Semiconductor laser element structure

A semiconductor laser device element substrate includes a plurality of semiconductor laser device elements arranged in an array on a semiconductor substrate, the array including a plurality of rows and a plurality of columns, laser resonator facets being located at the boundaries between respective rows of the semiconductor laser device elements, and element separation guiding grooves, for guiding separation of the substrate into a plurality of divided semiconductor laser devices, the grooves being located at the boundaries between the semiconductor laser device elements of the respective columns, wherein the element separation guiding grooves are arranged at positions on different straight lines running in the column direction for each group at least two adjacent rows. Therefore, even if some forces are applied to the substrate, the forces are not concentrated on a point, whereby wafer cracking can be prevented.

FIELD OF THE INVENTION 
The present invention relates to a semiconductor laser element substrate 
and a method for producing a semiconductor laser device, and, more 
particularly, to a semiconductor laser element substrate that includes 
element separation guiding grooves and a method for producing a 
semiconductor laser device using this semiconductor laser element 
substrate. 
BACKGROUND OF THE INVENTION 
FIG. 7 is a perspective view of a prior art semiconductor laser having 
element separation guiding grooves viewed from the bottom surface side, 
and FIGS. 8(a) to 8(e) are perspective views illustrating process steps in 
a production method thereof. 
In the figures, reference numeral 1 designates a semiconductor laser 
substrate of about 3 cm.times.3 cm on which a plurality of semiconductor 
lasers each having the area of about 300 .mu.m.times.300 .mu.m are 
produced in an array comprising a plurality of rows and a plurality of 
columns on an n-type GaAs substrate that is processed at the front 
surface. Reference numeral 2 designates a glass plate for adhering to the 
semiconductor substrate 1. Reference numeral 3 designates wax for adhering 
the plate. Reference numeral 4 designates a photoresist which becomes an 
etching mask. Reference numeral 5 designates an element separation guiding 
groove for separating the plural semiconductor lasers in an array. 
Reference numeral 6 designates gold plated on a rear surface of each 
semiconductor laser, which becomes an electrode. Reference numeral 7 
designates a blade for separating elements. 
A laser resonator in a semiconductor laser is conventionally produced by 
cleaving facet of a crystal. To realize this, the substrate 1 is made as 
thin as 100 .mu.m so that cleavage of the crystal is smoothly carried out. 
After producing the laser resonator by cleaving, the wafer is divided into 
respective elements. In order to facilitate this element separation, a 
method of providing element separations guiding grooves on the substrate 
is often employed. 
A description will be given of a flow for producing element separation 
guiding grooves for semiconductor lasers produced on the n-type GaAs 
substrate with reference to FIGS. 8(a) to 8(e). 
First, the semiconductor laser substrate 1 of which front surface 
processing has been completed is attached to the glass plate 2 by wax 3 at 
the front surface of the substrate. A material having almost the same 
thermal expansion coefficient as the substrate 1 is employed as the glass 
plate 2, and a material which is melted at around 100.degree. C. is 
employed as the wax 3. The whole thickness of the substrate 1 is made 100 
.mu.m by lapping the rear surface (FIG. 8(a)). 
Next, a stripe shaped resist pattern 4 having a width of about 7 .mu.m is 
formed on the rear surface of the substrate 1 between the elements formed 
on the front surface of the substrate 1. Successively, the substrate 1 is 
etched through apertures of the pattern by an etchant such as a 
bromine-methanol solution and a mixture of tartaric acid and hydrogen 
peroxide, thereby producing V-shaped element separation guiding grooves 5 
each having the depth of about 7 .mu.m (FIG. 8(b)). 
The element separation guiding grooves 5 are grooves for facilitating the 
element separation as described above, and in order to surely perform 
separation along this groove 5, the configuration of the groove is 
required to be a V-shape having an acute angle. Generally, since an active 
region is formed along the (011) direction (the direction perpendicular to 
the (011) surface) in a semiconductor laser, an element separation guiding 
groove is also produced in the (011) direction. Therefore, it is necessary 
to form the grooves at the rear surface of the substrate in order to form 
the V-shaped grooves utilizing the difference in etching rate of various 
crystal surfaces by a bromine-methanol solution or a mixture of tartaric 
acid and hydrogen peroxide. 
