CN117673895A - Preparation method for improving uniformity of laser grating morphology and epitaxial wafer thereof - Google Patents
Preparation method for improving uniformity of laser grating morphology and epitaxial wafer thereof Download PDFInfo
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 7
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
The invention relates to a preparation method for improving the uniformity of the grating morphology of a laser and an epitaxial wafer thereof. The method mainly comprises the following steps: growing a layer of SiO on the surface of the initial epitaxial wafer structural material 2 Film layer and at SiO 2 Coating photoresist on the film layer; exposing the photoresist in partial area with electron beam to transfer the grating pattern to the photoresist; siO corresponding to photoresist in exposure area 2 The film layer is etched cleanly, and the grating pattern is transferred from the photoresist to SiO 2 On the film layer, siO which is not etched at this time 2 The film layer is used as a masking layer of the semiconductor material below the film layer; preparing a bromine-containing corrosive liquid and a sulfur-containing corrosive liquid, and corroding SiO-free through the bromine-containing corrosive liquid 2 Film-masked binary InP material free of SiO by sulfur-containing etchant 2 A film masked quaternary InGaAsP material; and after the initial epitaxial wafer is cleaned, carrying out secondary epitaxy on the initial epitaxial wafer. The invention adopts film maskingThe sectional etching process ensures consistent grating morphology and prevents the occurrence of quantum well damage caused by corrosion of the etching stop layer.
Description
Technical Field
The invention relates to the technical field of lasers, in particular to a preparation method for improving the uniformity of the grating morphology of a laser and an epitaxial wafer thereof.
Background
The grating fabrication process in a conventional DFB (Distributed Feed Back ), DBR (Distributed Bragg reflection, distributed bragg reflection) laser generally uses wet etching and dry etching of semiconductor materials, such as iii-v compound semiconductor materials: inP, inGaAs, inGaAsP.
For dry etching, the grating morphology consistency of the dry etching process is good, rectangular and trapezoidal gratings can be obtained, but material damage can be brought in the etching process, so that the reliability of a chip is affected, and the surface of the dry etching process is not smooth, so that the subsequent secondary epitaxy is also adversely affected; for wet etching, the most common wet etching solution is bromine etching solution, the etching rate of the bromine etching solution is isotropic for the III-group and V-group semiconductor materials, the bromine etching solution can etch InP, inGaAs, inGaAsP materials, the etching crystal orientation of the bromine etching solution is about 60 degrees for the III-V-group semiconductor materials, the etching depth is often limited by lateral etching in the etching process, the top materials are completely etched laterally when the etching depth is not deep enough, once the top materials are etched, the etching depth is not increased any more and the grating morphology can be damaged; and the bromine corrosive liquid has unstable speed due to volatile corrosion, and the binary InP material below the quaternary grating layer can be corroded due to the corrodible InP material, so that the light-emitting area of the quantum well laser is damaged.
In summary, the existing dry etching and wet etching techniques often damage the grating morphology, and it is difficult to ensure that the material is not damaged, so how to overcome the defects or demands of the prior art, and solve the above technical problems is a problem to be solved in the technical field.
Disclosure of Invention
Aiming at the defects or improvement demands in the prior art, the invention provides a preparation method for improving the uniformity of the grating morphology of a laser and an epitaxial wafer thereof, wherein the uniformity of the grating morphology is ensured by adopting a film masking and sectional etching process, and the occurrence of the phenomenon that an etching stop layer is corroded to damage a quantum well is avoided.
The embodiment of the invention adopts the following technical scheme:
in a first aspect, the present invention provides a preparation method for improving uniformity of a laser grating morphology, including:
growing a layer of SiO on the surface of the initial epitaxial wafer structural material 2 Film layer and at SiO 2 Coating photoresist on the film layer;
exposing partial region photoresist with electron beam to transfer grating pattern onto photoresist, wherein the unexposed region photoresist is used as SiO below 2 Is a masking layer of (a);
SiO corresponding to photoresist in exposure area 2 The film layer is etched cleanly, and the grating pattern is transferred from the photoresist to SiO 2 On the film layer, siO which is not etched at this time 2 The film layer is used as a masking layer of the semiconductor material below the film layer;
preparing a bromine-containing corrosive liquid and a sulfur-containing corrosive liquid, and corroding SiO-free through the bromine-containing corrosive liquid 2 Film-masked binary InP material free of SiO by sulfur-containing etchant 2 A film masked quaternary InGaAsP material;
and after the initial epitaxial wafer is cleaned, carrying out secondary epitaxy on the initial epitaxial wafer.
