Preparation method of EML laser and air bridge

Abstract

The invention provides an EML laser and a preparation method of an air bridge, belongs to the technical field of optical communication lasers, and is used for solving the problem that the stray capacitance of connecting metal between a waveguide electrode and a PAD electrode of the EML laser is too large. The preparation method of the air bridge process of the EML comprises the following steps: growing a mask layer on the surface of an epitaxial InP wafer, photoetching to form a ridge waveguide pattern, etching the mask layer by adopting ICP (Inductively Coupled Plasma), and removing photoresist; etching the ohmic contact layer by adopting ICP (Inductively Coupled Plasma) and removing the mask layer; gluing and photoetching the surface of the wafer to form a pier pattern; adopting ICPCVD to grow a dielectric film at low temperature; gluing and photoetching the surface of the wafer to form a dielectric film bridge pattern; carrying out ICP etching on the dielectric film and removing the bridge and pier photoresist to form a dielectric film bridge; and performing wet etching on the InP epitaxial layer to the etching stop layer. According to the method, the dielectric film bridge is built at the connecting metal between the waveguide electrode and the PAD electrode, the low dielectric constant characteristic of air is utilized, the distance between the metal and the quantum well is greatly increased, the stray capacitance of the EML is reduced, and the bandwidth is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor lasers, and in particular relates to a method for preparing an EML laser and an air bridge. Background Art

[0002] Optical communication has developed rapidly as a new technology industry. Driven by people's growing needs and increasingly advanced technology, it has gradually become the fundamental foundation of information technology and modern society. In recent years, with the development of AI technology, the speed requirements for data centers have become increasingly higher. As the core component of high-speed optical modules in data centers, the bandwidth improvement of EML has become the goal pursued by major optical communication chip manufacturers. However, the parasitic capacitance of the connecting metal between the waveguide electrode and the PAD electrode of the EML laser is too large, which limits the development of EML lasers.

[0003] Patent publication number CN 115967012A discloses a method for preparing a semiconductor laser structure, including S1, growing a primary epitaxial structure; S2, making a grating by secondary epitaxy on the primary epitaxial structure; S3, then growing a first mask layer on the grating layer and making a ridge waveguide, the middle ridge width of the ridge waveguide is greater than the ridge width at both ends; S4, then using photolithography to protect the two ends of the ridge waveguide, corroding the middle area to the substrate of the primary epitaxial structure, forming two expanded chambers; S5, removing the first mask layer, and regrowing a second mask layer, the second mask layer covers the remaining ridge waveguide and the surface of the two expanded chambers; S6, applying BCB or polyimide, exposing and developing, so that BCB is only filled in the two expanded chambers; S7, regrowing a third mask layer to wrap the BCB and the ridge waveguide; S8, obtaining a semiconductor laser. This patent reduces the device capacitance by filling PI or BCB in the double groove of the waveguide. However, filling the double grooves with PI or BCB increases the difficulty of the process, and PI or BCB will affect chip reliability. Summary of the invention

[0004] In order to solve the technical problem of excessive parasitic capacitance of the connecting metal between the waveguide electrode and the PAD electrode of the EML laser, the present invention proposes a method for preparing an EML laser and an air bridge. Compared with the traditional preparation method, it is not necessary to fill PI or BCB in the double groove of the waveguide, and the distance between the connecting metal and the quantum well is greatly increased, which greatly improves the reliability and reduces the parasitic capacitance.

