KR970004499B1 - A method for manufacture of semiconductor laser - Google Patents

Abstract

forming an N+ first clad layer, an active layer and a P second clad layer on an N+ semiconductor substrate in sequence; forming an etch mask on the second clad layer; forming an undercut of the active layer by removing the second clad layer, the active layer and the first clad layer in sequence, keeping some part of the first clad layer remained; forming a buried layer burying the undercut of the active layer by mass transport method; forming a P first current blocking layer contacting to the side wall of the first clad layer and the buried layer on the first clad layer; and forming an N second current blocking layer contacting to the side wall of the second clad layer on the first current blocking layer.

Description

Manufacturing method of semiconductor laser

1 (A)-(C) is a manufacturing process chart of a semiconductor laser different from the prior art.

2 (A) to (C) are manufacturing process diagrams of a semiconductor laser according to the present invention.

* Description of the symbols for the main parts of the drawings *

11, 31: semiconductor substrate 12, 32: first clad layer

13, 33: active layer 14, 34: second clad layer

15: thermal damage prevention layer 16, 36: etching mask

17, 37: first current blocking layer 18, 38: second current blocking layer

19, 39: planarization layer 20, 40: metal contact layer

41: buried layer 42: insulation current blocking layer

43: upper electrode 44: lower electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser, and in particular, the first layer, the active layer, and the second clad layer formed on the semiconductor substrate are mesa-etched by a four-step etching method to etch the active layer undercut. After that, the present invention relates to a method of manufacturing a semiconductor laser capable of reducing leakage current at a thermally damaged interface and improving reliability by forming a separate current blocking layer that fills an undercut using a mass transport shape.

Recently, due to the rapid development of the semiconductor industry, the necessity of information communication is increasing, and as a transmission means for effective information communication, a single wavelength and laser having excellent straightness (LASER; light amplificiation by stimulated emission of radition) has attracted attention. . The laser is classified into gas, liquid, solid, semiconductor, and chemical laser according to the type of laser medium. Among them, the semiconductor laser has smaller driving current and smaller size than other lasers, and changes the intensity and frequency of light according to the change of current. It can be directly modulated, the efficiency of the laser is usually very high, such as 70% or more, and has the advantage of having a wide wavelength range. Therefore, it is widely used in office equipment such as laser printers and bar code readers or optical communication equipment. Such a semiconductor laser is a kind of light emitting diode, and is formed of a III-V or II-IV compound semiconductor, and a principle of amplifying light having a single wavelength generated from a PN junction formed on a semiconductor substrate among materials having different reflectances. It is grown by a method such as metal organic chemical vapor deposition (hereinafter referred to as MOCVD), liquid phase epitaxy (hereinafter referred to as LPE).

However, current semiconductor lasers are usually formed by epi growth for 2 to 3 days at high temperatures of about 550 to 650 ° C. However, reliability problems such as low production yields such as long-term exposure to air and deterioration of characteristics when used for long periods of time are encountered. have.

FIG. 1 (A)-(C) is a manufacturing process chart of the semiconductor laser which concerns on a prior art, and is an example using an InP substrate as a semiconductor substrate.

First, the first cladding layer 12 of N ⁺ type InP continuously on the N ⁺ type InP semiconductor substrate 11, and the active layer 13 of InGaAsP which is not doped with impurities (hereinafter referred to as I). The second cladding layer 14 made of P-type InP and the thermal damage preventing layer 15 made of InGaAsP are sequentially formed by LPE or MOCVD (see FIG. 1 (A)).

Then, after cooling the semiconductor substrate 11 of the above structure, the thermal damage prevention layer 15 is removed, and an oxide film (not shown) is deposited by a conventional chemical vapor deposition (hereinafter referred to as CVD) method. Thereafter, the oxide film is photo-etched to form an etching mask 16 that protects a portion to be a driving region of the semiconductor laser. Then, the mesa-etched mesa structure of all of the second cladding layer 14 and the active layer 13 exposed by the etching mask 16 and the first cladding layer 12 is mesa-etched to form an inverted triangular mesa structure. It forms (refer FIG. 1 (B)).

