JP2011192728A - Method of manufacturing semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure of a semiconductor laser that suppresses variations in film thickness of a dielectric film on a light emitting edge, and to provide a method of manufacturing the same. <P>SOLUTION: The method of manufacturing the semiconductor laser includes the steps of: forming a semiconductor wafer 100 having a semiconductor layer, including an active layer, laminated on a semiconductor substrate; forming a plurality of recesses 106 deeper than the active layer in the semiconductor wafer 100; forming a first dielectric film (AR coat film 108) so as to cover at least first edges in the recesses 16 and second edges opposed to the first edges; forming an isolation film (Au film) so as to cover the AR coat film 108 on the first edges; forming a second dielectric film (HR coat film) on the AR coat film 108 on the Au film and the second edges; and removing the HR coat film on the Au film and also removing the Au film, the Au film having an etching selection ratio of ≥10 to the AR coat film 108 and the HR coat film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a semiconductor laser manufacturing method.

  In recent years, as a method of manufacturing a semiconductor laser, a semiconductor wafer in which a clad layer, an active layer, and a clad layer are laminated on a semiconductor substrate is prepared, a groove is formed in the semiconductor wafer, and the light is reflected on the groove side wall serving as a light emitting end face. A method of obtaining a semiconductor laser bar by dividing a semiconductor wafer along a groove after forming a film is employed. As this type of technology, there are those described in Patent Documents 1 and 2.

  In the technique described in Patent Document 1, a groove is formed by dry etching, a dielectric film is formed on the entire surface, a metal film is formed in a state where one groove is entirely protected by a mask, and the mask is removed. Thus, a dielectric film is formed on both side walls of the groove, and a metal film is formed on both side walls of one of the grooves. A technique is disclosed in which a semiconductor wafer is divided to form an asymmetric coating film in which one end face is a dielectric film and the other end face is a metal film. A vapor deposition method is used to form the dielectric film.

  Patent Document 2 discloses a technique in which a resist is applied on an epitaxial substrate, a Ni metal film is further formed, and then patterned by photolithography (PR) to form a pattern for dry etching using a metal mask. Has been.

JP-A 63-302586 JP 61-99395 A

  However, in the above technique, when different dielectric films are separately formed on two groove sidewalls serving as light emitting end faces in one groove in the wafer, one dielectric film is covered with a separation film. It is necessary to form the other dielectric film. Thereafter, when the separation film is removed, the thickness of the dielectric film on the light emitting end face may vary due to the separation film remaining on the dielectric film.

According to the present invention, a step of forming a semiconductor wafer in which a semiconductor layer including an active layer is stacked on a semiconductor substrate;
Forming a plurality of recesses deeper than the active layer in the semiconductor wafer;
Forming a first dielectric film so as to cover at least a first end face in the recess and a second end face facing the first end face;
Forming a separation film so as to cover the first dielectric film on the first end surface;
Forming a second dielectric film on the first dielectric film on the separation film and on the second end face;
Removing the second dielectric film on the separation film and removing the separation film,
There is provided a method of manufacturing a semiconductor laser, wherein the isolation film has an etching selection ratio of 10 or more with respect to the first dielectric film and the second dielectric film.

  According to the present invention, in order to make different dielectric films on two end faces in one groove in a wafer, the first dielectric film is covered with the separation film, while the second dielectric A film is formed. This separation film has a higher etching selectivity than the first dielectric film and the second dielectric film. For this reason, when the separation film is removed, it can be reduced that the separation film remains on the first dielectric film. Therefore, variation in the thickness of the first dielectric film on the first end face can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, the structure of the semiconductor laser which can suppress that the film thickness of the dielectric film on a light emitting end surface varies, and its manufacturing method are provided.

