CN107528214B - Preparation method of terahertz quantum cascade laser with bimetal waveguide structure and laser - Google Patents
Preparation method of terahertz quantum cascade laser with bimetal waveguide structure and laser Download PDFInfo
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- H01S5/00—Semiconductor lasers
- H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
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- H01S5/00—Semiconductor lasers
- H01S5/30—Structure or shape of the active region; Materials used for the active region
- H01S5/3013—AIIIBV compounds
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
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Abstract
The invention discloses a preparation method of a terahertz quantum cascade laser metal waveguide structure and a laser, which comprises the following steps: sequentially growing an etching stop layer, a lower contact layer, a multi-quantum well active region, an upper contact layer, an n-type heavily doped layer and a passivation layer by using a low-temperature growth method on a semi-insulating GaAs substrate; forming a non-alloy ohmic contact; sequentially depositing an electric contact enhancement metal layer, a metal In layer and a metal Au layer on a substrate of a receiver substrate; flip-chip bonding the device substrate and the receiver substrate, and depositing SiO2A protective layer, which is coated with photoresist and baked; stripping the photoresist; removal of SiO2A protective layer; forming a Schottky diode contact upper electrode metal layer; forming a lower electrode metal layer; and (4) cleaving the flip-chip bonded substrate and packaging. The method effectively reduces the contact impedance, avoids the large amount of free carrier leakage of the terahertz photoelectric device caused by the diffusion of the uncontrolled doping distribution, and effectively reduces the waveguide loss caused by the annealing process.
Description
Technical Field
The invention belongs to the field of preparation of semiconductor compound photoelectric devices, and particularly relates to a preparation method of a terahertz quantum cascade laser metal waveguide structure and a laser.
Background
The terahertz radiation source is a key device applied to the terahertz technology, and the lack of a portable high-power radiation source working at room temperature is an important reason for restricting the development of the terahertz technology. Recent researches show that a quantum cascade semiconductor laser adopting a resonant phonon structure, a chirped superlattice structure and a bound state to continuous state transition structure in an active region can cover a lasing wavelength from middle infrared to a terahertz (0.1-10THz) waveband to generate a stable coherent terahertz radiation source. Since the first terahertz quantum cascade laser appeared in 2002, researches aiming at improving the working temperature, the output power and other properties of the terahertz quantum cascade laser become hot spots of researches in the terahertz field. The terahertz quantum cascade laser waveguide structure mainly comprises a plasma waveguide, a semi-insulating surface plasma waveguide and a bimetallic waveguide, wherein the bimetallic waveguide structure is low in waveguide loss, high in optical mode limiting factor, low in power loss and easy to dissipate heat; therefore, the method has the advantages of improving the working temperature of the device and reducing the threshold current of the device.
The terahertz quantum cascade laser generally works under high bias voltage and current, most of input electric power is converted into joule heat, if the waveguide structure is not designed reasonably, the joule heat cannot be emitted from the inside of a device in time, so that the temperature of an active region is rapidly increased, non-radiative optical phonon scattering is increased, the population inversion is difficult, the device lasing is inhibited, and the radiation efficiency is reduced. In addition, the terahertz quantum cascade laser has large waveguide loss, so that the threshold current and the power loss of the device are increased, the internal temperature of the device is further increased, and the improvement of the working temperature performance of the device is influenced. Therefore, designing and preparing the waveguide with a low-loss and easy-heat-dissipation structure, inhibiting free carrier absorption and improving the cavity film limiting factor are the keys for improving the working performance of the terahertz quantum cascade laser. Providing a semi-insulating GaAs substrate, and sequentially growing an etching stop layer, a lower contact layer, a multi-quantum well active region, an upper contact layer, an n-type heavily doped layer and a passivation layer by using a low-temperature growth method on the substrate by using a molecular beam epitaxy method;
disclosure of Invention
The invention aims to solve the problems in the background art, and provides a preparation method of a terahertz quantum cascade laser with a bimetal waveguide structure and the laser, which are used for solving the problems of large waveguide loss and poor heat dissipation of the terahertz quantum cascade laser in the prior art.
