Monocrystalline compound semiconductor wafer including non-monocrystalline peripheral region

A method of fabricating a semiconductor wafer includes preparing a semiconductor wafer of a monocrystalline compound semiconductor having a side surface and upper and lower surfaces, and upper and lower corners at the intersections of the side surface and the upper and lower surfaces, respectively; and producing a non-monocrystalline region at the side surface of the semiconductor wafer including the corners. Since the semiconductor wafer includes a non-monocrystalline part at the side surface including the corners, even when a crack is produced in the non-monocrystalline part, unwanted cleaving of the wafer from the crack does not occur.

FIELD OF THE INVENTION 
The present invention relates a semiconductor wafer comprising a 
monocrystalline compound semiconductor with good cleavability and a method 
of fabricating the semiconductor wafer with reduced cracking and improved 
yield. 
BACKGROUND OF THE INVENTION 
FIG. 10 is a perspective view illustrating a conventional semiconductor 
wafer. In FIG. 10, reference numeral 1a designates an InP monocrystalline 
semiconductor wafer. The wafer 1a is fabricated in the following process 
steps. Initially, a bulk monocrystalline ingot comprising InP is grown the 
LEC (Liquid Encapsulated Czochralski) method and shaped into a cylindrical 
ingot having a desired diameter. This cylindrical ingot is cut into slices 
of desired thicknesses. Thereafter, each slice is formed into a desired 
shape as needed, followed by polishing or the like. 
A monocrystalline semiconductor wafer fabricated as described above is 
employed in an automated production line for semiconductor lasers. 
FIG. 11 is a perspective view of the semiconductor wafer 1a with a crack. 
In the figure, reference numeral 7 designates a crack and reference 
numeral 8 designates a cleavage line caused by the crack 7. 
Generally, monocrystalline semiconductor wafers, such as GaAs or InP 
wafers, employed for fabrication of semiconductor lasers have high 
cleavability. Therefore, in the fabrication of semiconductor lasers, chip 
separation is performed utilizing the high cleavability of the 
monocrystalline semiconductor wafer along a crystal plane. More 
specifically, when the monocrystalline semiconductor wafer is divided into 
laser chips by cleaving, a specular facet is produced at the end of the 
laser waveguide of each laser chip. 
However, in the fabrication of semiconductor lasers using a monocrystalline 
semiconductor wafer with high cleavability, the semiconductor wafer is 
sometimes cracked due to unwanted contact between the wafer and the 
apparatus or the like as shown in FIG. 11. Since the semiconductor wafer 
1a comprises a pure monocrystalline semiconductor with high cleavability 
to the periphery of the wafer, the crack 7 easily extends in the crystal 
axis direction, resulting in breakage of the wafer 1a. That is, wafer 
breakage is caused by the small crack 7 produced on the peripheral part of 
the wafer during the fabrication process and extends in the crystal axis 
direction along the cleavage plane. Therefore, even the small crack 7 
causes wafer breakage along the cleavage line 8 starting from the crack 7. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a monocrystalline 
compound semiconductor wafer having good clearability and reducing 
breakage of the wafer due to cracking in the wafer during the fabrication 
process. 
It is another object of the present invention to provide a method of 
fabricating the semiconductor wafer. 
Other objects and advantages of the invention will become apparent from the 
detailed description that follows. The detailed description and specific 
embodiments described are provided only for illustration since various 
additions and modifications within the spirit and scope of the invention 
will be apparent to those of skill in the art from the detailed 
description. 
According to a first aspect of the present invention, a method of 
fabricating a semiconductor wafer includes preparing a semiconductor wafer 
comprising a monocrystalline compound semiconductor having good 
cleavability, the wafer having a side surface and upper and lower 
surfaces, and upper and lower corners between the side surface and the 
upper and lower surfaces, respectively; and producing a 
non-monocrystalline part at the side surface of the semiconductor wafer 
including the upper and lower corners. Since the semiconductor wafer 
fabricated in this method includes the non-monocrystalline part having no 
cleavability at the side surface including the upper and lower corners, 
even when a crack is produced in the non-monocrystalline part, unwanted 
cleaving of the wafer from the crack does not occur. 