[0005] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A method for preparing an EML laser air bridge comprises the following steps:

[0007] (1) preparing an epitaxial structure on a wafer, wherein the top of the epitaxial structure is an ohmic contact layer, and preparing a mask layer above the ohmic contact layer;

[0008] (2) coating a photoresist on the mask layer, preparing a ridge waveguide pattern on the photoresist using a photolithography technique, and then dry-etching the mask layer above the double grooves on both sides of the ridge waveguide in the ridge waveguide pattern and removing the photoresist;

[0009] (3) dry etching of the ohmic contact layer to form shallow grooves on both sides of the ridge waveguide;

[0010] (4) wet etching the remaining mask layer on the wafer;

[0011] (5) coating a photoresist on the surface of the wafer and forming bridge piers in the shallow trenches using photolithography technology;

[0012] (6) preparing a dielectric film on the surface of the wafer, coating a photoresist on the dielectric film, preparing a bridge pattern on the photoresist using a photolithography technique, wherein the bridge pattern covers the bridge pier area, dry etching the dielectric film to form a bridge, and removing the photoresist above the bridge and forming the bridge pier;

[0013] (7) Wet-etch the epitaxial layer to form a ridge waveguide.

[0014] The epitaxial layer includes an etch stop layer and an InP layer, and an ohmic contact layer is located above the InP layer; the material of the etch stop layer is InGaAsP.

[0015] The mask layer is prepared by vapor deposition, and the material of the mask layer is SiO2 or SiN x .

[0016] The thickness of the mask layer is not less than 100 nm.

[0017] The etching gas sources for dry etching in steps (2) and (6) are CHF3 and Ar.

[0018] The material of the ohmic contact layer is InGaAs, and the etching gas source for dry etching in step (3) is Cl2, CH4, or H2, and the ohmic contact layer not covered by the mask layer is etched away.

[0019] In the step (3), a portion of the InP layer is etched when etching the ohmic contact layer, and the etching depth of the InP layer is not greater than 200 nm; preferably, the etching depth of the InP layer is 50-150 nm.

[0020] The etching solution used for wet etching in step (4) is BOE solution.

[0021] The dielectric film is prepared by vapor deposition, and the material of the mask layer is SiO2, SiN x Or SiNO x .

[0022] The etching solution for wet etching in step (7) is a mixture of HCl and H3PO4.

[0023] An EML laser comprises a substrate, an epitaxial layer and a dielectric film bridge. A ridge strip is arranged on the epitaxial layer, the ridge strip is a double groove structure, and the dielectric film bridge covers the double groove.

[0024] Beneficial effects of the present invention: The present invention first forms a double groove structure by shallow etching, then prepares a dielectric film bridge by photolithography and ICPCVD low-temperature growth, and wet-etches to the InGaAsP etching stop layer. The present invention avoids the problem of deep groove glue flattening, and can first easily flatten the glue in the shallow groove to form a bridge pier pattern, and further form a dielectric film bridge. The method of the present invention builds a dielectric film bridge at the connecting metal between the waveguide electrode and the PAD electrode, utilizes the low dielectric constant characteristics of air, and greatly increases the distance between the metal and the quantum well, reduces the parasitic capacitance of the EML, and improves the bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 Schematic diagram after the growth of the mask layer.

[0027] Figure 2 Schematic diagram of etching a double trench region on a mask layer.

[0028] Figure 3 Schematic diagram of shallow trench etching.

[0029] Figure 4 This is a schematic diagram after removing the mask layer.

[0030] Figure 5 Schematic diagram of bridge pier photolithography.

[0031] Figure 6 Schematic diagram of low-temperature growth of the first dielectric film by ICPCVD.

[0032] Figure 7 Schematic diagram of the dielectric film bridge after photolithography.

[0033] Figure 8 Schematic diagram of the bridge after etching, stripping and cleaning.

[0034] Fig. 9Schematic diagram of wet etching to the etching stop layer.

[0035] In the figure, 1, mask layer; 2, ohmic contact layer; 3, InP layer; 4, etching stop layer; 5, double groove; 6, bridge pier; 7, dielectric film; 8, bridge; 9, ridge waveguide. DETAILED DESCRIPTION

[0036] 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.