It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 1st Embodiment of this invention. It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 1st Embodiment of this invention. It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 1st Embodiment of this invention. It is a figure which shows the relationship between the film thickness of the reflecting film in the semiconductor laser of 1st Embodiment, and a reflectance. It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 2nd Embodiment of this invention. It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 2nd Embodiment of this invention. It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 2nd Embodiment of this invention. It is process sectional drawing which shows the manufacturing procedure of the semiconductor laser in the 2nd Embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(First embodiment)
A method for manufacturing the semiconductor laser according to the first embodiment will be described.
1 to 3 are process cross-sectional views illustrating the manufacturing procedure of the semiconductor laser in the present embodiment.
The semiconductor laser manufacturing method of the present embodiment includes a step of forming a semiconductor wafer 100 in which a semiconductor layer including an active layer is stacked on a semiconductor substrate, and a plurality of recesses 106 deeper than the active layer in the semiconductor wafer 100. Forming the first dielectric film (AR coating film 108) so as to cover at least the first end face in the recess 106 and the second end face facing the first end face; A step of forming an isolation film (Au film 112) so as to cover the AR coat film 108 on the first end face, and a second dielectric on the Au film 112 and the AR coat film 108 on the second end face A step of forming a body film (HR coat film 114), a step of removing the HR coat film 114 on the Au film 112, and a step of removing the Au film 112. The Au film 112 includes the AR coat film 108 and HR It is etching selectivity of 10 or more with respect to preparative layer 114.

  First, an n-type GaAs substrate (semiconductor substrate, thickness 450 μm), an n-GaAs buffer layer (thickness 0.3 μm), an n-GaInAsP cladding layer (thickness 1.1 μm), an un-GaInAsP guide layer (thickness) 0.05 μm), MQW active layer (4 wells, un-GaInP well layer: 7.3 nm, un-AlInGaP barrier layer: 4 nm), un-GaInAsP guide layer (thickness 0.05 μm), p-GaInAsP cladding layer (Thickness 1.1 μm) and a p-GaAS cap layer (thickness 4.3 μm) are epitaxially grown by MOCVD (metal organic chemical vapor deposition). Thereby, a semiconductor wafer 100 (epi-grown wafer) in which a semiconductor layer including an active layer is stacked on a semiconductor substrate is formed.

Subsequently, a SiO ₂ film 102 is formed on the semiconductor wafer 100. For example, a CVD (Chemical Vapor Deposition) method can be used to form the SiO ₂ film 102. Subsequently, a resist is applied, exposed and developed on the SiO ₂ film 102. A pattern of a photoresist (resist 104) is formed by such PR method. (FIG. 1 (a)). In this pattern, an opening having a period of the cavity length of the semiconductor laser is provided.

Subsequently, the SiO ₂ film 102 is selectively removed using the resist 104 as a mask (FIG. 1B). For example, the SiO ₂ film 102 is removed by wet etching. Thereby, the pattern of the resist 104 is transferred to the SiO ₂ film 102. Thereafter, the resist 104 is removed.

Subsequently, by performing selective removal using the SiO ₂ film 102 as a mask, a recess 106 (dry etch groove) deeper than the active layer is formed in the semiconductor wafer 100 (FIG. 1C). For the selective removal, for example, dry etching by an ICP method or the like can be performed. Thereby, the inner side walls on both sides of the recess 106 can be used as the light emitting end faces of the semiconductor laser, respectively.

Here, the groove depth of the recess 106 can be, for example, 15 μm, while the groove width can be 30 μm (at this time, the groove depth of the recess 106 is from the bottom of the recess 106 to the surface layer of the semiconductor wafer 100. Distance).
Moreover, the cross-sectional shape of the recessed part 106 can be made into a rectangle. The side wall of the recess 106 is formed to be parallel to the stacking direction of the semiconductor layers including the active layer. In other words, the side walls (first end face and second end face) on both sides of the recess 106 are formed so as to be parallel to the vertical direction with respect to the semiconductor wafer 100.

  On the other hand, when viewed from above, the recesses 106 are provided in stripes in a direction parallel to the direction of the resonator of the semiconductor laser. That is, the first end face and the second end face are each parallel to the resonator direction. The recesses 106 are spaced apart with the resonator length of the semiconductor laser as a period. The resonator length can be set to 300 μm, for example. The distance between the concave portions 106 in the direction orthogonal to the resonator direction is not particularly limited, but corresponds to the lateral width of the semiconductor laser. The distance in the horizontal width direction can be set to 250 μm, for example.

