KR100584541B1 - Vertical cavity surface emitting laser and method for manufacturing it - Google Patents

Abstract

It has a semiconductor laminated structure of a lower reflector layer, an active layer, a guide layer and an upper reflector layer sequentially stacked on the substrate and the substrate, and a post from which the laser light is emitted through a window, and an upper reflector layer and a guide to form a space around the post. Trenches formed over at least a portion of the layer, active layer, and bottom reflector layer, blocks formed to enclose the posts spaced apart by the trenches at predetermined intervals, and posts, trenches, and blocks except for windows and / or portions thereof. And an insulating layer formed on the upper reflector layer, an upper electrode formed on at least a portion of the exposed upper reflector layer and the insulating layer, and a lower electrode formed on the lower surface of the substrate. The guide layer is applied through upper and lower electrodes. Selective oxidation method is used to guide current flow by defining a current guide region through which a current flows and a current guide region. It consists of a high-resistance part formed by oxidizing from the outer side adjacent to the trench, and the post has a non-circular shape in which the planar shape is composed of a circular area and a compensation area of the outer circumference so as to compensate for the difference in oxidation depth according to the crystal direction when the high-resistance part is formed. A surface light laser is disclosed.

Description

Surface cavity laser and method for manufacturing the same

1 is a perspective view schematically showing the structure of a surface light laser proposed by the applicant;

2 is a cross-sectional view showing a laminated structure of the surface light laser shown in FIG.

3 is a plan sectional view showing the guide layer structure of FIG.

4 is a perspective view schematically showing the structure of a surface light laser according to an embodiment of the present invention;

5 is a cross-sectional view showing a laminated structure of the surface light laser shown in FIG.

6 is a plan sectional view showing the guide layer structure of FIG.

Figure 7 is a plan sectional view showing a guide layer structure according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100 ... substrate 110,140 ... lower and upper reflector layer 120 ... active layer

130 ... Guide layer 130a ... Current guide area 130b ... High resistance part

150 Insulation layer 160, 170 Upper and lower electrodes 200 Post

200a ... Origin area 200b ... Compensation area 210 ... Windows

220 ... Trench 300 ... Block

The present invention relates to a surface cavity laser (VCSEL; Vertical Cavity Surface Emitting Laser) and a method of manufacturing the same, and more particularly, to a surface laser including a high resistance portion for guiding the flow of current by a selective oxidation method; It relates to a manufacturing method.

In general, since the surface light laser emits a Gaussian beam close to a circular shape in the stacking direction of the semiconductor material layer unlike the edge emitting laser, an optical system for shape correction of the emitted light is unnecessary. In addition, since the size can be reduced, a plurality of surface light lasers can be integrated on one semiconductor wafer, thereby facilitating two-dimensional arrangement. Due to these advantages, the surface light laser can be widely applied in the field of optical applications such as optical communication, electronic calculators, acoustic imaging devices, laser printers, laser scanners and medical equipment.

This surface light laser has a high resistance portion formed in the upper reflector layer to guide the flow of current supplied through the electrode to improve the light output characteristic. One way to form this high resistance portion is a selective oxidation method that oxidizes the peripheral portion except for the guide region of the current by controlling the exposure time to the oxidation atmosphere.

로 적층한 상태로, 기판 상에 성장된 표면광 레이저 포스트 주변을 식각한 후, 산화분위기[

(↑)]에서 시간을 조절하면 상기

층이 외측에서 내측으로 산화되어

산화 절연층 즉, 고저항부가 형성되는 방법이다. This selective oxidation method removes a portion of the lower layer of the upper reflector layer, i.

After etching the surroundings of the surface light laser post grown on the substrate in a stacked state, the oxidation atmosphere [

(↑)] to adjust the time

The layer is oxidized from outside to inside

The oxide insulating layer, that is, the high resistance portion is formed.

A surface light laser having a high resistance portion formed by such a selective oxidation method has been proposed by the applicant through the patent application No. 4248 (filed date: October 12, 1998) in 1998. Referring to FIG. 1, the surface light laser proposed by the applicant is formed as follows.