The technical scheme of the invention is a preparation method of a terahertz quantum cascade laser with a bimetal waveguide structure, which comprises the following steps:
s1 growing an etching stop layer, a lower contact layer, a multi-quantum well active region, an upper contact layer, an n-type heavily doped layer and a passivation layer by low-temperature growth in sequence on the semi-insulating GaAs substrate by using a molecular beam epitaxy method;
s2, forming a lower metal layer window on the passivation layer in the step S1 by using first photoetching, buffering, oxidizing and etching, depositing electrode metal, stripping with glue to form a lower metal layer, and annealing to form non-alloy ohmic contact;
s3, sequentially depositing an electric contact enhancement metal layer, a metal In layer and a metal Au layer on the n-doped GaAs receiver substrate;
s4 flip-chip bonding the device substrate in step S2 and the receiver substrate in step S3;
s5 Flip-chip bonding the substrate around and on top using low temperature plasma enhanced chemical vapor deposition of SiO in step S42A protective layer;
s6 grinding the semi-insulating GaAs substrate of the flip chip bonded substrate in the step S5, cleaning, coating photoresist on the n-doped GaAs receiver substrate of the flip chip bonded substrate, and baking;
s7, wet etching is carried out to remove the residual semi-insulating GaAs substrate in the step S6 to the etching stop layer, and the photoresist in the step S6 is stripped;
s8 dipping the flip chip bonded substrate in the step S7 into HF acid to remove the etching stop layer and simultaneously remove SiO2A protective layer;
s9, coating photoresist and performing secondary photoetching on the lower contact layer of the flip chip bonding substrate in the step S8 to form an upper electrode window, forming upper electrode metal in the upper electrode window, and stripping the tape to form a Schottky diode contact upper electrode metal layer;
s10, in step S9, a ridge waveguide structure is formed on the back of the n-doped GaAs receiver substrate of the flip-chip bonding substrate by adopting an etching process, and a lower electrode metal layer is formed;
s11 is performed by cleaving the flip chip bonded substrate in the step S10 to perform packaging.
Preferably, in step S2, the surface of the passivation layer is subjected to buffer oxidation etching for 8-12 seconds, and then an electron beam evaporation process is used to deposit electrode metal and form a non-alloy ohmic contact.
Preferably, in step S3, the electrical contact enhancement metal layer is a metal Pd layer, a metal Ge layer, and a metal Pd layer deposited on the n-doped GaAs receiver substrate in sequence, and after the metal Pd layer is deposited; immersing an n-doped GaAs receiver substrate wafer in aqueous NH4-HF2And after 8-10 seconds of the buffer oxide etching solution, depositing a metal In layer by adopting an electron beam evaporation process, wherein the thickness of the metal In layer is controlled to be 1.0-1.2 mu m.
Preferably, In step S4, the device substrate and the receiver substrate are first subjected to surface purification treatment, then the device substrate is inverted to make the lower metal layer of the device substrate and the metal Au layer crystal axis of the receiver substrate face to face, and then the temperature is raised to 200-300 ℃ and kept for 8-12 minutes, and at the same time, uniform pressure is applied to the two substrates, and eutectic alloy is generated through In-Au reaction to bond the two substrates.
Preferably, the step S5 is to etch SiO2The thickness of the protective layer is 150-250 nm.
Preferably, when the semi-insulating GaAs substrate is ground in step S6, the thickness of the semi-insulating GaAs substrate after thinning is 50 μm to 70 μm using grit size reduction.
Preferably, the wet etching rate in step S7 is controlled to be 1-2 μm/min.