Subsequently, an AR coat film 108 (low reflection film) made of a dielectric film is formed so as to cover at least the inside of the recess 106. In the present embodiment, an AR coat film 108 is formed on the entire surface of the semiconductor wafer 100 (FIG. 1D).
As a method for forming the AR coat film 108, a sputtering method in which Ar gas is added from the vertical direction of the wafer (semiconductor wafer 100) surface can be used. At this time, the wafer is placed horizontally on the stage with the dry etch groove (concave portion 106) visible, and set so that the distance between the sputter target and the wafer is constant. The film thickness adhering to the light emitting end face is 0.45 times the film thickness adhering to the wafer surface. For this reason, the film thickness formed by sputtering is set to be 2.22 times the film thickness formed on the light emitting end face.

Here, the sputtering method of the present embodiment will be described in detail.
In the present embodiment, the dielectric film is formed on the light emitting end surface of the vertical wall surface by utilizing the wraparound of the film in the sputtering method. Thereby, the film thickness of the dielectric film can be made uniform, and the reflectance of the dielectric film can be controlled with high accuracy.

  In general, in the sputtering method, it is known that the film thickness changes depending on the distance between the sputtering target and the wafer to be sputtered, that is, the shorter the distance, the thicker the film thickness, and the farther the distance, the thinner the film thickness. It has been. If the sputtering method is used with the wafer tilted obliquely, the distance between the sputtering target and the wafer differs depending on the position in the wafer. Therefore, the film thickness is thicker toward the wafer surface closer to the sputtering target and thinner toward the far wafer surface. Further, as the wafer size increases, this tendency becomes more prominent, and the film thickness distribution of each LD end face within the wafer surface differs several times. For this reason, it may be difficult to use the low reflectance coating film or the high reflectance coating film of the semiconductor laser.

  In contrast, in the sputtering method according to the present embodiment, the wafer (semiconductor wafer 100) is set horizontally, and the distance between the sputtering target and the wafer is made constant, so that the film thickness distribution in the wafer surface is made constant. Can be.

  However, the film thickness of the dielectric film on the light emitting end surface of the vertical wall surface inside the recess 106 (groove) may not be uniform in each chip.

On the other hand, in the present embodiment, 5-15 vol% of Ar gas is further added during sputtering, and conditions such as pressure and bias power during sputtering can be appropriately set. As a result, the amount of the sputtered target material that flies in a random direction and repeatedly adheres to the vertical wall surface of the dry etch groove of the wafer by repeatedly colliding and reflecting with plasmaized Ar atoms and inert Ar atoms. Can be controlled. In this way, by controlling the thickness of the film wrapping around by sputtering, it is possible to control the reflectivity of each of the low-reflectance coat film and the high-reflectance coat film made of a dielectric film with high accuracy. It becomes.
Here, the addition of Ar gas means that 5 to 15 vol% of Ar gas is further added to the Ar gas flow rate when the uniformity of the film thickness on the flat wafer in the 50 mm range is ± 2%. means.
On the other hand, if the added Ar gas is less than 5 vol%, the sputtered target material has a low collision frequency and reflection frequency with Ar atoms, and a sufficient film thickness uniforming effect may not be obtained. On the other hand, if the added Ar gas exceeds 15 vol%, the film formation rate decreases, which may not be practical. Further, as the additive gas, an inert gas such as N ₂ can be used instead of Ar gas.

The AR coating film 108 is not particularly limited as long as it is a dielectric film, but oxides such as Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , AlN, SiN, A nitride such as Si ₃ N ₄ can be used. The AR coating film 108 may be a single layer or a multilayer structure. In the present embodiment, SiO ₂ can be used as the AR coating film 108.

  The film thickness of the AR coat film 108 can be set to, for example, 50 nm to 200 nm. Further, the AR coating film 108 can have an end surface reflectance with respect to the laser light of 1 to 30%. For example, when the thickness of the AR coat film 108 is 112 nm, the reflectance of the AR coat film 108 can be set to 7%.