After forming the element separation guiding grooves 5 through the 
above-described steps, an electrode 6b is formed on the entire rear 
surface by vapor deposition, and gold 6a is plated for each element, 
forming electrodes. Thereafter, a heat treatment at about 400.degree. C. 
is conducted in order to make an ohmic contact of the electrode, and the 
semiconductor laser substrate 1 and the glass plate 2 are separated by 
heating and melting the wax 3 (FIG. 8(c)). 
Next, in order to form a laser resonator, the laser is attached to a 
pressure sensitive adhesive sheet and a wafer is cleaved, i.e., a crystal 
is cleaved by making a flat at an end of the wafer and by dividing the 
wafer along the crystal surface from the flat, and bars in which the 
elements are arranged on a line is produced (FIG. 8(d)). 
At last, the wafer is separated from the pressure sensitive adhesive sheet, 
the blade 7 is applied to a portion of the wafer from the side opposite 
the element separation guiding groove 5 on the rear surface of the wafer, 
and the wafer is divided into respective elements (FIG. 8(e)). 
The production method of the prior art semiconductor laser is constituted 
as described above, and the element separation guiding grooves are formed 
on straight lines from one end to an other end of the substrate 1 which 
has an extremely weak mechanical strength after being lapped to the 
thickness of 100 .mu.m. Therefore, during the process, for example, when 
the wafer is held with a tweezer after the substrate 1 is separated from 
the glass plate 2, the substrate 1 is unfavorably cracked from the element 
separation guiding groove 5 even when only a little force is applied. Not 
only does the later process become difficult but also the yield is 
.significantly lowered. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a semiconductor laser 
device element substrate that enables element separation similar to that 
of the prior art as well as suppressing wafer cracking during wafer 
processing. 
It is another object of the present invention to provide a method of 
producing a semiconductor laser device employing this semiconductor laser 
device element substrate. 
Other objects and advantages of the present invention will become apparent 
from the detailed description given hereinafter; it should be understood, 
however, that the detailed description and specific embodiment are given 
by way of illustration only, since various changes and modifications 
within the spirit and scope of the invention will become apparent to the 
those skilled in the art from this detailed description. 
According to a first aspect of the present invention, in a semiconductor 
laser device element substrate, element separation guiding grooves 
facilitating the separation of elements are arranged at positions on 
different lines running in the column direction for each row or for each 
several rows. Therefore, even if forces are applied from the outside, the 
forces are not concentrated at a point, whereby wafer cracking hardly 
occurs. 
According to a second aspect of the present invention, in a semiconductor 
laser device element substrate, gold forming a part of an electrode of a 
laser element is plated close to the element separation guiding grooves 
which are arranged at positions on different lines running in the column 
direction for each of row or for each several rows of elements. Therefore, 
the plated gold functions as a material for reinforcing the neighboring 
separation groove portion, whereby wafer cracking hardly occurs. 
