Single crystal silicon substrate

A single crystal silicon substrate which comprises an electric insulation member and a single crystal silicon film formed on the insulation member. The silicon film has first regions and second regions. Each of the first regions is formed as a strip shape and has a high density of inorganic impurities implanted thereinto. Each of the second regions is formed as a strip shape and has a low density of the impurities. The first and second regions are alternatively arranged contacting with each other so that the first regions are separated from each other.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a single crystal silicon substrate which 
contains inorganic impurity atoms and which substrate is used as a basic 
material for obtaining a silicon film by a hetero-epitaxial growth method, 
or manufacturing a high quality semiconductor device. 
2. Description of the Related Art 
A high quality semiconductor device comprises a single crystal silicon 
substrate made from an insulation material such as a glass plate on which 
a single crystal silicon film is formed. The substrate is produced by a 
zone melt recrystallization method. 
However, the method involves a problem of grain boundary. To cope with the 
problem, a method has been adopted in which the grain boundary is 
generated only in a region where the material thereof does not influence 
the characteristic of the substrate so as to avoid the degradation of the 
device due to the grain boundary. More precisely, a film layer of Si.sub.3 
N.sub.4 is disposed in a form of strips on a surface of the substrate 
covered with a film of SiO.sub.2. The Si.sub.3 N.sub.4 film absorbs 
optical rays so that the region under the film is heated. As a result, 
recrystallization of the heated region is retarded so that grain 
boundaries of different crystal face are concentrated at the region. 
Therefore, by disposing the Si.sub.3 N.sub.4 film at a desirable region, 
it becomes possible to generate the grain boundaries only in that region 
of the substrate. 
However, in accordance with the grain boundary control method mentioned 
above, heat distribution is changed according to a slight difference of 
film quality and film thickness so that the refractive index of the 
substrate is changed due to a slight change of the film quality as well as 
the optical absorption coefficient thereof, which makes it difficult to 
obtain a substrate of stable and even characteristic distribution. 
Besides, cracks are generated due to the difference of film thickness and 
film quality in the substrate. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a single 
crystal silicon substrate in which the problems of the related art 
mentioned above are obviated and the grain boundaries are easily 
concentrated in a desired strip region of the substrate without 
degradation of the characteristic of the substrate and generating cracks 
therein. 
The object of the invention can be achieved by a single crystal silicon 
substrate comprising an electric insulation member and a single crystal 
silicon film formed on the insulation member, the film comprising a 
plurality of first strip regions having a high density of inorganic 
impurity atoms and a plurality of second strip regions having a low 
density of inorganic impurity atoms, the first and second regions being 
disposed alternately and in contact with each other so that the first 
regions are disconnected from each other. 
The present invention utilizes a freezing point depression phenomenon of 
the silicon film due to the inorganic impurity atoms contained therein 
instead of forming a film of Si.sub.3 N.sub.4 as an optical ray absorbent 
on the SiO.sub.2 film on the surface of the substrate as is the case of 
the related art mentioned before. By implanting impurities to strip 
regions in a polycrystalline silicon or an amorphous silicon film, the 
freezing point of the strip regions is depressed at the time of 
recrystallization after being melted, which causes the retardation of 
recrystallization at the regions so that the grain boundaries are 
concentrated in the regions. 
Also, it is possible to arrange a MOS transistor device using the substrate 
mentioned above in such a way that the source portion and the drain 
portion of the transistor are made from the region of high density of the 
impurities in which the grain boundaries are generated, while the active 
portion of the transistor is made from the region in which the grain 
boundaries are not generated. By such an arrangement, the characteristic 
of the transistor is upgraded and it becomes possible to shorten the time 
of diffusion process since the source and drain portions contain much 
impurities. 
An advantage of the above-mentioned single crystal silicon substrate in 
accordance with the present invention is that, due to the arrangement 
wherein the high impurity density strip regions and the low impurity 
density strip regions are alternately disposed in contact with each other, 
the freezing point of the high density region is depressed at the time of 
recrystallization thereof so that the recrystallization of the regions is 
retarded compared with the regions of low impurity density, which 
concentrates the grain boundaries to generate in the high density regions 
and no grain boundaries are generated in the low density regions. 