Preferably, in step S10, a ridge waveguide structure is etched by dry etching or wet etching; the dry etching is electron cyclotron resonance reaction ion dry etching, a Schottky diode is used for contacting the upper metal layer as a self-aligned mask, and the etching gas is BCl of 15sccm3And N of 5sccm2The pressure in the chamber is 5mTorr, the ECR power is 600W, the RF power is 15W, the temperature is 80 ℃, and the dry etching is stopped when the lower metal layer is etched; the wet etching adopts H with the volume ratio of 1:1:253PO4:H2O2:H2O etchant, and the speed is controlled at 400 nm/min.
Preferably, the sequence of the step S8 and the step S9 cannot be reversed.
A terahertz quantum cascade laser with a bimetal waveguide structure is prepared by the preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure.
The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure provided by the invention has the following beneficial effects:
(1) in the step S2, the traditional alloy ohmic contact is replaced by the non-alloy ohmic contact, so that the method not only effectively reduces the contact impedance, but also avoids the large amount of free carriers leakage of the terahertz photoelectric device caused by the diffusion of the uncontrolled doping distribution, and effectively reduces the waveguide loss caused by the annealing process. The key point for forming the non-alloy ohmic contact is that the Fermi level is fixed on the surface of the n-type heavily doped layer by utilizing the surface state, and the high doping level is formed on the surface of the heavily doped layer, but the heavily doped layer is easily oxidized when being exposed to the air, so that a passivation layer is grown on the heavily doped layer by utilizing a low-temperature growth method in step S1, the passivation layer has the anti-oxidation characteristic, the high concentration characteristic of the defect state in the passivation layer grown at the low temperature is still fixed, and the surface doping level can still be kept at the high level, thereby ensuring that the effective non-alloy ohmic contact is formed
(2) In the step S4, the melting point of the eutectic alloy generated by the In-Au reaction bonding method is far higher than 450 ℃, so that the bonding stability of the device can be still ensured at high temperature, and the mechanical strength of the waveguide structure is improved. Due to the action of melting In, the method has far lower requirements on the cleanliness and flatness of the surfaces of the two substrate metal layers during bonding than an Au-Au hot-pressing bonding method, simplifies the preparation process and improves the yield of the device process;
(3) in step S5 of the invention, a layer of SiQ is deposited in advance before thinning the GaAs substrate of the device substrate and etching the waveguide structure2A protective layer which is automatically removed during grinding of the upper part of the substrate, and which is applied on both sides of the bonded substrates and covers them in front and back, for protecting the receiver substrate and the epitaxial layer during etching of the GaAs substrateThe method can effectively avoid the generation of lateral undercut in the active region due to the long side surface of the active region. Step S6 applies a photoresist to the back side of the receiver substrate to further protect the substrate during etching.
Drawings
FIG. 1 is a schematic cross-sectional view of a terahertz quantum cascade laser of a bimetallic waveguide structure according to the present invention;
FIG. 2 is a flow chart of the preparation method of the terahertz quantum cascade laser with the bimetallic waveguide structure according to the invention;
FIG. 3 is a schematic diagram of a device substrate structure and a receiver substrate structure of a terahertz quantum cascade laser with a bimetallic waveguide structure according to the present invention, and flip-chip bonding of the two structures;
FIG. 4 is a schematic structural diagram presented in step S5 of a method for manufacturing a terahertz quantum cascade laser with a bimetallic waveguide structure according to the present invention;
FIG. 5 is a schematic structural diagram presented in step S6 of a method for manufacturing a terahertz quantum cascade laser with a bimetal waveguide structure according to the present invention;
FIG. 6 is a schematic structural diagram presented in step S6 of a method for manufacturing a terahertz quantum cascade laser with a bimetallic waveguide structure according to the present invention;
FIG. 7 is a schematic structural diagram presented in step S7 of a method for manufacturing a terahertz quantum cascade laser with a bimetal waveguide structure according to the present invention;
fig. 8 is a schematic structural diagram presented in step S8 of the method for manufacturing a terahertz quantum cascade laser with a bimetal waveguide structure according to the present invention.
