U.S. patent application number 09/776269 was filed with the patent office on 2001-08-16 for semiconductor wafer including a dot mark of a peculiar shape and method of forming the dot mark.
Invention is credited to Chiba, Teiichirou, Mori, Akira.
Application Number | 20010014543 09/776269 |
Document ID | / |
Family ID | 18554668 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010014543 |
Kind Code |
A1 |
Chiba, Teiichirou ; et
al. |
August 16, 2001 |
Semiconductor wafer including a dot mark of a peculiar shape and
method of forming the dot mark
Abstract
A fine protruded dot-like mark is formed on part of a
semiconductor wafer surface. A growth layer is grown by epitaxial
treatment on an entire surface of a semiconductor wafer including
the dot mark so as to form a dot mark. During this growth process,
the dot-like mark is changed into a polygon pyramid shape including
a clear ridge line indicating the same azimuth of the crystal axis
as that of the wafer. This ridge line is optically read out so that
the azimuth of the crystal axis of the wafer can be specified.
Therefore, it is possible to obtain a semiconductor wafer including
a dot mark having a peculiar shape excellent in optical visibility
and indicating the azimuth of the crystal axis and to provide a
method of forming the dot mark.
Inventors: |
Chiba, Teiichirou;
(Kanagawa-ken, JP) ; Mori, Akira; (Kanagawa-ken,
JP) |
Correspondence
Address: |
Bell, Boyd & Lloyd LLC
P.O. Box 1135
Chicago
IL
60690-1135
US
|
Family ID: |
18554668 |
Appl. No.: |
09/776269 |
Filed: |
February 2, 2001 |
Current U.S.
Class: |
438/758 ;
257/E21.102; 257/E23.179 |
Current CPC
Class: |
H01L 2223/5442 20130101;
H01L 23/544 20130101; C30B 25/18 20130101; H01L 2924/0002 20130101;
H01L 2924/00 20130101; H01L 2924/0002 20130101; H01L 2223/54453
20130101 |
Class at
Publication: |
438/758 |
International
Class: |
H01L 021/31 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 7, 2000 |
JP |
P2000-29396 |
Claims
What is claimed:
1. A semiconductor wafer including a dot mark protruded from a
surface of a semiconductor wafer at an arbitrary position, wherein
said dot mark has a shape that allows an azimuth of a crystal axis
to be optically recognized.
2. A semiconductor wafer according to claim 1, wherein said dot
mark includes a ridge line indicating the azimuth of the crystal
axis.
3. A semiconductor wafer according to claim 2, wherein the shape of
said dot mark is either of a polygonal pyramid or a truncated
polygonal pyramid each having polygonal faces.
4. A semiconductor wafer according to any one of claims 1 to 3,
wherein said dot mark is formed on part of a peripheral face of the
semiconductor wafer.
5. A method of forming at least one dot mark having a peculiar
shape, comprising steps of: forming a dot-like mark having an
arbitrary shape protruded from a surface of a semiconductor wafer
at a predetermined position of the semiconductor wafer; forming a
thin film composed of a single crystal on an entire surface of said
semiconductor wafer by epitaxial growth; and during said epitaxial
growth, converting said dot-like mark into either of a polygonal
pyramid shape or a truncated polygonal pyramid shape each having
polygonal faces and including a ridge line indicating an azimuth of
a crystal axis.
6. A method according to claim 5, wherein a maximum length of the
dot-like mark parallel to the surface of the semiconductor wafer is
1 to 15 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor wafer that
includes a dot mark having a peculiar shape and formed on a part of
the wafer. More particularly, it relates to a semiconductor wafer
including a dot mark having a shape that is excellent in optical
visibility and enables the azimuth of a crystal axis of the
semiconductor wafer to be optically recognized. It also relates to
a method of forming such a dot mark.
[0003] 2. Description of the Related Art
[0004] Electric characteristic of silicon, which is a substrate
material of a semiconductor integrated circuit, depends on the
azimuth of a crystal axis thereof. Therefore, when a circuit is
printed onto a silicon wafer, which is a substrate material of a
general semiconductor, its circuit pattern has to be matched with
the azimuth of a crystal axis of the material. Thus,
conventionally, a mark indicating the azimuth of the crystal axis
is made on the semiconductor wafer.