Another advantage of the substrate structure of the present invention is 
that, since the high density regions do not come in contact with each 
other, by using the atoms of one element of groups III to V in the 
periodic table as the impurity materials, it becomes possible to use the 
impurity containing region exclusively as the source or drain of the MOS 
transistor where the grain boundaries do not impair the characteristic of 
the transistor. 
Still another advantage of the substrate structure of the present invention 
is that, by arranging such that the width of the strip region of high 
impurity density is narrower than that of the low density strip, the 
freezing point depression effect is enhanced at the time of 
recrystallization and it becomes possible to widen the effective area of 
the low impurity density region which is used as the active portion of the 
transistor. 
Further objects and advantages of the present invention will be apparent 
from the following description of the preferred embodiments of the present 
invention as illustrated in the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiments of the single crystal silicon substrate in accordance with the 
present invention are described hereinafter with reference to the 
drawings. 
FIGS. 1a to 1f represent in sequence a flow chart of a process for 
producing the substrate of the present invention using a quartz glass as 
an electric insulation material. 
FIGS. 2a to 2g represent in sequence another flow chart of a process for 
producing the substrate of the present invention using a single crystal 
silicon wafer having an oxide film formed thereon as an electric 
insulation material. 
Referring to FIGS. 1, first, a mirror grinded quartz glass plate 101 is 
prepared, as illustrated in FIG. 1a. The thickness of the glass plate 101 
is 0.5 to 2 mm, preferably 0.8 to 1.6 mm. 
Second, a polycrystal silicon or an amorphous silicon film 102 is stacked 
on the glass plate 101 by an appropriate method such as a thermal CVD 
method, an ECR method, an optical CVD method, an LPCVD method or a plasma 
CVD method, using SiH.sub.4, Si.sub.2 H.sub.6, SiF.sub.4 or SiCl.sub.4, as 
illustrated in FIG. 1b. The thickness of the film 102 is 0.1 .mu.m to 1 
.mu.m, preferably 0.3 to 0.5 .mu.m. 
Third, impurities 103 are implanted into the film 102 at a regular interval 
to form rows of strips by an ion implantation method or a thermal 
diffusion method, as illustrated in FIG. 1c. The amount of the impurities 
103 is 10.sup.18 to 10.sup.21 cm.sup.-3, preferably 10.sup.20 to 10.sup.21 
cm.sup.-3. Impurities are selected from elements of group III to V in the 
periodic table, such as N, O, P, B, As, Sb or Ga. 
After that, a surface protection layer 104 made from SiO.sub.2 of 1.5 .mu.m 
thick is deposited on the substrate by a normal pressure CVD method, an 
optical CVD method, an ECR method, or an LPCVD method, using SiH.sub.4, 
Si.sub.2 H.sub.6, SiF.sub.4, SiCl.sub.4, N.sub.2 O, O.sub.2, NO.sub.2, 
N.sub.2 O.sub.4, N.sub.2 O.sub.5, CO, or CO.sub.2, as illustrated in FIG. 
1d. 
After that, a heat source 105 such as an infrared heater, a laser beam, a 
radio frequency heater, or a graphite heater is moved relative to the 
substrate to heat the implanted regions one after another in series, as 
illustrated in FIG. 1e. In this step, the impurity-implanted regions of 
the film 102 are molten and recrystallized (zone melt recrystallization). 
In accordance with the steps mentioned above, a substrate is obtained which 
substrate has a zone melt recrystallization film 106 which comprises strip 
shaped regions 107 of high density of impurities and partially formed 
grain boundaries, as illustrated in FIG. 1f. The film 106 has a surface 
crystal plane (100). 
On the other hand, referring to FIG. 2, first, a mirror grinded wafer 201 
of Si is prepared as illustrated in FIG. 2a. The thickness of the wafer 
201 is 0.3 to 0.7 mm, preferably 0.4 to 0.6 mm. The wafer 201 has a 
crystal plane (100) or (111) on the surface thereof. 
