JP2003282551A - Single crystal sapphire substrate and manufacturing method thereof - Google Patents

Abstract

[PROBLEMS] Even if a single crystal sapphire substrate is polished by chemical polishing, the surface roughness is flattened, but the irregularity distribution has no regularity, so that a nitride semiconductor is epitaxially grown. Not suitable for A sapphire substrate has a stripe-shaped groove on a main surface thereof, and an angle between a side surface of the groove and the main surface is 60 ° or more and 90 ° or more.
Less than

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal sapphire substrate having a stripe-shaped step on the surface, which is suitable for film formation of wide-gap semiconductors, SOS (Silicon on Sapphire) devices, etc.

[0002]

2. Description of the Related Art GaN is attracting attention not only for optical devices but also for high temperature electronics and environment resistant devices. It is difficult to obtain a lattice-matched substrate for epitaxial growth of GaN-based compound semiconductor crystals.
Generally, sapphire, SiC, magnesia spinel, etc. are used as a substrate for crystal growth. Originally, a single crystal sapphire substrate is exposed to a specific crystal plane on the surface, and then mechanically polished and chemically polished to a mirror surface state, on which a Group III nitride compound used for a light emitting device or the like is formed. A semiconductor element is deposited. However, only by chemical polishing, there is still a lattice mismatch between the crystal growth substrate and the GaN-based compound semiconductor crystal, which causes dislocations (see, for example, JP 2001-210598 A).

For example, as shown in FIG. 4, a saf whose main surface is the C surface
GaN film 2 acting as a buffer layer on the surface of the air substrate 1
Is formed by low temperature CVD, and n-type Al is formed on the GaN film 2._xG
a_yIn _zN film 3 is formed by epitaxial growth of CVD,
On top of that p-type Al_xGa_yIn_zN film 4 is epitaxially grown by CVD
It is formed by the length, and this p-type Al_xGa_yIn_zOn N film 4
Low resistance p-type Al_xGa_yIn_zN film 5 is also a CVD epitaxy
It is formed by growth.

[0004] n-type Al _x Ga _y In _z N surface of the film 3 and the p-type Al _x G
Electrodes 6 and 7 are formed on the surface of the _ay In _z N film 5, respectively.

In manufacturing such a light emitting diode, when the n-type Al _x Ga _y In _z N film 3 is directly epitaxially grown on the sapphire substrate 1 by CVD, the GaN film has many defects and crystallinity. And the surface flatness is also poor. Such Al _x Ga _y In _z N film 3
The light emitting diode using the LED has a very low luminous efficiency.

Therefore, n-type Al is formed on the surface of the sapphire substrate 1.
_{The x} Ga _y In _z N film 3 is not directly formed, but the GaN film 2 acting as a buffer layer is formed by low temperature CVD epitaxial growth. In such epitaxial growth by low temperature CVD, the lattice constant of the sapphire substrate 1 and the n-type Al _x Ga _y In _z N
A difference of 10% or more from the lattice constant of the film 3 can be compensated, and good surface flatness important in the heterojunction can be realized.

On the other hand, it has been proposed to form an AlN film by low temperature CVD epitaxial growth instead of the GaN film 2.

However, the GaN film 2 and Al that function as a buffer layer are formed by such low temperature CVD epitaxial growth.
When an N film is formed and an Al _x Ga _y In _z N film 3 containing Al as an essential component is epitaxially grown on the N film, dislocations increase significantly. The dislocation density of such an Al _x Ga _y In _z N film is as high as 10 ⁹ cm ^-2 , for example.

When the dislocation density is high as described above, it constitutes an absorption center of light, which deteriorates the characteristics of the device. In particular, this is a serious problem in optical devices such as laser diodes that require high efficiency. Further, since such dislocations cause deterioration of the pn junction, reduction of dislocations becomes a serious problem even when manufacturing electronic devices.

Therefore, various studies have been conducted to minimize dislocations caused by the difference in lattice constant between the crystal growth substrate and the deposited crystal.