[0005] As a typical example of this mark, an orientation flat is
formed by cutting out part of a disc-shaped semiconductor wafer
along a chord of the semiconductor wafer, which is perpendicular to
the azimuth of its crystal axis. Generally, such an orientation
flat is applied to a semiconductor wafer 150 mm in diameter.
Sometimes it is also applied to a wafer 200 mm in diameter.
Recently, as the semiconductor wafer to be used has been enlarged
(diameter: 200 mm or more), a V-shaped notch has been applied for a
mark. The V-shaped notch is formed in part of a periphery of a
semiconductor wafer such that the azimuth of its crystal axis is
matched with a line connecting a vertex of the V-shaped notch with
a center of the wafer. This is because a demand of the
manufacturers who want to obtain as many semiconductors integrated
circuits as possible by enlarging the semiconductor wafer.
Furthermore, minute disparity in film-forming quality during
formation of the circuits due to the orientation flat has
significantly influenced upon the degree of integration.
[0006] However, the azimuth mark of the aforementioned notch can
also make a disadvantageous influence upon the degree of
integration. Furthermore, because the notch forms a minute space,
dust such as contamination or the like tends to be accumulated in
the notch. Therefore, considering such influence, there has been a
trend that the azimuth of the crystal axis on the semiconductor
wafer is indicated by marking with a laser marker, instead of the
aforementioned markings. However, marking of the azimuth of the
crystal axis by the laser marker has not been so standardized as
the aforementioned marking technology because it accompanies change
of the existing equipment and leads to an increase of production
cost.
[0007] On the other hand, through a manufacturing process for a
semiconductor wafer and a semiconductor device, a laser marker is
often used for marking management information including ID
information, processing history and electric characteristics on
part of the semiconductor wafer surface. Therefore, if a mark
formed by the laser marker only indicates the azimuth of the
crystal axis of the semiconductor wafer directly, the azimuth of
the crystal axis need not to be measured by preliminarily using an
X ray. Further, the semiconductor wafer does not need to be cut out
at all. Therefore, this method can satisfy both the demands of the
wafer manufacturers and the semiconductor device manufacturers.
SUMMARY OF THE INVENTION
[0008] The present invention has been achieved in views of these
circumstances. Specifically, an object of the present invention is
to provide a semiconductor wafer having a single azimuth mark or
plural azimuth marks, which is not affected by cutting out and
enables the azimuth of a crystal axis to be recognized by the mark
or marks, by means of combining improved laser marking technology
with ordinary general processing technology. Furthermore, the
present invention has an object to provide a method of forming a
mark having such peculiar characteristics.
[0009] The inventors of the present invention proposed a dot mark
having a peculiar shape, which is different from a conventional dot
mark of a concave hole type dot mark formed by means of
conventional laser marking technology, and a forming method thereof
through Japanese Patent Application No. 10-334009. The dot mark
according to the invention of this prior application is formed by
marking a surface of a product to be marked by laser beam as an
energy source. A center portion of each of the dot marks has a
protruded portion which is protruded upward from the surface of the
product to be marked. This is a very fine dot mark having a length
of 1 to 15 .mu.m along the marking surface, and a height of the
protruded portion in a range of 0.01 to 5 .mu.m. This dot mark has
an optically excellent visibility in spite that it is such a very
fine dot mark.
[0010] When the inventors formed a thin film on the mark forming
surface of the semiconductor wafer which has the aforementioned dot
mark with such a protruded portion by expitaxial growth, they found
that its initial dot shape had changed to a different one. Then,
the inventors repeated experiments by changing a length of the dot
mark along the marking surface and changing a thickness of a single
crystal by the aforementioned epitaxial growth. Consequently, it
has been found that if the thickness of the grown crystal is within
an appropriate range, the dot mark grows to a polygonal pyramid or
truncated polygonal pyramid having clear ridge lines. Furthermore,
when the inventors formed a single crystal by epitaxial growth
after forming the plural dot marks on the surface of the
semiconductor wafer, they found that the respective dot marks have
the same shapes after their shapes are changed and further, the
corresponding ridge lines are oriented in the same direction.
