JP3254436B2 - A method of manufacturing an etching mask for a gallium nitride-based compound semiconductor. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an Al _x Ga _{1 -X} N (0 ≦ X
≦ 1) The present invention relates to a method of forming a surface for dry etching, which relates to a method of processing a surface of a semiconductor by dry etching.

[0002]

2. Description of the Related Art Conventionally, Al _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductors have been attracting attention as materials for blue light emitting diodes and light emitting elements in a short wavelength region. As with other compound semiconductors, it is necessary to establish surface processing techniques such as mesas and recesses.

An Al _x Ga _{1 -X} N semiconductor is a very chemically stable substance, and is generally used as an etching solution for other III-V compound semiconductors, such as hydrochloric acid, sulfuric acid, and hydrofluoric acid (HF).
Does not dissolve in the acid or the mixture thereof. For this reason,
The following few etching techniques are known for Al _x Ga _1-X N semiconductors.

The first method is wet etching using a solution of caustic soda, caustic potash or potassium pyrosulfate heated to 800 ° C. or higher. The second method is electrolytic jet etching using a 0.1N sodium hydroxide solution.
The third method is a wet etching method using a mixture of phosphoric acid and sulfuric acid at a mixing ratio of 1: 2 to 1: 5 at a temperature of 180 ° C. to 250 ° C.

[0005]

However, the above first and second methods have practical difficulties due to the use of a high-temperature corrosive substance. Further, the third method has a problem that the etching rate greatly changes due to a slight temperature change, and none of the above methods has been put to practical use.

Further, since all of the above-mentioned methods are wet etching, it is not possible to eliminate disadvantages peculiar to the wet etching such as generation of undercut. On the other hand, there is no known dry etching method for an Al _x Ga _{1 -X} N semiconductor. What reactive gas should be selected in plasma etching cannot be predicted because the reaction mechanism is affected by the combination of atoms and the crystal structure of the compound semiconductor to be etched. Therefore, it cannot be predicted whether the existing reactive gas is effective for etching the Al _x Ga _{1 -X} N semiconductor.

Further, it is necessary to use a mask material having an etching rate lower than that of the material to be etched.
This is also determined by the relationship with the etching gas, and it is unclear whether a mask material used in other conventional wet etching of semiconductors can be used. Therefore, the present inventors conducted intensive experimental research on the etching rate of the semiconductor and mask material, the type of reaction gas used, and other conditions in plasma etching of Al _x Ga _{1 -X} N semiconductor. The invention has been completed.

[0008]

That is, the constitution of the present invention is as follows.
Al _x Ga _1-X N (0 ≦ X ≦ 1) A silicon dioxide (SiO ₂ ) is formed on a semiconductor, a photoresist is formed thereon, and the photoresist is patterned by exposing and removing a predetermined pattern. the patterned photoresist as a mask, by etching the silicon dioxide (SiO _2), silicon dioxide
Mask (SiO ₂ ) and a photoresist layer
Al having a double structure comprising a second mask layer comprising
_{x Ga 1-X N (0} ≦ X ≦ 1) Al x Ga 1-X N (0 ≦ X ≦ 1) , characterized by forming a semiconductor etching mask is a manufacturing method of an etching mask in a semiconductor.

Another feature of the invention is that Al _x Ga _{1 -X} N (0 ≦ X ≦ 1)
Aluminum oxide (Al ₂ O ₃ ) is formed on a semiconductor, a photoresist is formed thereon, and the photoresist is patterned by exposing and removing the photoresist in a predetermined pattern.Using the patterned photoresist as a mask, the aluminum oxide is used. (Al ₂ O ₃ ) by etching, Al _x Ga _1-X N (0 ≦ X ≦ 1)
Forming a semiconductor etching mask.
This is a method for manufacturing an etching mask for an Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor. Yet another feature of the invention is etching.
The mask is made of silicon dioxide (SiO ₂ ) and / or aluminum oxide.
(Al ₂ O ₃ ) first mask layer and a
And a second mask layer made of photoresist.
Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor
This is a method for manufacturing an etching mask.

In the etching after the formation of the etching mask, usually, an electrode to which high-frequency power is applied is arranged in parallel, and a parallel electrode type device in which an object to be etched is arranged on the electrode, or an electrode to which high-frequency power is applied. Are arranged in a cylindrical shape, and an object to be etched is arranged in parallel to the cross section of the cylinder, using a cylindrical electrode type device or other devices.

[0011]

As described above, silicon dioxide (SiO ₂ )
Alternatively, an etching mask made of aluminum oxide (Al ₂ O ₃ ) can be easily formed. Also, silicon dioxide (S
If a patterned photoresist for forming a mask of iO ₂ ) or aluminum oxide (Al ₂ O ₃ ) is also used as an etching mask, silicon dioxide (S
The thickness of iO ₂ ) or aluminum oxide (Al ₂ O ₃ ) can be reduced, and the manufacturing time can be shortened.