According to a second aspect of the present invention, the above-described 
method includes melting and resolidifying an edge portion of the 
semiconductor wafer including the upper and lower corners to change 
characteristics of the monocrystalline semiconductor in that portion 
without a macro change in the shape of the wafer, thereby producing the 
non-monocrystalline part. In this method, since the monocrystalline 
semiconductor at the side surface of the wafer is changed to 
non-monocrystalline semiconductor, the semiconductor wafer has no 
cleavability at the side surface including the upper and lower corners. 
Therefore, even when a crack is produced in the non-monocrystalline part, 
unwanted cleaving of the wafer from the crack does not occur. 
According to a third aspect of the present invention, the above-described 
method includes applying a non-monocrystalline material to the side 
surface of the semiconductor wafer including the upper and lower corners, 
thereby producing the non-monocrystalline part. Since the semiconductor 
wafer fabricated in this method includes the non-monocrystalline part 
having no cleavability at the side surface including the upper and lower 
corners, even when a crack is produced in the non-monocrystalline part, 
unwanted cleaving of the wafer from the crack does not occur. 
According to a fourth aspect of the present invention, the above-described 
method includes applying a laser beam to the side surface of the 
semiconductor wafer while rotating the semiconductor wafer, thereby 
melting and resolidifying the side portion of the semiconductor wafer. 
Therefore, the melting and resolidifying of the side portion of the 
semiconductor wafer is carried out with high efficiency. 
According to a fifth aspect of the present invention, in the 
above-described method, the semiconductor wafer is a circular 
semiconductor wafer having a peripheral side surface, and the laser beam 
is applied to the circular semiconductor wafer in the tangent direction of 
the peripheral side surface of the circular semiconductor wafer and within 
the upper and lower surfaces of the wafer. Therefore, the upper and lower 
corners of the semiconductor wafer are simultaneously and uniformly melted 
and resolidified using a single laser oscillator. In addition, the laser 
beam is prevented from being applied to the center portion of the 
semiconductor wafer. 
According to a sixth aspect of the present invention, the above-described 
method includes applying a plurality of laser beams, simultaneously or 
successively, to portions of the side surface of the semiconductor wafer. 
Therefore, the upper and lower corners of the semiconductor wafer are 
melted and resolidified with high reliability. 
According to a seventh aspect of the present invention, a method of 
fabricating a semiconductor wafer includes preparing a semiconductor ingot 
comprising a monocrystalline compound semiconductor having good 
cleavability; forming the semiconductor ingot into a cylindrical 
semiconductor ingot having a desired diameter and a peripheral side 
surface; producing a non-monocrystalline part at the peripheral side 
surface of the cylindrical semiconductor ingot; and cutting the 
cylindrical semiconductor ingot into slices and polishing each slice, 
thereby producing a circular semiconductor wafer including a 
non-monocrystalline part at its peripheral side surface including upper 
and lower corners of the wafer. In this method, since the formation of the 
non-monocrystalline part of the semiconductor wafer is performed before it 
is sliced out of an ingot, the fabricating process is significantly 
simplified. Further, since the semiconductor wafer fabricated in this 
method includes the non-monocrystalline part having no cleavability at the 
side surface including the upper and lower corners, even when a crack is 
produced in the non-monocrystalline part, unwanted cleaving of the wafer 
from the crack does not occur. 
According to an eighth aspect of the present invention, the above-described 
method includes melting and resolidifying a peripheral side portion of the 
semiconductor ingot to change characteristics of the monocrystalline 
semiconductor in that portion, thereby producing the non-monocrystalline 
part of the ingot. In this method, since the monocrystalline semiconductor 
at the side surface of the wafer is changed to non-monocrystalline 
semiconductor, the semiconductor wafer has no cleavability at the side 
surface including the upper and lower corners. Therefore, even when a 
crack is produced in the non-monocrystalline part, unwanted cleaving of 
the wafer from the crack does not occur. 
According to an ninth aspect of the present invention, the above-described 
method includes applying a non-monocrystalline material to the peripheral 
side surface of the semiconductor ingot, thereby producing the 
non-monocrystalline part of the ingot. Since the semiconductor wafer 
fabricated in this method includes the non-monocrystalline part having no 
cleavability at the side surface including the upper and lower corners, 
even when a crack is produced in the non-monocrystalline part, unwanted 
cleaving of the wafer from the crack does not occur. 
