Search

CN-116247514-B - Terahertz quantum cascade laser ridge waveguide etching method

CN116247514BCN 116247514 BCN116247514 BCN 116247514BCN-116247514-B

Abstract

The invention relates to a terahertz quantum cascade laser ridge waveguide etching method. The method comprises the steps of (1) providing a terahertz quantum cascade laser material, (2) etching a groove (7) with the depth identical to the thickness of a lower contact layer on the surface of the material, (3) adopting a dry etching system equipped with a laser interferometer to etch the material again to form a ridge structure (8), synchronously etching the groove (7), and carrying out online detection on the bottom of the groove by the laser interferometer, (4) when the oscillation signal intensity of the laser interferometer jumps, etching the bottom of the groove (7) to the interface between the lower contact layer (4) and the etching stop layer (3), and at the moment, etching two sides of the ridge structure (8) to the interface between the multi-quantum well active region (5) and the lower contact layer (4). According to the method, the optimal etching depth can be effectively judged only by adding a simple groove pre-etching process, and the accuracy of the etching depth of the ridge waveguide of the laser is improved.

Inventors

  • WAN WENJIAN
  • CAO JUNCHENG

Assignees

  • 中国科学院上海微系统与信息技术研究所

Dates

Publication Date
20260505
Application Date
20230314

Claims (8)

  1. 1. A terahertz quantum cascade laser ridge waveguide etching method is characterized by comprising the following steps: The terahertz quantum cascade laser material comprises a substrate (1), a buffer layer (2), an etching stop layer (3), a lower contact layer (4), a multi-quantum well active region (5) and an upper contact layer (6) from bottom to top, wherein the thickness of the etching stop layer (3) is 100 nm-300 nm, the material is high-aluminum-component undoped Al x Ga 1-x As, x is 0.5-0.6, the thickness of the lower contact layer (4) is 400 nm-600 nm, the material is n-type Si doped GaAs, and the Si doping concentration is 2X 10 18 cm -3 ～3×10 18 cm -3 ; (2) Etching a groove (7) on the surface of the material for the first time, wherein the depth of the groove (7) is the same as the thickness of the lower contact layer (4); (3) Carrying out secondary etching on the material by adopting a dry etching system with a laser interferometer, etching a ridge structure (8) with a convex cross section, wherein the top of the ridge structure (8) is not etched all the time, two sides of the ridge structure (8) comprise the grooves (7) and are synchronously etched, so that the thickness of a lower contact layer (4) at the bottom of the groove (7) is always deeper than that at the two sides of the ridge structure (8), the laser interferometer carries out online detection on the bottom of the groove, and the signal intensity of the laser interferometer is smoothly oscillated along with time; (4) When the oscillation signal of the laser interferometer is not changed smoothly any more and the intensity is jumped, the bottom of the groove (7) is just etched to the interface between the lower contact layer (4) and the etching stop layer (3), and at the moment, the two sides of the ridge structure (8) are just etched to the interface between the multi-quantum well active region (5) and the lower contact layer (4), so that the etching depth is optimal.
  2. 2. The method for etching the ridge waveguide of the terahertz quantum cascade laser, which is disclosed in claim 1, is characterized in that in the step (1), the substrate (1) is made of semi-insulating GaAs single crystal, the thickness of the buffer layer (2) is 100-500 nm, and the substrate is made of undoped GaAs.
  3. 3. The method for etching the ridge waveguide of the terahertz quantum cascade laser according to claim 1, wherein in the step (1), the thickness of the active region (5) of the multiple quantum well is 10 μm to 12 μm, the material is a part of n-type Si lightly doped GaAs/Al x Ga 1-x As multiple quantum well, x is 0.15 to 0.25, the Si doping concentration in a part of GaAs layer is 1×10 16 cm -3 ～1×10 17 cm -3 , the thickness of the upper contact layer (6) is 50nm to 100nm, the material is n-type Si doped GaAs, and the Si doping concentration is 3×10 18 cm -3 ～5×10 18 cm -3 .
  4. 4. The method for etching the ridge waveguide of the terahertz quantum cascade laser according to claim 1, wherein in the step (2), the first etching is performed on the surface of the material, and a groove (7) is etched by manufacturing a first patterned mask on the surface of the material, wherein the area to be etched is not covered by the mask, and then the groove is etched.
  5. 5. The method for etching the ridge waveguide of the terahertz quantum cascade laser according to claim 1, wherein the first etching in the step (2) adopts wet etching or inductively coupled plasma dry etching.
  6. 6. The terahertz quantum cascade laser ridge waveguide etching method according to claim 1, wherein the width of the groove (7) in the step (2) is 50-300 μm.
  7. 7. The method for etching the ridge waveguide of the terahertz quantum cascade laser according to claim 1, wherein in the step (3), a dry etching system equipped with a laser interferometer is adopted to etch the material for the second time, namely, a first mask after the surface of the material is etched is removed, a second patterned mask is manufactured again, the area to be etched comprises a groove which is not covered by the second mask, and then the dry etching system equipped with the laser interferometer is adopted to etch the material.
  8. 8. The method for etching the ridge waveguide of the terahertz quantum cascade laser according to claim 1, wherein the etching in the step (3) adopts an inductively coupled plasma dry etching system, and the etching gas comprises one or more of Cl 2 、Ar、BCl 3 .