[0037] Example 1

[0038] A method for preparing an EML laser air bridge process comprises the following steps:

[0039] (1) An epitaxial layer is prepared on a wafer, which includes, from bottom to top, a buffer layer generated by primary epitaxy, an N-type lower confinement layer, an active region with a quantum well structure, a P-type upper confinement layer, an InP-I layer, an etching stop layer 4, a P-type InP layer 3, and an InGaAs ohmic contact layer 2.

[0040] (2) SiO2 with a thickness of 200 nm is grown on the surface of the epitaxial InP wafer using a CVD method as a mask layer 1, as shown in FIG. Figure 1 As shown, the gas sources for CVD growth are SiH4 and N2O, the gas flow rates are 5sccm and 1500sccm, and the growth power is 100w. Then, photoresist is spin-coated on the surface of the wafer, and the ridge waveguide 9 pattern is exposed using photolithography technology. Then, the first mask layer is etched and the resist is removed using a dry etching device, as shown in FIG. Figure 2 As shown, the dry etching equipment adopts an inductively coupled plasma equipment, the etching gas sources are CHF3 and Ar, the flow rates of CHF3 and Ar are 40sccm and 30sccm respectively, the upper RF power is 300w, and the lower RF power is 20w.

[0041] (3) Use ICP equipment to etch the InGaAs contact layer, such as Figure 3 As shown, the gas sources for etching the InGaAs contact layer are Cl2, CH4, and H2, with gas flow rates of 4 sccm, 15 sccm, and 40 sccm, respectively, and the InP layer 3 is overetched by about 100 nm. After etching, the InGaAs contact layer on the double grooves 5 on both sides of the ridge waveguide 9 is removed.

[0042] (4) The first mask layer 1 is removed using BOE solution. The cross section of the chip after etching is shown in FIG. 4 .

[0043] (5) Apply glue on the surface of the wafer at a speed of 3000 r / min, and photolithography to form a bridge pier 6 pattern, such as Figure 5 shown.

[0044] (6) The dielectric film 7 is grown by ICPCVD method. The dielectric film 7 is 100 nm SiO2. The growth temperature is 50°. The growth gases are SiH4, O2 and Ar. SiH4 is He-diluted gas. The SiH4 concentration is 5%. The flow rates are 15 sccm, 10 sccm and 100 sccm respectively. The chip cross section of the dielectric film 7 after growth is as follows: Figure 6 shown.

[0045] (7) Use photolithography to form the bridge 8 pattern, and use ICP to etch the dielectric film 7 not covered by the photoresist, such as Figure 7 Then, the top of the dielectric film 7 and the photoresist forming the bridge pier 6 are removed. The chip cross section after the removal of the photoresist is as shown in FIG. Figure 8 As shown, the ICP etching gases are CHF3 and Ar, the flow rates of CHF3 and Ar are 40 sccm and 30 sccm respectively, the upper RF power is 300w, and the lower RF power is 20w.

[0046] (8) Wet etching the InP epitaxial material until the InGaAsP etching stop layer 4 is formed. The wet etching solution is a mixture of HCl and H3PO4 in a volume ratio of 90:1800. The structure of the bridge 8 of the EML laser finally prepared is as follows: Fig. 9 shown.

[0047] Example 2

[0048] A method for preparing an EML laser air bridge process comprises the following steps:

[0049] (1) An epitaxial layer is prepared on a wafer, which includes, from bottom to top, a buffer layer generated by primary epitaxy, an N-type lower confinement layer, an active region with a quantum well structure, a P-type upper confinement layer, an InP-I layer, an etching stop layer 4, a P-type InP layer 3, and an InGaAs ohmic contact layer 2.

[0050] (2) Using the CVD method, a 150nm thick SiO2 is grown on the surface of the epitaxial InP wafer as a mask layer 1, as shown in FIG. Figure 1 As shown, the gas sources for CVD growth are SiH4 and N2O, the gas flow rates are 5sccm and 1500sccm, and the growth power is 100w. Then, photoresist is spin-coated on the surface of the wafer, and the ridge waveguide 9 pattern is exposed using photolithography technology. Then, the first mask layer is etched and the resist is removed using a dry etching device, as shown in FIG. Figure 2As shown, the dry etching equipment adopts an inductively coupled plasma equipment, the etching gas sources are CHF3 and Ar, the flow rates of CHF3 and Ar are 40sccm and 30sccm respectively, the upper RF power is 250w, and the lower RF power is 20w.