According to a tenth aspect of the present invention, the above-described 
method includes applying a laser beam to the peripheral side surface of 
the semiconductor ingot while rotating the semiconductor ingot, thereby 
melting and resolidifying the peripheral side portion of the semiconductor 
ingot. Therefore, the melting and resolidifying of the semiconductor ingot 
is performed with high efficiency. 
According to an eleventh aspect of the present invention, the 
above-described method includes marking the semiconductor wafer with a 
laser beam. Therefore, the marked semiconductor wafer can be distinguished 
from other wafers. 
According to a twelfth aspect of the present invention, a semiconductor 
wafer comprises a monocrystalline compound semiconductor wafer having good 
cleavability, the wafer having a side surface and upper and lower 
surfaces, and upper and lower corners between the side surface and the 
upper and lower surfaces, respectively; and a non-monocrystalline part 
disposed at the side surface of the monocrystalline compound semiconductor 
wafer including the upper and lower corners. Therefore, even when a crack 
is produced in the non-monocrystalline part, unwanted cleaving of the 
wafer from the crack does not occur.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1! 
FIG. 1 is a perspective view illustrating a semiconductor wafer in 
accordance with a first embodiment of the present invention. In the 
figure, an InP monocrystalline semiconductor wafer 1 comprises a 
monocrystalline part 1a and a non-monocrystalline part 1b. The 
non-monocrystalline part 1b is a peripheral part of the wafer including 
corners between the side surface and the upper and lower surfaces of the 
wafer. 
According to this first embodiment of the invention, since the 
semiconductor wafer 1 includes the non-monocrystalline part 1b at the 
periphery of the wafer including the corners between the side surface and 
the upper and lower surfaces of the wafer, the peripheral part of the 
wafer has no cleavability. Therefore, even when a small crack 7 as shown 
in FIG. 11 is produced on the peripheral part of the wafer during the 
fabrication of semiconductor lasers, the crack 7 does not extend across 
the wafer along the cleavage line because of the absence of cleavability 
in the non-monocrystalline part 1b. As a result, unwanted breaking of the 
wafer is significantly reduced. 
Embodiment 2! 
FIG. 2 is a perspective view for explaining a method of fabricating the 
semiconductor wafer 1a shown in FIG. 1, in accordance with a second 
embodiment of the present invention. In the figure, the same reference 
numerals as in FIG. 1 designate the same or corresponding parts. Reference 
numeral 2 designates a laser beam for producing the non-monocrystalline 
part 1b in the InP monocrystalline semiconductor wafer 1a, numeral 3 
designates a laser oscillator emitting the laser beam, and numeral 4 
designates a rotatable susceptor on which the semiconductor wafer 1a is 
mounted. In this method, the non-monocrystalline part 1b of the wafer is 
produced by melting and resolidifying the peripheral part of the wafer 
using the laser beam 2. 
A description is given of the method of fabricating the semiconductor wafer 
according to the second embodiment of the invention. 
Initially, as in the prior art method, a bulk monocrystalline InP ingot is 
produced by the LEC method. Then, the ingot is shaped into a cylindrical 
ingot having a desired diameter. The cylindrical ingot is cut into slices 
of desired thicknesses, followed by polishing of each slice, resulting in 
the monocrystalline semiconductor wafer 1a. 
In this second embodiment of the invention, the semiconductor wafer 1a is 
mounted on the rotatable susceptor 4 as shown in FIG. 2, and a part of the 
semiconductor wafer 1a is irradiated with the laser beam 2 emitted from 
the laser oscillator 3 in the direction of the tangent of the periphery of 
the wafer 1a to melt and resolidify that part, whereby the 
non-monocrystalline part 1b shown in FIG. 2 is produced. The annular 
non-monocrystalline part 1b shown in FIG. 1 is produced by melting and 
resolidifying the peripheral part of the wafer with the laser beam while 
rotating the susceptor 4. 
Since the heating of the wafer 1a with the laser beam 2 is for producing 
the non-monocrystalline part 1b in the monocrystalline semiconductor wafer 
1a, the intensity of the laser beam 2 should not be as high as an 
intensity that causes macro changes in the shape of the wafer 1a. 
Although the formation of the non-monocrystalline part 1b is performed 
after polishing of the wafer, it may be performed before polishing of the 
wafer. 
A description is given of the function of this second embodiment of the 
invention. 
