Silicon wafer for a semiconductor substrate and the method for making the same

A silicon wafer for a semiconductor substrate comprises a flat wafer body, with a polycrystalline silicon layer formed only on the rear surface of said wafer body. The silicon wafer is manufactured by the steps of forming a polycrystalline silicon layer on the entire surface of the silicon wafer body, etching and removing the portion of the polycrystalline silicon layer which is formed on the side surface of silicon wafer body, and polishing and removing the polycrystalline silicon layer on the front surface of the silicon wafer body.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a silicon wafer for a semiconductor 
substrate and the method for making the same and, more particularly, it 
relates to a silicon wafer for a semiconductor substrate having 
polycrystalline silicon deposited on the surface thereof and the method 
for making the same. 
2. Description of the Prior Art 
As shown in FIG. 1, in a conventional silicon wafer for a semiconductor 
substrate, only the front surface of a wafer body 1 is exposed and other 
surfaces are covered with a deposited polycrystalline silicon layer 2. 
Namely, in the conventional silicon wafer for a semiconductor substrate, 
the polycrystalline silicon layer 2 is provided on the side surfaces of 
the wafer body 1 besides the polycrystalline silicon layer 2 deposited on 
the back surface of the silicon wafer body 1, which is required for its 
function. 
The above described conventional silicon wafer for a semiconductor 
substrate is manufactured by the following steps, namely, the 
polycrystalline silicon layer 2 is deposited on the entire surface of the 
wafer body 1 by chemical vapor deposition method and, thereafter, the 
mirror-like finishing is effected by the mechanochemical polish on the 
front surface of the wafer. 
Meanwhile, U.S. Pat. No. 4,608,095 discloses reinforcing the getter effect 
by depositing a polycrystalline silicon of 0.05 to 2.0 .mu.m in thickness 
on the back surface of the semiconductor substrate. U.S. Pat. No. 
4,053,335 discloses depositing polycrystalline silicon on the rear surface 
of the semiconductor substrate and sealing heavy metal movable ions in the 
polycrystalline silicon during high temperature processing. 
In the above described conventional silicon wafer for a semiconductor 
substrate, the polycrystalline silicon 2 deposited on the periphery of the 
wafer body 1 is liable to peel off due to the abrupt change of the shape 
of the silicon wafer periphery during the manufacturing process of the 
semiconductor device. Therefore, in the silicon wafer for a semiconductor 
substrate obtained in accordance with the conventional manufacturing 
method, the polycrystalline silicon layer 2 on the periphery of the wafer 
body 1 is a cause of dust. 
SUMMARY OF THE INVENTION 
The present invention was made to solve the above described problems and 
its object is to provide a silicon wafer for a semiconductor substrate 
capable of preventing dust made by the polycrystalline silicon layer. 
The silicon wafer for a semiconductor substrate in accordance with the 
present invention is provided with a polycrystalline silicon layer on the 
surface of a flat wafer body, characterized in that the polycrystalline 
silicon layer is provided only on the rear surface of the wafer body. 
The method for manufacturing the silicon wafer for a semiconductor 
substrate in accordance with the present invention basically comprises the 
steps of forming a polycrystalline silicon layer on the entire surface of 
the silicon wafer body, and removing the polycrystalline silicon layer on 
the front surface of the silicon wafer body by polishing. In addition, the 
manufacturing method in accordance with the present invention further 
comprises the step of etching a portion of the polycrystalline silicon 
layer formed on the side surfaces of the silicon wafer body. 
Preferably, the formation of the polycrystalline silicon layer is effected 
by, for example, chemical vapor deposition method. The said removal by the 
polishing may be accompanied with a mirror-like finishing. As for the said 
etching, the dipping in the mixed acid of hydrogen fluoride, nitric acid 
and acetic acid is employed. The said etching is carried out by, for 
example, stacking a plurality of silicon wafers in the direction of its 
thickness and by dipping the stack in the mixed acid. 
The silicon wafer for a semiconductor substrate in accordance with the 
present invention obtained from the above described manufacturing method 
has the polycrystalline silicon layer only on the rear surface of the 
wafer body. Therefore, even if the shape of the peripheral part of the 
silicon wafer changes abruptly during the manufacturing process of the 
semiconductor device, there will be no dust made by the peeled 
polycrystalline silicon layer on the periphery of the silicon wafer. 