[0051] (3) Use ICP equipment to etch the InGaAs contact layer, such as Figure 3 As shown, the gas sources for etching the InGaAs contact layer are Cl2, CH4, and H2, with gas flow rates of 4 sccm, 15 sccm, and 40 sccm, respectively, and the InP layer 3 is overetched by about 200 nm. After etching, the InGaAs contact layer on the double grooves 5 on both sides of the ridge waveguide 9 is removed.

[0052] (4) Use BOE solution to remove the first mask layer 1. The cross section of the chip after etching is as follows: Figure 4 shown.

[0053] (5) Apply glue on the surface of the wafer at a speed of 3500 r / min, and photolithography to form a bridge pier 6 pattern, such as Figure 5 shown.

[0054] (6) The dielectric film 7 is grown by ICPCVD method. The dielectric film 7 is 100 nm SiO2. The growth temperature is 50°. The growth gases are SiH4, O2 and Ar. SiH4 is He-diluted gas. The SiH4 concentration is 5%. The flow rates are 15 sccm, 10 sccm and 100 sccm respectively. The chip cross section of the dielectric film 7 after growth is as follows: Figure 6 shown.

[0055] (7) Use photolithography to form the bridge 8 pattern, and use ICP to etch the dielectric film 7 not covered by the photoresist, such as Figure 7 Then, the top of the dielectric film 7 and the photoresist forming the bridge pier 6 are removed. The chip cross section after the removal of the photoresist is as shown in FIG. Figure 8 As shown, the ICP etching gases are CHF3 and Ar, the flow rates of CHF3 and Ar are 40 sccm and 30 sccm respectively, the upper RF power is 300w, and the lower RF power is 20w.

[0056] (8) Wet etching the InP epitaxial material until the InGaAsP etching stop layer 4 is formed. The wet etching solution is a mixture of HCl and H3PO4 in a volume ratio of 90:1800. The structure of the bridge 8 of the EML laser finally prepared is as follows: Fig. 9 shown.

[0057] Example 3

[0058] A method for preparing an EML laser air bridge process comprises the following steps:

[0059] (1) An epitaxial layer is prepared on a wafer, which includes, from bottom to top, a buffer layer generated by primary epitaxy, an N-type lower confinement layer, an active region with a quantum well structure, a P-type upper confinement layer, an InP-I layer, an etching stop layer 4, a P-type InP layer 3, and an InGaAs ohmic contact layer 2.

[0060] (2) Using the CVD method, a 150nm thick SiO2 is grown on the surface of the epitaxial InP wafer as a mask layer 1, as shown in FIG. Figure 1 As shown, the gas sources for CVD growth are SiH4 and N2O, the gas flow rates are 5sccm and 1500sccm, and the growth power is 100w. Then, photoresist is spin-coated on the surface of the wafer, and the ridge waveguide 9 pattern is exposed using photolithography technology. Then, the first mask layer is etched and the resist is removed using a dry etching device, as shown in FIG. Figure 2 As shown, the dry etching equipment adopts an inductively coupled plasma equipment, the etching gas sources are CHF3 and Ar, the flow rates of CHF3 and Ar are 40sccm and 30sccm respectively, the upper RF power is 300w, and the lower RF power is 20w.

[0061] (3) Use ICP equipment to etch the InGaAs contact layer, such as Figure 3 As shown, the gas sources for etching the InGaAs contact layer are Cl2, CH4, and H2, with gas flow rates of 4 sccm, 15 sccm, and 40 sccm, respectively, and the InP layer 3 is overetched by about 100 nm. After etching, the InGaAs contact layer on the double grooves 5 on both sides of the ridge waveguide 9 is removed.