Second, a thermal oxide film 202 is formed on the wafer 201 by oxidizing 
the wafer 201 by a steam oxidation method or a dry oxidation method using 
O.sub.2 gas, at a temperature of 900.degree. to 1200.degree. C., 
preferably 1000.degree. to 1100.degree. C., as illustrated in FIG. 2b. The 
thickness of the film 202 is 0.1 to 0.5 .mu.m, preferably 0.2 to 0.3 
.mu.m. 
After that, the oxidized wafer 201 having the oxide film 202 formed thereon 
is treated in the same manner as the first embodiment of FIGS. 1b to 1f. 
That is, a polycrystal silicon or an amorphous silicon film 203 is formed 
on the oxide film 202 (FIG. 2c). Impurities 204 are implanted to form rows 
of strip shaped regions of high density of impurities in the film 203 at a 
regular interval (FIG. 2d). After that, a surface protection layer 205 of 
SiO.sub.2 is formed (FIG. 2e). A zone melt recrystallization step is 
conducted by using a heat source 206 (FIG. 2f). Thus, a recrystallized 
single crystal silicon film 207 having strip shaped regions 208 of high 
impurity-density is formed (FIG. 2g). 
In each of the first embodiment of FIG. 1 and the second embodiment of FIG. 
2, it is desirable that the width of the impurity-implanted strip shaped 
region is narrower than that of the region of low density of impurities. 
It is to be noted that the insulation member to support the single crystal 
silicon film may be made from a ceramic material such as Al.sub.2 O.sub.3, 
AlN, ZrO.sub.2, Si.sub.3 N.sub.4, or SiC instead of the quartz glass 101 
of the first embodiment or the Si wafer 201 of the second embodiment. 
The zone melt recrystallization step of FIG. 1e or FIG. 2f is further 
described hereinafter wherein the heat source comprises a high-frequency 
heater. 
FIG. 3 illustrates an example of the zone melt recrystallization device. 
Numeral 301 designates the substrate in the state of FIG. 1d or FIG. 2e. 
Numeral 302 designates a quartz pipe. Numeral 303 designates a work coil 
for applying a high frequency wave. Numeral 304 designates a carbon 
susceptor. Numeral 305 designates a support member made from quartz. 
Numeral 306 designates a rod made from quartz for moving the sample 
(substrate 301). Numeral 307 designates a driving direction of a 
reversible motor. It is to be noted that when the substrate of FIG. 1d is 
used as the substrate 301, the substrate is placed on the susceptor 304 in 
such a manner that the insulation member comes in contact with the 
susceptor 304. While when the substrate of FIG. 2e is used as the 
substrate 301, the substrate is placed on the susceptor 304 in such a 
manner that the insulation member is disposed in the opposite side to the 
susceptor 304. 
FIG. 4 represents a temperature profile on the susceptor 304. As 
illustrated in FIG. 4, the susceptor temperature exceeds the melting point 
of silicon at one point or small region of the susceptor 304. 
The substrate 301 is placed on the susceptor 304 having the temperature 
profile of FIG. 4 and scanned from the left to the right at a constant 
velocity as indicated by the arrow 307. During this scanning motion, the 
zone melt recrystallization step is conducted so that a single crystal 
thin film of silicon having a crystal plane (100) on the surface thereof 
is obtained. 
The present invention is further described referring to actual data of 
examples of the substrate which were experimentally produced. 
EXAMPLE 1 
A first example of actually produced substrate is described with reference 
to FIGS. 5a and 5b. 
The insulation member 401 comprises a quartz glass plate of 1 mm thick the 
surface of which is mirror grinded. A polycrystal silicon 402 is stacked 
on the glass plate 401 by an LPCVD method to form a layer of 0.35 .mu.m 
thick. After that, oxygen atoms are implanted to the layer 402 to form 
strip shaped diffused regions 403 at a regular interval in the layer 402, 
each region having a 5 .mu.m width, by an ion implantation method. The 
amount (density) of the implanted atoms is 10.sup.17 to 10.sup.21 
cm.sup.-3. The width of the region 404 between every adjacent two diffused 
regions 403 is 50 .mu.m. A surface protection film 405 of SiO.sub.2 is 
deposited on the layer 402 by an LPCVD method to form a layer of 1.5 .mu.m 
thick. 