FIG. 9 is a schematic structural diagram of the terahertz quantum cascade laser with the bimetallic waveguide structure according to the present invention after the step S9 of the method for manufacturing the terahertz quantum cascade laser with the bimetallic waveguide structure is performed with photolithography
Fig. 10 is a schematic structural diagram presented in step S9 of the method for manufacturing a terahertz quantum cascade laser with a bimetal waveguide structure according to the present invention.
Description of the element reference numerals
1A lower metal layer
2A LTG-GaAs passivation layer
3A GaAs heavily doped layer
4A upper contact layer
5A active region
Contact layer under 6A
7A Al0.5Ga0.5As etch stop layer
8A semi-insulating GaAs substrate
9A first resist protective layer
10A SiO2Protective layer
11A second resist protective layer
12A top electrode metal layer
13A glass slide
1B metal Au layer
2B metal In layer
3B electrical contact enhancement metal layer
4B n doped GaAs receiver substrate
5B heating flat plate
6B eutectic alloy AuIn2Layer(s)
7B lower electrode metal layer
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.
Please refer to fig. 1 to 10. It should be noted that the drawings provided in this embodiment are only for illustrating the basic concept of the present invention, and only the components related to the present invention are shown in the drawings rather than being drawn according to the number, shape and size of the components in actual implementation, and the form, quantity and proportion of each component in actual implementation may be changed arbitrarily, and the layout of the components may be more complicated.
The invention provides a preparation method of a terahertz quantum cascade laser with a bimetal waveguide structure, which comprises the following steps as shown in figure 2:
a preparation method of a terahertz quantum cascade laser with a bimetal waveguide structure comprises the following steps:
s1 growing an etching stop layer, a lower contact layer, a multi-quantum well active region, an upper contact layer, an n-type heavily doped layer and a passivation layer by low-temperature growth in sequence on the semi-insulating GaAs substrate by using a molecular beam epitaxy method;
s2, forming a lower metal layer window on the passivation layer in the step S1 by using first photoetching, buffering, oxidizing and etching, depositing electrode metal, stripping with glue to form a lower metal layer, and annealing to form non-alloy ohmic contact;
s3, sequentially depositing an electric contact enhancement metal layer, a metal In layer and a metal Au layer on the n-doped GaAs receiver substrate;
s4 flip-chip bonding the device substrate in step S2 and the receiver substrate in step S3;
s5 Flip-chip bonding the substrate around and on top using low temperature plasma enhanced chemical vapor deposition of SiO in step S42A protective layer;
s6 grinding the semi-insulating GaAs substrate of the flip chip bonded substrate in the step S5, cleaning, coating photoresist on the n-doped GaAs receiver substrate of the flip chip bonded substrate, and baking;
s7, wet etching is carried out to remove the residual semi-insulating GaAs substrate in the step S6 to the etching stop layer, and the photoresist in the step S6 is stripped;
s8 dipping the flip chip bonded substrate in the step S7 into HF acid to remove the etching stop layer and simultaneously remove SiO2A protective layer;
s9, coating photoresist and performing secondary photoetching on the lower contact layer of the flip chip bonding substrate in the step S8 to form an upper electrode window, forming upper electrode metal in the upper electrode window, and stripping the tape to form a Schottky diode contact upper electrode metal layer;
s10, in step S9, a ridge waveguide structure is formed on the back of the n-doped GaAs receiver substrate of the flip-chip bonding substrate by adopting an etching process, and a lower electrode metal layer is formed;
s11 is performed by cleaving the flip chip bonded substrate in the step S10 to perform packaging.
Preferably, in step S2, the surface of the passivation layer is subjected to buffer oxidation etching for 8-12 seconds, and then an electron beam evaporation process is used to deposit electrode metal and form a non-alloy ohmic contact.