That is, the lower reflector layer 11, the active layer 12, the preliminary oxide layer 13, and the upper reflector layer 14 are sequentially stacked on the substrate 10, and then the surface light laser post 20 is formed. When the trench 22 is formed by etching the outer portion of the lower reflector layer 11 to a depth of the lower reflector layer 11, the cylindrical surface light laser post 20 is surrounded by the block 30 around the trench 22. Is formed.

층이 트렌치(22)에 접한 외주로부터 산화되어 도 2에 도시된 바와 같은 고저항부(13b)가 형성된다. 이때, 상기 예비산화층(13) 중 산화되지 않은 중앙 부분은 전류 가이드영역(13a)이 된다. 여기서, 상기 고저항부(13b) 및 전류 가이드영역(13a)은 가이드층을 이룬다.Then, when the surface light laser post 20 is exposed to the oxidation atmosphere, the pre-oxidation layer 13, that is,

The layer is oxidized from the outer periphery in contact with the trench 22 to form the high resistance portion 13b as shown in FIG. At this time, the central portion of the pre-oxidation layer 13 that is not oxidized becomes the current guide region 13a. Here, the high resistance portion 13b and the current guide region 13a form a guide layer.

Then, the insulating layer 15 is laminated and formed on the posts 20, the trenches 22, and the blocks 30 except for the window 21 and the peripheral portion of the laser light emitted therefrom, and then the upper electrode 16 is formed. Is formed directly on the insulating layer 15 and the upper reflector layer 14 around the window 21, and the lower electrode 17 is formed on the lower surface of the substrate 10.

층은 그 결정 방향에 따라 산화율이 다르기 때문에, 단면 형상이 원형인 표면광 레이저 포스트(20)를 산화분위기에 노출시키는 경우, 결정 방향에 따라 산화 깊이 차이가 생겨,

산화 절연막 즉, 고저항부(13b)에 둘러싸여 전류가 가이드되는 영역(13a)은 실질적으로 원형이 되지 않는다. By the way,

Since the layer has a different oxidation rate depending on the crystal direction, when the surface light laser post 20 having a circular cross-sectional shape is exposed to the oxidation atmosphere, an oxidation depth difference occurs depending on the crystal direction.

The region 13a surrounded by the oxide insulating film, that is, the high resistance portion 13b, through which the current is guided, is not substantially circular.

That is, as shown in FIG. 3 due to the difference in oxidation depth according to the crystal direction, if the high resistance portion 13b is formed by the selective oxidation method after the post 20 having a circular cross-sectional shape is formed, the current surrounded by Guide area | region 13a becomes substantially a rhombus shape.

Therefore, the surface light laser as described above forms the circular window 21 through which the laser light is emitted by the insulating layer 15 and the upper electrode 16 pattern above the rhombus-shaped current guide region 13a in the manufacturing process. In this case, it is difficult to accurately center the current guide region 13a and the window 21, and the far-field pattern is a cross-sectional shape of the laser beam at a distance from the laser depending on the degree of the center twist. ) Is a sensitive asymmetric change.

In addition, the degree to which the center is distorted as a whole of the substrate 10 also varies, and it is difficult to obtain a uniform far-field pattern from a plurality of surface light laser posts formed on the same substrate.

Therefore, due to such asymmetry and non-uniformity of the far-field pattern, it is difficult to obtain a plurality of surface light lasers of uniform characteristics in mass production of surface light laser devices, so that the yield may be low.

The present invention has been made in view of the above, and the far-field pattern characteristics are improved and laser beams emitted from a plurality of surface light lasers manufactured on one substrate can exhibit a more uniform far-field pattern. It is an object of the present invention to provide a surface light laser and a method of manufacturing the same.