According to a third aspect of the present invention, a method for 
producing a semiconductor laser device includes a step of attaching a 
semiconductor laser element substrate for which front surface processing 
has been to a glass plate with wax at the front surface of the substrate, 
a step of lapping the entire element substrate to a required thickness, a 
step of producing a resist pattern having stripe shaped apertures on the 
rear surface with shifted positions of the stripe shaped apertures for 
each row or for each several rows of elements in accordance with element 
patterns formed on the front surface of the element substrate, and etching 
portions exposed to the apertures of the resist pattern using the resist 
pattern as a mask thereby to produce element separation guiding grooves, a 
step of producing electrodes on the entire rear surface by vapor 
deposition and then plating gold on respective element positions thereby 
to produce electrodes for the respective laser device elements, a step of 
separating the semiconductor laser element substrate and the glass plate, 
a step of cleaving the substrate to produce resonator facets and producing 
a bar including plural elements arranged on a row or several rows and, at 
last, a step of dividing the bar into plural elements by applying a blade 
to the side opposite the element separation guiding groove of the element 
substrate, to prevent wafer cracking. Further, since the element 
separation guiding grooves are shifted for each several rows, the method 
is applicable to a wafer having a large diameter, resulting in a 
remarkable increase in the yield.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Embodiment 1, 2 
FIG. 1 is a perspective view of a semiconductor laser device element 
substrate viewed from the bottom surface in accordance with a first 
embodiment of the present invention. FIGS. 2(a) to 2(e) are perspective 
views illustrating a process flow of a method for producing a 
semiconductor laser device, using the semiconductor laser device element 
substrate of the first embodiment, in accordance with a second embodiment 
of the present invention. FIGS. 3(a) to 3(f) are cross sectional views 
illustrating a structure of the semiconductor laser device element 
substrate and a process flow for production thereof. In the figures, the 
same reference numerals as those of the prior art designate the same or 
corresponding parts. 
First, a description will be given of a process flow for a semiconductor 
laser device after producing the semiconductor laser element structure on 
a wafer with reference to FIGS. 2(a) to 2(e). 
The semiconductor laser device element substrate 1 which has had a 
production process at the front surface completed is attached to the glass 
plate 2 with wax 3 on the front surface of the substrate 1. The whole 
thickness of the substrate 1 is reduced to 100 .mu.m by lapping the rear 
surface of the substrate 1 (FIG. 2(a)). 
Successively, the stripe-shaped resist pattern 4 having a width of about 7 
.mu.m is formed on the rear surface of the substrate 1 in accordance with 
an element pattern on the front surface of the substrate 1. At this time, 
there is a space of about 50 .mu.m between adjacent elements each having 
the area of about 300 .mu.m.times.300 .mu.m, and positions of the stripe 
patterns are shifted; i.e., offset, by about 20 .mu.m for each adjacent 
element in a column of elements so that the respective patterns are not 
connected to each other on a straight line. Then, by etching the substrate 
1 through apertures of the pattern with an etchant, for example, a mixture 
of tartaric acid and hydrogen peroxide, the V-shaped element separation 
guiding grooves 5 each having the depth of about 7 .mu.m are produced in a 
state where the grooves 5 in a column are disconnected from each other 
(FIG. 2(b)). 
Then, after forming the electrode 6b on the entire rear surface by vapor 
deposition, the gold 6a is plated at a position of each element, forming 
electrodes for respective laser devices. Thereafter, the semiconductor 
laser substrate 1 and the glass plate 2 are separated (FIG. 2(c)). 
Next, in order to produce a laser resonator, the crystal is cleaved, 
producing a bar state where the elements are arranged on a line (FIG. 
2(d)). 
At last, the blade 7 is applied from the side opposite the element 
separation guiding groove 5, and the wafer is divided into respective 
elements (FIG. 2(e)). 
Next, a description will be given of a flow for producing the semiconductor 
laser element structure on the substrate front surface with reference to 
FIGS. 3(a) to 3(f). 
First of all, there are successively grown on an n-type GaAs substrate 10 
by epitaxial crystal growth, for example, MOCVD, an n-type AlGaAs cladding 
layer 11, an undoped AlGaAs active layer 12, a p-type AlGaAs cladding 
layer 13, and a p-type GaAs first contact layer 14 (FIG. 3(a)). 
After the above-described epitaxial crystal growth, an insulating film 15 
such as SiN or SiO.sub.2 is produced on the wafer by, for example, 
sputtering, thermal CVD, or plasma CVD. A photoresist is applied and a 
stripe shaped pattern is produced by photolithography leaving a portion 
corresponding to the width W of a ridge 16. Thereafter, the insulating 
film exposed at each aperture of the photoresist is removed by wet etching 
employing hydrofluoric acid or dry etching employing CF.sub.4, producing 
the stripe shaped insulating films 15 on the wafer, each having the width 
W corresponding to the ridge width. Using this insulating film 15 as an 
etching mask, all the p-type GaAs first contact layer 14 except the ridge 
part 16 and a part of the p-type AlGaAs cladding layer 13 in the thickness 
direction, are etched away leaving the cladding layer 13 about 0.2 .mu.m 
thick (FIG. 3(b)). As an etchant, for example, a mixture of sulfuric acid, 
hydrogen peroxide and water, a mixture of phosphoric acid, hydrogen 
peroxide and water, or a mixture of tartaric acid and hydrogen peroxide is 
employed. 