As described above, in this second embodiment of the invention, the 
peripheral part of the monocrystalline semiconductor wafer is irradiated 
with the laser beam 2 to melt the monocrystalline semiconductor at that 
part and, thereafter, the molten part is cooled and solidified, whereby 
the regularity of the monocrystalline semiconductor in the peripheral part 
is disordered and changed into a non-monocrystalline semiconductor, i.e., 
amorphous or polycrystalline semiconductor. The peripheral part of the 
wafer comprising the non-monocrystalline semiconductor has no 
cleavability. 
In the method of fabricating a semiconductor wafer according to this second 
embodiment of the invention, after the circular semiconductor wafer 1a is 
put on the rotatable susceptor 4, the laser beam 2 is applied to the wafer 
in the tangential direction of the wafer. Therefore, only the peripheral 
part of the wafer is irradiated with the laser beam 2, and the center part 
of the wafer is not irradiated with the laser beam 2. Further, the corners 
of the wafer between the side surface and the upper surface and between 
the side surface and the lower surface are simultaneously irradiated with 
the laser beam 2 emitted from the single laser oscillator 3. Furthermore, 
since the heating of the peripheral part of the semiconductor wafer 1a 
with the laser beam 2 is carried out while rotating the wafer 1a using the 
rotatable susceptor 4, the cooling of the heated and molten part of the 
wafer is successively carried out with high efficiency. Furthermore, by 
appropriately selecting the intensity of the laser beam 2 and the rotating 
speed of the susceptor 4, conditions in the formation of the 
non-monocrystalline part 1b can be controlled according to the material of 
the semiconductor wafer and desired crystal structure. 
As described above, according to the second embodiment of the present 
invention, the peripheral part of the monocrystalline semiconductor wafer 
1a including the corners between the side surface and the upper and lower 
surfaces of the wafer is irradiated with the laser beam 2, applied to the 
wafer in the tangential direction while rotating the wafer 1a, thereby to 
change the characteristics of the monocrystalline semiconductor in the 
peripheral part with no macro change in the shape of the wafer. Therefore, 
the monocrystalline semiconductor in the peripheral part of the wafer can 
be changed into non-monocrystalline semiconductor using a single laser 
oscillator 3. In this wafer, even when a crack is produced in the 
peripheral part, since the peripheral part comprises a non-monocrystalline 
semiconductor having no cleavability, cleaving of the wafer does not occur 
from the crack. As a result, a hardly breaking semiconductor wafer is 
obtained. 
Embodiment 3! 
FIG. 3(a) is a perspective view illustrating a method of fabricating a 
semiconductor wafer in accordance with a third embodiment of the present 
invention. FIG. 3(b) shows a modification of the third embodiment. In 
these figures, the same reference numerals as those in FIG. 2 designate 
the same or corresponding parts. Reference numerals 3a, 3b, and 3c 
designate laser oscillators emitting laser beams 2a, 2b, and 2c, 
respectively. The laser beam 2a is applied to a first portion of the wafer 
adjacent to an upper corner between the side surface and the upper surface 
of the wafer, the laser beam 2b is applied to a second portion of the 
wafer adjacent to a lower corner between the side surface and the lower 
surface of the wafer, and the laser beam 2c is applied to a third portion 
of the wafer in the center of the side surface. These laser beams are 
applied to the wafer in the tangential direction of the circular wafer 1a. 
Non-monocrystalline semiconductor portions 1b are produced by the laser 
beams. 
A description is given of the method of fabricating a semiconductor wafer 
according to the present invention. 
Initially, a bulk monocrystalline InP ingot is produced by the LEC method. 
Then, the ingot is shaped into a cylindrical ingot having a desired 
diameter. The cylindrical ingot is cut into slices of desired thicknesses, 
followed by polishing of each slice, resulting in the monocrystalline 
semiconductor wafer 1a. 
While in the above-described second embodiment the non-monocrystalline 
semiconductor part 1b is produced by irradiating a peripheral part of the 
wafer with a laser beam emitted from a single laser oscillator 3, in this 
third embodiment it is produced by irradiating the wafer with three laser 
beams in different directions. More specifically, after the semiconductor 
wafer 1a is mounted on the rotatable susceptor 4, as illustrated in FIG. 