  Subsequently, a resist is applied to the entire surface of the AR coating film 108. Subsequently, resist is patterned using the PR method. Then, a pattern of the resist 110 is formed so as to cover only the AR coat film 108 on one end face of the both end faces (FIG. 2A). That is, the resist 110 is formed so as to cover the AR coat film 108 on the second end face and to expose the AR coat film 108 on the first end face. Thereby, only the high reflectance side (second end face side) of the AR coating film 108 is protected by the resist 110.

  Subsequently, a film (Au film 112) containing Au having a high etching selectivity with respect to the AR coat film 108 is formed so as to cover the low reflectance side (on the first end face) of the AR coat film 108 (FIG. 2 ( b)). In order to form a film containing Au, for example, a sputtering method or a wafer revolution type vapor deposition method can be performed. At this time, step breakage is prevented from occurring at the corner of the wafer surface and the bottom of the groove (recess 106). Further, the metal (Au film 112) can be deposited at room temperature without heating the substrate. As a result, the resist 110 can be prevented from burning and the Au film 112 from biting into the oxide film (AR coating film 108).

  In addition, as a film containing Au used for protecting the AR coating film 108, any metal film made of Au or an alloy film containing Au can be used from the viewpoint of protection and peelability. The film thickness of the Au film 112 can be set to, for example, about 100 nm.

  Subsequently, the Au film 112 on the resist 110 is removed at the same time while removing the resist 110 protecting the end face on the high reflectance side with an organic solvent by a lift-off method or the like. (FIG. 2 (c)). Thereby, the AR coating film 108 on the high reflectance side is exposed.

  Subsequently, an HR coat film 114 (high reflection film) is formed on the AR coat film 108 exposed on at least the end face on the high reflectance side by using the same sputtering method as that for the AR coat film 108. In this embodiment, the HR coat film 114 is formed on the entire surface of the wafer by sputtering using Ar gas added from the vertical direction of the wafer surface (FIG. 2D). At this time, the wafer is placed horizontally on the stage with a dry etch groove visible, and set so that the distance between the sputter target and the wafer is constant. Since the film thickness attached to the light emitting end face is 0.45 times the film thickness attached to the wafer surface, the film thickness formed by sputtering is set to be 2.22 times the film thickness formed on the light emitting end face. To do.

The HR coating film 114 is not particularly limited as long as it is a dielectric film, but oxides such as Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , AlN, SiN, A nitride such as Si ₃ N ₄ or amorphous silicon can be used. The HR coat film 114 may be a single layer or a multilayer structure. In the present embodiment, a two-layer structure made of Al ₂ O ₃ and TiO ₂ can be used as the HR coat film 114.

The film thickness of the HR coat film 114 can be, for example, 200 nm to 1000 nm. Further, the HR coat film 114 can have an end face reflectance with respect to the laser light of 70 to 99%. For example, when the HR coating film 114 has a five-layer structure of Al ₂ O ₃ (97 nm), TiO ₂ (67 nm), Al ₂ O ₃ (97 nm), TiO ₂ (67 nm), and Al ₂ O ₃ (194 nm). The reflectance of the HR coat film 114 can be 80%.

  The combination of the AR coating film 108 and the HR coating film 114 can be determined from the refractive index and the film thickness. For example, the combinations described in Table 1 and Table 2 can be used. Table 1 shows combinations of film types of the AR coating film 108 (low reflection film). Table 2 shows combinations of film types of the HR coat film 114 (high reflection film). The first layer is present on the surface layer side from the second layer in the film thickness direction.

  Subsequently, patterning is performed by the PR method to fill the recess 106 (dry etch groove portion) with the resist 116 (FIG. 3A).