After the above-described etching, an n-type GaAs current blocking layer 17 
is produced by the second crystal growth (FIG. 3(c)). 
Next, after removing the stripe shaped insulating films 15, the third 
crystal growth is carried out, forming a p-type GaAs second contact layer 
18 (FIG. 3(d)). 
Successively, an electrode 19 comprising a metal, for example, gold or 
titanium, is formed on the p-type GaAs second contact layer 18 by vapor 
deposition, sputtering and the like, and thereafter gold 20 is plated on 
the electrode 19 (FIG. 3(e)). 
Next, after a photoresist 21 is applied on the front surface as a 
protecting film, the wax 3 is applied thereon. Thereafter, the substrate 
front surface where the wax 3 is applied is attached to the glass plate 2 
with the front surface toward the glass plate 2 side, and heated above the 
melting point of the wax 3, fixing the wafer to the glass plate 2. As the 
wax, a material having the melting point of about 100.degree. C. can be 
employed. 
Next, the rear surface side of the n-type GaAs substrate 10 is lapped to a 
thickness of about 100 .mu.m. FIG. 3(f) is a cross sectional view showing 
a state after lapping of the substrate. The perspective view of FIG. 3(f) 
corresponds to the FIG. 2(a). 
In such a semiconductor laser device of this first embodiment, on the 
semiconductor laser element substrate 1 where a plurality of semiconductor 
laser elements are formed, the element separation guiding grooves 5 for 
each row of elements are discontinuous and the positions of the adjacent 
grooves 5 for each row are offset with respect to each other by about 20 
.mu.m. Therefore, even if some forces are applied to the substrate, the 
forces are not concentrated on a point, whereby the substrate 1 is hardly 
cracked. 
In the production process in accordance with the second embodiment of the 
present invention, by changing only the mask pattern for producing the 
photoresist for forming the element separation guiding grooves, production 
can be carried out utilizing the conventional process as it is. In the 
element separation step, since element separation is conducted using the 
blade 7 after cleaving the semiconductor wafer to produce the state, as 
shown in FIG. 2(d), there arises no problem even when the element 
separation guiding grooves 5 are shifted for each row. In addition, even 
when the position of cleavage and the position of the element separation 
guiding grooves 5 are a little shifted from the design, the wafer is 
divided into respective elements without problems, because the grooves are 
located at most of the portions where the element separation guiding 
grooves are to be positioned. 
Embodiment 3 
FIGS. 4(a) and 4(b) show semiconductor laser device element substrates in 
accordance with a third embodiment of the present invention. 
In the figures, the same reference numerals as those of the prior art 
designate the same or corresponding parts. 
FIG. 4(a) shows the semiconductor laser device element substrate up to a 
state where the element separation guiding grooves 5 are produced by the 
same process as that of FIGS. 2(a) and 2(b) of the second embodiment. 
As illustrated in FIG. 4(a), after producing the element separation guiding 
grooves 5, the electrode 6b is formed on the entire rear surface by vapor 
deposition, and thereafter gold 6a (about 5 .mu.m thick) is plated at the 
position of each element to a position adjacent to (about 10 .mu.m from) 
the guiding groove 5, producing electrodes for respective laser device 
elements. Since this plated gold 6a is grown only in an aperture of the 
photoresist, it is possible to easily deposit the gold 6a just to the side 
of the guiding groove 5 using the conventional photolithographic process 
(FIG. 4(b)). 
Thereafter, similar to the first embodiment, the substrate 1 and the glass 
plate 2 are separated, and the process is carried out up to the step of 
element separation. 