3(a), three portions of the semiconductor wafer 1a, i.e., the first 
portion adjacent to the upper corner between the side surface and the 
upper surface, the second portion adjacent to the lower corner between the 
side surface and the lower surface, and the third portion in the center of 
the side surface, are irradiated with the laser beams 2a, 2b, and 2c 
emitted from the laser oscillators 3a, 3b, and 3c, respectively, in the 
tangential direction of the semiconductor wafer, thereby producing the 
non-monocrystalline portions 1b. Since the irradiation of the wafer with 
the laser beams is carried out while rotating the susceptor 4, a 
semiconductor wafer having a non-monocrystalline part 1b at the entire 
periphery as shown in FIG. 1 is obtained. The intensity of the laser beams 
is the same as that described in the second embodiment of the invention. 
A description is given of the function and effect of the third embodiment 
of the invention. 
Also in this third embodiment, the laser beams 2a, 2b, and 2c are not 
applied to the center part of the semiconductor wafer 1a by mistake. 
Further, since the heating of the semiconductor wafer 1a is carried out 
while rotating the wafer, the cooling of the heated and molten portions of 
the wafer is successively carried out with high efficiency. In addition, 
since the semiconductor wafer 1a is irradiated with a plurality of laser 
beams in different directions, the upper and lower corners of the 
semiconductor wafer are changed into non-monocrystalline semiconductor 
material with high reliability. 
In the method shown in FIG. 3(a), the laser oscillators 3a and 3b apply the 
laser beams 2a and 2b to the upper corner of the wafer between the side 
surface and the upper surface and the lower corner of the wafer between 
the side surface and the lower surface in the tangential direction of the 
semiconductor wafer. However, as shown in FIG. 3(b), the laser oscillators 
3a and 3b may apply the laser beams 2a and 2b to the upper corner and the 
lower corner of the wafer in the direction perpendicular to the upper 
surface and the lower surface of the wafer, respectively. Also in this 
case, the same effects as described above are achieved. 
According to the third embodiment of the present invention, since the 
peripheral part of the monocrystalline semiconductor wafer is irradiated 
with a plurality of laser beams in different directions simultaneously or 
successively to change the characteristics of the monocrystalline 
semiconductor wafer, the peripheral part of the monocrystalline 
semiconductor wafer including the upper and lower corners is changed into 
non-monocrystalline semiconductor material with high reliability. 
Therefore, even when a crack is produced in the non-monocrystalline 
peripheral part of the wafer, since this part has no cleavability, 
cleaving does not occur from the crack, resulting in a hardly breaking 
semiconductor wafer. 
Although in the second and third embodiments a circular wafer is employed 
and a laser beam is applied to the peripheral part of the wafer including 
the upper and lower corners between the side surface and the upper and 
lower surfaces of the wafer, the method of forming a non-monocrystalline 
part in a monocrystalline semiconductor wafer can be applied to a circular 
semiconductor wafer having an orientation flat or a semiconductor wafer 
having a shape other than circular by controlling the position on the 
wafer irradiated with the laser beam using a movable laser oscillator. 
Embodiment 4! 
FIG. 4 is a perspective view for explaining a method of fabricating a 
semiconductor wafer in accordance with a fourth embodiment of the present 
invention. In the figure, the same reference numerals as in FIG. 2 
designate the same or corresponding parts. Reference numeral 3d designates 
a laser oscillator applying an identification mark 5 to a monocrystalline 
semiconductor wafer 1a with a laser beam (hereinafter referred to as laser 
marking) and melting and resolidifying a portion of the semiconductor 
wafer 1a to change that portion into non-monocrystalline semiconductor 
(hereinafter referred to as non-monocrystallization). 
A description is given of a method of fabricating a semiconductor wafer 
according to this fourth embodiment of the invention. In this method, the 
process steps of forming the non-monocrystalline part 1b in the 
monocrystalline wafer 1a are fundamentally identical to those described in 
the second or third embodiment of the invention. The laser oscillator 3d 
shown in FIG. 4 is identical to the laser oscillator 3a shown in FIG. 3(b) 
except that the laser oscillator 3d has the function of laser marking in 
addition to the function of non-monocrystallization. In FIG. 4, laser 
oscillators used only for the non-monocrystallization are not shown. 
Although the laser oscillator 3d has the functions of laser marking and 
non-monocrystallization, it may have the function of laser marking alone 
when it is used with the laser oscillator 3 shown in FIG. 2, or the laser 
oscillators 3a, 3b, and 3c shown in FIG. 3(a). Further, the laser marking 
may be performed on the lower surface of the wafer. 