[0011] The inventors further considered that the ridge lines were
somehow related to the azimuth of the crystal axis. Therefore, they
measured the azimuth of the crystal axis in the semiconductor wafer
after the epitaxial growth. Consequently, they found that the ridge
lines coincide with the azimuth of the crystal axis completely.
Although a cause of such a change of the dot mark shape is not
proved, the epitaxial growth apparently grows a crystal having the
same surface azimuth as that of a substrate surface on the single
crystal substrate. Because characteristics such as atomic density
differs depending on the surface azimuth of the substrate, the
growth velocity has an anisotropy of the growth that differs
depending on the surface azimuth.
[0012] Therefore, it can be considered that the velocity of the
epitaxial growth at a minute point protruded from the surface of
the substrate differs depending on the surface azimuth. Therefore,
the minute point will grow to a polygonal pyramid having ridge line
extending along the azimuth of the crystal axis. From this
estimation, it can be considered that the dot mark formed on the
semiconductor prior to the epitaxial growth does not always have to
be formed by a laser marker but may be formed by chemical vapor
deposition method or the like, which also makes it possible to form
a dot mark having a protruded part from the dot mark forming
surface.
[0013] The present invention has been based on the above described
knowledge. According to a first aspect of the present invention,
there is provided a semiconductor wafer including a dot mark
protruded from a surface of a semiconductor wafer at an arbitrary
position, wherein the dot mark has a shape that allows an azimuth
of a crystal axis to be optically recognized.
[0014] Specifically, the dot mark having the aforementioned shape
is formed at an arbitrary position of the semiconductor wafer so
that the azimuth of the crystal axis can be recognized directly
from the shape of the dot mark. Therefore, it is not necessary to
form an orientation flat or a V-shaped notch especially after the
azimuth of the crystal axis is measured. Thus, not only an
apparatus for measuring the azimuth of the crystal axis becomes
unnecessary, but also the cutting part can be eliminated, which
makes it possible to efficiently obtain a number of integrated
circuits.
[0015] Further, because the dot mark for indicating the azimuth of
the crystal axis has no locally deformed portion due to the
orientation flat and V-shaped notch, no dust is accumulated even
through multiple steps processes, so that cleanness can be
maintained.
[0016] Furthermore, according to the first aspect of the present
invention, it is preferable that the dot mark includes a ridge line
indicating the azimuth of the crystal axis. As described
previously, the dot mark formed on the semiconductor wafer after
the epitaxial growth has clear ridge lines, which are oriented
along the azimuth of the crystal axis of the wafer. Therefore, the
azimuth of the crystal axis can be recognized easily by specifying
the azimuth of the ridge lines.
[0017] Still further, according to the first aspect of the present
invention, the shape of the dot mark is specified. Namely, it is
preferably a polygonal pyramid or a truncated polygonal pyramid
each having polygonal faces. If the number of polygonal faces is
even, a diagonal line passing a center of the mark is a straight
line so that the azimuth of the crystal axis can be recognized
easily. Further, the number of the polygonal faces is preferably
six or less. Further, it is more preferable that it has four faces.
In this case, the ridge lines are disposed in a cross shape, so
that when plural dot marks are formed, the ridge lines are arranged
on a straight line, thereby making it possible to recognize the
azimuth of the crystal axis indicated by the straight lines. If the
number of the polygonal faces is eight or more, the entire shape
almost becomes a circle, which makes it difficult to specify the
direction of the ridge lines and the azimuth of the crystal
axis.
[0018] Still further, according to the first aspect of the present
invention, it is preferable that the dot mark is formed on part of
a peripheral face of the semiconductor wafer. Front and rear sides
of the peripheral face of the semiconductor wafer are partially
chamfered. These chamfered regions of the front and rear sides and
a side face region between these chamfered regions are very minute.