According to this third embodiment, similar to the above-described first 
and second embodiments, since the element separation guiding groove 5 is 
discontinuous for each row of elements, wafer cracking hardly occurs. 
Further, since the plated gold 6a is disposed adjacent to the groove 5, 
the plated gold 6a functions reinforces the element separation guiding 
groove 5 in the neighboring column, thereby generating wafer cracking less 
than the first embodiment. 
While the positions of the separation guiding grooves 5 are shifted for 
each row of elements in the first and second embodiments, the positions 
can be shifted for each several rows (5.about.10 rows) of elements, 
whereby the same effects can be obtained. 
While the plated gold 6a is employed as the reinforcement material in the 
second embodiment, other materials, for example, nickel and the like can 
be used, whereby the same effects can be obtained as a matter of course. 
Embodiment 4 
FIGS. 5(a) and 5(b) show semiconductor laser device element substrates in 
accordance with a fourth embodiment of the present invention. In FIGS. 
5(a) and 5(b), the same reference numerals as those of the prior art 
designate the same or corresponding parts. Here, reference numeral 8 
designates an active region of a laser. 
In this fourth embodiment illustrated in FIGS. 5(a) and 5(b), active 
regions 8 of lasers are shifted for each of several rows of elements, 
whereby the elements are not on lines but are shifted for each of several 
rows, and accordingly the element separation guiding grooves 5 are 
disconnected for each several rows and formed at the positions which are 
shifted each other. 
A description will be given of a method for producing the semiconductor 
laser device in accordance with this fourth embodiment. 
In the production method of this fourth embodiment, first of all, the 
production flow of the semiconductor laser element structure is different 
from that of the above-described first and second embodiments. 
More specifically, in the step of producing the stripe shaped insulating 
film 15 illustrated in FIG. 3(b), in the production flow of the 
semiconductor laser element structure of the first and second embodiments, 
as shown in FIG. 5(b), the stripe shaped insulating film patterns 15 are 
formed at different positions for each of several rows in regions where 
the active regions are to be produced. For instance, in a case where the 
chip size is 300 .mu.m.times.300 .mu.m and the positions of the active 
regions are shifted for each of the five rows of elements, the stripe 
shaped insulating films 15 are shifted at an interval of 1500 .mu.m by an 
arbitrary width, for example, about 150 .mu.m. Further, in a case where 
the chip size is 300 .mu.m.times.300 .mu.m and the positions of the active 
regions are shifted for each of two rows of elements (FIG. 5(a)), the 
stripe shaped insulating films 15 are shifted with an interval of 600 
.mu.m by an arbitrary width, for example, about 150 .mu.m. 
Thereafter, similar to the production flow of the semiconductor laser 
element structure of the first and second embodiments, the same process 
steps are carried out, for example, using the insulating film 15 as an 
etching mask, all the p-type GaAs first contact layers 14 except the ridge 
part 16 and a part of the p-type AlGaAs cladding layer 13 in the thickness 
direction are etched away leaving the cladding layer 13 about 0.2 .mu.m 
thick, producing the semiconductor laser element structure. 
Then, after producing this semiconductor laser element structure, similar 
to the process of the first and second embodiments illustrated in FIGS. 
2(a) to 2(e), production of the element separation guiding grooves 5 and 
production of the rear surface electrodes 6b and 6a are carried out 
according to the patterns of the element regions formed on the front 
surface side. More specifically, in a case where the chip size is 300 
.mu.m.times.300 .mu.m, the element separation guiding grooves 5 are 
shifted by 150 .mu.m, at an interval of 1500 .mu.m for each five rows or 
600 .mu.m for each of two rows, and the rear surface electrodes 6b and 6a 
are formed at the positions corresponding to these grooves. Then, element 
separation is conducted using the element separation guiding grooves 5, 
producing the semiconductor laser devices. 