Next, the first current blocking layer 17 of P-type InP is formed on the first clad layer 12 by the LPE or MOCVD growth process of the semiconductor substrate 11 having the mesa structure. And a second current blocking layer 18 of N ⁺ type InP at the height of the surface of the second clad 14 on the first current blocking layer 17. . Then, after removing the etching mask 16, the planarization layer 19 of P ⁺ type InP and the P ⁺ type InGaAsP on the second clad 14 and the second current blocking layer 18. The metal contact layer 20 is formed sequentially (refer FIG. 1 (C)).

Thereafter, an insulating current blocking layer (not shown) and upper and lower electrodes (not shown) are formed on the metal contact layer 20.

As described above, in the semiconductor laser according to the related art, the interface between the mesa etched clad layers and the active layer is exposed to air for a long time, and point defects and predecisions are generated by thermal damage during the subsequent growth process, and the life of the device is shortened. And, there is a problem that the leakage current is increased to reduce the reliability of the semiconductor laser.

The present invention is to solve the above problems, the object of the present invention is to carry out the mesa etching of the cladding layer and the active layer in four steps to make the active layer undercut, and to fill the undercut portion by mass transport method buried layer And the subsequent process to prevent the interface of the active layer from being exposed to air, to prevent thermal damage by the subsequent growth process to prevent the occurrence of point defects and predefects, to reduce the leakage current, and to improve the life of the device It is to provide a method for manufacturing a semiconductor laser that can be increased.

Features of the semiconductor laser manufacturing method according to the present invention for achieving the above object, the first conductive type of the first cladding layer and the intrinsic active layer and the second conductive type of the first conductive type semiconductor substrate Forming a second cladding layer sequentially; forming an etching mask on the second cladding layer; and a second cladding layer, an active layer, and a first cladding layer exposed by the etching mask. Forming the active layer so that the undercut is formed and leaving the predetermined thickness of the first cladding layer; forming a buried layer filling the undercut portion of the active layer by a mass transport method; Forming a first current blocking layer of a second conductivity type on the sidewall of the cladding layer and the sidewall of the buried layer on the etched and remaining first cladding layer; 1st challenge The consists in a second current blocking layer comprises a step of forming on said first current blocking layer.

Hereinafter, a method of manufacturing a semiconductor laser according to the present invention will be described in detail with reference to the accompanying drawings.

2 (A) to (C) are manufacturing process diagrams of the semiconductor laser according to the present invention, and are examples of a subsequent process performed in the state of FIG.

Referring to FIG. 2A, the first conductive type II-IV or III-V semiconductor substrate, for example, the N ⁺ type InP is formed on a semiconductor substrate 31 of N ⁺ type InP. The first cladding layer 32, the active layer 3 made of type I InGaAsP, the second cladding layer 34 made of P type InP, and the thermal damage prevention layer made of P type InGaAsP (not shown) are sequentially LPE or After forming by MOCVD method, it is cooled. In this case, the first and second cladding layers 32 and 34 are formed of a material having a refractive index greater than that of the active layer 33 for optical amplification, and the thermal damage preventing layer is a second clad made of InP, which is weak in heat. After layer 34 is grown at high temperatures, for example 550-650 ° C., it is prevented from being exposed to air while cooling.

Then, an etch mask 36 is formed by patterning an oxide film to define an area where light is generated by applying a current on the second clad layer 34, and then exposed by the etch mask 36. All of the second cladding layer 34 and the active layer 33 and the predetermined thickness of the first cladding layer 32 are etched by a selective mesa etching method to form an inverted triangular structure in which the active layer 33 is undercut. .

