FIG. 2 has a structure in which a shaft 5 
of metallic material is concentrically disposed within a roller coat 6 of 
carbon fiber reinforced polyether. Or, as shown in FIG. 3, the guide 
roller 4 can be constructed as an integral roller in which the shaft and 
the roller coat form one body 7 of the same material. In this embodiment, 
the shaft has two parts, one on either end of the guide roller 4. In 
either embodiment, because the surface of the guide roller 4 coat that 
rotates in contact with the wafer 2 is made of carbon fiber reinforced 
polyether, static electricity which can be generated by friction during 
the rotation is discharged by the carbon fiber. As a result, the 
accumulation of the static electricity charges on the surfaces of the 
wafers 2 and the guide roller 4 is prevented. 
Furthermore, polyetheretherketone including carbon fiber is very stable 
thermally. It undergoes heat-transformation at a temperature of 
310.degree. C. under a pressure of 18.6 kilogram-force per square 
centimeter (kgf/cm.sup.2), and its melting point is 344.degree. C. In 
addition carbon fiber reinforced polyetheretherketone is very stable 
chemically. It does not react with the methylethylketone group such as 
acetone, widely-used as organic solvents, or with the nitryl group such as 
acetonitryl. It does not react with the halogenide group such as 
dichloromethane, or the alcohol group such as isopropyl alcohol, or the 
hydrogen carbide group such as isooctane, or the ether group such as 
tetrahydrofuran. Therefore, carbon fiber reinforced polyetheretherketone 
is relatively stable under any of the processing conditions usually found 
in semiconductor device fabrication. 
As described above, according to the present invention, both the 
accumulation of particles attracted by static charges and also the surface 
corrosion of wafer caused by the sudden discharge of accumulated static 
charges are prevented. Therefore, the yield of semiconductor devices is 
increased and productivity is improved by employing the guide roller of 
the present invention having a low surface resistivity. 
While the present invention has been described in detail in the above 
embodiments, it should be understood that various changes, substitutions 
and alterations can be made hereto by those of ordinary skill in the art 
without departing from the spirit and scope of the invention as defined by 
the appended claims and their equivalents.