Surface light laser according to the present invention for achieving the above object, the substrate; A post having a semiconductor stack structure of a lower reflector layer, an active layer, a guide layer, and an upper reflector layer sequentially stacked on the substrate, the laser light being emitted through a window; A trench formed over at least a portion of the upper reflector layer, guide layer, active layer and lower reflector layer to form a space around the post; A block formed to surround the post while being spaced apart by a predetermined interval from the trench; An insulating layer formed on the posts, trenches and blocks except for the window and / or a portion of the peripheral area; At least a portion of the exposed upper reflector layer and an upper electrode formed on the insulating layer; A lower electrode formed on a lower surface of the substrate, wherein the guide layer includes: a current guide region through which current applied through the upper and lower electrodes flows; And a high resistance portion formed by oxidizing from an outer portion adjacent to the trench by a selective oxidation method to limit the current guide region to guide current flow, wherein the post has an oxidation depth along a crystal direction when forming the high resistance portion. In order to compensate for the difference, the planar shape is characterized in that the non-circular consisting of the compensation area and the circular region.

According to a feature of the invention, it is preferable that the compensation region is formed convexly on the periphery of each quadrant of the original region.

Further, according to a feature of the present invention, it is preferable that the post is a polygon whose planar shape is made up of at least four angles.

On the other hand, the method for manufacturing a surface light laser according to the present invention comprises the steps of stacking sequentially on the prepared substrate to form a lower reflector layer, an active layer, a pre-oxidation layer and an upper reflector layer; A pattern is formed on the upper reflector layer so that the planar shape of the post from which the laser light is emitted is non-circular, and the peripheral area of the post is etched over at least a part of the upper reflector layer, the pre-oxidation layer, the active layer, and the lower reflector layer. Forming a trench that spatially separates the non-circular post and the block; Forming an oxidizing atmosphere for a predetermined time to oxidize from an outer side of the pre-oxidation layer adjacent to the trench to form a high resistance portion; Forming an insulating layer on the posts, trenches and blocks except for the windows and / or the periphery where laser light is emitted; Forming an upper electrode on at least a portion of the exposed upper reflector layer and the insulating layer; And forming a lower electrode on a lower surface of the substrate, wherein the non-circular planar shape of the post includes a compensation region of the original region and the outer circumference thereof to compensate for a difference in oxidation depth according to a crystal direction when the high resistance portion is formed. Characterized in that consisting of.

Hereinafter, a surface light laser and a manufacturing method thereof according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

Looking at the shape of the surface light laser according to an embodiment of the present invention shown in Figures 4 and 5, the flat cross-sectional shape of the non-circular post 200, the block 300 surrounding the post 200 and It is divided into a trench 220 that spatially separates the post 200 and the block 300.

The post 200 has a window 210 which is a region from which light is emitted and functions to generate and irradiate light according to an applied current. The post 200 has an oxidation depth according to a crystal direction when forming the high resistance portion 130b to be described later. In order to compensate for the difference, the flat cross-sectional shape is a non-circular shape consisting of the original region 200a and the outer region compensation region 200b. 4 illustrates a boundary of the original area 200a and the compensation area 200b in a dotted line for convenience, and the window 210 may be included in the original area 220a.

The block 300 is used to prevent damage to the semiconductor material layers and is used as a bonding pad for wire bonding. The block 300 surrounds the post 200 at a predetermined distance from the post 200.

In this case, the post 200 and the block 300 preferably have the same semiconductor stacked structure to simplify the manufacturing process, the upper reflector layer 140, as will be described later the area around the post 200, By forming the trench 220 by etching the high resistance portion 135, the active layer 120, and the partial reflector layer 110, the structure as described above is formed.

On the other hand, the surface light laser according to the present invention, when looking at the laminated structure, as shown in Figs. 4 and 5, the substrate 100, the lower electrode 170 formed on the lower surface of the substrate 100, the substrate 100 The lower reflector layer 110, the active layer 120, the guide layer 130, the upper reflector layer 140, the insulating layer 150, and the upper electrode 160 are sequentially formed on the laminate.

등으로 되어 있으며, 이 기판(100) 상에 동일 공정에 의해 복수의 표면광 레이저가 동시에 형성된다. The substrate 100 is, for example, a semiconductor material containing n-type impurities

And a plurality of surface light lasers are simultaneously formed on the substrate 100 by the same process.