As will be apparent from the examples described later, Al
Dichlorodifluoromethane (CCl ₂ F ₂ ) gas plasma was effective for etching _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductor. Also, a dual structure or a first mask layer comprising a first mask layer of silicon dioxide (SiO ₂ ) and / or aluminum oxide (Al ₂ O ₃ ) and a second mask layer of a photoresist laminated thereon. Has been found to be effective as a mask for the plasma etching. It has also been found that the plasma etching does not cause crystal defects in the semiconductor. Therefore, the surface processing method according to the present invention can greatly improve the productivity of devices, ICs, and the like using Al _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductors.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to specific embodiments. The GaN semiconductor used in the method of this embodiment was formed into a structure shown in FIG. 1A by vapor phase growth by metalorganic compound vapor phase epitaxy (hereinafter referred to as "M0VPE"). The gases used were NH ₃ , carrier gas H ₂ , trimethylgallium (Ga (CH ₃ ) ₃ ) (hereinafter referred to as “TMG”), and trimethylaluminum (Al (CH ₃ ) ₃ ) (hereinafter “TMA”). Note).

First, a single-crystal sapphire substrate 1 whose main surface is the c-plane cleaned by organic cleaning and heat treatment is mounted on a susceptor placed in a reaction chamber of an MOVPE apparatus. Next, the pressure in the reaction chamber was reduced to 5 Torr, and H ₂ was supplied at a flow rate of 0.3 liter /
Sapphire substrate 1 at a temperature of 1100 ° C
Was subjected to gas phase etching. Next, the temperature was lowered to 800 ° C., and H ₂ was flowed at a flow rate of 3 liter / min, and NH ₃ was flowed at a flow rate of ₂ liter / minute.
And TMA was supplied at a rate of 7 × 10 ⁻⁶ mol / min and heat-treated for 1 minute. By this heat treatment, an AlN buffer layer 2 was formed to a thickness of about 500 °.

Next, when one minute has passed, the supply of TMA is stopped, the temperature of the sapphire substrate 1 is maintained at 1000 ° C., and H ₂ is discharged.
2.5Liter / min, the NH ₃ 1.5liter / min, 1.7 × the TMG
The GaN layer 3 was supplied at a rate of 10 ⁻⁵ mol / min for 100 minutes to form a GaN layer 3 having a thickness of about 5 μm. Next, the sample thus formed was taken out of the reaction chamber, and SiO ₂ was sputtered on the GaN layer 3 to form a first mask layer 4 having a thickness of 3000 °. Next, a photoresist is applied on the first mask layer 4 by using a spinner.
It was applied to a thickness of 5 μm and baked at 90 ° C. for 30 minutes to form a second mask layer 5.

Next, as shown in FIG. 1 (b), after exposing the photoresist of the second mask layer 5 using a mask 6 corresponding to the pattern of the fine processing, the photoresist is developed and pure water is developed. And wash it thoroughly as shown in Fig. 1 (c).
A sample from which the photoresist at the exposed portion was removed was obtained. Next, after baking the sample at 120 ° C. for 30 minutes, the sample was immersed in hydrofluoric acid for 2 minutes, and the exposed portion of SiO ₂ was removed by etching using the photoresist as a mask. In this way, as shown in FIG.
A mask having a laminated structure of a first mask layer 4 and a second mask layer 5 having a predetermined shape was formed thereon. Since GaN is not etched by hydrofluoric acid, the etching of SiO ₂ stops on the upper surface of GaN.

Next, the sample 30 shown in FIG. 1D was washed with pure water, dried, and the exposed GaN layer 3 was etched using the plasma etching apparatus shown in FIG. FIG.
In the parallel electrode type apparatus shown in FIG. 1, an introduction pipe 12 for introducing an etching gas is continuously provided on a side wall of a stainless steel vacuum vessel 10 forming a reaction chamber 20, and the introduction pipe 12 has a gas flow rate. It is connected via a variable mass flow controller 14 to a tank 16 storing CCl ₂ F ₂ gas. Then, CCl ₂ F ₂ gas is introduced from the tank 16 into the reaction chamber 20 via the mass flow controller 14.

The reaction chamber 20 is evacuated by a diffusion pump 19, and the degree of vacuum in the reaction chamber 20 is controlled by a conductance valve 18 interposed between the reaction chamber 20 and the diffusion pump 19.
Is adjusted by On the other hand, an electrode 22 and an electrode 24 that are insulated from the vacuum vessel 10 by a fluorinated resin are disposed in the reaction chamber 20 so as to face in the vertical direction. Then, the electrode 22 is grounded, and the electrode 24 is supplied with high-frequency power. The high frequency power is a high frequency power supply 28 having a frequency of 13.56 MHz.
Through the matching unit 26.

On the electrode 24, the structure shown in FIG.
Samples 30 and 32 are placed. The device with such a configuration
When performing plasma etching, first,
After placing samples 30 and 32 on 24, diffusion pump 1
9 to exhaust the residual gas in the reaction chamber 20 sufficiently.
5 × 10^-FiveSet to Torr. Then CCl_Two
F_TwoGas flow rate 10cc by mass flow controller 14
/ Min and introduced into the reaction chamber 20, where the
The degree of vacuum in the reaction chamber 20 is precisely 0.04
Adjusted to rr. And 200 between the electrode 24 and the electrode 22.
W (0.41W / cm ^Two) When high frequency power is supplied, the
Low discharge is started and introduced CCl_TwoF_TwoGas is plasma
And etching of the samples 30 and 32 is started.
Was.