Preferably, in step S3, the electrical contact enhancement metal layer is a metal Pd layer, a metal Ge layer, and a metal Pd layer deposited on the n-doped GaAs receiver substrate in sequence, and after the metal Pd layer is deposited; immersing an n-doped GaAs receiver substrate wafer in aqueous NH4-HF2And after 8-10 seconds of the buffer oxide etching solution, depositing a metal In layer by adopting an electron beam evaporation process, wherein the thickness of the metal In layer is controlled to be 1.0-1.2 mu m.
Preferably, In step S4, the device substrate and the receiver substrate are first subjected to surface purification treatment, then the device substrate is inverted to make the lower metal layer of the device substrate and the metal Au layer crystal axis of the receiver substrate face to face, and then the temperature is raised to 200-300 ℃ and kept for 8-12 minutes, and at the same time, uniform pressure is applied to the two substrates, and eutectic alloy is generated through In-Au reaction to bond the two substrates.
Preferably, the step S5 is to etch SiO2The thickness of the protective layer is 150-250 nm.
Preferably, when the semi-insulating GaAs substrate is ground in step S6, the thickness of the semi-insulating GaAs substrate after thinning is 50 μm to 70 μm using grit size reduction.
Preferably, the wet etching rate in step S7 is controlled to be 1-2 μm/min.
Preferably, in step S10, a ridge waveguide structure is etched by dry etching or wet etching; the dry etching is electron cyclotron resonance reaction ion dry etching, a Schottky diode is used for contacting the upper metal layer as a self-aligned mask, and the etching gas is BCl of 15sccm3And N of 5sccm2The pressure in the chamber is 5mTorr, the ECR power is 600W, the RF power is 15W, the temperature is 80 ℃, and the dry etching is stopped when the lower metal layer is etched; the wet etching adopts H with the volume ratio of 1:1:253PO4:H2O2:H2Etchant of OThe speed was controlled at 400 nm/min.
Preferably, the sequence of the step S8 and the step S9 cannot be reversed.
The following describes in detail a method for manufacturing a terahertz quantum cascade laser with a bimetal waveguide structure according to the present invention with reference to specific drawings.
Step S1 is first performed, and as shown in fig. 3, a semi-insulating GaAs substrate 8A is provided, and Al with a thickness of 500nm is sequentially grown on the surface of the semi-insulating GaAs substrate 8A from bottom to top by a Molecular Beam Epitaxy (MBE) method0.5Ga0.5An As etching stop layer 7A, a 600nm thick Si-doped GaAs lower contact layer 6A, a 10 μm thick GaAs or AlGaAs multi-quantum well active region 5A, a 60nm thick Si-doped GaAs upper contact layer 4A, a 10nm thick GaAs heavily doped layer 3A, and a LTG-GaAs passivation layer 2A grown at a low temperature and having a thickness of 3.5 nm;
and then executing step S2, coating photoresist on the LTG-GaAs passivation layer 2A, performing first photoetching, metalizing, stripping the photoresist to form a lower metal layer 1A, and annealing to form a non-alloy ohmic contact. In this embodiment, the surface of the material is first subjected to buffer oxidation etching for about 10 seconds, and then the metal layer 1A under Ti/Au (20/1000nm) is deposited by an electron beam evaporation process, and annealed to form a non-alloy ohmic contact.
Then, step S3 is performed, as shown in FIG. 3, providing an n-doped GaAs receiver substrate piece 4B, depositing a 25nm thick metal Pd layer, a 10nm thick metal Ge layer, a 25nm thick metal Pd layer in this order by electron beam evaporation on the n-doped GaAs receiver substrate piece 4B to form an electrical contact enhancing metal layer 3B, and then immersing the n-doped GaAs receiver substrate piece in aqueous NH4-HF2After about 10 seconds of the Buffered Oxide Etch (BOE) solution, a layer of metallic In 2B having a thickness of 1.2 μm and a layer of metallic Au 1B having a thickness of 120nm were deposited using an electron beam evaporation process.
