Testing method and manufacturing method of horizontal cavity surface laser

Abstract

The invention relates to a testing method of a horizontal cavity surface laser. The testing method comprises the following steps: S1, manufacturing a light emitting surface on an epitaxial structure; s2, cutting the epitaxial structure to form an inclined surface, wherein the inclined surface faces the light emitting surface; s3, coating a film on the inclined plane, taking the inclined plane as a reflecting surface of the light emitting surface for emitting laser, and reflecting the laser to the outside of the epitaxial structure by the reflecting surface; and S4, collecting the laser reflected to the outside of the epitaxial structure and analyzing the laser to judge whether the chip before tape-out is qualified or not. The invention further provides a manufacturing method of the horizontal cavity surface laser, and the testing method is adopted. According to the invention, by manufacturing the reflecting surface capable of reflecting the laser emitted from the light emitting surface to the outside of the epitaxial structure, key parameters such as material gain, central wavelength, contact resistance, threshold and the like of the laser can be directly represented at a wafer level, and a finished laser chip does not need to be manufactured for testing.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a testing method and a manufacturing method of a horizontal cavity surface laser. Background Art

[0002] For the product development and production of horizontal cavity lasers, under normal circumstances, the stage from the growth of wafer epitaxial materials to the completion of the wafer electrode process belongs to the wafer-level process. After that, the semi-finished wafer needs to be cleaved and cut into bars to form the end face of the resonant cavity, and an optical medium film is coated on the cleaved end face. Then the bar is cleaved into independent chips and tested and screened to complete the development of the horizontal cavity laser chip. The preparation process from semi-finished wafers to laser chips requires a certain amount of time, equipment and labor costs. In addition, some specific laser products have strict requirements for the central wavelength working range (such as dense wavelength division multiplexing DWDM laser products for optical communications, 1653.7 nm laser products for methane gas sensing, etc.). During the research and development or production process, key information such as the laser working center wavelength cannot be obtained, resulting in a long product development iteration cycle and a reduced mass production yield. Summary of the invention

[0003] The purpose of the present invention is to provide a testing method and a manufacturing method for a horizontal cavity surface laser. By means of wafer-level monitoring of the horizontal cavity laser during the development process, some key parameters such as laser material gain and operating wavelength can be tested in advance, effectively evaluating whether the wafer has achieved the development purpose, shortening the development cycle and improving the production yield.

[0004] To achieve the above object, the embodiment of the present invention provides the following technical solution: a method for testing a horizontal cavity surface laser, comprising the following steps: S1, making a smooth surface on the epitaxial structure; S2, then cutting the epitaxial structure to form an inclined surface, wherein the inclined surface faces the light emitting surface; S3, coating the inclined surface, using the inclined surface as a reflection surface for emitting laser light from the light emitting surface, and the reflection surface reflects the laser light out of the epitaxial structure; S4, collecting and analyzing the laser reflected outside the epitaxial structure to determine whether the chip before tape-out is qualified.

[0005] Furthermore, in the step S2, a cutting device is used to cut and form the inclined surface.

[0006] Furthermore, a grinding wheel with an inclined blade is used to cut and form an inclined groove, and then the inclined groove is etched to obtain a smooth inclined surface.

[0007] Furthermore, the cutting depth is between 20 and 50 μm, the cutting width is between 20 and 50 μm, and the feed speed is between 0.1 and 0.5 mm / s.

[0008] Furthermore, before manufacturing the light output surface, a buried heterojunction waveguide or a ridge waveguide is manufactured on the epitaxial structure.

[0009] Furthermore, a specific method for making a buried heterojunction waveguide is as follows: growing a buried heterojunction mask layer on the epitaxial structure; then removing the mask layer on both sides of the buried heterojunction waveguide region, and corroding to the substrate under the epitaxial structure, retaining the mask layer of the buried heterojunction waveguide region; then growing a restriction layer on both sides of the buried heterojunction waveguide region to form a buried heterojunction waveguide.