Further, these regions are least affected by an interference with a
surrounding apparatus or by chemical polishing in a wafer
production process or a semiconductor device production process.
Particularly, the front and rear side chamfered regions are stable
in configuration. Therefore, if the aforementioned dot mark can be
formed in these regions, it is never eliminated even through many
manufacturing processes, so that the azimuth of the crystal axis
can be always recognized whenever necessary. In order to form a
desired number of dot marks in the aforementioned regions, the dot
marks themselves are required to be fine. In this respect, the dot
mark forming technology of the aforementioned prior invention
proposed by the inventors is very effective.
[0019] According to a second aspect of the present invention, there
is provided a method of forming at least one dot mark having a
peculiar shape, comprising steps of: forming a dot-like mark having
an arbitrary shape protruded from a surface of a semiconductor
wafer at a predetermined position of the semiconductor wafer;
forming a thin film composed of a single crystal on an entire
surface of the semiconductor wafer by epitaxial growth; and during
the epitaxial growth, converting the dot-like mark into a polygonal
pyramid shape or a truncated polygonal pyramid shape each having
polygonal faces and including a ridge line indicating an azimuth of
a crystal axis.
[0020] The dot-like mark, which is to be formed prior to the
epitaxial growth, can be formed easily by means of the laser marker
according to the prior invention proposed by the inventors.
Alternatively, the dot-like mark having such a shape can be formed
by other processing technology, such as chemical vapor growth
method. Further, the aforementioned epitaxial growth method in the
present invention can employ a conventionally well known technology
and it does not have to be modified especially for the present
invention.
[0021] Furthermore, according to the second aspect of the present
invention, it is preferable that a maximum length of the dot-like
mark parallel to the surface of the semiconductor wafer is 1-15
.mu.m. Since the dot-like mark is so fine, a required number of the
dot-like marks can be formed on a peripheral face of the wafer as
described above. Further, this dot mark has an optically excellent
visibility even after the epitaxial growth. Therefore, this can be
used for various kinds of management information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is an explanatory diagram schematically showing an
example of a laser marker for forming a dot-like mark M' having a
peculiar shape according to the present invention.
[0023] FIG. 2 is a three-dimensional view of typical dot-like marks
M' formed by the aforementioned marker and arrangement thereof, as
observed by AFM.
[0024] FIG. 3 is a sectional view of FIG. 2 as observed by the same
AFM.
[0025] FIG. 4 is a three-dimensional view showing an example of the
dot-like mark M' according to an embodiment of the present
invention, as observed by the AFM.
[0026] FIG. 5 is a three-dimensional view showing an example of the
dot-like mark M' according to another embodiment of the present
invention, as observed by the AFM.
[0027] FIGS. 6A through 6D are plan views for showing changes of
the shape of the dot-like mark shown in FIG. 4 to that after the
epitaxial growth, as observed by the AFM.
[0028] FIGS. 7A through 7D are plan views for showing changes of
the shape of the dot-like mark shown in FIG. 5 to that after the
epitaxial growth, as observed by the AFM.
[0029] FIGS. 8A through 8D are three-dimensional views of enlarged
marks corresponding to FIG. 6.
[0030] FIGS. 9A through 9D are three-dimensional views of enlarged
marks corresponding to FIG. 7.
[0031] FIG. 10 is an explanatory diagram showing a method for
determining the azimuth of a crystal axis from the dot mark shape
according to the present invention.
[0032] FIG. 11 is an explanatory diagram showing another method of
determining the azimuth of a crystal axis from the dot mark shape
according to the present invention.
DESCRIPTION OF EMBODIMENTS
[0033] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying
drawings.
[0034] First, a preferred example of a laser marker to be used will
be described simply based on the laser marker disclosed in the
aforementioned prior invention as proposed by the present
inventors. This laser marker serves to form dot-like protruded
marks in part of a semiconductor wafer before epitaxial growth of
the present invention.
