KR100809401B1 - Method of formation of a fine optical waveguide layer of semiconductor laser diode - Google Patents

Abstract

A method for manufacturing a semiconductor laser diode having a light guiding layer which can shorten the processing time and has a tip with a line width smaller than the exposure limit value is disclosed. The disclosed invention forms a multilayer active layer on a compound semiconductor substrate and then forms a hard mask film on the multilayer active layer. Thereafter, a photoresist pattern is formed on the hard mask film, and the photoresist pattern is baked to improve adhesion between the photoresist pattern and the hard mask film. Thereafter, using the baked photoresist pattern as a mask, the hard mask film is subjected to undercut etching to form a hard mask pattern, then the photoresist pattern is removed, and the multilayered active layer is etched in the form of the hard mask pattern Thereby forming a light guide layer.

Undercut, BOE, silicon nitride film, optical waveguide layer

Description

TECHNICAL FIELD The present invention relates to a method of forming a fine optical waveguide layer of a semiconductor laser diode,

FIGS. 1A to 1E are perspective views for explaining a method of forming a fine optical waveguide layer of a semiconductor laser diode according to an embodiment of the present invention.

Figs. 2A to 2E are cross-sectional side views of each of Figs. 1A to 1E, showing output portions of the laser diode.

FIGS. 3 and 4 are photomicrographs showing a state in which the hard mask film is undercut-etched after the baking process of the photoresist pattern.

Description of the Related Art

100: compound substrate 110: InP buffer layer

115: first SCH layer 120: MQW layer

125: second SCH layer 130: InP cover layer

135: hard mask film 140: photoresist pattern

The present invention relates to a method of manufacturing a semiconductor laser diode, and more particularly, to a method of forming a fine optical waveguide layer of a semiconductor laser diode.

As is known, a laser diode is composed of a bonded n-type semiconductor layer and a p-type semiconductor layer. When the current is injected into the semiconductor layer to which the laser diode is injected, the p-type semiconductor layer corresponding to the electron band of the n-type semiconductor layer corresponding to the conduction band of the energy band and the valence band of the n- As the holes of the semiconductor layer are recombined, energy corresponding to the energy band gap is emitted in the form of optic. In particular, a laser diode uses stimulated emission light of an active layer made of a material having a relatively low energy band gap between semiconductor layers having a large energy band gap. Accordingly, when oscillation that increases the coherence of the light is generated, all light generated in the active layer is amplified with the same direction and phase, and a very high light output is obtained.

Here, the optical output characteristics of the laser diode are influenced by the composition and structure of the waveguide layer (waveguide layer) of the active layer that generates light. Particularly, it is known that the smaller the thickness and the width of the waveguide layer of the active layer, the higher the optical output characteristics.

Accordingly, in the conventional laser diode, the active layer located at the output portion is formed into a tip shape with a sharp tip so that the active layer located at the output portion can serve as a spot size converter (SSC). Such a tip-type active layer is obtained by an etching process using a photolithography process or an electron beam lithography process.

However, in the conventional photolithography process, it is difficult to manufacture a mask pattern having a line width of 0.5 μm or less due to the limitations of the exposure source and the exposure equipment, and it is difficult to form the optical waveguide layer of the SSC structure.

On the other hand, in the case of electron beam lithography, a mask pattern having a finer line width than that of the photolithography process can be produced. However, since the electron beam must be scanned one by one, the process time is very long. This makes it difficult to mass-produce laser diodes in the electron beam lithography process.

Accordingly, an object of the present invention is to provide a method of forming a light guide layer of a semiconductor laser diode having a tip with a line width less than the exposure limit, while shortening the processing time and facilitating mass production.

In order to accomplish the object of the present invention, the present invention forms a multi-layer active layer on a compound semiconductor substrate, and then forms a hard mask film on the multi-layer active layer. Thereafter, a photoresist pattern is formed on the hard mask film, and the photoresist pattern is baked to improve adhesion between the photoresist pattern and the hard mask film. Thereafter, using the baked photoresist pattern as a mask, the hard mask film is subjected to undercut etching to form a hard mask pattern, then the photoresist pattern is removed, and the multilayered active layer is etched in the form of the hard mask pattern Thereby forming a light guide layer.

The photoresist pattern is formed to have a shape in which the line width of one end portion is relatively narrowed.

The hard mask film may be a silicon nitride film or a silicon oxide film, and the undercut etching of the hard mask film proceeds to a buffered oxide etchant (BOE) solution.

The step of baking the photoresist pattern comprises heat-treating the photoresist pattern at a temperature of 100 to 150 ° C for 1 to 5 minutes.