The substrate mentioned above is then treated by the device of FIG. 3 on 
the condition that the input power is 9.7 KW and the scanning speed is 0.1 
mm/sec to conduct the zone melt recrystallization process. 
FIG. 5b illustrates the substrate in the state after the zone mele 
recrystallization treatment. 
With respect to the polycrystal silicon film 402, the film is deposited 
under the condition that SiH.sub.4 gas and N.sub.2 gas (carrier gas) are 
used at a flow rate ratio of 1/10 and that the substrate temperature is 
650.degree. C. 
With respect to the surface protection film 405, the film is deposited 
under the condition that SiH.sub.4 gas and N.sub.2 O gas are used at a 
flow rate ration of 1/50 and that the substrate temperature is 750.degree. 
C. 
Table 1 represents the evaluation of the characteristic of the region 403 
in relation to the density of oxygen atom. The evaluation items are the 
orientation of the crystal plane of the region 407, the ratio of the grain 
boundary number included in the region 406 in comparison to that included 
in the region 407 and the surface roughness (Ra) of the region 407. With 
respect to the surface roughness Ra, mark .circle. represents the state 
Ra&lt;200 .ANG., mark .DELTA. represents the state 200 .ANG.&lt;Ra, and 
mark.times.represents the state Ra&gt;1000 .ANG.. 
As can be seen from the table 1, a good result is obtained when the oxygen 
atom density in the region 403 is 10.sup.20 to 10.sup.21 cm.sup.-3. The 
grain boundary ratio of the region 406 is reduced when the oxygen atom 
density is lowered. This is because the freezing point effect is not 
obtained due to the shortage of the oxygen atoms. 
TABLE 1 
______________________________________ 
OXYGN DEN. 
PLN ORNT. SRF ROUGH. GRN BNDRY 
______________________________________ 
10.sup.17 
cm.sup.-3 
(100) X 50% 
10.sup.18 (100) .DELTA. 60 
10.sup.19 (100) .largecircle. 
80 
10.sup.20 (100) .largecircle. 
100 
10.sup.21 (100) .largecircle. 
100 
______________________________________ 
EXAMPLE 2 
A second example of the substrate in accordance with the present invention 
is described hereinafter with reference again to FIGS. 5a and 5b. 
The insulation member 401 comprises a quartz plate which is mirror grinded 
and has a thickness of 1.5 mm. An amorphous silicon 402 is deposited on 
the plate 401 to form a film of 0.5 .mu.m thick thereon. Nitrogen atoms 
are implanted into the film 402 to form strip shaped ion diffused regions 
403 at a regular interval by an ion implantation method. The amount of the 
atoms is 10.sup.17 to 10.sup.21 cm.sup.-3. The width of each strip shaped 
region 403 is 5 .mu.m. The width of the region 404 formed between every 
two adjacent diffusion regions 403 is 50 .mu.m. A surface protection layer 
405 of SiO.sub.2 is deposited on the film 402 to form a film of 1.5 .mu.m 
thick thereon by an LPCVD method. 
The substrate treated as mentioned above is then subjected to the zone melt 
recrystallization process using a graphite heater under the condition that 
the input power is 10.3 KW and that the scanning speed is 1 mm/sec. 
FIG. 5b represents the substrate in the state after the treatment of zone 
melt recrystallization process. 
The amorphous film 402 is deposited by a plasma CVD method using SiH.sub.4 
gas and H.sub.2 gas (as a carrier gas) under the condition that the flow 
rate ratio of SiH.sub.4 and H.sub.2 is 1/10 and that the substrate 
temperature is 350.degree. C. 
The surface protection film 405 is deposited by an LPCVD method using 
SiH.sub.4 gas and O.sub.2 gas under the condition that the flow rate ratio 
of SiH.sub.4 and O.sub.2 is 1/50 and that the substrate temperature is 
450.degree. C. 
Table 2 represents the evaluation of the characteristic of the region 403 
of the substrate in relation to the density of nitrogen atoms implanted to 
the region 403 with respect to the same items as in the case of example 1 
mentioned before. 
As can be seen from the table 2, a good result is obtained when the 
nitrogen atom density in the region 403 is 10.sup.20 to 10.sup.21 
cm.sup.-3. The grain boundary ratio of the region 406 is reduced when the 
nitrogen atom density is lowered. This is because the freezing point 
effect is not obtained due to the shortage of the nitrogen atoms. 