Subsequently, the HR coat film 114 (high reflectivity coating film) on the Au film 112 is removed by wet etching such as buffered hydrofluoric acid. Subsequently, the Au film 112 on the AR coating film 108 (low reflectance coating film) is removed by wet etching such as K + KI. Thereafter, the resist 116 is peeled and removed (FIG. 3B). At this time, (i) the Au film 112 formed at room temperature does not bite with a dielectric film such as SiO ₂ , and the characteristics of the Au film 112 are (ii) low adhesion to the dielectric film, (Iii) Furthermore, the selectivity by the etchant is excellent. For this reason, no Au film remains on the dielectric film, and no dielectric film remains on the Au film.
Here, the Au film 112 has an etching selectivity different from that of the AR coat film 108 and the HR coat film 114. The etching selectivity of the Au film 112 can be 10 or more and 500 or less, preferably 100 or more and 300 or less.

  In this way, in the wafer state, a semiconductor laser diode in which a low reflectance coating film and a high reflectance coating film are separately formed on the light emitting end surface of the vertical wall surface in one groove is formed. At this time, the low reflectance film coating film (AR coating film 108) is formed on the entire surface of the semiconductor wafer 100. The high reflectivity coat film (HR coat film 114) is formed only on the high reflection side of the light emitting end face. The cross-sectional shape of the HR coat film 114 is, for example, a crank shape.

Thereafter, electrodes (not shown) are formed on the front surface and the back surface of the semiconductor wafer 100. Then, the semiconductor wafer 100 is divided at a dividing position 118 as shown in FIG. That is, it is possible to obtain individual pellets by dividing the concave portion 106 (dry etching groove) in the central portion and its vertical direction. To divide, for example, scratching with a scriber, braking after half-cut dicing, or full-cut dicing can be performed.
As described above, the semiconductor laser of the present embodiment can be obtained.

Next, the semiconductor laser of this embodiment will be described.
FIG. 4 shows the relationship between the thickness of the reflective film and the reflectance in the semiconductor laser of the present embodiment.
The semiconductor laser according to the present embodiment includes a semiconductor substrate, a semiconductor layer including an active layer stacked on the semiconductor substrate, a first end surface of the semiconductor layer parallel to the stacking direction of the semiconductor layer, and a second A first dielectric film (AR coat film 108) provided on the end face of the first layer, and an HR coat film 114 provided on the AR coat film 108 on the second end face. The variation coefficient CV of the film thickness of the AR coating film 108 on the first end face in the region within ± 2.5 μm from the first end surface is 5% or less.

In the semiconductor laser obtained by the above-described manufacturing method, the coefficient of variation CV (coefficient of variation) of the coating film thickness of each element in a region within ± 2.5 μm from the active layer (surface side and groove bottom side from the active layer). ) May be 5% or less.
As shown in FIG. 4, for example, the relationship between the film thickness and the reflectance in the case of a SiO ₂ single layer (low reflectance coating film) is indicated by a COS curve. Looking at the COS curve, for example, when the reflectance of the low reflectance coating film is 10%, the required film thickness is 80 nm (800 mm).
Here, when the CV value is 5%, the variation S is 4 nm (40 Å). The variation range of the film thickness necessary to realize the product guarantee of 99.7% is 80 ± 3S = 68 to 92 (nm). At this time, the maximum reflectance is 14% and the minimum reflectance is 7%. The maximum reflectance / minimum reflectance is 2.0, which satisfies the requirement. As described above, the low reflectance coating film of the semiconductor laser has a maximum reflectance / minimum reflectance of 2 or less, and can sufficiently guarantee the product. On the other hand, if the CV value exceeds 5%, the ratio between the maximum reflectance and the minimum reflectance becomes larger than 2, so that sufficient product guarantee cannot be performed.