As a result, it has been revealed that a substrate having a stripe-shaped groove on the surface of a film-forming substrate is advantageous for epitaxial growth of a gallium nitride-based semiconductor compound (see, for example, Japanese Patent Laid-Open No. 2001-210598, Open 2001-274093 and other publications). When a gallium nitride-based compound is epitaxially grown on this substrate, it grows by selective lateral growth so as to fill the stripe-shaped groove, and it becomes possible to form a film including a region with a small dislocation density.

In the method of forming the stripe-shaped groove, a photoresist is formed on the main surface of the sapphire substrate, and an opening is formed in the photoresist by photolithography. Using the photoresist as a mask, the underlying sapphire substrate body is selectively etched to form a plurality of grooves, and the photoresist is removed. This etching was mainly dry etching such as ion beam etching or reactive ion etching.

[0013]

However, the manufacturing method of the single crystal sapphire substrate having the stripe-shaped groove on the main surface is mainly based on the reactive ion etching method,
Reactive ion etching is not suitable for mass production because it has a very slow processing speed and has a problem that the number of sheets that can be processed at one time is limited.

Further, in the conventional manufacturing method, the side surface of the groove can be etched only perpendicularly to the main surface, and there is a disadvantage that the processing takes time.

[0015]

The single crystal sapphire substrate of the present invention is characterized in that a stripe-shaped groove is formed on the main surface and the angle between the side surface of the groove and the main surface is 60 ° or more and less than 90 °. And That is, by making the angle between the side surface and the surface of the groove less than 90 °, the volume of the portion to be removed by etching can be reduced and the processing time can be shortened.

Further, the present invention is characterized in that a pattern is formed on a main surface of a sapphire substrate by using a polyimide as a resist, and a stripe-shaped groove is formed by etching with phosphoric acid. That is, by processing the groove by wet etching with phosphoric acid, it is possible to shorten the etching time per time and collectively process, which is also suitable for mass production.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, in the sapphire substrate 1 of the present invention, stripe-shaped grooves 1b having a width w1, a distance w2 between adjacent grooves and a depth h are regularly formed on the main surface 1a. Also,
The angle θ between the side surface 1c of the stripe-shaped groove 1b and the main surface 1a is 60 °
It is above 90 °.

When a nitride semiconductor is epitaxially grown on the main surface 1a of the sapphire substrate 1, the vertical growth and the lateral growth of the nitride semiconductor are combined to form a nitride semiconductor film having a flat surface. . As a result, the dislocation density on the main surface 1a of the sapphire substrate 1 main body is reduced to 10 ⁶ cm ^-2, and it is possible to form a light emitting device with high luminous efficiency.

Here, the angle θ formed by the main surface 1a and the side surface 1c is 60
The reason why the angle is 90 ° or more and less than 90 ° is that if the angle is 90 °, it takes too much processing time, and if it is less than 60 °, lateral growth is difficult when epitaxially growing the nitride semiconductor.

The width w1 of the groove and the distance w2 from the adjacent groove are preferably 2 to 50 μm, and the depth h is preferably 2 to 10 μm.
Within this range, a gallium nitride semiconductor having a flat surface can be formed when a nitride semiconductor is epitaxially grown. In addition, the main surface 1a of the sapphire substrate 1
The surface orientation of can be applied not only to C surface but also to A surface, M surface, and R surface.

Next, a method for manufacturing the single crystal sapphire substrate of the present invention will be described. First, as shown in FIG. 2A, a resist 32 made of polyimide is formed on the main surface 1a of the sapphire substrate 1, and an opening 33 is formed in the resist 32 made of polyimide by photolithography. At that time, the resist
Since the width of 32 becomes the interval w2 and the width of the opening 33 between the resists 32 becomes the width w1 of the groove, these are adjusted to fall within the above-mentioned range.

Next, using the resist 32 as a mask, the sapphire substrate 1 therebelow is selectively etched to form a plurality of regular stripe-shaped grooves. At this time, Figure 2
As shown in (b), the etching is performed by wet etching with phosphoric acid 34 at 250 ° C to 300 ° C. After that, by removing only the resist 32 as shown in FIGS. 2 (c) and 2 (d), it becomes possible to form the single crystal sapphire substrate 1 having the stripe-shaped grooves 1b on the main surface 1a.