TABLE 2 
______________________________________ 
NTRGN DEN. 
PLN ORNT. SRF ROUGH. GRN BNDRY 
______________________________________ 
10.sup.17 
cm.sup.-3 
(100) X 40% 
10.sup.18 (100) .DELTA. 50 
10.sup.19 (100) .DELTA. 70 
10.sup.20 (100) .largecircle. 
100 
10.sup.21 (100) .largecircle. 
100 
______________________________________ 
EXAMPLE 3 
A third example of the substrate in accordance with the present invention 
is described hereinafter with reference again to FIGS. 5a and 5b. 
The insulation member 401 comprises a quartz plate which is mirror grinded 
and has a thickness of 0.8 mm. A polycrystal silicon 402 is deposited on 
the plate 401 to form a film of 0.5 .mu.m thick thereon by an LPCVD 
method. P (phosphorus) atoms are implanted into the film 402 to form strip 
shaped ion diffused regions 403 at a regular interval by an ion 
implantation method. The amount of the atoms is 10.sup.21 cm.sup.-3. The 
width of each strip shaped region 403 is 2 to 10 .mu.m. The width of the 
region 404 formed between every two adjacent diffusion regions 403 is 2 to 
100 .mu.m. A surface protection layer 405 of SiO.sub.2 is deposited on the 
film 402 to form a film of 1.5 .mu.m thick thereon by a normal pressure 
CVD method. 
The substrate treated as mentioned above is then subjected to the zone melt 
recrystallization process using the device of FIG. 3 under the condition 
that the input power is 9.7 KW and that the scanning speed is 0.1 mm/sec. 
FIG. 5b represents the substrate in the state after the treatment of zone 
melt recrystallization process. 
The polycrystal silicon film 402 is deposited by an LPCVD method using 
SiH.sub.4 gas and H.sub.2 gas (as a carrier gas) under the condition that 
the flow rate ratio of SiH.sub.4 and H.sub.2 is 1/10 and that the 
substrate temperature is 650.degree. C. 
The surface protection film 405 is deposited by a normal pressure CVD 
method using SiH.sub.4 gas and O.sub.2 gas under the condition that the 
flow rate ratio of SiH.sub.4 and O.sub.2 is 1/250 and that the substrate 
temperature is 400.degree. C. 
Within the film recrystallized from the film 402 (FIG. 5a), there are 
formed a high density region 406 (FIG. 5b) which corresponds to the region 
403 and has a P atom density of 10.sup.19 cm.sup.-3 and a low density 
region 407 which corresponds to the region 404 and has a P atom density of 
10.sup.15 cm.sup.-3. 
Table 3 represents the evaluation of the characteristic of the substrate in 
relation to the width of each of the regions 403 and 404 with respect to 
the same items as in the case of example 1 mentioned before. 
As can be seen from the table 3, the grain boundary ratio of the region 406 
is reduced when the width of the region 406 having P atom density 
10.sup.19 cm.sup.-3 is narrower than that of the region 407 having P atom 
density 10.sup.15 cm.sup.-3 since a sufficient freezing point effect is 
not obtained. 
TABLE 3 
______________________________________ 
WIDTH WIDTH GRAIN BNDRY 
OF 404 OF 403 PLANE SURF RATIO 
(.mu.m) 
(.mu.m) ORTN. ROUGH. (%) 
______________________________________ 
2 100 (100) X 8 
5 90 (100) X 10 
10 70 (100) X 16 
30 50 (100) .DELTA. 50 
50 30 (100) .largecircle. 
100 
70 15 (100) .largecircle. 
100 
90 5 (100) .largecircle. 
100 
100 2 (100) .largecircle. 
100 
______________________________________ 
EXAMPLE 4 
A fourth example of the actually produced substrate in accordance with the 
present invention is described hereinafter with reference to FIGS. 6a and 
6b. 