Then, step S4 is performed, as shown in FIG. 3, by first using high purity N for the device substrate and the receiver substrate2Air drying, surface purifying in ultraviolet ozone cleaning instrument for 15 min, and purifying with high purity N2Air-blowing the particles, and then inverting the device substrate such that the lower metal layer 1A faces the metal Au layer 1B of the receiver substrateThe device substrate and the receiver substrate are flip-chip bonded by placing their crystal axes on a heating plate 5B, placing a glass slide 13A on the upper side for pressurization, then injecting an inert gas to prevent oxidation of the bonding surface, raising the temperature to 250 ℃ for about 10 minutes while uniformly applying pressure to the glass slide 13A, and then lowering the temperature to room temperature for 20 minutes. The principle of the bonding method is that when the temperature rises to the melting point of the metal In, namely 156 ℃, bonding is started, the melted metal In flows transversely to fill gaps and wrap particles on the bonding surface, and then the liquid metal In diffuses into and passes through the metal Au layer 1B and reacts with the metal Au layer rapidly to generate eutectic alloy AuIn2Layer (6B in fig. 4), the melting point of which is much higher than 450 c, ensures the stability of the flip-chip bonding at high temperatures. The method has the advantage that the requirements on the cleanliness and flatness of the bonding surface can be greatly reduced by the bonding method due to the filling of the voids and the wrapping effect of the molten metal In on the particles. The step is implemented by selecting appropriate thicknesses of the metal In layer and the metal Au layer, so that the metal In completely reacts to avoid low-melting-point metal residues, and the metal Au layer adjacent to the active region is reserved to prevent the low-conductivity Au-In alloy from introducing additional waveguide loss.
Then, step S5 is performed to deposit SiO around and on top of the flip-chip bonded substrate using low temperature Plasma Enhanced Chemical Vapor Deposition (PECVD) to a thickness of about 200nm2The protective layer 10A, resulting in a device material structure, is shown in fig. 4.
Then, step S6 is performed, the flip chip bonded substrate is mounted and fixed on a chuck with pure water wax, then the semi-insulating GaAs substrate 8A of the device substrate is ground and thinned, the size of the sand grains used for grinding is gradually reduced until the thickness of the semi-insulating GaAs substrate 8A is measured by a micrometer to be about 50 μm, then the flip chip bonded substrate is cleaned with ultrasonic solvent, finally the back of the receiver substrate is coated with photoresist (Shipey1813) to generate a first photoresist protection layer 9A, and the flip chip bonded substrate is placed in an oven at 120 ℃ and baked for 20-30 minutes to complete the film hardening, so as to generate the device material structure as shown in fig. 5 and fig. 6.
Then step S7 is executed, using NH with a volume ratio of 1:194OH:H2O2Etchant for etching away the upper part by wet methodThe device substrate is a residual semi-insulating GaAs substrate 8A to Al0.5Ga0.5And (3) controlling the etching speed of the As etching stop layer 7A to be 1-2 μm per minute, and then putting the device material into an acetone solution for 3-5 minutes to strip the first photoresist protective layer 9A in the step S6 to generate a device material structure As shown in FIG. 7.
Then, step S8 is performed to immerse the device material in 48% HF acid for 1-2 min to remove Al0.5Ga0.5As etch stop layer 7A and SiO2The protective layer 10A, resulting in a device material structure, is shown in fig. 8.