A description is given of the function of this fourth embodiment. 
Since the identification mark 5 is given to the semiconductor wafer using 
the laser oscillator 3d for laser marking, the wafer is distinguished from 
other wafers with high reliability in an automated fabricating process. In 
addition, the front and rear surfaces of the wafer are distinguished by 
detecting the mark 5 optically. Although an ordinary circular 
semiconductor wafer has an orientation flat for detecting front and rear 
surfaces thereof, the orientation flat can be dispensed with in the 
semiconductor wafer according to this fourth embodiment. 
As described above, according to the fourth embodiment of the present 
invention, since the identification mark is given to the semiconductor 
wafer using the laser oscillator for laser marking, distinguishing the 
wafer from other wafers and detection of the front and rear surfaces of 
the wafer are facilitated. In addition, in the method of forming the 
non-monocrystalline part in the monocrystalline wafer according to the 
second or third embodiment of the invention, the laser oscillator for 
laser marking can be used as a laser oscillator for 
non-monocrystallization. 
Embodiment 5! 
FIG. 5 is a perspective view illustrating a method of fabricating a 
semiconductor wafer in accordance with a fifth embodiment of the present 
invention. In the figure, reference numeral 10a designates a bulk 
monocrystalline InP ingot, numeral 10b designates a non-monocrystalline 
part produced in the semiconductor ingot 10a, numeral 4a designates a 
rotatable ingot susceptor, and numeral 3e designates a laser oscillator 
emitting a laser beam 2 for making the non-monocrystalline part 10b. 
A description is given of a method of fabricating a semiconductor wafer 
according to this fifth embodiment of the invention. 
Usually, a semiconductor wafer is produced by slicing a cylindrical 
semiconductor ingot. In this fifth embodiment, before slicing a 
cylindrical semiconductor ingot 10a, a non-monocrystalline part 10b is 
produced at the periphery, i.e., side surface, of the ingot 10a and, 
thereafter, the ingot is sliced to produce a semiconductor wafer having a 
non-monocrystalline peripheral part. 
Initially, a bulk monocrystalline InP ingot grown by the LEC method is 
shaped into a cylindrical semiconductor ingot 10a having a desired 
diameter. Then, the semiconductor ingot 10a is mounted on the rotatable 
susceptor 4a as shown in FIG. 5, and a portion of the side surface of the 
ingot 10a is irradiated with the laser beam 2 emitted from the laser 
oscillator 3 while rotating the susceptor 4a, whereby the peripheral 
portion of the monocrystalline semiconductor ingot 10a is changed into a 
non-monocrystalline semiconductor material. After the 
non-monocrystallization, the ingot is cut into slices, followed by 
polishing of each slice, resulting in an InP monocrystalline semiconductor 
wafer having a non-monocrystalline peripheral part including the upper and 
lower corners between the side surface and the upper and lower surfaces, 
respectively, as shown in FIG. 1. 
A description is given of the function of this fifth embodiment of the 
invention. 
As described above, in this fifth embodiment of the invention, a portion on 
the periphery of the monocrystalline semiconductor ingot 10a is irradiated 
with the laser beam 2 to melt the monocrystalline semiconductor at that 
portion and, thereafter, the molten portion is cooled and solidified, 
whereby the regularity of the monocrystalline semiconductor in the 
peripheral portion of the ingot is disordered and changed into 
non-monocrystalline semiconductor material, i.e., amorphous or 
polycrystalline semiconductor material. The peripheral portion of the 
ingot comprising the non-monocrystalline semiconductor has no 
cleavability. 
In addition, since the non-monocrystalline peripheral portion is produced 
in the semiconductor ingot and, thereafter, the ingot is cut into slices, 
i.e., individual wafers, a plurality of semiconductor wafers each having a 
non-monocrystalline peripheral portion are produced by only one 
non-monocrystallization step whereas that step is performed for each 
semiconductor wafer in the above-described second and third embodiments. 
As described above, according to the fifth embodiment of the present 
invention, after a monocrystalline semiconductor ingot is shaped into a 
cylindrical ingot having a desired diameter, a peripheral portion of the 
ingot is changed into non-monocrystalline semiconductor material. Then, 
the ingot is cut into slices, followed by polishing, to produce a 
plurality of semiconductor wafers each having a non-monocrystalline 
peripheral portion including the upper and lower corners of the wafer. 