[0035] Referring to FIG. 1, a laser marker 1 comprises a laser
oscillator 2, a beam homonizer 3 for smoothing energy distribution
of laser beam irradiated from the laser oscillator 2, a liquid
crystal mask 4 which is driven so as to or not to allow the laser
beam to transmit in accordance with a display of a pattern, a beam
profile converter 5 for forming and converting energy density
distribution of laser beam corresponding to each pixel of the
liquid crystal mask 4 to a required distribution formation, and a
lens unit 6 for imaging the beam having passed the liquid crystal
mask 4 on a surface of a semiconductor wafer by the dot. A maximum
length of a single dot on the liquid crystal mask 4 is 50 to 200
.mu.m and a maximum length of a single dot by the lens unit 6 is 1
to 15 .mu.m.
[0036] In the laser marker 1, laser beam having a Gaussian shaped
energy density distribution, which is emitted from the laser
oscillator 2, passed through the beam homonizer 3 so that it is
formed to be top-hat type energy density distribution having
substantially uniform peak values. After the energy density
distribution is thus formed uniformly, the laser beam is irradiated
onto the surface of the liquid crystal mask 4. At this time, as
well known, the liquid crystal mask 4 is capable of driving and
displaying a predetermined marking pattern on the mask.
Consequently, the laser beam transmits pixel portions within the
pattern display region, which are light-transmittable. The
respective energy density distributions of the transmitted light
after divided into respective pixels have the same shape as that
formed by the beam homonizer 3 so that the energy density is
distributed equally.
[0037] The beam homonizer 3 is a general term of an optical
component for forming laser beam having energy density distribution
of, for example, a Gaussian shape to be a smoothed energy density
distribution shape. This optical component may apply, for example,
a method of batch-irradiating laser beam onto a surface of the mask
using fly eye lens, binary optics, or cylindrical lens, or a method
of scanning the surface of the mask by driving a mirror by an
actuator such as a polygonal mirror, a mirror scanner or the
like.
[0038] According to the present invention, as previously described,
the laser beam is controlled such that a pulse width of the laser
beam is 10 to 500 ns and its energy density is 1.0 to 15.0
J/cm.sup.2. Preferably, the energy density is 1.5 to 11.0
J/cm.sup.2. When the laser beam is controlled within such a
numerical value range, the aforementioned dot mark having a
peculiar shape of the present invention can be formed.
[0039] According to this embodiment, a region of the liquid crystal
mask 4 to be irradiated once is 10.times.11 dots. Although those
dots are all irradiated by laser beam at one time, the number of
the dots often does not meet a required number of dot marks. In
such a case, it is permissible to divide a mark pattern into
several sections, display these sections successively on the liquid
mask and switch them, so that an entire mark pattern is formed on a
surface of the wafer by combining those divided sections. In this
case, it is necessary to control and move the wafer or an
irradiation position when the laser beam is imaged on the surface
of the wafer. For such control method, various methods, which are
well known conventionally, can be applied.
[0040] The laser beam in dots having passing the liquid crystal
mask 4 is irradiated to the beam profile converter 5. This beam
profile converter 5 is arranged in a matrix so as to correspond to
the individual liquid crystals disposed in a matrix in the liquid
crystal mask 4. Therefore, the laser beam having transmitted the
liquid crystal mask 4 passes the beam profile converter 5 dot by
dot in one-to-one correspondence, so that the laser beam having
smoothed energy density distribution by the beam homonizer 3 is
converted to an energy density distribution required for forming a
dot mark having a fine hole peculiar to the present invention.
Although according to this embodiment, the laser beam having passed
the liquid crystal mask 4 is made to pass the beam profile
converter 5 so as to convert its energy density distribution, it is
permissible to introduce the laser beam directly to the lens unit 6
without converting the profile of the energy density distribution
by the beam profile converter 5.