Then, step S9 is performed to coat Shipey1813 on the device substrate to form a second photoresist protection layer 11A, and to form an upper electrode window by a second photolithography so that the second photoresist protection layer 11A covers the sidewall of the device substrate and the eutectic AuIn2Layer 6B, as shown in fig. 9, then depositing a 20nm thick Ti and 400nm thick Au metal layer by electron beam evaporation to form an upper electrode metal layer 12A, then dipping the device into an acetone solution to strip with glue, annealing to form a schottky diode contact, and forming a device material structure as shown in fig. 10;
then, step S10 is executed, a ridge waveguide structure is formed by using a dry or wet etching process, and then a 20nm thick metal Ti layer and a 400nm metal Au layer are deposited on the GaAs substrate on the back side of the flip-chip bonded substrate by using an electron beam evaporation method to form a lower electrode metal layer 7B, so as to generate the device material structure shown in fig. 1. In this embodiment, electron cyclotron resonance reactive ion dry etching (ECR-RIE) is used to perform etching, the device is placed in ECR equipment, the upper electrode metal layer 12A is used as a self-aligned mask, and the etching gas is BCl3：N2(15: 5sccm), the pressure in the bore is 5mTorr, the ECR power is 600W, the RF power is 15W, the temperature is 80 ℃, and the etching is stopped when the dry etching reaches the lower metal layer 1A, so that the ridge waveguide structure is formed. It is noted that cleaning and conditioning of the chamber of the ECR apparatus is required prior to etching. If a wet etching process is used, the device substrate is coated with Shipey1813 photoresist, a third time of photoetching is carried out, and then H with the volume ratio of 1:1:25 is recommended to be used3PO4:H2O2:H2O etchant with a rate of 400 nm/min, and dry methodAnd stopping etching when the etching is the same as that of the lower metal layer 1A, and finally removing the photoresist to form the ridge waveguide structure.
And finally, executing step S11, scribing and cleaving the device with the length of 1-3mm, welding an In sheet on the copper heat sink, and leading out electrodes on the upper electrode metal layer 12A and the lower electrode metal layer 7B through gold wire ball bonding to finish the device manufacturing.
As described above, the present invention provides a method for preparing a terahertz quantum cascade laser with a bimetal waveguide structure, wherein in step S1, a passivation layer is grown by using a low temperature growth method, and the oxidation resistance of the passivation layer is used to successfully apply a non-alloy ohmic contact in step S2 instead of a conventional alloy ohmic contact, thereby effectively reducing contact impedance and reducing waveguide loss caused by an annealing process; in step S4, an In-Au reactive bonding method is used to perform the flip-chip bonding of the device substrate to the receiver substrate, and the high melting point of the eutectic alloy is used to ensure the stability of the device bonding at high temperature and improve the mechanical strength of the waveguide structure. The requirements of the bonding method on the cleanliness and the flatness of the surfaces of the two substrate metal layers during bonding are far lower than those of an Au-Au hot-pressing bonding method, the preparation process is simplified, and the yield of the device process is improved; in step S5, SiQ is used2The protective layer effectively protects the receiver substrate and the side face of the active region grown by the epitaxial layer when the GaAs substrate is etched, so that lateral undercut is avoided in the active region, and the photoelectric performance of the device is improved.