These objects and other objects, features, aspects and advantages of the 
present invention will become more apparent from the following detailed 
description of the present invention when taken in conjunction with the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 shows four silicon wafers for the semiconductor substrate in 
accordance with the present invention. Referring to FIG. 2, a 
polycrystalline silicon layer 11 is provided on the rear surface 10a of a 
flat wafer body 10. the polycrystalline silicon layer 11 is not provided 
on either the front surface 10b or the side surface 10c of the wafer body 
10, so that the surface of the wafer body 10 is exposed. 
Therefore, when this silicon wafer is employed, the conventional 
disadvantage is not caused that the polycrystalline silicon layer in the 
periphery is liable to peel off due to the abrupt change of the shape of 
the silicon wafer periphery during the manufacturing process of the 
semiconductor device. Therefore, the problem of dust made of the 
polycrystalline silicon in the silicon wafer periphery can be eliminated. 
The method for manufacturing the silicon wafer for a semiconductor 
substrate shown in FIG. 2 will be hereinafter described. 
First, a single crystal flat wafer body 10 is set in a chemical vapor 
deposition device shown in FIG. 3. In FIG. 3, the wafer bodies 10 are 
placed spaced apart from each other on a quartz boat 13 arranged in a 
quartz tube 12. A mixed gas of SiH.sub.4 serving as a source gas and 
N.sub.2 serving as a carrier gas is introduced in the quartz tube 12 of 
FIG. 3 and, a polycrystalline silicon is deposited on the surface of the 
wafer body 10 by the chemical vapor deposition method. Thus, a silicon 
wafer having the entire surface covered with the polycrystalline silicon 
layer 11, as shown in FIG. 4 is manufactured. 
The obtained plurality of silicon wafers are stacked in the direction of 
its thickness as shown in FIG. 5, and held by a holder of 
polytetrafluoroethylene (hereinafter referred to as PTFE) having the 
holding area as wide as or wider than the main surface of the silicon 
wafer. The silicon wafers fixed in the holder 14 are dipped in the mixed 
acid 16 reserved in an etching tub shown in FIG. 6. The mixed acid 16 
comprises, for example a mixture of hydrogen fluoride, nitric acid and 
acetic acid. The etching tub 15 is formed of PTFE. Since only the side 
surface of the silicon wafer dipped in the mixed acid 16 are in contact 
with the mixed acid, the polycrystalline silicon layers 11 only on the 
side surfaces of the silicon wafer are etched, thus the side surfaces 10c 
of the wafer body 10 are exposed as shown in FIG. 7. Consequently, a 
silicon wafer can be obtained in which the polycrystalline silicon layer 
11 only in the periphery is removed. 
Next, the mechanochemical polish process is effected on the obtained 
silicon wafer. FIG. 8 shows the polishing device, in which a disk form 
ceramic plate 22 is integrally provided on the lower end of the central 
rotary axis 21. The silicon wafer with the polycrystalline silicon layer 
11 in the periphery removed is fixed on the lower surface of the ceramic 
plate 22 by means of wax 23. In this case, it is fixed such that the 
ceramic plate 22 side of the silicon wafer corresponds to the rear 
surface. Thereafter, the ceramic plate 22 with the silicon wafer fixed 
thereon is placed on a polishing cloth 24 and the ceramic plate 22 is 
rotated with an abrasive powder 25 flown between the silicon wafer and the 
polishing cloth 24. In this manner, the front surface of the silicon wafer 
is mirror polished. Thus, a silicon wafer for a semiconductor substrate is 
provided in which the polycrystalline silicon layer 11 is provided only on 
the rear surface 10a of the wafer body 10 and not on either the front 
surface 10b or the side surface 10c. 
Although the above embodiment description was made of a silicon wafer 
without chamfering, the present invention can be similarly applied to a 
chamfered silicon wafer such as shown in FIG. 9. 
Although the present invention has been described and illustrated in 
detail, it is clearly understood that the same is by way of illustration 
and example only and is not to be taken by way of limitation, the spirit 
and scope of the present invention being limited only by the terms of the 
appended claims.