Here, the reflectance can be obtained by calculation from the oscillation wavelength and equivalent refractive index of the semiconductor LD to which the film is attached and the thickness and refractive index of the film formed by sputtering. For example, the reflectance R when the film thickness of SiO ₂ is d1 (nm) can be obtained by the following calculation formula.
Reflectance: R = (A × COS (X) + B) × 100 (%)
X = (d1 / d0) × (π / 2)
d0 = λp / (2 × NS)
Refractive index of SiO ₂ : NS = 1.48
LD wavelength: λp = 650 nm
Constants: A = 0.13, B = 0.19

Further, in the semiconductor laser manufacturing method of the present embodiment, since the wafer is leveled and coating is performed by adding Ar gas, variation in the coating film thickness of the light emitting end face can be reduced.
For example, in an example in which the wafer is inclined, the variation coefficient CV value is 13.4% for the film thickness within ± 2.5 μm from the active layer position to the surface side and the groove bottom side. On the other hand, when the wafer is leveled and Ar gas is added as in the embodiment, the variation coefficient CV value can be improved to 4.4%.

When the wafer is set obliquely, the film thickness distribution increases in the wafer because the distance between the sputter target and the wafer differs greatly in the wafer plane when the wafer size increases.
On the other hand, when the wafer is set horizontally as in this embodiment, the distance from the target is constant, so that the present invention can be applied to a large-diameter wafer.

The effect of this Embodiment is demonstrated.
In the present embodiment, a groove (concave portion 106) is formed on the semiconductor wafer 100, and an AR coating film 108 is formed on the side wall (first end surface) on the low reflection side of both side walls in the groove. On the other hand, the HR coat film 114 is formed on the side wall (second end face) on the high reflection side. Thereafter, by dividing the semiconductor wafer 100, both side walls become the light emitting end faces of the semiconductor laser. Therefore, in the present embodiment, the first dielectric film (AR coating film 108) is used as the Au film 112 in order to make different dielectric films on the two end faces that are the light emitting end faces in one recess 106. The other second dielectric film (HR coat film 114) is formed in a state of being covered with. The Au film 112 has a high etching selectivity with respect to the AR coat film 108 and the HR coat film 114, but is low. Thereby, when the Au film 112 is removed, it is possible to reduce the remaining of the Au film 112 on the AR coating film 108. In addition, film loss of the dielectric film can be prevented. Therefore, variation in the film thickness of the AR coat film 108 on the first end face can be suppressed.

  In the present embodiment, a condition for forming a dry etch surface perpendicular to the semiconductor wafer 100 is employed. Thus, the side walls (first end surface and second end surface) on both sides of the recess 106 are formed to be parallel to the vertical direction with respect to the semiconductor wafer 100. For this reason, it can reduce that contaminants, such as a metal and an organic substance, adhere to both end surfaces perpendicular | vertical with respect to a wafer surface. By keeping the end surface clean, variations in the thickness of the AR coat film 108 and the HR coat film 114 formed on the end surface can be suppressed.

  In the present embodiment, when dry etching is performed to form the recess 106, a silicon oxide film is used as a mask. Thereby, it is not necessary to use an organic substance such as a resist or a metal as a mask. Therefore, it is possible to reduce the adhesion of contaminants on both end faces when the recess 106 is formed. Thereby, it is possible to suppress the variation in the film thickness of the dielectric film due to the contaminants remaining between the dielectric film such as the AR coat film 108 and the end face.

  Further, in the sputtering method according to the present embodiment, the wafer (semiconductor wafer 100) is set horizontally and an inert gas is added more than usual. Thereby, the film thickness of the dielectric film formed on the end surface perpendicular to the wafer surface can be accurately controlled.

  In this way, contamination of impurities on the light emitting end face of the semiconductor laser can be prevented while still in the wafer state, and the film thickness of the asymmetric coating formed on the vertical surface of the light emitting end face of a large-diameter wafer can be made uniform. Thus, the reflectance can be easily controlled.

  Further, in the present embodiment, a process of separately forming the HR coat film 114 on the side wall in the same recess 106 is performed with both side walls of the recess 106 covered with the AR coat film 108. Thereby, both end surfaces can be protected from contaminants during the formation of the asymmetric coating film. Therefore, a semiconductor laser excellent in reliability can be obtained.

  In the present embodiment, the position where the HR coat film 114 is formed on the side wall of the recess 106 is aligned for each semiconductor laser bar. For this reason, the process of aligning the direction becomes unnecessary, and the productivity of pellets is improved.