[0062] (4) Use BOE solution to remove the first mask layer 1. The cross section of the chip after etching is as follows: Figure 4 shown.

[0063] (5) Apply glue on the surface of the wafer at a speed of 3500 r / min, and photolithography to form a bridge pier 6 pattern, such as Figure 5 shown.

[0064] (6) The dielectric film 7 is grown by ICPCVD method. The dielectric film 7 is 100 nm SiO2. The growth temperature is 80°. The growth gases are SiH4, O2 and Ar. SiH4 is He-diluted gas. The SiH4 concentration is 5%. The flow rates are 15 sccm, 10 sccm and 100 sccm respectively. The chip cross section of the dielectric film 7 after growth is as follows: Figure 6 shown.

[0065] (7) Use photolithography to form the bridge 8 pattern, and use ICP to etch the dielectric film 7 not covered by the photoresist, such as Figure 7 Then, the top of the dielectric film 7 and the photoresist forming the bridge pier 6 are removed. The chip cross section after the removal of the photoresist is as shown in FIG. Figure 8As shown, the ICP etching gases are CHF3 and Ar, the flow rates of CHF3 and Ar are 40 sccm and 30 sccm respectively, the upper RF power is 300w, and the lower RF power is 20w.

[0066] (8) Wet etching the InP epitaxial material until the InGaAsP etching stop layer 4 is formed. The wet etching solution is a mixture of HCl and H3PO4 in a volume ratio of 90:1800. The structure of the bridge 8 of the EML laser finally prepared is as follows: Fig. 9 shown.

[0067] Example 4

[0068] A method for preparing an EML laser air bridge process comprises the following steps:

[0069] (1) An epitaxial layer is prepared on a wafer, which includes, from bottom to top, a buffer layer generated by primary epitaxy, an N-type lower confinement layer, an active region with a quantum well structure, a P-type upper confinement layer, an InP-I layer, an etching stop layer 4, a P-type InP layer 3, and an InGaAs ohmic contact layer 2.

[0070] (2) SiO2 with a thickness of 100 nm is grown on the surface of the epitaxial InP wafer using a CVD method as a mask layer 1, as shown in FIG. Figure 1 As shown, the gas sources for CVD growth are SiH4 and N2O, the gas flow rates are 5sccm and 1500sccm, and the growth power is 100w. Then, photoresist is spin-coated on the surface of the wafer, and the ridge waveguide 9 pattern is exposed using photolithography technology. Then, the first mask layer is etched and the resist is removed using a dry etching device, as shown in FIG. Figure 2 As shown, the dry etching equipment adopts an inductively coupled plasma equipment, the etching gas sources are CHF3 and Ar, the flow rates of CHF3 and Ar are 40sccm and 30sccm respectively, the upper RF power is 300w, and the lower RF power is 25w.

[0071] (3) Use ICP equipment to etch the InGaAs contact layer, such as Figure 3 As shown, the gas sources for etching the InGaAs contact layer are Cl2, CH4, and H2, with gas flow rates of 4 sccm, 15 sccm, and 40 sccm, respectively, and the InP layer 3 is overetched by about 100 nm. After etching, the InGaAs contact layer on the double grooves 5 on both sides of the ridge waveguide 9 is removed.

[0072] (4) Use BOE solution to remove the first mask layer 1. The cross section of the chip after etching is as follows: Figure 4 shown.

[0073] (5) Apply glue on the surface of the wafer at a speed of 3000 r / min, and photolithography to form a bridge pier 6 pattern, such as Figure 5 shown.

[0074] (6) The dielectric film 7 is grown by ICPCVD method. The dielectric film 7 is 250nm SiO2. The growth temperature is 100°. The growth gases are SiH4, O2 and Ar. SiH4 is He-diluted gas. The SiH4 concentration is 5%. The flow rates are 20sccm, 10sccm and 150sccm respectively. The chip cross section of the dielectric film 7 after growth is as follows: Figure 6 shown.

