DE102011118364B3 - Method of etching and semiconductor device - Google Patents

Abstract

Method for etching a III / V compound using an etching gas (22) which contains hydrogen (H2) and sulfur hexafluoride (SF6), the etching gas (22) based on the partial pressure of the hydrogen (H2) being between 2% and contains 20% sulfur hexafluoride (SF6).

Description

The invention relates to a method of etching gallium nitride using an etching gas containing hydrogen and sulfur hexafluoride. According to a second aspect, the invention relates to a semiconductor device.

A promising concept for producing light-emitting diodes is to etch out microspheres or nanopillars from a gallium nitride substrate, subsequently to coat the lateral surface of the pillars in such a way that a pn junction or a quantum well dot results and the two complementary ones Then contact layers so that a light emitting diode is obtained. Central to this but also in other manufacturing processes of optical components based on gallium nitride, for example, is to have a suitable etching process that has to fulfill several requirements simultaneously in order to be suitable.

Thus, the etching process must be highly anisotropic, so that the column produced has the highest possible aspect ratio, that is as slim as possible. At the same time, the surface of the columns must be as smooth as possible, so that the optical components produced have a sufficiently high efficiency. Furthermore, the etching rate must be sufficiently high to allow economical production. For example, with gallium nitride etching rates of up to 100 nanometers per minute have been achieved, but significantly higher etching rates are desirable.

From the JP 2003309105 A For example, an etching process using chlorine is known. A disadvantage of the use of chlorine is that it leads to a highly toxic etching atmosphere and therefore requires expensive safety measures. Chlorine-containing compounds also attack the inside surfaces of the process equipment, potentially causing damage.

From the WO 2005/071721 A1 For example, a plasma etching method by means of which semiconductor substrates can be etched is known. That the described etching process could be suitable for gallium nitride is not described.

From the US 2009/0053901 A1 For example, a method of removing a mask that is applied during dopant implantation is known. The method is also suitable for ablating the atoms of the doping material remaining in the mask, for example gallium. About the etching of gallium nitride makes the document no information.

The invention has for its object to provide an etching process, with the high aspect ratios can be achieved.

The invention solves the problem by a method for etching a III / V compound, wherein an etching gas is used, based on the partial pressure of hydrogen between 2% and 20% sulfur hexafluoride and based on the partial pressure less than 1% Cl ₂ or contains chlorine-releasing substances in the etching process. A content of at least 3% sulfur hexafluoride based on the partial pressure of the hydrogen is particularly favorable, with particularly good results being achievable with a content of not more than 15%.

An advantage of the invention is that etch rates of over 450 nanometers per minute can be achieved.

Another advantage is that chlorine is unnecessary. This results in less problematic reaction products, so that can be dispensed with costly security measures.

In addition, a high aspect ratio of greater than at least four can be achieved, which makes the method according to the invention particularly suitable for the production of microparticles or nanopillars. The resulting surfaces are also very smooth.

In addition, a method for etching Al ₂ O ₃ or ZrO ₂ (zirconium oxide) is also according to the invention. Statements made in the following about the preferred embodiments apply equally to these substances. The process according to the invention can be carried out at room temperature, which represents a particular advantage.

According to a preferred embodiment, the compound is a nitride of an element of the 3rd main group. In particular, it is a method of etching gallium nitride. Gallium nitride is particularly suitable as a substrate in the production of blue light-emitting diodes and causes particularly great problems in etching, so that the inventive method is a particular advantage here.

Preferably, the etching gas is chlorine-free at least to traces.

It is also favorable if the etching gas contains less than 5% of alkane halides, based on the partial pressure of the hydrogen. These compounds are difficult to handle, so that the inventive method is particularly easy to carry out.

It is favorable if the etching gas, based on the partial pressure of the hydrogen, contains less than 5% of gases which are not inert in the etching process. In other words, in this case, the sulfur hexafluoride and the hydrogen are by far predominantly or exclusively reacting substances. It is possible according to a preferred embodiment that the etching gas contains argon or another inert gas.

Preferably, the etching gas is selected so that the etching process can be carried out without activation. By this is meant in particular that no radiation is necessary to initiate the chemical reaction, which leads to the removal of the substrate material. In particular, the etching gas is chosen so that no ultraviolet radiation and / or no microwave radiation is necessary to sustain the etching process.

Preferably, the process pressure during the etching is below 10 Pascal, in particular below 2 Pascal. An advantage of the method according to the invention is that despite this low pressure, a high removal rate can be achieved.

According to a preferred embodiment, the method comprises the following steps: (a) introducing a semiconductor substrate into a vacuum chamber, wherein the semiconductor substrate is in particular GaN coated with a mask that is stable to the etching gas, (b) etching the semiconductor substrate with the etching gas, so that micro or nanopillars arise, which have an aspect ratio of more than four. In this case, micro- or nanopillars are understood in particular as columnar structures which are essentially prismatic and have an outer diameter of at most 50 micrometers.

Preferably, the method comprises the steps of: (c) doping the micro- or nano-columns, (d) applying a complementary layer to a lateral surface of the micro- or nano-column and (e) contacting the micro- or nano-column and the complementary layer such that a light-emitting diode or an electrical switching element is created. The doping of the micro- or nanopillars is understood in particular to mean that the method is carried out in such a way that the resulting micro- or nano-column consists at least locally of doped material. It is possible, but not necessary, for the substrate to be already doped. It is also possible that the micro- or nanopillars are etched out of undated material and the doping is introduced in a subsequent work step.