  In addition, since the semiconductor laser wafer with asymmetric coating can be formed in the wafer state, the man-hour and the working time can be greatly reduced.

  Next, the effects of the present embodiment will be further described in comparison with the prior art.

  In Patent Document 1, a metal or dielectric multilayer film is formed by a vapor deposition method. In this case, in vapor deposition from the vertical direction, vapor deposition molecules fly linearly and deposit on the wafer to form a film, so that it is difficult to control the film thickness on the wall surface formed perpendicular to the wafer surface. For this reason, in the case of metal, a high reflectivity surface can be easily formed by ignoring the film thickness distribution of the light emitting end face and increasing the metal thickness, but the end face reflectivity is fixed to about 99%, As with a semiconductor laser, monitoring by light output from the high reflectance side is difficult. Further, in the case of a dielectric multilayer film, it is difficult to control the end face reflectance because each film thickness cannot be controlled.

  On the other hand, in this embodiment, the sputtering method is used for forming the dielectric film. Thereby, the film thickness of the dielectric film can be controlled with high accuracy.

  In Patent Document 2, when dry etching is performed and when an end surface coating film is formed, Ni metal and a resist component under the metal are involved to perform dry etching and end surface coating. For this reason, organic substances such as Ni metal and resist are deposited on the light emitting end face formed perpendicular to the wafer. As a result, in the formation of the end face protective film, film swelling due to organic matter occurs, and the reflectance of the light emitting end face differs from the design.

  In contrast, in this embodiment, when dry etching is performed to form the recess 106, a silicon oxide film is used as a mask, and it is not necessary to use an organic substance such as a resist or a metal as the mask. Therefore, it is possible to reduce the adhesion of contaminants on both end faces when the recess 106 is formed. Further, since the contamination of the light emitting end face can be prevented, the deterioration hardly occurs when the semiconductor laser is operated for a long time.

(Second Embodiment)
A method of manufacturing the semiconductor laser according to the second embodiment will be described.
5 to 8 are process cross-sectional views showing the manufacturing procedure of the semiconductor laser in the present embodiment.

  In the second embodiment, an example of a method for simultaneously forming the reflective film and the contact electrode which are separately formed in the first embodiment will be described. In the present embodiment, an alloy film of Au and another metal such as AuGe is used as the film containing Au.

First, sequentially grown wafers (semiconductor wafer 100) are formed by epitaxial growth of a cladding layer, an active layer, a cladding layer, or the like made of an InP-based material, a GaAs-based material, or a GaN-based material. As shown in FIG. 5A, an SiO ₂ film 102 is formed on the surface of the semiconductor wafer 100. As shown in FIG. 5B, a pattern PR of a resist 104 is formed by the PR method for opening a dry etching groove portion having a period of the resonator length of the semiconductor laser. As shown in FIG. 5C, dry etching is performed to form a recess 106 (dry etch groove portion). Then, as shown in FIG. 5D, an AR coat film 108 is formed on the entire surface of the semiconductor wafer 100.

  As shown in FIG. 6A, the resist 110 is patterned using the PR method so as to be formed inside the recess 106 and on the wafer surface near the recess 106. As shown in FIG. 6B, the AR coating film 108 is etched with BHF or the like using the resist 110 as a mask. This forms a window opening for the contact electrode.

  Subsequently, the resist 110 is removed and PR is performed again. Thereby, as shown in FIG. 6C, only the high reflectance side of the AR coating film 108 is protected by the resist 110.

  As shown in FIG. 7A, an alloy thin film (up to 100 nm) such as AuGe122 is formed by sputtering or wafer revolving type vapor deposition. At this time, step breakage is prevented from occurring at the corner of the wafer surface and the bottom of the recess 106. Further, by depositing metal at room temperature without heating the substrate, resist burn-in and metal biting on the oxide film can be prevented.

  As shown in FIG. 7B, the resist 110 protecting the high reflectance side of the AR coating film 108 is removed with an organic solvent by the lift-off method or the like, and at the same time, the AuGe film 122 is removed. Thereby, the AuGe film 122 protecting the high reflectance side can be removed simultaneously with the formation of the contact electrode.