A terahertz quantum cascade laser with a bimetal waveguide structure is prepared by the preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (10)
1. A preparation method of a terahertz quantum cascade laser with a bimetal waveguide structure is characterized by comprising the following steps:
s1 growing an etching stop layer, a lower contact layer, a multi-quantum well active region, an upper contact layer, an n-type heavily doped layer and a passivation layer by low-temperature growth in sequence on the semi-insulating GaAs substrate by using a molecular beam epitaxy method;
s2, forming a lower metal layer window on the passivation layer in the step S1 by using first photoetching, buffering, oxidizing and etching, depositing electrode metal, stripping with glue to form a lower metal layer, and annealing to form non-alloy ohmic contact;
s3, sequentially depositing an electric contact enhancement metal layer, a metal In layer and a metal Au layer on the n-doped GaAs receiver substrate;
s4 flip-chip bonding the device substrate in step S2 and the receiver substrate in step S3;
s5 Flip-chip bonding the substrate around and on top using low temperature plasma enhanced chemical vapor deposition of SiO in step S42A protective layer;
s6 grinding the semi-insulating GaAs substrate of the flip chip bonded substrate in the step S5, cleaning, coating photoresist on the n-doped GaAs receiver substrate of the flip chip bonded substrate, and baking;
s7, etching away the residual semi-insulating GaAs substrate in the step S6 to the etching stop layer by adopting a wet method, and stripping the photoresist in the step S6;
s8 dipping the flip chip bonded substrate in the step S7 into HF acid to remove the etching stop layer and simultaneously remove SiO2A protective layer;
s9, coating photoresist and performing secondary photoetching on the lower contact layer of the flip chip bonding substrate in the step S8 to form an upper electrode window, forming upper electrode metal in the upper electrode window, and stripping the tape to form a Schottky diode contact upper electrode metal layer;
s10, in step S9, a ridge waveguide structure is formed on the back of the n-doped GaAs receiver substrate of the flip-chip bonding substrate by adopting an etching process, and a lower electrode metal layer is formed;
s11 is performed by cleaving the flip chip bonded substrate in the step S10 to perform packaging.
2. The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized by comprising the following steps: and in the step S2, performing buffer oxidation etching on the surface of the passivation layer for 8-12 seconds, depositing electrode metal by adopting an electron beam evaporation process, and forming non-alloy ohmic contact.
3. The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized by comprising the following steps: in the step S3, the electrical contact enhancement metal layer is a metal Pd layer, a metal Ge layer and a metal Pd layer deposited on the n-doped GaAs receiver substrate in sequence, and after the metal Pd layer is deposited; and (3) immersing the n-doped GaAs receiver substrate into an aqueous NH4-HF2 buffer oxide etching solution for 8-10 seconds, and then depositing a metal In layer by adopting an electron beam evaporation process, wherein the thickness of the metal In layer is controlled to be 1.0-1.2 mu m.
4. The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized by comprising the following steps: in the step S4, the device substrate and the receiver substrate are first subjected to surface purification treatment, then the device substrate is inverted to make the lower metal layer of the device substrate and the metal Au layer crystal axis of the receiver substrate aligned and placed face to face, the temperature is raised to 200-300 ℃ and kept for 8-12 minutes, and at the same time, uniform pressure is applied to the two substrates, and eutectic alloy is generated through In-Au reaction to bond the two substrates.
5. The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized by comprising the following steps: etching SiO in the step S52The thickness of the protective layer is 150-250 nm.
6. The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized by comprising the following steps: when the semi-insulating GaAs substrate is ground in step S6, the size of the sand is gradually reduced, and the thickness of the semi-insulating GaAs substrate after thinning is 50 μm to 70 μm.
7. The preparation method of the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized by comprising the following steps: the wet etching speed in the step S7 is controlled to be 1-2 μm/min.
8. The method for preparing the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized in that: in the step S10, a ridge waveguide structure is etched by a dry etching method or a wet etching method; the dry etching is electron cyclotron resonance reaction ion dry etching, a Schottky diode is used for contacting the upper metal layer as a self-aligned mask, and the etching gas is BCl of 15sccm3And N of 5sccm2The pressure in the chamber is 5mTorr, the ECR power is 600W, the RF power is 15W, the temperature is 80 ℃, and the dry etching is stopped when the lower metal layer is etched; the wet etching adopts H with the volume ratio of 1:1:253PO4:H2O2:H2O etchant, and the speed is controlled at 400 nm/min.
9. The method for preparing the terahertz quantum cascade laser with the bimetal waveguide structure according to claim 1, characterized in that: the sequence of the step S8 and the step S9 cannot be reversed.
10. A terahertz quantum cascade laser with a bimetal waveguide structure, characterized by being prepared by the method for preparing the terahertz quantum cascade laser with the bimetal waveguide structure of any one of claims 1 to 9.
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