[0010] Furthermore, waveguide isolation regions are formed at both ends of the buried heterojunction waveguide or the ridge waveguide.

[0011] Furthermore, the epitaxial structure is also provided with a backlight surface, which is located at an end of the epitaxial structure away from the inclined surface, the light-emitting surface is coated with an anti-reflection film, and the inclined surface and the backlight surface are both coated with a high-reflection film. The material of the light-emitting surface is the same as that of the passivation layer, and the material of the backlight surface is the same as that of the electrode.

[0012] Furthermore, electrodes are fabricated on the epitaxial structure, carriers are injected into the electrodes using a test probe, the light emitting surface is stimulated to radiate laser light, and then a detector and an optical fiber are used to test and analyze the laser light.

[0013] The embodiment of the present invention provides another technical solution: a method for manufacturing a horizontal cavity surface laser. Select a wafer with several semi-finished chips, At least one test area is selected on the wafer, wherein some of the semi-finished chips are in the test area, The semi-finished chips on the test area are tested using the above-mentioned horizontal cavity surface laser testing method. If the semi-finished chips on the test area pass the test, the semi-finished chips outside the test area will continue to be taped out to the subsequent production process until the finished chips are obtained. If the semi-finished chips tested by the test method fail to pass the test, the taping of all semi-finished chips outside the test area will be terminated.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: by manufacturing a reflection surface that can reflect the laser emitted from the light-emitting surface to the outside of the epitaxial structure, the key parameters of the laser, such as material gain, central wavelength, contact resistance, threshold, etc., can be directly characterized at the wafer level, without the need to manufacture finished laser chips for testing. As a monitoring method during the research and development and production of horizontal cavity lasers, when abnormalities in key parameters such as material gain and central wavelength are detected, it can be determined in advance whether it is worthwhile to continue to develop the laser chip, or to scrap the wafer and re-spin it while optimizing the design parameters and process flow, thereby accelerating the research and development iteration of horizontal cavity lasers, effectively shortening the wafer development cycle, and improving the yield of product production, thereby reducing research and development and production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A schematic diagram of a test area design for a test method for a horizontal cavity surface laser provided by an embodiment of the present invention (showing multiple test areas); Figure 2 A front view of an epitaxial structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Figure 3 A three-dimensional diagram of an epitaxial structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Figure 4 A top view of a buried heterojunction waveguide structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Figure 5 A three-dimensional diagram of a buried heterojunction waveguide structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Figure 6 A front view of a laser resonant cavity surface structure in a test area of ​​a horizontal cavity surface laser test method provided by an embodiment of the present invention; Figure 7 A three-dimensional diagram of a laser resonant cavity surface structure in a test area of ​​a horizontal cavity surface laser test method provided by an embodiment of the present invention; Figure 8 A schematic diagram of grinding wheel cutting of a test area of ​​a test method for a horizontal cavity surface laser provided by an embodiment of the present invention; Fig. 9 A physical SEM image of the inclined surface cut by a grinding wheel in a test area of ​​a test method for a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.10 A front view of a test area cutting structure of a test method for a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.11 A three-dimensional diagram of a test area cutting structure of a test method for a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.12 A front view of an anti-reflection film structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.13 A three-dimensional diagram of an anti-reflection film structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.14 A front view of a reflective mirror structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.15 A three-dimensional diagram of a reflective mirror structure of a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.16 A schematic diagram of the effect of a reflector in a method for testing a horizontal cavity surface laser provided by an embodiment of the present invention; Fig.17 A wafer-level test schematic diagram of a test method for a horizontal cavity surface laser provided by an embodiment of the present invention; In the figure markings: 0-test area; 1-InP substrate; 2-active layer; 3-InP transition layer; 4-grating layer; 5-grating buried layer; 6-InP confinement layer; 7-InP transition layer; 8-contact layer; 9-HR end waveguide partition area; 10-AR end waveguide partition area; 11-reflector cutting area; 12-anti-reflection film; 13-P electrode pad; 14-reflector Au metal thin layer; 15-emitted laser; 16-cutting equipment vacuum suction cup; 17-expansion ring bottom film; 18-grinding wheel; 19-N electrode; 20-test equipment carrier; 21-test probe; 22-light receiving optical fiber. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] See also Figures 1 to 17An embodiment of the present invention provides a method for testing a horizontal cavity surface laser, comprising the following steps: S1, making a light-emitting surface on an epitaxial structure; S2, then cutting the epitaxial structure to form an inclined surface, wherein the inclined surface faces the light-emitting surface; S3, coating the inclined surface, and using the inclined surface as a reflection surface for the light-emitting surface to emit laser light, wherein the reflection surface reflects the laser light to the outside of the epitaxial structure; S4, collecting the laser light reflected to the outside of the epitaxial structure and analyzing the laser light to determine whether the chip before tape-out is qualified. In this embodiment, by making a reflective surface that can reflect the laser emitted from the light-emitting surface to the outside of the epitaxial structure, it is not necessary to make the wafer into a laser chip, and the key parameters of the laser such as material gain, center wavelength, threshold, etc. can be directly characterized at the wafer level. As a monitoring method in the development and production process of horizontal cavity lasers, when abnormalities in key parameters such as material gain and center wavelength are detected, it can be judged in advance whether it is worth continuing to develop into a laser chip, or scrapping the wafer and re-investing it while optimizing the design parameters and process, speeding up the development and iteration of horizontal cavity lasers, shortening the product development cycle and improving the yield of product production, thereby reducing production costs. Preferably, the epitaxial structure includes the structure of epitaxial material, waveguide structure, insulating layer and electrode injection channel.