The lower reflector layer 110 is formed on the substrate 100, and is formed by alternately stacking two compound semiconductors having different refractive indices from an impurity semiconductor material of the same type as the substrate 100. For example, the lower reflector layer 110 has different compositions, and n-type Al _x Ga _1-x As and Al _y Ga _1-y As (x ≠ y) having different refractive indices are alternated to have a thickness of λ / 4. It is made of laminated. The upper reflector layer 140 is made of the same kind of impurity semiconductor material containing impurities of the opposite type to the lower reflector layer 110. For example, the upper reflector layer 140 has p-type Al _x Ga _1-x As and Al _y Ga _1-y As (x ≠ y) having different compositions on the active layer 120 to have a thickness of λ / 4. Alternately stacked. The upper reflector layer 140 and the lower reflector layer 110 induce the flow of electrons and holes by the current applied through the upper and lower electrodes 160 and 170. Is the wavelength of the emitted laser light of the surface light laser.

The active layer 120 is a region that generates light by energy transition due to recombination of electrons and holes provided in the upper and lower reflector layers 140 and 110, and has a single or multiple quantum-well structure and a superlattice. lattice) structure. Here, the active layer 120 is made of AlGaAs, GaAs, InGaAs and the like according to the emission wavelength of the surface light laser.

Here, a cladding layer (not shown) may be further provided between the lower reflector layer 110 and the active layer 120 and between the active layer 120 and the upper reflector layer 140, as is well known.

The guide layer 130 defines a current guide region 130a as a pre-oxidation layer through which the current applied through the upper and lower electrodes 160 and 170 flows, and defines the current guide region 10a to provide current flow. The high resistance portion 130b is formed by oxidizing the preliminary oxide layer from an outer portion adjacent to the trench 220 by a selective oxidation method to guide the same.

Here, the pre-oxidation layer which is the base of the guide layer 130 is formed between the upper reflector layer 140 and the active layer 120 or in the upper reflector layer 140, and is basically a layer rich in Al, for example, a material thereof. The AlAs or y value is approximately 0.9 or more and is made of p-type Al _y Ga _1-y As having the same structure as the upper reflector layer 140.

In addition, the high resistance portion 135 is Al ₂ O ₃ formed by oxidizing the preliminary oxide layer by a predetermined depth from the outer side contacting the trench 220 in contact with the oxidation atmosphere by being oxidized by H ₂ O in the vapor state for a predetermined time. It is an insulating oxide layer.

At this time, the Al ₂ O ₃ is a crystal structure, and since the oxidation rate is different depending on the crystal direction, the oxidation depth is different depending on the crystal direction, whereby the current guide region 130a and the high resistance portion 130b. ) Is not at the same distance from the outer side contacting the trench 220.

However, since the post 200 according to the present invention is composed of the original region 200a and the compensation region 200b for compensating for the difference in oxidation depth according to the crystal direction, the difference in oxidation depth as described above is compensated for. As illustrated in FIG. 6, the current guide region 130a limited by the high resistance portion 130b may have a shape near to a circle.

4 to 6 illustrate a case in which the compensation area 200b of the post 200 is convexly formed at the outer circumference of each quadrant of the original area 200a, so that the post 200 has four petals. In this case, the pre-oxidation layer is oxidized from the outer side contacting the trench 220 in the oxidizing atmosphere to become the high resistance portion 130b. After a predetermined time, as shown in FIG. 130a) is formed.

On the other hand, the post 200 may be variously modified in addition to the petal shape described above. That is, the post 200 of FIG. 3 may be formed in a quadrangular shape as shown in FIG. 7 so that the difference in oxidation depth according to the crystal direction is compensated for to form a substantially circular current guide region 130a.

The rectangular post 200 may be divided into a circumferential region and an angular compensation region of the outer circumference thereof. As shown in FIG. 6, when the pre-oxidation layer is exposed to an oxidizing atmosphere, the rectangular post 200 is oxidized from an outer portion adjacent to the trench 220 to form a high resistance portion 130b. The circular current guide region 130a can be formed.