[0041] The laser beam having passed the beam profile converter 5 is
contracted by the lens unit 6 and irradiated to a predetermined
position on the surface of a semiconductor wafer W, so that a
necessary dot marking is made on that surface. According to the
present invention, if a maximum length of a single pixel of the
liquid crystal is 50 to 2000 .mu.m, the pixel is contracted to 1 to
15 .mu.m on the surface of the semiconductor wafer W by the lens
unit 6. If this micro marking is intended to be made equally on the
surfaces of the plural wafers, it is necessary to adjust a distance
between the marking surface and the condensing lens as well as an
optical axis thereof by the unit of micron. According to this
embodiment, for detection of a focal point, a height is measured by
a confocal method that is used generally in a laser microscope and
then, its measurement result is fed back to a minute positioning
mechanism in a vertical direction of the lens so that the focal
point is automatically determined. Generally known methods are used
for setting the optical axis and positioning and adjusting of
optical components. For example, it is permissible to adjust them
to a reference spot, which is preliminarily set, by a screw
adjustment mechanism through a guide beam such as He--Ne laser.
This adjustment only has to be carried out once during the
assembly.
[0042] A fine dot-like mark M' according to this embodiment has a
maximum length in a range of 1 to 15 .mu.m, and a substantial
height dimension in a range of 0.01 to 5 .mu.m considering that a
surrounding of its protruded portion is slightly dented. In order
to form the dot-like mark M' having such dimensions, the length of
one side of each dot of the liquid crystal mask 4 has to be 50 to
2000 .mu.m so as not to cause a collapse in the image formation on
an irradiated point on the surface of the semiconductor wafer W due
to resolution or the like of a condensing lens unit. Further, if a
distance between the beam profile converter 5 and the liquid
crystal mask 4 is too large or too small, the laser beam tends to
be affected by light in the surrounding or unstable condition of
the optical axis so that the image formation on the surface of the
semiconductor wafer tends to be disordered. Thus, according to this
embodiment, a distance X between the beam profile converter 5 and
the liquid crystal mask 4 is set to be 0 to 10 times a maximum
length Y of each of the pixels of the liquid crystal mask 4. By
setting the distance X within such a range, the image formation on
the surface of the wafer becomes clear.
[0043] The aforementioned beam profile converter 5 is an optical
component for converting the energy density distribution smoothed
by the beam homonizer 3 into an optimum energy density distribution
so as to obtain a dot shape peculiar to the present invention. This
converter 5 serves to convert a profile of the energy density
distribution of an incident laser beam into an arbitrary shape by
making diffraction phenomenon, refraction phenomenon or arbitrarily
varying light transmittance at a laser irradiation point. As the
optical component, for example, a holographic optical element, a
convex type micro lens array, or liquid crystals can be employed.
These devices are disposed in a matrix so as to construct the beam
profile converter 5.
[0044] FIGS. 2 and 3 show a typical example of a shape and an
arrangement of the dot marks formed according to the method of the
present invention. FIG. 2 is a three-dimensional view observed by
means of an AFM and FIG. 3 is a sectional view observed by the AFM.
According to this embodiment, each dot-like mark M' imaged on the
surface of the semiconductor wafer W is a square of 3.6
.mu.m.times.3.6 .mu.m and an interval between the respective dots
is set to be 4.5 .mu.m.times.4.5 .mu.m. As understood from these
Figures, substantially conical dot-like marks M' are formed on the
surface of the semiconductor wafer W, each of which corresponds to
each divided laser beam corresponding to each pixel of the liquid
crystal mask 4. Further, the dot-like marks M' are arranged orderly
in the formation of 11.times. 10 and their heights are arranged
substantially equally. This is because the energy distribution of
laser beam irradiated to the liquid crystal mask 4 has been
smoothed uniformly by the beam homonizer 3.
[0045] FIGS. 4 and 5 respectively show a shape of the dot-like mark
M' peculiar to the present invention, which is formed under a
condition of the method of the present invention by the laser
marker 1 employed in this embodiment, and a shape of a dot-like
mark M' formed under another condition by the laser marker 1. The
specification of the laser marker 1 is as follows:
1 Laser medium Nd. YAG laser Laser wavelength 532 nm Mode TEM00
Average output 4W @ 1 KHz Pulse width 100 ns @ 1 KHz
[0046] Although the wavelength of the laser beam here is 532 nm, it
should not be limited to be so uniformly.