In this case, the active layer 33 is overetched and undercut than the second and first cladding layers 4 and 32, and the selective mesa etching process is performed through the second cladding layer 24 and the active layer 23. ) And the first cladding layer 22 using an etching solution having a high selectivity, for example, using HCI + 2H ₃ PO _{4 for} InP and 3H ₂ SO ₄ + H ₂ O ₂ + H ₂ O etching solution for InGaAsP. After etching, the active layer 23 is again etched with 3H ₂ SO ₄ + H ₂ O ₂ + H ₂ O etching solution using a four-step etching method to undercut, or only undercut in the first etching process The same shape can be obtained by etching in three steps.

Referring to FIG. 2B, the semiconductor substrate 31 having the above structure is grown in a MOCVD or LPE device to form a first current blocking layer of P-type InP on the first clad layer 24. (37) and the second current blocking layer 38 made of N type InP are sequentially formed. At this time, the first current blocking layer 37 is grown to the height of the buried layer 41, the second current blocking layer 38 is grown to the height of the surface of the second clad layer 34.

Also, immediately before the first current blocking layer 37 is grown, a buried layer 41 including InP as a main component is grown on the sidewall of the undercut active layer 33 by mass transport phenomenon to fill the undercut.

In general, the growth process maintains about 30 to 40 minutes at a constant temperature, such as 600-700 ° C. for InP, so that the molten materials are sufficiently uniform. In this case, the buried layer 41 is formed by mass transport. Is grown. The growth of the buried layer 41 is

△ P / P = C / T × R

(DELTA P is the partial pressure, P is the pressure, T is the temperature, R is the curvature and C is a constant) The undercut portion of the active layer 33 has a low partial pressure, so the buried layer 41 due to mass transport phenomenon This is to be grown.

Thereafter, the etching mask 36 is removed, and the planarization layer 39 of P ⁺ type InP is formed on the second cladding layer 34 and the second current blocking layer 38 according to a conventional semiconductor laser manufacturing process. ) And a metal contact layer 40 made of P ⁺ type InGaAsP.

Referring to FIG. 2C, an insulating current blocking layer 42 made of an oxide film having a contact window is formed on the metal contact layer 40, and a P-type is formed on the insulating current blocking layer 42. After the upper electrodes 43 are formed, respectively, the back surface of the semiconductor substrate 31 is ground (lapping) to a predetermined thickness, and an N-type lower electrode (below) of the wrapped semiconductor substrate 31 is formed. 44).

The etching mask 36 may be removed after the second current blocking layer 38 is grown and subjected to two growth processes. However, when the etching mask 38 is removed before the buried layer 41 is formed, one growth process is performed. It can also be formed.

As described above, in the method of manufacturing a semiconductor laser according to the present invention, the active layer is formed during the etching process of selectively etching the first cladding layer, the active layer, and the second cladding layer formed on the semiconductor substrate so that only a predetermined portion remains. After the etching was performed to form the undercut, a buried layer filling the undercut was formed by using a mass transport phenomenon generated at a predetermined temperature or more, so that the interface of the active layer is not exposed to the air for a long time between the growth processes and prevents thermal damage of the interface. There is an advantage in that it is possible to prevent point defects or predefectures and to prevent leakage current to improve yield and reliability of semiconductor lasers.

Claims (4)

Sequentially forming a first cladding layer of a first conductivity type, an active layer, and a second cladding layer of a second conductivity type on a semiconductor substrate of a first conductivity type, on the second clad layer Forming an etch mask, and sequentially removing the second clad layer, the active layer, and the first clad layer exposed by the etching mask to form the active layer undercut, and the first clad layer Forming a buried layer that fills the undercut of the active layer by a mass transport method; and a second conductive type first contacting the sidewall of the first clad layer and the sidewall of the buried layer. Forming a current blocking layer on the etched and remaining first cladding layer, and forming a second current blocking layer of a first conductivity type on and in contact with the sidewall of the second cladding layer on the first current blocking layer. Semiconductor having process to do Laser method. The method of manufacturing a semiconductor laser according to claim 1, wherein the first conductive type and the second conductive type are opposite conductive types. The method of manufacturing a semiconductor laser according to claim 1, wherein the semiconductor substrate is an InP substrate. The method of claim 1, wherein the undercut of the active layer is formed by four selective etching methods.