The support member 501 comprises a P type silicon wafer which is mirror 
grinded and has a thickness of 0.5 mm. The silicon wafer 501 is heated to 
a temperature of 1000.degree. C. in an atmosphere of oxygen gas to form an 
oxide film 502 of SiO.sub.2 having a thickness of 0.2 .mu.m on the wafer 
501. A polycrystal silicon 503 is deposited on the film 502 by an LPCVD 
method to form a film of 0.4 .mu.m thick. Boron (B) atoms are implanted 
into the film 503 to form strip shaped diffusion regions 505 at a regular 
interval by an ion implantation method. The density of B atoms implanted 
is 10.sup.17 to 10.sup.21 cm.sup.-3. The width of the strip shaped region 
505 is 5 .mu.m. The width of the region 504 between every two adjacent 
regions 505 is 50 .mu.m. A surface protection layer 506 of SiO.sub.2 is 
deposited on the film 503 to form a film of 1.5 .mu.m thick thereon by an 
LPCVD method. 
The substrate treated as mentioned above is then subjected to the zone melt 
recrystallization process using an Ar laser under the condition that the 
input power is 15 W, the scanning speed is 10 cm/sec and that the 
temperature of the substrate is 450.degree. C. 
The polycrystal silicon layer 503 is deposited by an LPCVD method using 
SiH.sub.4 gas and N.sub.2 gas under the condition that the gas flow rate 
ratio of SiH.sub.4 and N.sub.2 is 1/10 and that the temperature of the 
substrate is 650.degree. C. 
The surface protection layer 506 is deposited by an LPCVD method using 
SiH.sub.4 gas and N.sub.2 O gas under the condition that the gas flow rate 
ratio of SiH.sub.4 and N.sub.2 O is 1/50 and that the temperature of the 
substrate is 750.degree. C. 
Table 4 represents the evaluation of the characteristic of the layer 505 of 
the substrate in relation to the doping amount (density) of boron atoms. 
The evaluation items are (1) the plane orientation of the crystal surface 
in the region 507, (2) ratio of the number of grain boundaries generated 
in the region 508 with respect to that of the region 507, (3) the surface 
roughness of the layer and (4) the conductivity of the region 507. 
As can be seen from the table, a preferable characteristic can be obtained 
when the B atom doping density in the region 505 is 10.sup.20 to 10.sup.21 
cm.sup.-3 wherein the grain boundaries are concentrated to generate in the 
region 508. 
Since B atom forms the acceptor level, the region 507 bears P type 
semiconductor characteristics due to the diffusion of B atoms from the 
regions 505 in the both sides thereof after the recrystallization process. 
Also, the conductivity of the region 507 increases when the doping amount 
of the B atoms in the regions 505 is increased so that the diffusion of 
the atoms is enhanced. 
Accordingly, it becomes possible to shorten the time of manufacturing 
process of MOS transistors and upgrade the characteristic thereof by using 
the region 507 as the active region of the transistor and the region 508 
as the source/drain regions thereof. 
TABLE 4 
______________________________________ 
GRN 
B ATOM BND. CNDCTIVITY 
IN 505 PLN SUFC OF 508 OF 507 
(cm.sup.-3) 
ORNTN ROUGH. (%) (S) 
______________________________________ 
10.sup.17 
(100) X 40 0.003 
10.sup.18 
(100) .DELTA. 60 0.02 
10.sup.19 
(100) .DELTA. 80 0.5 
10.sup.20 
(100) .largecircle. 
100 3 
10.sup.21 
(100) .largecircle. 
100 10 
______________________________________ 
EXAMPLE 5 
A fifth example of the actually produced substrate in accordance with the 
present invention is described hereinafter with reference again to FIGS. 
6a and 6b. 
The support member 501 comprises a P type silicon wafer which is mirror 
grinded and has a thickness of 0.5 mm. The silicon wafer 501 is heated to 
temperature of 1000.degree. C. in an atmosphere of oxygen gas to form an 
oxide film 502 of SiO.sub.2 having a thickness of 0.5 .mu.m on the wafer 
501. A polycrystal silicon 503 is deposited on the film 502 by an LPCVD 
method to form a film of 0.5 .mu.m thick. Phosphorus (P) atoms are 
implanted into the film 503 to form strip shaped diffusion regions 505 at 
a regular interval by an ion implantation method. The density of P atoms 
implanted is 10.sup.17 to 10.sup.21 cm.sup.-3. The width of the strip 
shaped region 505 is 5 .mu.m. The width of the region 504 between every 
two adjacent regions 505 is 50 .mu.m. A surface protection layer 506 of 
SiO.sub.2 is deposited on the film 503 to form a film of 1.5 .mu.m thick 
thereon by an LPCVD method. 