Therefore, even when a crack is produced in the peripheral part of the 
wafer, since the peripheral part comprises non-monocrystalline 
semiconductor material having no cleavability, cleaving does not occur 
from the crack. As a result, a hardly breaking semiconductor wafer is 
obtained. Further, since the non-monocrystalline part of the semiconductor 
wafer is produced before it is cut out of the semiconductor ingot, the 
fabrication process is simplified. 
Embodiment 6! 
FIG. 6 is a perspective view illustrating a semiconductor wafer in 
accordance with a sixth embodiment of the present invention. In the 
figure, a semiconductor wafer 100 comprises a monocrystalline 
semiconductor wafer 1a and a non-monocrystalline part 1c. The 
non-monocrystalline part 1c is produced by applying a non-monocrystatline 
material to the peripheral side surface of the monocrystalline 
semiconductor wafer 1a. 
As described in BACKGROUND OF THE INVENTION, since a monocrystalline 
semiconductor wafer, such as GaAs or InP wafer, employed for fabrication 
of semiconductor lasers has high cleavability, it is easily cleaved along 
a crystal axis from a small crack produced in the wafer during the 
fabrication of semiconductor lasers, resulting in unwanted breaking of the 
wafer. In order to avoid the breaking of the wafer, in the sixth 
embodiment of the invention, a non-monocrystalline material is applied to 
the peripheral side surface of the monocrystalline semiconductor wafer 1a. 
In the semiconductor wafer 100 shown in FIG. 6, the peripheral part of the 
wafer including the upper and lower corners of the wafer between the side 
surface and the upper and lower surfaces is made of the 
non-monocrystalline material 1c having no cleavability. Therefore, even 
when a small crack is produced in the non-monocrystalline part 1c during 
fabrication of semiconductor lasers, since this part has no cleavability, 
cleaving does not occur from the crack along the crystal axis. As a 
result, unwanted breaking of the wafer is significantly reduced. 
Embodiment 7! 
FIGS. 7(a)-7(c) are diagrams for explaining a method of fabricating a 
semiconductor wafer 100 as shown in FIG. 6, in accordance with a seventh 
embodiment of the present invention. More specifically, FIG. 7(a) is a 
perspective view illustrating a monocrystalline semiconductor wafer before 
a non-monocrystalline material is applied, FIG. 7(b) is a sectional view 
illustrating an apparatus for applying the non-monocrystalline material to 
the monocrystalline semiconductor wafer, and FIG. 7(c) is a perspective 
view illustrating a semiconductor wafer fabricated by the method according 
to this seventh embodiment of the invention. In these figures, the same 
reference numerals as those shown in FIGS. 2 and 6 designate the same or 
corresponding parts. Reference numeral 21 designates a cathode electrode, 
numeral 22 designates an electrical ground connected to the cathode 
electrode 21, numeral 23 designates SiH.sub.4 reactive gas, numeral 24 
designates a pipe for introducing the SiH.sub.4 gas 23, numeral 25 
designates a plasma of the SiH.sub.4 gas 23, numeral 26 designates an 
anode electrode, and numeral 27 designates a high-frequency power supply. 
A description is given of the fabricating method. 
Initially, as described in the second and third embodiments of the 
invention, after an InP monocrystalline semiconductor ingot is produced by 
the LEC method, the ingot is shaped into a cylindrical ingot having a 
desired diameter and cut into slices, producing a monocrystalline 
semiconductor wafer 1a as shown in FIG. 7. The diameter of the 
semiconductor wafer 1a is reduced as needed in consideration of the 
thickness of the non-monocrystalline material which is later applied to 
the wafer 1a. Then, the semiconductor wafer 1a is put on a rotatable 
susceptor 4 of the apparatus shown in FIG. 7(b), and the 
non-monocrystalline material is applied to the peripheral side surface of 
the semiconductor wafer, preferably by plasma-CVD (Chemical Vapor 
Deposition), while rotating the susceptor 4, whereby a non-monocrystalline 
part 1c is produced on the entire side surface of the monocrystalline 
semiconductor wafer 1a. In this seventh embodiment, SiH.sub.4 is employed 
as the reactive gas and amorphous silicon is employed as the 
non-monocrystalline material. As a result, a semiconductor wafer 100 shown 
in FIG. 7(c) is obtained. 
A description is given of function and effect of this seventh embodiment of 
the invention. 