Further, a layer of SiO is grown on the surface of the initial epitaxial structure material 2 SiO during film formation 2 The thickness of the film layer is 30nm-70nm.
Further, the method is characterized in that 2 When the photoresist is coated on the film layer, the rotating speed of the gumming machine is 3000-4500 revolutions per minute, and the thickness of the photoresist is controlled to be 100-130nm.
Further, when the electron beam exposure is adopted for the photoresist in the partial area, the exposure and development time is controlled to enable the unexposed photoresist to be smaller than 5nm, and then the initial epitaxial wafer is subjected to glow for 0.5-1.5 minutes so as to completely remove residual photoresist which is not completely developed.
Further, the exposure area photoresist corresponds to SiO 2 Etching SiO when the film layer is etched cleanly 2 The gas of the membrane layer is CHF 3 :O 2 :CF 4 After etching was completed, the initial epitaxial wafer was glow for 5-10 min and heated with NMP for 10-15 min to list the initial epitaxial wafer =10:2:2-15:4:4The planar photoresist is completely removed.
Further, when preparing the bromine-containing corrosive liquid and the sulfur-containing corrosive liquid, the bromine-containing corrosive liquid is a mixed solution of saturated bromine water, hydrobromic acid, nitric acid and water, and the sulfur-containing corrosive liquid is a mixed solution of concentrated sulfuric acid, hydrogen peroxide and water;
the ratio of the bromine-containing corrosive liquid comprises saturated bromine water, hbr and HNO 3 :H 2 O=5:5:4:400, the ratio of the sulfur-containing corrosive liquid comprises H 2 SO 4 :H 2 O 2 :H 2 O=5:5:250, wherein the purity of hydrobromic acid, nitric acid and hydrogen peroxide is MOS grade, the corrosion rate of the bromine-containing corrosive liquid is 1nm +/-20% per second, and the corrosion rate of the sulfur-containing corrosive liquid is 0.2nm +/-20% per second.
Further, the initial epitaxial wafer structure comprises a first layer of binary InP material, a second layer of quaternary InGaAsP material, and a third layer of binary InP material.
Further, the method etches SiO-free by bromine-containing corrosive liquid 2 Masked binary InP material, siO-free etched by sulfur-containing etchant 2 The masked quaternary InGaAsP material specifically includes:
corrosion of SiO-free using bromine-containing corrosive liquids 2 Masking the binary InP material of the third layer in the range and etching a portion of the quaternary InGaAsP material of the second layer in the corresponding range;
measuring grating corrosion depth after corrosion, and adjusting corrosion time of subsequent sulfur-containing corrosive liquid according to corrosion depth of quaternary InGaAsP layer so as to eliminate SiO 2 The remaining quaternary InGaAsP material within the masking range is completely etched.
Further, after the initial epitaxial wafer is cleaned, performing secondary epitaxy on the initial epitaxial wafer specifically includes:
BOE rinsing masking layer SiO 2 And then washing the initial epitaxial wafer, carrying out secondary material growth on the initial epitaxial wafer, covering the binary InP material of the third layer again, and finally realizing a grating region formed by interleaving the binary InP material and the quaternary InGaAsP material in the second layer.
In a second aspect, the invention provides an epitaxial wafer for improving uniformity of laser grating morphology, which is manufactured by using the preparation method according to the first aspect, and comprises a first layer of binary InP material, a second layer of binary InP material, a quaternary InGaAsP material and a third layer of binary InP material, wherein the second layer of binary InP material and the quaternary InGaAsP material are staggered to form a grating region.