After etching for 20 minutes, the sample 30,
32 was removed from the apparatus. At this time, the photoresist of the second mask layer 5 was also etched, and the first mask layer 4 remained. The SiO ₂ of the first mask layer 4 was removed by etching with hydrofluoric acid, washed with pure water and dried, and
As shown in (e), a 1.3 μm deep micromachined surface with little sag was obtained. FIG. 4 shows a photograph of the surface by a microscope. It can be seen that a smooth surface was obtained without the appearance of etch pits, and that there was little sag in the shape.

Incidentally, GaN, SiO _2, Al ₂ O _{3 and} photoresist were respectively etched using the above-mentioned etching apparatus and CCl ₂ F ₂ gas, and their etching rates were measured.
The result is shown in FIG. As can be seen from the results, the etching rate was 1330Å / min for photoresist and GaN for
660 Å / min, SiO ₂ is 260 Å / min, Al ₂ O ₃ was 80 Å / min. In the above embodiment, after etching for 20 minutes, the photoresist of the second mask layer 5 having a thickness of 1.5 μm is about 11.5 μm.
Minutes, the first mask layer 4 is removed in about 8.5 minutes.
2200 ° of SiO ₂ is removed. However, since the first mask layer 4 is formed at 3000 °, it functions sufficiently as a mask.

If a mask is formed only of SiO ₂ , it is necessary to make the thickness to be able to withstand etching.
The lamination speed of O ₂ is slow, and the lamination thickness is limited. Therefore,
An effective mask is realized by forming a double structure in which a photoresist which can be thickened sufficiently and easily on SiO ₂ is provided.

As can be seen from the results shown in FIG. 3, Al ₂ O ₃ can be used for the first mask layer 4. In that case, a mixed solution of hydrofluoric acid and phosphoric acid (mixing ratio 4: 1) is used as an etching solution for removing Al ₂ O ₃ . Further, the etching of AlN was performed in the same manner as described above, but the surface was finely processed similarly. From this, it has been found that the present invention can be applied to fine processing of a general formula Al _x Ga _{1 -X} N semiconductor.

[Brief description of the drawings]

FIG. 1 is a process chart showing a surface processing method of the present invention.

FIG. 2 is a configuration diagram showing an etching apparatus for performing the surface processing method.

FIG. 3 is a measurement diagram of an etching rate.

FIG. 4 is a micrograph showing the crystal structure of the surface of GaN after etching.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... GaN layer 4 ... First mask layer 5 ... Second mask layer 6 ... Mask 10 ... Vacuum container 12 * Introduction pipe 14 ... Mass flow controller 16 ... Tank 19 ... Diffusion pump 18 ... Conductance valve 22, 24 ... electrode 28 ... high frequency power supply

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masahiro Kotaki 1 Ochiai Nagahata, Kasuga-cho, Nishi-Kasugai-gun, Aichi Prefecture Inside Toyoda Gosei Co., Ltd. (1) Inside Toyota Central Research Laboratory, Inc. (56) References JP-A-61-56474 (JP, A) JP-A-62-89882 (JP, A) JP-A-57-102081 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H01L 33/00 H01L 21/3065

Claims (3)

(57) [Claims] 1. A _{Al x Ga 1-X N (} 0 ≦ X ≦ 1) to form a semiconductor on the silicon dioxide (SiO _2), to form a photoresist thereon, exposing the photoresist to a predetermined pattern and Removed and patterned, using the patterned photoresist as a mask, etching silicon dioxide (SiO ₂ )
The first mask layer of silicon dioxide (SiO ₂₎ and is laminated thereon
And a second mask layer made of a photo resist.
A method of manufacturing an etching mask for an Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor, comprising forming an etching mask of an Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor having a structure . 2. An aluminum oxide (Al ₂ O ₃ ) is formed on an Al _x Ga _{1 -X} N (0 ≦ X ≦ 1) semiconductor, a photoresist is formed thereon, and the photoresist is formed into a predetermined pattern. Exposure and removal and patterning, using the patterned photoresist as a mask, etching aluminum oxide (Al ₂ O ₃ ) to form an Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor etching mask Al _x Ga _1-X N (0 ≦ X ≦
1) A method for manufacturing an etching mask in a semiconductor. 3. The etching mask according to claim 1, wherein said etching mask is silicon dioxide (S).
First mask of iO ₂ ) and / or aluminum oxide (Al ₂ O ₃ )
A second mask consisting of a layer and a photoresist laminated thereon.
And a double-layer structure comprising a disk layer.
Item 2. The edge in the Al _x Ga _1-X N (0 ≦ X ≦ 1) semiconductor described in item 2.
A method for manufacturing a tinting mask.