[0018] See also Figures 1 to 17 In the step S2, a cutting device is used to cut to form an inclined surface. In addition, it is also feasible to make the inclined surface by etching. A grinding wheel with an inclined blade is used to cut to form an inclined groove, and then the inclined groove is etched to obtain a smooth inclined surface. The grinding wheel used may have a blade inclined at 45 degrees, so that the inclined surface can be obtained by scratching. Preferably, the cutting depth is between 20 and 50 μm, the line width is between 20 and 50 μm, and the feed speed is between 0.1 and 0.5 mm / s. In addition, before cutting to form the inclined surface, first etch a groove between the light-emitting surface and the inclined surface.

[0019] See also Figures 1 to 17 , before making the light-emitting surface, a buried heterojunction waveguide or a ridge waveguide is made on the epitaxial structure. In this embodiment, the laser can be a ridge waveguide structure or a buried heterojunction structure. Preferably, the specific method for making a buried heterojunction waveguide is: growing a buried heterojunction mask layer on the epitaxial structure; then removing the mask layer on both sides of the buried heterojunction waveguide area, and corroding to the substrate under the epitaxial structure, retaining the mask layer of the buried heterojunction waveguide area; then growing a restriction layer on both sides of the buried heterojunction waveguide area to form a buried heterojunction waveguide. A waveguide partition area is formed at both ends of the buried heterojunction waveguide or the ridge waveguide. The mask layer of the buried heterojunction waveguide area is retained, and a waveguide partition area is formed at the HR and AR ends, the light-emitting cavity surface is kept vertical, and then the mask layer is removed to form the resonant cavity surface.