Compared with the prior art, the invention has the beneficial effects that: the invention provides a preparation method for improving the uniformity of the appearance of a laser grating, which comprises the steps of firstly growing a layer of SiO with a specific thickness range on the surface of an epitaxial structure 2 Coating a film layer, coating a glue on the film, transferring a grating fringe pattern to photoresist by adopting electron beam lithography, and transferring SiO corresponding to the photoresist in an exposure area 2 Etching cleanly to transfer the grating pattern from the photoresist to SiO 2 Etching the III-V semiconductor material by a bromine system and sulfuric acid hydrogen peroxide system etching solution sectional etching process, and finally removing the grating pattern from the SiO 2 Transferred to an epitaxial wafer. The invention adopts the film masking and sectional etching process to ensure the consistent grating morphology and avoid the phenomenon of damaging the quantum well caused by the corrosion of the etching stop layer.
Drawings
In order to more clearly illustrate the technical solution of the embodiments of the present invention, the drawings that are required to be used in the embodiments of the present invention will be briefly described below. It is evident that the drawings described below are only some embodiments of the present invention and that other drawings may be obtained from these drawings without inventive effort for a person of ordinary skill in the art.
FIG. 1 is a flowchart of a preparation method for improving uniformity of laser grating morphology according to embodiment 1 of the present invention;
fig. 2 is a schematic cross-sectional view of three material layers involved in the grating manufacturing process according to embodiment 1 of the present invention;
FIG. 3 is a schematic cross-sectional view of a grating profile after electron beam exposure according to embodiment 1 of the present invention;
FIG. 4 is a schematic diagram of a grating structure in a laser according to embodiment 1 of the present invention;
FIG. 5 is a schematic illustration of the preparation flow of example 2 of the present invention;
fig. 6 is a schematic diagram of a laser grating structure according to an example of embodiment 2 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
It should be noted that, in the embodiments of the present application, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a method or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such method or apparatus. Without further limitation, an element defined by the phrase "comprising.," does not exclude the presence of other related elements in a method or apparatus comprising the element (e.g., a step in a method or an element in an apparatus, e.g., an element may be part of a circuit, part of a processor, part of a program or software, etc.).
In addition, the technical features of the embodiments of the present invention described below may be combined with each other as long as they do not form a conflict with each other, and the steps may be exchanged in order if they are logical and do not conflict with each other. The invention will be described in detail below with reference to the drawings and examples.
Example 1:
the embodiment of the invention aims to provide a manufacturing method of a high-consistency morphology grating, which can be used for manufacturing DFB and DBR lasers, wherein an epitaxial structure of the laser is based on III-V semiconductor materials, a quaternary grating layer in the epitaxial structure is suitable for 15-60nm, an electron beam exposure technology is adopted for various exposure layout grating duty ratios, a film masking and sectional corrosion technology is adopted to ensure the consistency of the morphology of the grating, and the phenomenon that a quantum well is damaged due to corrosion of an etch stop layer is avoided.
As shown in fig. 1, embodiment 1 of the present invention provides a preparation method for improving uniformity of laser grating morphology, which includes the following steps.
Step 100: growing a layer of SiO on the surface of the initial epitaxial wafer structural material 2 Film layer and at SiO 2 And coating photoresist on the film layer. In a preferred embodiment of this step of this embodiment, a layer of SiO is grown on the surface of the initial epitaxial wafer structure material 2 SiO during film formation 2 The thickness of the film layer is 30nm-70nm. In a preferred embodiment of this step of the present embodiment, in SiO 2 When the photoresist is coated on the film layer, the rotating speed of the gumming machine is 3000-4500 revolutions per minute, and the thickness of the photoresist is controlled to be 100-130nm.
Step 200: exposing partial region photoresist by electron beam to transfer grating fringe pattern onto photoresist, wherein the unexposed region photoresist is used as SiO below 2 Is used for the masking layer of the (a). In a preferred embodiment of this step of this embodiment, when electron beam exposure is used to expose a partial region of the photoresist, the exposure and development time is controlled so that the unexposed primer is less than 5nm, and then the epitaxial wafer is subjected to short-time glow (0.5-1.5 minutes glow) to completely remove the residual primer that has not been developed completely.