The substrate treated as mentioned above is then subjected to the zone melt 
recrystallization process using an Ar laser under the condition that the 
input power is 15 W, the scanning speed is 10 cm/sec and that the 
temperature of the substrate is 450.degree. C. 
The polycrystal silicon layer 503 is deposited by an LPCVD method using 
SiH.sub.4 gas and N.sub.2 gas under the condition that the gas flow rate 
ratio of SiH.sub.4 and N.sub.2 is 1/10 and that the temperature of the 
substrate is 650.degree. C. 
The surface protection layer 506 is deposited by an LPCVD method using 
SiH.sub.4 gas and N.sub.2 O gas under the condition that the gas flow rate 
ratio of SiH.sub.4 and N.sub.2 O is 1/50 and that the temperature of the 
substrate is 750.degree. C. 
Table 5 represents the evaluation of the characteristic of the layer 505 of 
the substrate in relation to the doping amount (density) of P atoms. The 
evaluation items are (1) the plane orientation of the crystal surface in 
the region 507, (2) ratio of the number of grain boundaries generated in 
the region 508 with respect to that of the region 507, (3) the surface 
roughness of the layer and (4) the conductivity of the region 507. 
As can be seen from the table, a preferable characteristic can be obtained 
when the P atom doping density in the region 505 is 10.sup.20 to 10.sup.21 
cm.sup.-3 wherein the grain boundaries are concentrated to generate in the 
region 508. 
Since P atom forms the donor level, the region 507 bears N type 
semiconductor characteristics due to the diffusion of P atoms from the 
regions 505 in the both sides thereof after the recrystallization process. 
Also, the conductivity of the region 507 increases when the doping amount 
of the P atoms in the regions 505 is increased so that the diffusion of 
the atoms is enhanced. 
Accordingly, it becomes possible to shorten the time of manufacturing 
process of MOS transistors and upgrade the characteristic thereof by using 
the region 507 as the active region of the transistor and the region 508 
as the source/drain regions thereof. 
TABLE 5 
______________________________________ 
P ATOM GRN BND. CNDCTIVITY 
IN 505 PLN SUFC OF 508 OF 507 
(cm.sup.-3) 
ORNTN ROUGH. (%) (S) 
______________________________________ 
10.sup.17 
(100) X 50 0.003 
10.sup.18 
(100) .DELTA. 60 0.08 
10.sup.19 
(100) .DELTA. 80 0.3 
10.sup.20 
(100) .largecircle. 
100 4 
10.sup.21 
(100) .largecircle. 
100 18 
______________________________________ 
EXAMPLE 6 
A sixth example of the actually produced substrate in accordance with the 
present invention is described hereinafter with reference to FIGS. 7a, 7b 
and 7c. 
FIGS. 7 are explanatory sectional views of a MOS transistor using the 
substrate of the fifth example 5 mentioned before for explaining the 
structure thereof. 
FIG. 7a represents the single crystal silicon substrate of the example 5. 
The substrate comprises a P-type silicon wafer 501, an oxide film 502 of 
0.5 .mu.m thick, a surface protection layer 506 of SiO.sub.2 having a 
thickness of 1.5 .mu.m, n-type single crystal regions 507 which are formed 
at a regular interval and contain no grain boundaries and each of which 
regions 507 has a strip shape of 50 .mu.m wide and a conductivity of 0.3 
s, and n-type single crystal regions 508 which are formed at a regular 
interval and contain grain boundaries therein and each of which regions 
508 has a strip shape of 10 .mu.m wide and a conductivity of 130 s. 
FIG. 7b is a constructional view of a MOS transistor using the substrate of 
FIG. 7a. 
FIG. 7c is an enlarged view of the transistor of FIG. 7b. 