[0075] (7) Use photolithography to form the bridge 8 pattern, and use ICP to etch the dielectric film 7 not covered by the photoresist, such as Figure 7 Then, the top of the dielectric film 7 and the photoresist forming the bridge pier 6 are removed. The chip cross section after the removal of the photoresist is as shown in FIG. Figure 8 As shown, the ICP etching gases are CHF3 and Ar, the flow rates of CHF3 and Ar are 40 sccm and 30 sccm respectively, the upper RF power is 300w, and the lower RF power is 20w.

[0076] (8) Wet etching the InP epitaxial material until the InGaAsP etching stop layer 4 is formed. The wet etching solution is a mixture of HCl and H3PO4 in a volume ratio of 90:1800. The structure of the bridge 8 of the EML laser finally prepared is as follows: Fig. 9 shown.

[0077] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing an EML laser air bridge, characterized in that: The following steps are involved: (1) preparing an epitaxial structure on a wafer, wherein the top of the epitaxial structure is an ohmic contact layer, and preparing a mask layer above the ohmic contact layer; (2) coating a photoresist on the mask layer, preparing a ridge waveguide pattern on the photoresist using a photolithography technique, and then dry-etching the mask layer above the double grooves on both sides of the ridge waveguide in the ridge waveguide pattern and removing the photoresist; (3) dry etching of the ohmic contact layer to form shallow grooves on both sides of the ridge waveguide; (4) wet etching the remaining mask layer on the wafer; (5) coating a photoresist on the surface of the wafer and forming bridge piers in the shallow trenches using photolithography technology; (6) preparing a dielectric film on the surface of the wafer, coating a photoresist on the dielectric film, preparing a bridge pattern on the photoresist using a photolithography technique, wherein the bridge pattern covers the bridge pier area, dry etching the dielectric film to form a bridge, and removing the photoresist above the bridge and forming the bridge pier; (7) Wet-etch the epitaxial layer to form a ridge waveguide.

2. The method for preparing an EML laser air bridge according to claim 1, characterized in that: The epitaxial layer includes an etch stop layer and an InP layer, and an ohmic contact layer is located above the InP layer; the material of the etch stop layer is InGaAsP.

3. The method for preparing an EML laser air bridge according to claim 2, characterized in that: The mask layer is prepared by vapor deposition, and the material of the mask layer is SiO2 or SiN x .

4. The method for preparing an EML laser air bridge according to claim 3, characterized in that: The etching gas sources for dry etching in steps (2) and (6) are CHF3 and Ar.

5. The method for preparing an EML laser air bridge according to claim 2, characterized in that: The material of the ohmic contact layer is InGaAs, and the etching gas source for dry etching in step (3) is Cl2, CH4, or H2, and the ohmic contact layer not covered by the mask layer is etched away.

6. The method for preparing an EML laser air bridge according to claim 5, characterized in that: In the step (3), a portion of the InP layer is etched when etching the ohmic contact layer, and the etching depth of the InP layer is not greater than 200 nm.

7. The method for preparing an EML laser air bridge according to claim 6, characterized in that: The etching solution used for wet etching in step (4) is BOE solution.

8. The method for preparing an EML laser air bridge according to claim 7, characterized in that: The dielectric film is prepared by vapor deposition, and the material of the mask layer is SiO2, SiN x Or SiNO x .

9. The method for preparing an EML laser air bridge according to claim 8, characterized in that: The etching solution for wet etching in step (7) is a mixture of HCl and H3PO4.

10. An EML laser, characterized in that: The invention comprises a substrate, an epitaxial layer and a dielectric film bridge. A ridge strip is arranged on the epitaxial layer. The ridge strip is a double groove structure. The dielectric film bridge covers the double groove.

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