Step 300: siO corresponding to photoresist in exposure area 2 The film layer is etched cleanly, and the grating pattern is transferred from the photoresist to SiO 2 At this time, siO which is not etched 2 As a masking layer for the semiconductor material beneath it. In a preferred embodiment of this step of this embodiment, the exposure area photoresist is subjected to SiO 2 Etching SiO when etching cleanly 2 The gas of the membrane layer is CHF 3 :O 2 :CF 4 =10:2:2-15:4:4, wherein CHF 3 Performs etching and can provide sidewall protection, O 2 CF (compact flash) 4 The etching speed can be increased, the grating edge morphology and the duty ratio can be maintained in the etching process, and after the etching is finished, the initial epitaxial wafer is glow for 5-10 minutes and heated by NMP for 10-15 minutes, so that the photoresist on the surface of the initial epitaxial wafer is completely removed. It should be noted that wet etching is classified into a dielectric film and a photoresist as a masking layer, and the dielectric film has higher stability and higher stability than the photoresistCorrosion resistance, no degluing phenomenon is caused to lead the material below the masking layer to be corroded, good grating morphology can be obtained, and SiO (silicon oxide) in the dielectric film 2 Film system is higher than SiN x The film system has smaller stress, easier removal, less damage introduction and strong etching resistance, so the embodiment selects SiO 2 The film layer serves as a dielectric film. And commonly etch SiO 2 Is CHF (CHF) 3 /CF 4 Argon, fluorine-based gas (CHF) 3 /CF 4 ) For etching, argon has the effect of removing polymer by physical bombardment glow, but the physical bombardment removal effect of the argon can change the grating etching morphology, so that the edge is irregular, so the embodiment replaces the grating etching morphology with a small amount of O 2 A small amount of oxygen can remove the bottom photoresist, and the opening is opened to avoid the polymer blocking to change the grating morphology, CF 4 Compared with CHF 3 Higher etch rate but CHF 3 Has side wall protecting effect and polymer resolving effect, and after a large number of experiments, CHF is selected in this embodiment 3 :O 2 :CF 4 Etching gas of 10:2:2-15:4:4 to achieve optimal effect.
Step 400: preparing a bromine-containing corrosive liquid and a sulfur-containing corrosive liquid, and corroding SiO-free through the bromine-containing corrosive liquid 2 Masked binary InP material, siO-free etched by sulfur-containing etchant 2 A masked quaternary InGaAsP material. In a preferred embodiment of this step of this embodiment, when preparing the bromine-containing etching solution and the sulfur-containing etching solution, the bromine-containing etching solution is a mixed solution of saturated bromine water, hydrobromic acid, nitric acid and water, and the sulfur-containing etching solution is a mixed solution of concentrated sulfuric acid, hydrogen peroxide and water. In a preferred embodiment of this step of this embodiment, the bromine-containing etching solution comprises saturated bromine water, hbr, HNO 3 :H 2 O=5:5:4:400, the ratio of the sulfur-containing corrosive liquid comprises H 2 SO 4 :H 2 O 2 :H 2 O=5:5:250, wherein the purity of hydrobromic acid, nitric acid and hydrogen peroxide is MOS grade, the corrosion rate of the bromine-containing corrosive liquid is 1nm plus or minus 20 percent per second, the corrosion rate of the sulfur-containing corrosive liquid is 0.2nm plus or minus 20 percent per second, and the bromine-containing corrosive liquid and the sulfur-containing corrosive liquid are subjected to ice bath standing for 1 hour after being configured, and then are used for corrosionEtching the epitaxial wafer. It should be noted that the initial epitaxial wafer structure of this embodiment includes a first layer of binary InP material, a second layer of quaternary InGaAsP material, and a third layer of binary InP material, and in a preferred embodiment of this step of this embodiment, the SiO-free layer is etched by a bromine-containing etchant 2 Masked binary InP material, siO-free etched by sulfur-containing etchant 2 The masked quaternary InGaAsP material specifically includes: corrosion of SiO-free using bromine-containing corrosive liquids 2 Masking the binary InP material of the third layer in the range and etching a portion of the quaternary InGaAsP material of the second layer in the corresponding range; measuring grating corrosion depth after corrosion, and adjusting corrosion time of subsequent sulfur-containing corrosive liquid according to corrosion depth of quaternary InGaAsP layer so as to eliminate SiO 2 The quaternary InGaAsP material of the remaining second layer within the masking range is completely etched. The proportion of the corrosive liquid in the step is extremely important, and the corrosion time is required to provide a larger control tolerance for the corrosion depth but cannot affect the production efficiency too slowly.