Description

Terahertz quantum cascade laser ridge waveguide etching method Technical Field The invention belongs to the technical field of semiconductor lasers, and particularly relates to a terahertz quantum cascade laser ridge waveguide etching method. Background The terahertz quantum cascade laser is a unipolar multi-quantum well semiconductor laser, and the basic working principle is that electrons radiate in a multi-quantum well conduction band to transfer and release photons, wherein the photon frequency is 1-5 THz. The terahertz quantum cascade laser has the advantages of easiness in solid state integration and high conversion efficiency, and is a research hotspot of a terahertz radiation source. The waveguide structure of the terahertz quantum cascade laser has two types of semi-insulating surface plasmon waveguide and double-sided metal waveguide, wherein the semi-insulating surface plasmon waveguide structure has relatively simple process, good laser directivity and high coupling output power, and the high-power terahertz quantum cascade laser usually adopts the waveguide structure. The semi-insulating surface plasma waveguide process comprises the processes of sputtering (evaporating) an upper electrode metal layer, ridge waveguide etching, evaporating a lower electrode metal layer, thinning a substrate, cleaving a patch and the like. The ridge waveguide etching is a key process in the whole flow, and the etching depth is required to reach the lower contact layer and cannot exceed the lower contact layer, otherwise, the device cannot realize electrical conduction. And to reduce parasitic series resistance, the thicker the lower contact layer that remains, the better. Therefore, the etching depth just reaches the interface between the multi-quantum well active region and the lower contact layer, and the optimal electrical performance is achieved. Typically the etch depth is measured by a step gauge. In the etching process, a sample step is taken out of an etching system for multiple times to determine whether the etching depth is reached, and the steps are complicated. The thickness of the active region of the terahertz quantum cascade laser reaches 10 mu m, and the lower contact layer is only 400-600 nm, which means that the accuracy of etching depth cannot exceed 4% -6%, otherwise, the lower electrode is in poor contact. In addition, the mask can be etched by dry etching, the actual etching depth can be estimated by considering the thickness of the residual mask, and the accuracy can not meet the process requirement of the terahertz quantum cascade laser. The mainstream dry etching system can be equipped with a laser interferometer. The laser interferometer irradiates the sample surface with a laser beam, and detects the reflected signal with a detector. If the surface of the sample is provided with heterogeneous film materials, laser is reflected by the upper interface and the lower interface of the film to form interference, when the film is etched, the thickness of the layer is continuously changed, and the laser reflection signal has approximate sine oscillation characteristic. Thus the laser interferometer can be used for film etching endpoint determination. The laser of the conventional laser interferometer is visible red light, has good transmittance for dielectric films such as silicon dioxide and the like, and has strong signal. For GaAs materials, the red light transmittance is poor, and only when the GaAs material is as thin as two to three hundred nm, the laser interferometer generates an oscillation signal. Even with longer wavelength laser interferometers, the interface of the multiple quantum well active region and the lower contact layer cannot be distinguished from the laser interferometer signal because the multiple quantum well active region material is thick and has a refractive index very close to that of the lower contact layer material. Disclosure of Invention The invention aims to solve the technical problem of providing a terahertz quantum cascade laser ridge waveguide etching method, which aims to solve the problems that in the prior art, the etching depth of the terahertz quantum cascade laser ridge waveguide is not well controlled and poor contact of a lower electrode is easily caused. The invention provides a terahertz quantum cascade laser ridge waveguide etching method, which comprises the following steps: (1) Providing a terahertz quantum cascade laser material, wherein the material comprises a substrate, a buffer layer, an etching stop layer, a lower contact layer, a multiple quantum well active region and an upper contact layer from bottom to top in sequence; (2) Etching a groove on the surface of the material for the first time; (3) Carrying out secondary etching on the material by adopting a dry etching system with a laser interferometer, etching a ridge structure with a convex section, wherein the top of the ridge structure is not etched all the time, and both sides of t