  As shown in FIG. 7C, an HR coat film 114 is formed on the entire surface of the wafer by sputtering using Ar gas added from the vertical direction of the wafer surface. At this time, the wafer is placed horizontally on the stage in a state where the dry etching groove (recess 106) is visible, and set so that the distance between the sputtering target and the wafer is constant. Since the film thickness attached to the light emitting end face is 0.45 times the film thickness attached to the wafer surface, the film thickness formed by sputtering is set to be 2.22 times the film thickness formed on the light emitting end face. To do.

  As shown in FIG. 8A, patterning is performed by the PR method so that the high reflectance side of the recess 106 is covered with a resist 116.

  As shown in FIG. 8B, the HR coat film 114 on the AuGe film 122 is removed by wet etching such as buffered hydrofluoric acid.

Subsequently, after removing the resist 116, a mask 120 (photoresist) is formed by the PR method so as to further protect the contact electrode portion by the PR method. Subsequently, as shown in FIG. 8C, the AuGe film 122 on the AR coat film 108 is removed by wet etching such as K + KI. Thereafter, the mask 120 is peeled and removed. At this time, the dielectric film such as SiO ₂ and the AuGe film 122 formed at room temperature do not bite, have low adhesion to the dielectric film, and have excellent selectivity by the etchant. For this reason, the AuGe film 122 does not remain in the dielectric film, and the dielectric film does not remain in the AuGe film 122.

In this way, in the wafer state, a semiconductor laser diode in which a low reflectance coating film and a high reflectance coating film are separately formed on the light emitting end surface of the vertical wall surface in one groove is formed.
In later steps, electrodes are formed on the front and back surfaces. Then, the semiconductor wafer 100 is divided at a dividing position 118 as shown in FIG. That is, it is divided into the central portion of the dry etch groove and its vertical direction to obtain individual pellets.

  In the second embodiment, even when the separation film is an alloy film containing Au, the same effect as in the first embodiment can be obtained.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

100 Semiconductor wafer 102 SiO ₂
104 Resist 106 Recess 108 AR coating film 110 Resist 112 Au film 114 HR coating film 116 Resist 118 Dividing position 120 Mask 122 AuGe film

Claims (8)

Forming a semiconductor wafer in which a semiconductor layer including an active layer is stacked on a semiconductor substrate;
Forming a plurality of recesses deeper than the active layer in the semiconductor wafer;
Forming a first dielectric film so as to cover at least a first end face in the recess and a second end face facing the first end face;
Forming a separation film so as to cover the first dielectric film on the first end surface;
Forming a second dielectric film on the first dielectric film on the separation film and on the second end face;
Removing the second dielectric film on the separation film and removing the separation film,
The method of manufacturing a semiconductor laser, wherein the isolation film has an etching selectivity of 10 or more with respect to the first dielectric film and the second dielectric film.   The method of manufacturing a semiconductor laser according to claim 1, wherein the separation film is a film containing Au.   3. The semiconductor laser according to claim 1, wherein in the step of forming the recess, the first end face and the second end face are formed so as to be parallel to a stacking direction of the semiconductor layers. Manufacturing method. The step of forming the recess includes the step of forming a pattern made of a silicon oxide film on the semiconductor wafer;
The method for manufacturing a semiconductor laser according to claim 1, further comprising: forming the concave portion in the semiconductor wafer using the pattern as a mask.   The method of manufacturing a semiconductor laser according to claim 1, wherein the step of removing the separation film is performed by wet etching.   The method for manufacturing a semiconductor laser according to claim 1, further comprising a step of dividing the semiconductor wafer along the recess. The first dielectric film and the second dielectric film are made of Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , AlN, SiN, Si ₃ N ₄ , The method for manufacturing a semiconductor laser according to claim 1, comprising at least one selected from the group consisting of amorphous silicon.   8. The method of manufacturing a semiconductor laser according to claim 1, wherein the second dielectric film has a higher reflectance than the first dielectric film. 9.

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