Step 500: and after the initial epitaxial wafer is cleaned, carrying out secondary epitaxy on the initial epitaxial wafer. In a preferred embodiment of this step of this embodiment, after cleaning the initial epitaxial wafer, performing secondary epitaxy on the initial epitaxial wafer specifically includes: BOE rinsing masking layer SiO 2 And then washing the initial epitaxial wafer, carrying out secondary material growth on the initial epitaxial wafer, covering the InP material of the third layer again, and finally realizing a grating region formed by interleaving the binary InP material and the quaternary InGaAsP material in the second layer.
Based on the steps, the embodiment of the invention firstly grows a layer of SiO with a specific thickness range on the surface of the initial epitaxial structure material 2 The film layer is coated with electron beam photoresist, the electron beam lithography machine is used for exposure, the oxygen glow is used for removing the bottom film after development to optimize the grating duty ratio, and the RIE equipment is used for dry etching of SiO by using trifluoromethane, oxygen and carbon tetrafluoride 2 The film layer transfers the grating pattern from the photoresist to SiO 2 Etching III-V semiconductor material by sectional etching process to obtain grating pattern from SiO 2 Transferred to an epitaxial wafer. RIE etching of SiO 2 The grating can be realized by selecting the gas proportion, flow and cavity pressure of the film layerFull transfer of duty cycle, siO 2 The film layer masking avoids the phenomenon that photoresist falls off to influence the grating morphology in the corrosion process, and the segmented corrosion process can further improve the grating depth consistency. In the above process of this embodiment, the grating period commonly used value is Λ=200-250 nm, and the staged etching process involves two etching solutions, wherein etching solution 1 (bromine-containing etching solution) is saturated bromine water: hydrobromic acid: the nitric acid is water mixed solution which is used for corroding the binary InP layer and part of the quaternary InGaAsP layer, and the corrosive liquid 2 (sulfur-containing corrosive liquid) is concentrated sulfuric acid: hydrogen peroxide: the water mixed solution is used for corroding the residual quaternary InGaAsP layers, so that the quaternary InGaAsP materials of the grating layers are guaranteed to be corroded cleanly and the corrosion depths are consistent. The corrosive liquid 2 uses H 2 SO 4 /H 2 O 2 The system etchant may etch ternary quaternary InGaAs, inGaAsP material but hardly etch InP material.
The above is a description of the steps of the embodiments of the present invention, and the preparation method is described in more detail below through schematic diagrams of the various stages in the manufacture.
It should be noted that, generally, the laser structure that extends on the substrate is a growth buffer layer, a lower confinement layer, a multiple quantum well and an upper confinement layer, on which an etch stop layer and three layers of materials forming a grating structure are grown, and the three layers of materials involved in the grating manufacturing process according to the embodiment of the present invention are shown in the schematic cross-sectional view of fig. 2: the bottom layer 2-1 in fig. 2 is a binary indium phosphide layer (i.e., the binary InP material of the first layer described above), the middle layer 2-2 in fig. 2 is a quaternary grating layer (i.e., the quaternary InGaAsP material of the second layer described above), and the top layer 2-3 in fig. 2 is a binary indium phosphide layer (i.e., the binary InP material of the third layer described above); growing a layer of SiO with specific thickness on the surface of the epitaxial wafer 2 The method comprises the steps of carrying out a first treatment on the surface of the On the surface of which SiO grows 2 The epitaxial wafer is glued, the rotating speed of the glue coater is 4000 revolutions per minute, and the glue thickness is controlled to be 100-130nm; and (3) carrying out electron beam exposure on the epitaxial wafer, and controlling exposure and development time to enable the unexposed primer to be smaller than 5nm. The epitaxial wafer is glow for a short time by a glow machine, the residual primer which is not developed completely is completely removed, and SiO 2 The unexposed part of the surface is masked by photoresist, and the grating morphology is truncated after the electron beam exposureThe schematic surface diagram is shown by referring to FIG. 3, the bottommost layer is marked 3-1 in FIG. 3 as an epitaxial structure material (namely 2-1, 2-2 and 2-3 in FIG. 2, and the middle layer is marked 3-2 as SiO in FIG. 3) 2 The uppermost layer of the film layer is marked with 3-3 in figure 3 as photoresist. Etching SiO on epitaxial wafer surface by using RIE equipment 2 SiO without photoresist masking 2 And (5) partial etching is complete. Glow for 5min, heating for 10min with NMP, and completely removing photoresist on the surface of the wafer; siO (SiO) 2 As a masking layer, firstly, etching a binary InP material without a masking range (a binary InP material of a third layer) and a part of quaternary InGaAsP material (a quaternary InGaAsP material of a second layer) by using etching solution 1 (bromine-containing etching solution), measuring grating etching depth by using an AFM atomic force microscope after etching, generally, adjusting etching time of etching solution 2 (sulfur-containing etching solution) according to the etching depth of the quaternary InGaAsP layer of the second layer, and completely etching the residual quaternary InGaAsP material. BOE rinsing masking layer SiO 2 And then washing the epitaxial wafer. And (3) carrying out secondary epitaxy on the epitaxial wafer after the process, and finally forming a periodic grating structure formed by interlacing two materials with a certain refractive index difference, wherein a schematic diagram of the formed grating structure is shown by referring to FIG. 4, wherein 4-1 is marked as a binary Inp material, and 4-2 is marked as a quaternary InGaAsP material.