The complementary layer is understood as meaning a layer in the material which is constructed in such a way that, together with the microcolumn or nanopillar, a structure results which emits light by applying an electrical voltage. By way of example, the complementary layer is a p-doped semiconductor. Alternatively, it may be a layer of InGaN / GaN designed to yield quantum wells. Quantum wells designate local structures in the material, which cause an electronic potential course, which restricts the freedom of movement of a charged particle, for example electron, in a spatial dimension, so that the particles are only movable in one plane.

According to the invention is also a semiconductor device, which is produced according to a method of the invention.

In the following the invention will be explained in more detail with reference to an embodiment. In the accompanying drawings shows

1 schematically the etching system and the

2 and 3 Microcolumns produced by a method according to the invention.

1 schematically shows a Sentech ICP etching system 10 in their vacuum chamber 12 a semiconductor substrate 14 is positioned. The semiconductor substrate 14 includes a sapphire substrate 16 on which a gallium nitride layer 18 grew up. The gallium nitride layer 18 is with a mask 20 provided with the structure that should not be removed by the etching.

It then becomes an etching gas 22 through an etching gas line 24 in the vacuum chamber 12 directed. A pressure p ₁₂ in the vacuum chamber 12 p ₁₂ = 0.5 Pascal, the temperature is T = 23 ° C. The etching gas flow φ ₂₂ of etching gas 22 comprises 100 sccm H ₂ and 12% sulfur hexafluoride based on the partial pressure p _{H2 of} the hydrogen. The sulfur hexafluoride gas flow φ ₂₂ at sulfur hexafluoride is thus 12 sccm. The etching gas flow φ _{22 also} includes an argon gas flow φ _Ar = 20 sccm of argon. Other gases are - except where appropriate, in traces - not included.

The ICP system 10 includes a high frequency source 26 for dispensing microwaves into the vacuum chamber 12 , However, it is not necessary in the context of the method according to the invention to irradiate microwaves.

1 also shows a lock 28 , by means of which the semiconductor substrate 14 in the vacuum chamber 12 can be introduced and discharged from it. The lock 28 is, as well as the vacuum chamber 12 , with a vacuum pump 30 connected, for example, a turbomolecular pump. The ICP system 10 also has a gas box 32 , which could also be referred to as Zudosiereinheit, by means of the etching gas 22 from the partial gases, such as hydrogen and sulfur hexafluoride and argon, is mixed together.

2 shows a substrate converted by the method according to the invention, which has a plurality of nanopillars 34.1 . 34.2 , ... having. The nanopillars 34 have a diameter of about 2.5 microns and a height of about 15 microns.

The nanopillars 34 (Reference signs without counting suffix denote the object as such) have lateral surfaces 36 , for example, has the nanopillar 34.1 the lateral surface 36.1 , In a step, not shown, on the lateral surfaces 36 grown a complementary layer. This is done, for example, by epitaxy in the in 1 shown ICP system. As a complementary layer, a p-doped semiconductor can be applied. Alternatively, quantum wells may be deposited in the gallium nitride InGaN-GaN. It is also possible to fill the remaining spaces then with deflection elements, for example, with small glass objects, which cause that emerging from the lateral surfaces of light quanta are deflected and extend at a smaller angle to the lateral surface.

3 shows a precursor for a semiconductor device, in particular a light-emitting diode or an electrical switching element, wherein by means of the method described above nano-columns 34 were manufactured. The aspect ratio is about 2, the diameter of the nanocolumns is about 1.5 microns.

LIST OF REFERENCE NUMBERS

10

ICP etcher

12

vacuum chamber

14

Semiconductor substrate

16

Sapphire substrate

18

Gallium nitride layer

20

mask

22

etching

24

etching gas line

26

RF source

28

lock

30

vacuum pump

32

gasbox

34

Nano column

36

lateral surface

φ

gas flow

Claims (9)

Method for etching a III / V compound, in which an etching gas ( 22 ) containing hydrogen (H ₂ ) and sulfur hexafluoride (SF ₆ ), characterized in that the etching gas ( 22 ) - Based on the partial pressure of hydrogen (H ₂ ) between 2% and 20% sulfur hexafluoride (SF ₆ ) contains and - based on the partial pressure less than 1% Cl ₂ or in the etching process chlorine-releasing substances. A method according to claim 1, characterized in that the compound is a nitride of an element of the 3rd main group, wherein the compound is in particular gallium nitride. Method according to one of the preceding claims, characterized in that the etching gas ( 22 ) based on the partial pressure of hydrogen (H ₂ ) contains less than 5% of alkane halides. Method according to one of the preceding claims, characterized in that the etching gas ( 22 ) based on the partial pressure of hydrogen (H ₂ ) contains less than 5% of gases which are not inert in the etching process. Method according to one of the preceding claims, characterized in that the etching gas ( 22 ) is selected so that the etching process is activating-free feasible. Method according to one of the preceding claims, characterized in that a process pressure (P ₁₂ ) during the etching is less than 10 Pa. Method according to one of the preceding claims, characterized by the steps: (a) introduction of a semiconductor substrate ( 14 ) in a vacuum chamber ( 12 ), (b) etching the semiconductor substrate with the etching gas so that micro- or nanopillars ( 34 ), which have an aspect ratio of at least 4. Method according to one of the preceding claims, characterized by the steps: (c) doping of the micro- or nanopillars ( 34 ), (d) applying a complementary layer to a lateral surface ( 36 ) of the micro or nanopillars ( 34 ), and (e) contacting the micro- or nanopillars ( 34 ) And the complementary layer, so that a light emitting diode or an electrical switching element is formed. Semiconductor component, in particular light-emitting diode or electrical switching element, which is produced by a method according to one of the preceding claims.

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