A wafer 3 cm-square was conventionally employed, but a large wafer of 3 
inch.phi. or 4 inch.phi. has been utilized in recent years. When the wafer 
diameter is increased, in a case where the wafer is unfavorably cracked 
during the wafer process, the larger the wafer is, the more elements 
formed thereon cannot be used. Under these circumstances, in this fourth 
embodiment, since the alignment of elements in itself is shifted for each 
of several rows and the element separation guiding grooves 5 are also 
shifted for each of several rows, the distance of shifting the element 
separating guiding grooves 5 is about 150 .mu.m, which can be lengthened 
relative to about 20 .mu.m of the first embodiment, thereby occurring less 
cracking of the wafer. This represents a significant effect in the 
improvement in the yield. In this case, the complexity of producing the 
mask patterns in a case where the alignment of elements and the alignment 
of element separation guiding grooves are shifted for each row can be also 
solved. 
Embodiment 5 
FIG. 6 shows a semiconductor laser device in accordance with a fifth 
embodiment of the present invention. In the figure, the same reference 
numerals as those of the prior art designate the same or corresponding 
parts. 
In the semiconductor laser device element substrate of this fifth 
embodiment illustrated in FIG. 6, while the active regions on the wafer 
are positioned on a line for all elements, the positions of the active 
regions 8 of respective lasers are shifted, toward the right end, the left 
end, the right end, and the left end for respective elements, by shifting 
the positions where the respective element regions are produced for each 
of several rows, for example, in this case, for each of two rows. 
A description will be given of a production method of this fifth 
embodiment. 
In the production method of this fifth embodiment, the production flow of a 
semiconductor laser element structure is the same as that of the 
above-described first and second embodiments, but a later chip separation 
process shown in FIGS. 2(b) and 2(c) is different from that of the first 
and second embodiments. 
More specifically, after producing the semiconductor laser element 
structure according to the production flow of the semiconductor laser 
element structure of the above-described first and second embodiments 
shown in FIGS. 3(a) to 3(f), in the process steps for producing the 
element separation guiding grooves 5 and the rear surface electrodes 6b 
and 6a shown in FIGS. 2(b) and 2(c), as illustrated in FIG. 6 which is a 
plan view of the semiconductor laser element substrate 1 (10) viewed from 
the bottom surface, the element separation guiding grooves 5 are formed so 
that the active region 8 of each laser is located at a position close to 
the right end, the left end, the right end and the left end of each 
element in each element region of 300 .mu.m.times.300 .mu.m, which 
position is spaced apart from the position of the element separation 
guiding groove 5 located at the end of the element region by 75 .mu.m, and 
the electrodes 6b and 6c are formed corresponding to the elements. 
Thus, in this fifth embodiment, by positioning the active region 8 at the 
end part of each element, the element separation guiding grooves 5 can be 
shifted so as to have the distance of 150 .mu.m between the adjacent 
grooves, which is larger than that of the first embodiment, whereby wafer 
cracking hardly ever occurs. 
Embodiment 6 
While in the above-described embodiments a semiconductor laser produced on 
an n-type GaAs substrate is employed, a semiconductor laser employing 
other substrates having a similar structure, for example, an InP 
substrate, can be used. 
Embodiment 7 
While in the above-described embodiments the element separation guiding 
grooves are formed on the rear surface side of the substrate, the element 
separation guiding grooves can be formed on the front surface side of the 
substrate if V-shaped configuration can be realized. 
As described above, according to the present invention, since adjacent 
element separation guiding grooves facilitating the separation of the 
elements of the semiconductor laser device are offset for each of several 
rows of the laser chips, even if some forces are applied to the substrate, 
the forces are not concentrated on a point, whereby wafer cracking can be 
prevented. 
In addition, according to the present invention, reinforcement of the 
element separation guiding grooves which are shifted for each of several 
rows of the laser chips is carried out by plating gold electrodes of the 
semiconductor laser devices, whereby wafer cracking can be further 
prevented. 
Further, according to the present invention, since the alignment of 
elements is shifted for each of several rows of the laser chips, the 
element separation guiding grooves are shifted for each of several rows 
accordingly, whereby the element separation guiding grooves are 
discontinuous, thereby preventing wafer cracking, resulting in a 
remarkable increase in the yield.