The reason why polyimide is used as the resist is that it has adhesiveness to sapphire and is excellent in acid resistance against phosphoric acid. The reason for using phosphoric acid is to dissolve sapphire without dissolving polyimide. This is because only the etching can be performed. The etching rate of sapphire with phosphoric acid is shown in Fig. 3.
become that way. This figure makes it possible to freely change the depth of the groove. Further, the angle θ formed by the side surface 1c and the surface 1a of the stripe-shaped groove 1b is determined by the temperature and time conditions of phosphoric acid.
It is possible to change within the range of 60 ° or more and less than 90 °.

[0025]

Example A single crystal sapphire substrate 1 of the present invention having a stripe-shaped groove on the surface was produced as follows.

Chemically polished single crystal sapphire substrate 1
The C surface of is used as the main surface 1a, and precision cleaning is performed to improve the adhesion with the polyimide. After that, a polyimide resist 32 having a width w2 and an interval w1 set to 20 μm is applied to the main surface 1a. After that, the sapphire substrate 1 coated with the resist 32
Is post-baked at 330 ° C. for 1 hour.

Next, the sapphire substrate coated with the resist 32 is immersed in phosphoric acid heated to 250 ° C. for about 30 minutes. At this time, the temperature is preferably 250 ° C to 270 ° C, but about 300 ° C is also possible. At this time, phosphoric acid is stirred so that the temperature distribution becomes constant.

After thoroughly washing the sapphire substrate taken out from the phosphoric acid solution, only the polyimide is removed with aqua regia.

From the above, a single crystal sapphire substrate 1 having a width w1 of the groove 1b of 20 μm, a distance w2 from the adjacent groove of 20 μm, and a depth h of 5 μm was prepared. In addition, the angle θ formed by the side surface 1c of the groove 1b and the main surface 1a is about 80 ° under the condition of 250 ° C. for 30 minutes, and this condition is the condition most suitable for mass production.

In this embodiment, the main surface 1a of the sapphire substrate 1 is
Is the C surface, but the same applies to the case where the main surface 1a of the sapphire substrate 1 is the A surface, the M surface, or the R surface.

Since the present invention can be etched only by immersing it in high temperature phosphoric acid, the number of sheets that can be processed at one time is increased to about 100 compared with the conventional reactive ion etching, and the processing time is about 30 minutes. It is possible to form the stripe-shaped groove in a short time. Compared to the conventional method using reactive ion etching, the number of processed sheets is large,
The processing time can be shortened by several hours.

[0032]

As described above, according to the present invention, the stripe-shaped grooves are regularly formed on the main surface of the single crystal sapphire substrate, so that when a nitride semiconductor is epitaxially grown on sapphire, the surface undulations occur. It is possible to manufacture a high-performance device without Further, by changing the width of the opening of the resist, or the temperature and time of etching, the width of the stripe, the distance between adjacent stripes, the depth, and the angle formed between the side surface and the surface of the groove can be easily controlled. . Furthermore, the wet etching has enabled mass production.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a single crystal sapphire substrate of the present invention.

2A to 2D are cross-sectional views showing a method for manufacturing a single crystal sapphire substrate of the present invention.

FIG. 3 is a graph showing the temperature dependence of the etching rate of sapphire.

FIG. 4 is a cross-sectional view showing a configuration of a conventional light emitting diode.

[Explanation of symbols]

1: Sapphire substrate 1a: Main surface 1b: groove 1c: Side 32: Resist 33: Open 34: phosphoric acid w1: width w2: interval h: depth

Claims (5)

[Claims] 1. A single crystal sapphire substrate having a stripe-shaped groove on a main surface, and an angle between a side surface of the groove and the main surface is 60 ° or more and less than 90 °. 2. The single crystal sapphire substrate according to claim 1, wherein the groove has a width and an interval of 2 to 50 μm and a depth of 2 to 10 μm. 3. A method for manufacturing a single crystal sapphire substrate, which comprises forming a pattern on the sapphire substrate with a resist and then forming a stripe-shaped groove by etching with phosphoric acid. 4. The method for manufacturing a single crystal sapphire substrate according to claim 3, wherein polyimide is used as the resist. 5. The method for manufacturing a single crystal sapphire substrate according to claim 3, wherein phosphoric acid at 250 to 300 ° C. is used for the etching.