In this fabricating method, the non-monocrystalline material having no 
cleavability is applied to the peripheral side surface of the 
monocrystalline semiconductor wafer 1a having cleavability, thereby 
producing the non-monocrystalline part 1c including upper and lower 
corners of the wafer 100. Therefore, even when a crack is produced in the 
non-monocrystalline part 1c during fabrication of semiconductor lasers, 
cleaving does not occur from the crack along a crystal axis. 
In the seventh embodiment, the non-monocrystalline part 1c is produced by 
plasma-CVD of amorphous silicon. However, the material having no 
cleavability and applied to the side surface of the monocrystalline 
semiconductor wafer 1a is not restricted to amorphous silicon. Other 
materials having adhesion to semiconductor materials having clearability, 
such as InP or GaAs, may be employed. In addition, sputtering or vacuum 
evaporation may be employed as the method of applying the 
non-monocrystalline material. 
Embodiment 8! 
FIGS. 8(a)-8(c) to 9(a)-9(c) are diagrams for explaining a method of 
fabricating a semiconductor wafer in accordance with an eighth embodiment 
of the present invention. In the figures, the same reference numerals as 
those shown in FIGS. 7(a)-7(c) designate the same or corresponding parts. 
Reference numeral 10 designates a bulk monocrystalline semiconductor ingot 
grown by the LEC method, numeral 10a designates a cylindrical 
semiconductor ingot having a desired diameter made out of the ingot 10, 
numeral 28 designates a cutter for slicing the ingot, numeral 80 
designates slices cut out of the ingot, and numeral 90 designates a 
semiconductor wafer after polishing. 
A description is given of the fabricating method. 
While in the seventh embodiment a non-monocrystalline material is applied 
to a semiconductor wafer, in this eighth embodiment a non-monocrystalline 
material is applied to a semiconductor ingot. 
Initially, a bulk monocrystalline InP ingot 10 is produced by the LEC 
method (FIG. 8(a)). 
Thereafter, the InP ingot 10 is shaped into a cylindrical ingot 10a having 
a desired diameter (FIG. 8(b)). In this step, the diameter of the 
cylindrical ingot 10a is selected in consideration of the thickness of the 
non-monocrystalline material which is later applied to the ingot 10a. 
In the step of FIG. 8(c), the semiconductor ingot 10a is put on a rotatable 
susceptor 4a, and a non-monocrystalline material is applied to the side 
surface of the cylindrical ingot 10a, preferably by plasma-CVD, while 
rotating the susceptor 4a, thereby producing a non-monocrystalline part 
10c on the entire side surface of the ingot 10a. In this eighth 
embodiment, SiH.sub.4 is employed as the reactive gas and amorphous 
silicon is employed as the non-monocrystalline material. The 
non-monocrystalline material and the method of applying that material are 
not restricted thereto as described in the seventh embodiment of the 
invention. 
After formation of the non-monocrystalline part 1c on the entire side 
surface of the cylindrical ingot 10a (FIG. 9(a), the ingot is cut into 
slices 80 of desired thickness with a cutter 28 (FIG. 9(b)). 
Thereafter, each slice is polished to produce a semiconductor wafer 90 
having a non-monocrystalline part 1c including upper and lower corners of 
the wafer (FIG. 9(c)). 
A description is given of the function and effect of this eighth embodiment 
of the invention. 
In this eighth embodiment, the non-monocrystalline material having no 
cleavability is applied to the peripheral side surface of the 
monocrystalline semiconductor ingot 10a having cleavability and, 
thereafter, the ingot 10a is sliced and polished to produce the 
semiconductor wafer 90 having the non-monocrystalline part 1c including 
the upper and lower corners of the wafer. Therefore, even when a crack is 
produced in the non-monocrystalline part 1c, cleaving across the wafer 
does not occur from the crack. In addition, a plurality of semiconductor 
wafers each having a non-monocrystalline part 1c are produced by only one 
application of the non-monocrystalline material whereas that step is 
performed for each semiconductor wafer in the seventh embodiment. 
While in the fifth and eighth embodiments a non-monocrystalline part is 
produced on a peripheral side surface of a cylindrical ingot, it may be 
produced on a peripheral side surface of a cylindrical ingot having an 
orientation flat. 
In the first to fourth, sixth, and seventh embodiments, the shape of the 
semiconductor wafer is not restricted to circular.