[0047] As a laser beam to be used in this embodiment, the second
harmonic of a YAG laser oscillator or a YVO4 laser oscillator and a
laser beam oscillated by titan sapphire laser oscillator or the
like can be employed.
[0048] As shown in FIGS. 4 and 5, a shallow ring-like concave
portion is formed around the dot-like mark M' and the center of the
dot-like mark M' protrudes upward to form a substantially conical
protruded portion. According to this dot shape, a portion having a
very high luminance is formed on that protruded portion so that a
difference of the luminance from the surrounding is increased.
Consequently, a sufficient visibility can be secured. According to
the dot-like mark shape prior to the epitaxial growth and the dot
marking method of this embodiment, it is possible to form a single
fine dot-like mark M' having a uniform shape of {fraction (3/20)}
to {fraction (1/100)} as large as the conventional one accurately
and neatly in a region for each of the dots on the surface of the
semiconductor wafer. Furthermore, the dot-like mark M' has such a
peculiar shape that its center portion is protruded unlike the
conventional ones.
[0049] Thus, the dot-like mark M' of this embodiment is made to be
fine to a larger extent than the conventional dot marks. Further,
because a boundary between adjacent dot-like marks M' can be
recognized clearly, a larger number of dot-like marks M' can be
formed in the same region. Consequently, not only the marking
region is increased largely, but also options of such a marking
region are increased.
[0050] According to the present invention, after the dot-like mark
M' is thus formed on the surface of the semiconductor wafer by the
above described method, a crystal layer composed of a new single
crystal is formed on the wafer surface including the same mark by
epitaxial growth.
[0051] According to this embodiment, the dot-like mark shape prior
to the aforementioned epitaxial growth is obtained by imaging an
optical image of the respective squares 9 .mu.m.times.9 .mu.m and 4
.mu.m.times.4 .mu.m by the laser beam on the surface of the
semiconductor wafer composed of Si single crystal. As understood
from FIGS. 6A and 7D, the obtained protruded dot-like mark shape is
not a pyramid but just a circular cone, which shows that it is not
always analogous to an optical image by laser beam in a plan view.
Further, according to this embodiment, difference of the dot shapes
are compared with each other when the crystal layer formed by the
epitaxial growth have thickness of 1 .mu.m, 5 .mu.m and 10 .mu.m
respectively.
[0052] For the epitaxial growth according to this embodiment,
chemical vapor phase growth method is employed. According to this
epitaxial growth, generally, a wafer is placed on a SiC coat carbon
pedestal, which is a heating body, and then, it is put in a growth
furnace. Then, the wafer is heated in an atmosphere of hydrogen
under a high temperature of about 1000 to 1200.degree. C. according
to high frequency method, resistance heating method or lamp heating
method. After that, the surface of the wafer is gas etched in depth
of 0.1 to 0.4 .mu.m by hydrogen diluted chlorine or sulfur
hexafluoride gas so that a clean silicon surface is exposed.
[0053] After this gas etching is completed, mixed gas composed of
reactive gas such as mono-silane gas or dopant gas is fed into a
furnace so that silicon single crystal is epitaxial grown on the
surface of the wafer. At this time, the thickness of the
epitaxially grown layer is determined by the growth time. It is
determined by concentration, flow rate, flow velocity, temperature,
pressure and the like of reactive gas. Therefore, the thickness and
the time of the growth are determined after those relations are
accurately recognized.
[0054] FIGS. 6A and 7A show the shapes of the dot-like marks M'
formed by the laser marker prior to the epitaxial growth, in which
each center portion is protruded on the surface of the
semiconductor wafer. FIGS. 6B to 6D and 7B to 7D respectively show
the dot mark shapes of the invention in plan views, which are
formed on the surface of the semiconductor wafer having the
dot-like marks M' shown in FIGS. 6A and 7A when the growth layer is
formed by epitaxial growth so as to have a thickness of 1 .mu.m, 5
.mu.m and 10 .mu.m respectively. FIGS. 8A to 8D and FIGS. 9A to 9D
are enlarged perspective views of the dot marks of FIGS. 6A to 6D
and FIGS. 7A to 7D.