After the step of forming the optical waveguide layer, a step of reducing the line width of the optical waveguide layer while healing the damage of the optical waveguide layer can be further carried out. The step of reducing the line width of the optical waveguide layer while healing the damage of the optical waveguide layer comprises the steps of cleaning the optical waveguide layer for 1 to 3 minutes with H ₂ SO _{4 and} cleaning the cleaned optical waveguide layer with HBr: Is dipped in a diluted solution of 8: 2: 100 to reduce the line width while removing the damaged portion of the optical waveguide layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments of the present invention may be modified into various other forms, and the scope of the present invention should not be interpreted as being limited by the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention. Therefore, the shapes and the like of the elements in the drawings are exaggerated in order to emphasize a clearer description, and elements denoted by the same symbols in the drawings denote the same elements.

FIGS. 1A through 1E are perspective views of a semiconductor laser diode according to an embodiment of the present invention, and FIGS. 2A through 2E are cross-sectional side views of the laser diode of FIG. 1A through FIG. 1E, respectively.

First, referring to FIGS. 1A and 2A, a laser diode includes an InP substrate 100. An InP buffer layer 110, a first SCH layer (separate confinement heterostructure) 115, an MQW layer (multi quantum well) 120, a second SCH layer 125 and a p-InP cover layer 130 ) Are sequentially formed. At least one of the InP buffer layer 110, the first SCH layer 115, the MQW layer 120, the second SCH layer 125 and the p-InP cover layer 130 may be formed by a metal organic chemical vapor deposition (MOCVD) Lt; RTI ID = 0.0 > epitaxial < / RTI > The hard mask layer 135 is formed on the p-InP cover layer 130. As the hard mask film, a silicon nitride film or a silicon oxide film can be used. In this embodiment, for example, a silicon nitride film is used as the hard mask film 135. The silicon nitride film used as the hard mask film 135 may be formed by, for example, plasma enhanced chemical vapor deposition (PECVD), and is formed to a thickness of about 1000 to 3000 nm. A photoresist pattern 140 for defining an active region is formed on the hard mask film 135 by a known photolithography process. The photoresist pattern 140 for defining the active region is configured such that the output portion is tip-shaped to improve the light output characteristic of the laser diode. At this time, it is preferable that the line width of the photoresist pattern 140 corresponding to the tip is about the exposure limit value that can be formed by the lithography process. In this embodiment, the tip portion linewidth w1 of the photoresist pattern 140 is about 1 to 2 mu m and the center line width w2 of the photoresist pattern 140 is 3 to 4 mu m.

Next, the photoresist pattern 140 is baked. The baking process of the photoresist pattern 140 is performed at a temperature of 100 to 150 DEG C for 1 to 5 minutes. Here, the baking process may be an additional baking process that is performed just before the hard mask film is etched in addition to the soft bake process and the hard bake process, which are included in a general photolithography process, or the photolithography process The hard bake process provided at the final stage can be carried out under the above-described conditions.

Then, as shown in FIGS. 1B and 2B, the hard mask film 135 is etched using the photoresist pattern 140 as a mask. In this case, for example, a buffered oxide etchant (BOE) solution diluted to 6 to 1 may be used. If the hard mask film 135 is a silicon nitride film, the etching process proceeds for about 30 seconds to 1 minute and 30 seconds.

1C and 2C, undercut etching is performed so that the etched hard mask layer 135 may have a line width narrower than that of the photoresist pattern 140 to form the hard mask pattern 135a . The undercut etching may also be performed by a wet etching process using the BOE solution. An undercut etching may be performed for a predetermined time, for example, 1 to 2 minutes so that the line width of the hard mask film 135a corresponding to the tip becomes 0.5 탆 or less Go ahead.

When the undercut etching is performed using a general photoresist pattern, the wet etching solution (BOE) penetrates the interface between the photoresist pattern and the hard mask film, thereby causing undesirable irregularities on the side walls and the upper surface of the hard mask film. Such deformation of the hard mask film can deform the shape of the optical waveguide layer and induce scattering loss.

However, in this embodiment, since the bonding force (adhesion) between the hard mask film 135 and the photoresist pattern 140 is improved by the baking process of the photoresist pattern 140 before the hard mask film 135 is etched, , Etching solution is prevented from penetrating between the hard mask film 135 and the photoresist pattern, thereby preventing the side surface and the top surface of the hard mask film 135 from being etched. Accordingly, even when the hard mask film 135 is subjected to undercut etching, the lateral linearity of the hard mask pattern 135a is ensured, and the scattering loss of the optical waveguide layer can be reduced.

Next, as shown in FIGS. 1D and 2D, the photoresist pattern 140 is removed. The photoresist pattern 140 is first removed by a resist remover and then secondarily removed by a plasma ashing process to completely remove the photoresist pattern 140 without residue .