[0020] See also Figures 1 to 17 , the epitaxial structure is also made with a backlight surface, which is located at one end of the epitaxial structure away from the inclined surface, the light-emitting surface is coated with an anti-reflection film, and the same silicon oxide / silicon nitride material as the passivation layer of the optical chip is used as the material of the anti-reflection film; the inclined surface and the backlight surface are both coated with a high-reflection film, and the same metal material as the P-side electrode metal is used as the material of the high-reflection film. In this embodiment, the left and right sides of the epitaxial structure have grooves, which are two waveguide partition areas respectively, to form a "convex"-shaped structure. The vertical surface of the left end of the "convex"-shaped structure is the backlight surface, and the vertical surface of the right end is the light-emitting surface. Photons oscillate back and forth between the backlight surface and the light-emitting surface and are amplified, and finally lasers are emitted from the active layer of the light-emitting surface. Preferably, the light-emitting surface uses the same silicon dioxide or silicon nitride as the passivation layer of the waveguide structure as the material of the anti-reflection film. Preferably, since the light-emitting surface and the backlight surface need to be coated in order to efficiently excite the laser, the light-emitting surface is made of the same material as the passivation layer, and the backlight surface is made of the same material as the metal electrode, wherein the electrode is made of a mixture of titanium, platinum, and gold. In this way, no additional complex processes are added during the test, so that the test method of this case only introduces two processes, namely, the waveguide partition area and the inclined surface cutting, for the chips in the monitoring test area, while the other processes are required for the chips produced normally and share the same processes. The test method of this embodiment is required to be as simple and fast as possible. If it is too complicated or the material / time cost is very high, it will have a counterproductive effect on the wafer-level monitoring test and will not achieve the purpose of reducing costs and improving efficiency. It is better to complete the remaining steps and directly test the finished chips.

[0021] See also Figures 1 to 17 , make electrodes on the epitaxial structure, use a test probe to inject carriers into the electrodes, the light-emitting surface is stimulated to radiate laser light, and then use a detector and optical fiber to test and analyze the laser light. By analyzing the laser light, it can be known whether the semi-finished chip is qualified. In the above embodiment, through this test method, if Figure 1As shown, when a chip is made on a wafer, the semi-finished chip is made to the extent that the chip can just be lit, that is, the epitaxial structure grows to: "Epitaxially grow an active structure containing a quantum well and a grating layer on the substrate, make a mode-selective grating, and then bury and grow it to the contact layer, grow a mask layer of a waveguide buried heterojunction on the epitaxial structure; then remove the mask layer on both sides of the buried heterojunction waveguide area, and etch it to the substrate under the epitaxial structure, retain the mask layer of the buried heterojunction waveguide area; then grow a restriction layer on both sides of the buried heterojunction waveguide area to form a buried heterojunction waveguide", when this extent (of course, a ridge waveguide can also be grown), stop making chips. At this time, select one or more test areas 0 on the wafer, and the chips in these test areas 0 are used for cutting to form an inclined surface for testing. If the test is qualified, several semi-finished chips that are not selected will continue to be taped out for subsequent manufacturing processes. If the test is unqualified, all semi-finished chips on the wafer will no longer be taped out, and can be used as a template for subsequent problem finding. In addition, regardless of whether the semi-finished chips in test area 0 are qualified, these semi-finished chips are discarded and no longer used, and are only used for wafer-level parameter monitoring in the chip production process.

[0022] The following is a specific implementation of the overall testing method: Take the preparation process of buried heterojunction waveguide structure as an example: See also Figure 1 , wafer-level test area layout design, test area 0 chips are arranged in a bar shape, which is convenient for subsequent cutting process and evenly distributed in the wafer to monitor the uniformity within the wafer; See also Figure 2 and Figure 3 , using MOCVD to sequentially grow an active layer 2, an InP transition layer 3, and a grating layer 4 on an InP substrate 1, using EBL technology and etching technology to make a grating, and using MOCVD to continue to bury and grow a grating buried layer 5; See also Figure 4 and Figure 5 , using photolithography technology and etching technology, the mask layer on both sides of the buried heterojunction waveguide area is removed, and a bromine-based etching solution is used to etch to the InP substrate 1, and the mask layer of the buried heterojunction waveguide area is retained; then, an InP confinement layer 6 is grown on both sides of the buried heterojunction waveguide area by MOCVD to form a buried heterojunction waveguide, and finally, the mask layer of the buried heterojunction waveguide area is removed, and a Top layer buried structure including an InP transition layer 7 and a contact layer 8 is grown by MOCVD; See also Figure 6 and Figure 7, using PECVD to grow the mask layer, using photolithography and etching processes, retaining the mask layer that buries the heterojunction waveguide area, and then using ICP etching technology to form waveguide partition areas at the HR end waveguide partition area 9 and the AR end waveguide partition area 10, respectively, keeping the light output cavity surface vertical, the etching depth is preferably 10~30μm, and then removing the mask layer. The purpose of this step is to form the resonant cavity surface of the laser and fix the cavity length; See also Figures 8 to 11 , the whole surface is spin-coated with photoresist, and the thickness of the photoresist is preferably 1μm. The mask glue in the reflector area is removed by photolithography technology. Note that the mask glue on the side wall of the cavity surface needs to be retained. Then, a 45° chopping knife is equipped with a cutting device to form a 45° bevel on the reflector cutting area 11 of the wafer. The cutting direction is perpendicular to the buried heterojunction waveguide, the cutting depth is 20~50μm, the cutting width is 20~50μm, and the feed speed is 0.1~0.5mm / s; thereby obtaining a 45° bevel, and then removing the mask glue; before cutting, the substrate 1 is first placed on the expansion ring bottom film 17, and then the expansion ring bottom film 17 is placed on the vacuum chuck 16 of the cutting device. The cutting device uses a grinding wheel 18.