[0055] As evident from these diagrams, it is understood that the
grown layer by the epitaxial growth is changed such that a vertex
of the dot mark M becomes a smooth surface with an increase of the
thickness of the grown layer, irrespective of the size of the
dot-like mark M' initially formed on the surface of the
semiconductor wafer. More specifically, the dot mark M has a
pyramid shape of a complete square when the thickness of the
epitaxial growth layer is 1 to 5 .mu.m, so that ridge lines
extending from the vertex of the dot mark M in a cross shape are
clear. If the thickness of the growth layer is 5 to 10 .mu.m,
however, the aforementioned pyramid shape is changed to a truncated
pyramid having a flat top portion, instead of the aforementioned
pyramid shape. Further, the smaller the size of the dot-like mark
M' is formed initially, the more the top portion of the pyramid is
truncated, so that its resultant shape becomes almost a simple cube
of a small height.
[0056] Although in the shown example, a silicon wafer in which the
azimuth of its crystal axis is <100> is used and the dot mark
shape after the epitaxial growth is a pyramid or a truncated
pyramid as described previously, the azimuth of the crystal axis on
a generally used wafer is often <111>. Even with this
azimuth, the dot mark after the epitaxial growth provides a
polygonal pyramid having or a truncated polygonal pyramid having
ridge lines. Therefore, this azimuth of the crystal axis can be
specified by the ridge lines as the azimuth of the crystal axis of
<100>.
[0057] In any way, what should be noted here is that the direction
of the ridge lines of all the dot marks M formed on the same wafer
surface are the same. Therefore, as described above, the extension
of the ridge lines coincides with the azimuth of the crystal axis
of the semiconductor wafer. FIGS. 10 and 11 are explanatory
diagrams showing a method of determining the azimuth of the crystal
axis of the wafer by using such phenomenon.
[0058] That is, as shown in FIG. 10, a single protruded dot-like
mark M' is formed near a peripheral face of the surface of the
semiconductor wafer by the aforementioned laser marker. Then,
epitaxial treatment is carried out on the entire surface of the
semiconductor wafer including that formed single protruded dot-like
mark M' so that a grown crystal layer is formed. The ridge lines,
which are optically clearly recognizable, are formed on the dot
mark M whose shape has been changed by formation of this grown
crystal layer as described before. The azimuth of the ridge lines
directly indicates the azimuth of the crystal axis.
[0059] According to a method of determining the azimuth as shown in
FIG. 11, first, two protruded dot-like marks M' are formed near a
peripheral face of the surface of the semiconductor wafer along a
diameter of the semiconductor wafer and three protruded dot-like
marks M' are formed linearly perpendicularly to the diameter under
the same processing condition by the aforementioned laser marker.
Next, expitaxial treatment is carried out on the entire surface of
the semiconductor wafer including the four protruded dot-like marks
M' so that the grown crystal layer is formed. The ridge lines,
which are optically clearly recognizable, are formed on the four
dot marks M whose shapes have been changed by formation of the
growth crystal layer. A linear direction connecting the ridge lines
of the two dot marks M arranged in the diameter direction and a
linear direction connecting the ridge lines of the two dot marks
disposed perpendicularly to that diameter respectively indicate the
azimuth of the crystal axis. When the azimuth of the crystal axis
is determined by such plural dot marks M, an azimuth can be
obtained with a higher precision than the azimuth determined by a
single dot mark M.
[0060] In the above-described example, the dot marks M are formed
on the surface of the wafer subjected to mirror treatment. The dot
mark having a fine shape has an excellent visibility as evident
from FIGS. 6 and 7. Therefore, when the dot mark M is formed on a
peripheral face of the wafer less affected by various film forming
treatment or circuit forming treatment, the dot mark can be used
effectively not only for determining the azimuth of the crystal
axis, but also for wafer management information as the conventional
ones.
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