As another embodiment, the post may be formed in a polygonal shape having at least four angles, for example, a hexagonal shape, and various other embodiments are of course possible.

Referring to FIG. 5 again, the insulating layer 150 is made of an insulating material, for example, SiO ₂ , and has a window 210 and a predetermined width around the window 210, which is a part of the light emitted from the post 200. Except for the upper surface of the post 200, the block 300 and the trench 220 are laminated.

The upper electrode 160 is formed on a predetermined width around the window 210 and the insulating layer 150, and is formed directly on the upper reflector layer 140 around the window 210 to form an ohmic contact. To achieve. Therefore, the current applied to the portion of the upper electrode 160 formed in the block 300 used as the bonding pad is input into the post 200 through the periphery of the window 210. Here, the upper electrode 160 may be formed directly on the window 210 by being made of a transparent electrode such as ITO. In this case, the current can be applied more evenly to the center of the post.

The lower electrode 170 is formed on the bottom surface of the substrate 100.

In the surface light laser according to the present invention as described above, the current flow is blocked by the insulating layer 150 when the current is applied to the upper and lower electrodes 160 and 170, the post through the window 210 surrounding the post Since the current is supplied only to the 200, the laser light is generated only in the post 200.

In the surface light laser having the shape and the laminated structure as described above, since the non-circular post 200 is provided to compensate for the difference in oxidation depth according to the crystal direction when forming the high resistance portion 130b by the selective oxidation method, the current guide The region 130a can be formed substantially circular, so that the far-field pattern characteristic of the laser light emitted therefrom is greatly improved.

That is, when the window 210 is formed by manufacturing the upper electrode 160 and / or the insulating layer 150, it is relatively easy to center the center of the window 210 and the current guide region 130a. As the centers are displaced, the asymmetrical change in the far field pattern becomes relatively insensitive.

Here, although the structure has been described taking a single surface light laser as an example, an array structure in which a plurality of surface light lasers are integrally formed on a single substrate is also possible.

Hereinafter, a process of manufacturing the surface light laser according to the present invention as shown in FIGS. 4 and 5 will be described.

First, a substrate is prepared, and the lower reflector layer 110, the active layer 120, the preliminary oxide layer 130, and the upper reflector layer 140 are sequentially formed on the prepared substrate to form a semiconductor laminate structure. Here, the substrate 100 is a state after the wrapping.

The pre-oxidation layer 130 is formed between the active layer 120 and the upper reflector layer 140, may be formed in the upper reflector layer 140.

Here, a protective film (not shown) may be further formed on the upper reflector layer 140 to prevent oxidation of the upper reflector layer 140 during an oxidation process described later. The protective film is preferably made of SiO ₂ , so that the protective film can be easily removed through dry etching after an oxidation process.

Subsequently, a predetermined pattern is formed on the upper reflector layer 140 or the protective layer so that the non-circular posts 200 and the block 300 are not etched, and the upper reflector layer 140, the pre-oxidation layer 130, the active layer 120, and the like. . The trench 220 is formed by, for example, dry etching over at least some depth of the lower reflector layer 110. Therefore, the post 200 and the block 300 are spatially separated by the boundary of the trench 220.

Here, the photoresist coating, exposure, and cleaning steps for making the above pattern follow a conventional method, and thus detailed description thereof will be omitted.

Next, if the oxidation atmosphere [H ₂ O (↑)] is formed for a predetermined time, the pre-oxidation layer 130 is oxidized from the outer side to the inside in contact with the trench 220, the high resistance of Al ₂ O ₃ The part 130b is formed. In this case, since the post 200 includes a compensation region 200b configured to compensate for the difference in oxidation depth according to the original region 200a and the crystal direction, the current guide region 130a defined by the fixing unit 130b is As shown in FIG. 6 (or FIG. 7), it is approximately circular.

Then, when the protective film is formed, the protective film is removed by dry etching or the like.