[0023] See also Fig.12 and Fig.13 , using PECVD to grow a passivation layer and an anti-reflection film 12 in the light-emitting direction, the thickness of the film layer is simulated and calculated according to the reflectivity requirements; See also Fig.14 and Fig.15 , using photolithography and etching processes, open the P electrode contact, make a P electrode pad 13 on the buried heterojunction waveguide, and then make an Au metal thin layer 14 on the reflective slope as the reflective surface of the reflector to reflect the laser 15 emitted vertically by the laser to the vertical direction. Note that the Au metal thin layer 14 cannot be connected to the P electrode pad 13; See also Fig.16 and Fig.17 , thin the wafer, make the N electrode 19 and alloy it, without the need for subsequent processes such as stripping, stacking, and cavity surface coating, the laser can be directly lit at the wafer level and key parameters can be tested and monitored. The test probe 21 is used to inject carriers into the electrode, and the resonant cavity surface is stimulated to radiate laser, and then the detector and light receiving fiber 22 are used to test and analyze the laser. The N electrode 19 is set on the test equipment carrier 20.

[0024] So far, the present invention uses lithography, etching and special cutting processes to form a horizontal cavity laser that can emit vertical light in a specific monitoring and testing area on the wafer during the wafer tape-out process of a conventional horizontal cavity laser, and performs carrier injection on a probe station on the wafer and uses a detector and a tapered optical fiber to test and analyze the laser of stimulated radiation, thereby realizing the process monitoring and characterization of the wafer-level parameters of the horizontal cavity laser. The key step of this scheme is that after the conventional horizontal cavity laser tape-out is developed to form a ridge waveguide or a buried heterojunction waveguide structure, the front and rear reflection surfaces are formed in the monitoring and testing area of ​​the wafer by lithography and dry etching, and in the waveguide partition area of ​​the front reflection surface, a grinding wheel type wafer cutting machine equipped with a 45° tilted grinding wheel is used to cut the monitoring and testing area on the horizontal cavity laser wafer to form a 45° inclined surface, an anti-reflection film is plated on the side wall of the front reflection surface, and gold is plated on the rear reflection surface and the 45° inclined surface to realize the resonant cavity of the horizontal cavity laser and the vertical light-emitting total reflection mirror, thereby realizing the monitoring and characterization of the wafer-level parameters.