In addition, the embodiment further provides an epitaxial wafer for improving the uniformity of the laser grating morphology, and the epitaxial wafer is manufactured by the manufacturing method for improving the uniformity of the laser grating morphology, and referring to fig. 4, the manufactured epitaxial wafer comprises a first layer of binary InP material, a second layer of binary InP material, a quaternary InGaAsP material and a third layer of binary InP material, wherein the second layer of binary InP material and the quaternary InGaAsP material are staggered to form a grating region.
In summary, the embodiment of the invention provides a method for manufacturing a high-uniformity morphology grating in a III-V semiconductor material based DFB/DBR laser with an epitaxial structure, which comprises the steps of firstly growing a layer of SiO with a specific thickness range on the surface of the epitaxial structure 2 The film layer is coated with glue, the grating fringe pattern is transferred to the photoresist by adopting electron beam lithography, and the grating duty ratio is optimized by adopting oxygen glow to remove the bottom film after developmentDry etching of SiO using trifluoromethane, oxygen, carbon tetrafluoride using RIE apparatus 2 A film layer for transferring the grating pattern from the photoresist to SiO 2 Etching the III-V semiconductor material by a bromine system and sulfuric acid hydrogen peroxide system etching solution sectional etching process, and finally removing the grating pattern from the SiO 2 Transferred to an epitaxial wafer. The grating manufacturing flow relates to a three-layer epitaxial structure which is sequentially epitaxial, the grating is a periodic structure formed by interlacing two materials with a certain refractive index difference, and material damage and reliability influence caused in the process of etching the III-V semiconductor material by a RIE dry method can be avoided by wet etching the III-V semiconductor material. The common electron beam photoresist has certain etching resistance and corrosion resistance, and the photoresist is not easy to fall off due to insufficient photoresist masking adhesion in the etching process of the wafer, so that the top of the grating is corroded, thereby affecting the uniformity of the grating morphology and further affecting the chip characteristics.
Example 2:
based on the preparation method for improving the uniformity of the laser grating morphology provided in the embodiment 1, the feasibility of the invention is verified by a specific example in the embodiment 2 of the invention.
The epitaxial layer material layer according to the embodiment of the present invention is a three-layer material as shown in fig. 2, the first layer material 2-1 is InP, the second layer material 2-2 is InGaAsP, and the third layer material 2-3 is InP, and in a specific example, for example, the depth of the material 2-1 is 30nm, the depth of the material 2-2 is 25nm, and the depth of the material 2-3 is 20nm. As shown in fig. 5, the following steps are included. It should be noted that the specific values in the following steps are only preferred examples, and are not limiting of the present invention.
Step 1: growth of 50nm deep SiO on epitaxial wafer 2 A film layer, which serves as a masking layer.
Step 2: growing SiO on the surface 2 Coating the epitaxial wafer of the film layer with a coating machine with a rotating speed of 4000 revolutions per minuteThe thickness of the gel is controlled to be 120nm.
Step 3: exposing the epitaxial wafer with electron beam, and transferring the pattern of grating stripes to SiO after development 2 The purpose of increasing the grating duty cycle on the film is to increase the tolerance of the etching time to the etching depth, and the epitaxial wafer is developed with a diluted developer to remove the unexposed portions.