Referring to FIGS. 1E and 2E, the InP cover layer 130, the second SCH layer 125, the MQW layer 120, the first SCH layer 115, And the InP buffer layer 110 are etched to form the optical waveguide layer 150. The InP cover layer 130, the second SCH layer 125, the MQW layer 120, the first SCH layer 115 and the InP buffer layer 110 are formed by dry etching, for example, reactive ion etching (RIE) And the InP buffer layer 110 is etched only a part of the entire thickness.

Then, in order to heal the damage of the optical waveguide layer 150 generated by the dry etching process, the resultant is cleaned with H ₂ SO ₄ for 1 to 3 minutes, and HBr: H ₂ O ₂ : H ₂ O 8: 2: 100 in order to remove the damaged portion of the optical waveguide layer 150. The line width of the optical waveguide layer 150 can be reduced by such a damage healing process.

FIGS. 3 and 4 are photomicrographs showing a state in which the hard mask film is undercut-etched after the baking process of the photoresist pattern as in the embodiment of the present invention. 3 and 4, when the photoresist pattern 140 is baked as described above and then the hard mask film is etched, the hard mask patterns 135a-1 and 135a-2 that maintain the linearity without causing irregularities on the sides are formed . Further, according to FIG. 3, although the photoresist pattern may be partially peeled off during the BOE process, since the hard mask film is formed to have a sufficient thickness and the baking process is performed as described above, A thin wave tip can be manufactured.

In the present embodiment, a silicon nitride film or a silicon oxide film is used as the hard mask, but it is needless to say that any film (for example, a metal film or the like) can be used as long as it is a film having a different etch selectivity from that of the underlying waveguide.

As described in detail above, according to the present invention, in the hard mask film etching process for forming the optical waveguide layer, the hard mask film is subjected to undercut etching to form the optical waveguide layer having a line width below the exposure limit. Accordingly, it is possible to form a reproducible fine optical waveguide layer below the exposure limit without a long process, and to improve the optical output characteristics.

At this time, in order to prevent lateral etching of the hard mask film during the undercut etching, a baking process is performed to improve the adhesion between the hard mask film and the photoresist pattern before etching the hard mask film. By this baking process, penetration of the etching solution between the hard mask film and the photoresist pattern is prevented, etching of the side wall of the hard mask pattern can be prevented, and light scattering loss of the optical waveguide layer can be prevented.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. Further, it is obvious that various modifications and variations can be made without departing from the scope of the technical idea of the present invention by anyone having ordinary skill in the art.

Claims (9)

Forming a multi-layered active layer on the compound semiconductor substrate; Forming a hard mask film on the active layer of the multilayer; Forming a photoresist pattern on the hard mask film; Baking the photoresist pattern to improve adhesion between the photoresist pattern and the hard mask film; Forming a hard mask pattern by undercut etching the hard mask film using the baked photoresist pattern as a mask; Removing the photoresist pattern; And And etching the multi-layer active layer in the form of the hard mask pattern. The method according to claim 1, wherein the photoresist pattern is formed to have a shape in which the line width of one end portion is relatively narrowed. The method of claim 1, wherein the hard mask film is a silicon nitride film or a silicon oxide film. The method of claim 3, wherein the undercut etching of the hard mask layer proceeds to a buffered oxide etchant (BOE). 5. The method of claim 4, wherein the undercut etching of the hard mask film comprises: Etching the hard mask film in the form of a photoresist pattern; And etching the hard mask film to have a line width smaller than that of the photoresist pattern until the line width of the hard mask film at one end becomes below the exposure limit. The method of claim 1, wherein baking the photoresist pattern comprises: Wherein the photoresist pattern is thermally treated at 100 to 150 ° C for 1 to 5 minutes. 2. The method of claim 1, wherein forming the multi- Forming an InP buffer layer on the compound semiconductor substrate; Forming a first SCH (separate confinement heterostructure) layer on the InP buffer layer; Forming a multi quantum well (MQW) layer on the first SCH layer; And And forming a second SCH layer over the MQW layer. The method of claim 1, wherein after forming the optical waveguide layer, Further comprising the step of reducing the line width of the optical waveguide layer while healing the damage of the optical waveguide layer. The method of claim 8, wherein the step of reducing the line width of the optical waveguide layer while healing the damage of the optical waveguide layer comprises: Cleaning the optical waveguide layer with H ₂ SO ₄ for 1 to 3 minutes; And And dipping the cleaned optical waveguide layer in a solution diluted with HBr: H 2 O 2: H 2 O of 8: 2: 100 to reduce the line width while removing damaged portions of the optical waveguide layer. Lt; / RTI >

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