[0025] The embodiment of the present invention provides a method for manufacturing a horizontal cavity surface laser, and adopts the above-mentioned method for testing a horizontal cavity surface laser, specifically: selecting a wafer with a number of semi-finished chips; selecting at least one test area 0 on the wafer, wherein some of the semi-finished chips are in the test area 0; adopting the above-mentioned test method to test the semi-finished chips on the test area 0; if the semi-finished chips on the test area 0 are tested to be qualified, the semi-finished chips outside the test area 0 are continued to be taped out to the subsequent manufacturing process until the finished chips are obtained, and if the semi-finished chips tested by the test method are unqualified, the taping out of all the semi-finished chips outside the test area 0 is terminated. The above-mentioned test method is used in the manufacture of horizontal cavity surface lasers, which can greatly improve the manufacturing efficiency and reduce the manufacturing cost, because tens of thousands of chips can be made on a wafer, and each test area 0 has only more than one hundred semi-finished chips dedicated to process monitoring. Even if the semi-finished chips in the test area 0 are discarded, at most only about 5% of the chips are wasted, which can greatly reduce the cost compared with the chips of the entire wafer that are wasted due to poor quality. Preferably, subsequent manufacturing processes include strip stripping, strip strip stacking, cavity surface coating and other subsequent processes.

[0026] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for testing a horizontal cavity surface laser, characterized in that: The steps include: S1, making a smooth surface on the epitaxial structure; S2, then cutting the epitaxial structure to form an inclined surface, wherein the inclined surface faces the light emitting surface; S3, coating the inclined surface, using the inclined surface as a reflection surface for emitting laser light from the light emitting surface, and the reflection surface reflects the laser light out of the epitaxial structure; S4, collecting and analyzing the laser reflected outside the epitaxial structure to determine whether the chip before tape-out is qualified.

2. The method for testing a horizontal cavity surface laser according to claim 1, wherein: In the step S2, a cutting device is used to cut and form the inclined surface.

3. The method for testing a horizontal cavity surface laser according to claim 2, characterized in that: The inclined groove is cut by a grinding wheel with an inclined blade, and then the inclined groove is etched to obtain a smooth inclined surface.

4. The method for testing a horizontal cavity surface laser according to claim 2, wherein: The cutting depth is between 20 and 50 μm, the cutting width is between 20 and 50 μm, and the feed speed is between 0.1 and 0.5 mm / s.

5. The method for testing a horizontal cavity surface laser according to claim 1, wherein: Before manufacturing the light output surface, a buried heterojunction waveguide or a ridge waveguide is manufactured on the epitaxial structure.

6. The method for testing a horizontal cavity surface laser according to claim 5, characterized in that: The specific method for making a buried heterojunction waveguide is: growing a buried heterojunction mask layer on an epitaxial structure; then removing the mask layer on both sides of the buried heterojunction waveguide region, and corroding to the substrate under the epitaxial structure, retaining the mask layer of the buried heterojunction waveguide region; then growing a restriction layer on both sides of the buried heterojunction waveguide region to form a buried heterojunction waveguide.

7. The method for testing a horizontal cavity surface laser according to claim 5, characterized in that: Waveguide isolation regions are formed at both ends of the buried heterojunction waveguide or the ridge waveguide.

8. The method for testing a horizontal cavity surface laser according to claim 1, wherein: The epitaxial structure is also made with a backlight surface, which is located at the end of the epitaxial structure away from the inclined surface. The light-emitting surface is coated with an anti-reflection film, and the inclined surface and the backlight surface are both coated with a high-reflection film. The material of the light-emitting surface is the same as that of the passivation layer, and the material of the backlight surface is the same as that of the electrode.

9. The method for testing a horizontal cavity surface laser according to claim 1, wherein: Electrodes are fabricated on the epitaxial structure, carriers are injected into the electrodes using a test probe, the light-emitting surface is stimulated to radiate laser light, and then a detector and an optical fiber are used to test and analyze the laser light.

10. A method for manufacturing a horizontal cavity surface laser, characterized in that: Select a wafer with several semi-finished chips, At least one test area is selected on the wafer, wherein some of the semi-finished chips are in the test area, The semi-finished chips on the test area are tested using the horizontal cavity surface laser testing method as described in any one of claims 1 to 9. If the semi-finished chips on the test area pass the test, the semi-finished chips outside the test area will continue to be taped out to the subsequent production process until the finished chips are obtained. If the semi-finished chips tested by the test method fail to pass the test, the taping of all semi-finished chips outside the test area will be terminated.

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