Step 4: and (3) glow the epitaxial wafer for 1min by using a glow machine for a short time, completely removing residual primer which is not completely developed, and adjusting the duty ratio of the grating pattern.
Step 5: RIE equipment etches SiO covered on epitaxial wafer surface 2 Film layer, etching gas flow is CHF 3 :15sccm、O 2 :3sccm、CF 4 2sccm, chamber pressure 40mTorr, etching time 4 minutes, and exposing the SiO of the area 2 Etching clean, and taking the photoresist of the unexposed area as SiO below 2 For transferring the grating fringe pattern from the photoresist to SiO 2 And the film layer is arranged on the film layer.
Step 6: glow for 5min with a glossing machine, heating with NMP for 20min, removing photoresist on the surface of the wafer, and removing residual SiO 2 The film layer serves as a masking layer.
Step 7: preparing a corrosive liquid 1: saturated bromine water, 5ml, hbr, 5ml, HNO 3 :5ml，H 2 O:400ml, preparing and completing ice bath standing for 1 hour, and then corroding the epitaxial wafer for 35 seconds, wherein the corrosion depth is 38-40 nm measured by an atomic force microscope; preparing a corrosive liquid 2: h 2 SO 4 :5ml，H 2 O 2 :5ml，H 2 O:250ml, after the preparation and standing for 1 hour in an ice bath, continuing to etch the epitaxial wafer for 65 seconds, and completely etching the residual quaternary InGaAsP.
Step 8: BOE rinsing masking layer SiO 2 min 2 And removing and washing with deionized water.
Step 9: and (3) carrying out secondary epitaxy on the epitaxial wafer after the process, and finally forming the periodic grating structure formed by interlacing two materials with a certain refractive index difference as shown in fig. 6. In fig. 6, 6-1 is InP,6-2 is InGaAsP, and 6-3 is a corrosion-cut-off layer, and the segment corrosion method of this embodiment does not damage the corrosion-cut-off layer, so that the underlying quantum well light-emitting region is not damaged.
In summary, in the embodiment of the invention, a layer of SiO with a specific thickness range is grown on the surface of the epitaxial structure 2 Coating a film layer, coating a glue on the film, transferring a grating fringe pattern onto a photoresist by adopting electron beam lithography, removing a bottom film by adopting oxygen glow after development to optimize the grating duty ratio, and etching SiO by adopting dry method of trifluoromethane, oxygen and carbon tetrafluoride by adopting RIE equipment 2 A film layer for transferring the grating pattern from the photoresist to SiO 2 Etching the III-V semiconductor material by a bromine system and sulfuric acid hydrogen peroxide system etching solution sectional etching process, and finally removing the grating pattern from the SiO 2 Transferred to an epitaxial wafer. The grating manufacturing flow relates to a three-layer epitaxial structure which is sequentially epitaxial, the grating is a periodic structure formed by interlacing two materials with a certain refractive index difference, and material damage and reliability influence caused in the process of etching the III-V semiconductor material by a RIE dry method can be avoided by wet etching the III-V semiconductor material. The common electron beam photoresist has certain etching resistance and corrosion resistance, and the photoresist is not easy to fall off due to insufficient photoresist masking adhesion in the etching process of the wafer, so that the top of the grating is corroded, thereby affecting the uniformity of the grating morphology and further affecting the chip characteristics.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention. What is not described in detail in this specification is prior art known to those skilled in the art.
Claims (10)
1. The preparation method for improving the uniformity of the appearance of the laser grating is characterized by comprising the following steps of:
growing a layer of SiO on the surface of the initial epitaxial wafer structural material 2 Film layer and at SiO 2 Coating photoresist on the film layer;
exposing partial region photoresist with electron beam to transfer grating pattern onto photoresist, wherein the unexposed region photoresist is used as SiO below 2 Is a masking layer of (a);
SiO corresponding to photoresist in exposure area 2 The film layer is etched cleanly, and the grating pattern is transferred from the photoresist to SiO 2 On the film layer, siO which is not etched at this time 2 The film layer is used as a masking layer of the semiconductor material below the film layer;
preparing a bromine-containing corrosive liquid and a sulfur-containing corrosive liquid, and corroding SiO-free through the bromine-containing corrosive liquid 2 Film-masked binary InP material free of SiO by sulfur-containing etchant 2 A film masked quaternary InGaAsP material;
and after the initial epitaxial wafer is cleaned, carrying out secondary epitaxy on the initial epitaxial wafer.