The transistor comprises an SiO.sub.2 region 601 which is subjected to an 
element separation treatment by a LOCOS method, a thermal oxidation gate 
film 602 having a thickness of 1000 .ANG., a polycrystal silicon gate 
electrode 603 of 5000 .ANG. thick deposited by an LPCVD method, aluminum 
electrodes 604 of 1.5 .mu.m thick, a source region 508 as explained in 
FIG. 7a, and a drain region 509 as explained also in FIG. 7a. 
FIG. 8 is a graphical view of drain current (Id) in relation to gate 
voltage (Vg) on the condition that a bias voltage V.sub.DS =0.1 V is 
applied between the source and the drain of the transistor. The drain 
current is represented in a logarithmic scale. The gate length of the 
transistor is 50 .mu.m and the gate width thereof is 100 .mu.m. 
It can be seen from FIG. 8 that the transistor functions in an enhancement 
mode and the electron mobility .mu.m is 764/cm, which guarantees an 
adequate characteristic as the bulk single crystal silicon. 
EXAMPLE 7 
A seventh example of the actually produced substrate in accordance with the 
present invention is described hereinafter with reference again to FIGS. 
5a and 5b. 
The insulation member 401 comprises an Al.sub.2 O.sub.3 plate which is 
mirror grinded and has a thickness of 1 mm. A polycrystal silicon 402 is 
deposited on the plate 401 by an LPCVD method to form a film of 0.5 .mu.m 
thick. Phosphorus (P) atoms are implanted into the film 402 to form strip 
shaped diffusion regions 403 at a regular interval by an ion implantation 
method. The density of P atoms implanted is 10.sup.17 to 10.sup.21 
cm.sup.-3. The width of the region 404 between every two adjacent regions 
403 is 50 .mu.m. A surface protection layer 405 of SiO.sub.2 is deposited 
on the film 402 to form a film of 1.5 .mu.m thick thereon by an LPCVD 
method. 
The substrate treated as mentioned above is then subjected to the zone melt 
recrystallization process using the device of FIG. 3 under the condition 
that the input power is 9.7 KW and that the scanning speed is 0.1 mm/sec. 
FIG. 5b illustrates the substrate in the state after the treatment of zone 
melt recrystallization process. 
The polycrystal silicon layer 402 is deposited by an LPCVD method using 
SiH.sub.4 gas and N.sub.2 gas under the condition that the gas flow rate 
ratio of SiH.sub.4 and N.sub.2 is 1/10 and that the temperature of the 
substrate is 650.degree. C. 
The surface protection layer 405 is deposited by an LPCVD method using 
SiH.sub.4 gas and N.sub.2 O gas under the condition that the gas flow rate 
ratio of SiH.sub.4 and N.sub.2 O is 1/50 and that the temperature of the 
substrate is 750.degree. C. 
Table 6 represents the evaluation of the characteristic of the layer 403 of 
the substrate in relation to the doping amount (density) of P atoms. The 
evaluation items are (1) the plane orientation of the crystal surface in 
the region 407, (2) ratio of the number of grain boundaries generated in 
the region 406 with respect to that of the region 407, and (3) the surface 
roughness of the layer. 
As can be seen from the table, a preferable characteristic can be obtained 
when the P atom doping density in the region 403 is 10.sup.20 to 10.sup.21 
cm.sup.-3 wherein the grain boundaries are concentrated to generate in the 
region 406. 
The ratio of the grain boundaries formed in the region 406 is decreased 
when the P atom density in the region 403 is decreased. This is because 
the freezing point depression effect is not obtained due to the shortage 
of the P atoms. 
TABLE 6 
______________________________________ 
P ATOM RATIO OF 
DENSITY PLN SUFC GRN BND. 
(cm.sup.-3) 
ORNTN ROUGH. (%) 
______________________________________ 
10.sup.17 (100) X 50 
10.sup.18 (100) .DELTA. 60 
10.sup.19 (100) .largecircle. 
80 
10.sup.20 (100) .largecircle. 
100 
10.sup.21 (100) .largecircle. 
100 
______________________________________ 
Many widely different embodiments of the present invention may be 
constructed without departing from the spirit and scope of the present 
invention. It should be understood that the present invention is not 
limited to the specific embodiments described in the specification, except 
as defined in the appended claims.