Next, the insulating layer 150 is formed of a material such as SiO ₂ to surround the post 200, the trench 220, and the block 300. Then, a portion of the insulating layer 150 formed on the upper surface of the post 200, that is, the portion where the window 210 is to be formed and the peripheral portion thereof is etched, so that a portion of the upper reflector layer 140 on the post 200 is etched. To be exposed. A portion of the insulating layer 150 is etched in a dry manner, and after forming a predetermined etching pattern, a portion of the insulating layer 0501 is removed through dry etching, wherein the upper electrode 160 is made of a transparent electrode such as ITO. In the case of forming, the insulating layer 150 only needs to be etched at the portion where the window 210 is to be formed.

Subsequently, the upper electrode 160 is formed on a portion except for the window 210 of the exposed portion of the upper reflector layer 140, that is, around the insulating layer 150. Here, the pattern for the upper electrode 160 forming portion may be formed through a photoresist and an exposure process.

Finally, the substrate is wrapped to a predetermined thickness to form a thin substrate 100, and the lower electrode 170 is formed on the wrapping surface to manufacture the surface light laser.

Since a plurality of surface light lasers as described above may be formed on a single substrate, they may be used as a single light source or may be used as an array structure.

As described above, the surface light laser according to the present invention has a non-circular post having a flat cross-section having a compensation area for compensating a difference in oxidation depth according to the original area and the crystal direction, thereby forming a high resistance part by selective oxidation. The current guide region limited by the high resistance portion can be formed in a substantially circular shape.                     

Accordingly, the surface light laser according to the present invention improves the far-field pattern characteristics of the laser light emitted therefrom, and enables the laser beams emitted from the plurality of surface light lasers produced on one substrate to exhibit a more uniform far-field pattern. do.

Claims (4)

A substrate; A post having a semiconductor stack structure of a lower reflector layer, an active layer, a guide layer, and an upper reflector layer sequentially stacked on the substrate, the laser light being emitted through a window; A trench formed over at least a portion of the upper reflector layer, guide layer, active layer and lower reflector layer to form a space around the post; A block formed to surround the post while being spaced apart by a predetermined interval from the trench; An insulating layer formed on the posts, trenches and blocks except for the window and / or a portion of the peripheral area; At least a portion of the exposed upper reflector layer and an upper electrode formed on the insulating layer; A lower electrode formed on the lower surface of the substrate; The guide layer, A current guide region through which current applied through the upper and lower electrodes flows; And a high resistance portion formed by being oxidized from an outer portion adjacent to the trench by a selective oxidation method to limit the current guide region to guide current flow. The post, The surface light laser, characterized in that the planar shape is a non-circular shape consisting of a circular region and a compensation region of the outer circumference to compensate for the difference in oxidation depth according to the crystal direction when forming the high resistance portion. The method of claim 1, The post, A surface light laser, wherein the planar shape is a polygon consisting of at least four angles. The method of claim 1, The compensation area is, Surface light laser, characterized in that formed in the convex periphery of each quadrant of the original region. Stacking sequentially on the prepared substrate to form a lower reflector layer, an active layer, a pre-oxidation layer, and an upper reflector layer; A pattern is formed on the upper reflector layer so that the planar shape of the post from which the laser light is emitted is non-circular, and the peripheral area of the post is etched over at least a part of the upper reflector layer, the pre-oxidation layer, the active layer, and the lower reflector layer. Forming a trench that spatially separates the non-circular post and the block; Forming an oxidizing atmosphere for a predetermined time to oxidize from an outer side of the pre-oxidation layer adjacent to the trench to form a high resistance portion; Forming an insulating layer on the posts, trenches and blocks except for the windows and / or the periphery where laser light is emitted; Forming an upper electrode on at least a portion of the exposed upper reflector layer and the insulating layer; And Forming a lower electrode on a lower surface of the substrate; The non-circular planar shape of the post is a surface light laser manufacturing method, characterized in that consisting of a compensation region of the original region and the outer circumference to compensate for the difference in oxidation depth according to the crystal direction when forming the high resistance portion.

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