2. The method for improving uniformity of laser grating morphology according to claim 1, wherein a layer of SiO is grown on the surface of the initial epitaxial structure material 2 SiO during film formation 2 The thickness of the film layer is 30nm-70nm.
3. The method for improving uniformity of laser grating morphology according to claim 1, wherein the step of forming the laser grating morphology comprises the steps of 2 When the photoresist is coated on the film layer, the rotating speed of the gumming machine is 3000-4500 revolutions per minute, and the thickness of the photoresist is controlled to be 100-130nm.
4. The method for improving uniformity of laser grating morphology according to claim 1, wherein when the partial region photoresist is exposed by electron beam, the exposure and development time is controlled to make the unexposed photoresist less than 5nm, and then the initial epitaxial wafer is subjected to glow for 0.5-1.5 minutes to completely remove residual photoresist which has not been developed completely.
5. The method for improving uniformity of laser grating morphology according to claim 1, wherein the exposure area is corresponding to the photoresist is SiO 2 Etching SiO when the film layer is etched cleanly 2 The gas of the membrane layer is CHF 3 :O 2 :CF 4 After etching was completed, the initial epitaxial wafer was glow for 5-10 min and heated with NMP for 10-15 min to completely remove the initial epitaxial wafer surface photoresist.
6. The method for improving the uniformity of the grating morphology of the laser according to claim 1, wherein when preparing the bromine-containing corrosive liquid and the sulfur-containing corrosive liquid, the bromine-containing corrosive liquid is a mixed solution of saturated bromine water, hydrobromic acid, nitric acid and water, and the sulfur-containing corrosive liquid is a mixed solution of concentrated sulfuric acid, hydrogen peroxide and water;
the ratio of the bromine-containing corrosive liquid comprises saturated bromine water, hbr and HNO 3 :H 2 O=5:5:4:400, the ratio of the sulfur-containing corrosive liquid comprises H 2 SO 4 :H 2 O 2 :H 2 O=5:5:250, wherein the purity of hydrobromic acid, nitric acid and hydrogen peroxide is MOS grade, the corrosion rate of the bromine-containing corrosive liquid is 1nm +/-20% per second, and the corrosion rate of the sulfur-containing corrosive liquid is 0.2nm +/-20% per second.
7. The method for improving uniformity of laser grating morphology according to any one of claims 1-6, wherein the initial epitaxial wafer structure comprises a first layer of binary InP material, a second layer of quaternary InGaAsP material, and a third layer of binary InP material.
8. The method for improving uniformity of laser grating topography according to claim 7, wherein the etching of SiO-free by a bromine-containing etching solution 2 Masked binary InP material, siO-free etched by sulfur-containing etchant 2 The masked quaternary InGaAsP material specifically includes:
corrosion of SiO-free using bromine-containing corrosive liquids 2 Masking the binary InP material of the third layer in the range and etching a portion of the quaternary InGaAsP material of the second layer in the corresponding range;
measuring grating corrosion depth after corrosion, adjusting according to the corrosion depth of the quaternary InGaAsP layerThe subsequent corrosion time of the sulfur-containing corrosive liquid is completed so as to avoid SiO 2 The remaining quaternary InGaAsP material within the masking range is completely etched.
9. The method for improving uniformity of laser grating morphology according to claim 8, wherein the step of performing secondary epitaxy on the initial epitaxial wafer after the initial epitaxial wafer is cleaned comprises:
BOE rinsing masking layer SiO 2 And then washing the initial epitaxial wafer, carrying out secondary material growth on the initial epitaxial wafer, covering the binary InP material of the third layer again, and finally realizing a grating region formed by interleaving the binary InP material and the quaternary InGaAsP material in the second layer.
10. The epitaxial wafer for improving the uniformity of the laser grating morphology is characterized by being manufactured by the manufacturing method according to any one of claims 1-9, and comprises a first layer of binary InP material, a second layer of binary InP material, a quaternary InGaAsP material and a third layer of binary InP material, wherein the second layer of binary InP material and the quaternary InGaAsP material are staggered to form a grating region.
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