JP2542608B2 - Diamond semiconductor etching method - Google Patents

Description

The present invention relates to a method for selectively etching a semiconductor made of diamond.

[Conventional technology]

Diamond has the same crystal structure as silicon
It is a Group IV semiconductor, with a large bandgear of 5.5 eV,
It has a low relative permittivity of 5.7, the highest thermal conductivity of any substance, and the mobility of electrons and holes is about 1800 cm ² / V ・ sec and about 1600.
It has excellent features such as being large with cm ² / V · sec.
For this reason, it is considered that the diamond semiconductor has a possibility of producing a semiconductor element that is more resistant to high temperature and higher in speed and power than conventional semiconductors such as silicon and gallium arsenide.

However, in order to form a semiconductor element on this diamond, a diamond etching technique is indispensable for performing fine processing. Moreover, in etching for manufacturing a semiconductor element, there are conditions such that selective etching using a mask or the like is possible, etching speed is large and controllable with good reproducibility, and the surface after etching is clean. Required.

Conventionally, as a method for etching a semiconductor such as silicon, a wet etching method using a solution of acid or alkali and a dry etching method using plasma of an inert gas or a halogen gas are known. However, since diamond is chemically very stable, it is not attacked by acids or alkalis at all, and therefore the wet etching method cannot be applied.

Further, the dry etching method also has a drawback that the etching rate of diamond is extremely low because the inert gas and the halogen gas used have poor reactivity with diamond.

Furthermore, even if an attempt is made to selectively etch diamond by the dry etching method, conventional mask materials such as polymer resists are etched faster than diamond because the etching speed is higher than the etching speed of diamond, and as a mask There was a problem that it was useless.

[Problems to be solved by the invention]

As described above, since it is difficult to perform high-speed and fine selective etching of diamond by the conventional etching method,
It has been extremely difficult to manufacture a semiconductor device from diamond having excellent properties.

In view of such circumstances, it is an object of the present invention to provide a method for etching a diamond semiconductor, which enables selective etching indispensable for fine processing of semiconductor elements and has a high etching speed.

[Means for solving problems]

The method for etching a diamond semiconductor of the present invention is characterized in that a mask of a metal compound is applied to a portion other than an etched portion of a semiconductor surface made of diamond, and selective etching is performed by using plasma of oxygen or a reaction gas containing oxygen. .

As the reaction gas to be used, etching may occur even with an inert gas such as a halide such as CF ₄ used for plasma etching of a silicon semiconductor or Ar used for ion beam etching, but in order to obtain a practical etching speed. Must use oxygen or a reaction gas containing oxygen.

Further, the etching method of the present invention may be a method of using plasma of oxygen or a reaction gas containing oxygen, in addition to plasma etching by parallel plate electrode discharge using direct current or high frequency, a voltage is applied to this plasma. Even ion beam type etching that accelerates by means of the above method can be performed.

The mask used must be a material having oxidation resistance to oxygen plasma.
A metal compound coating film selectively deposited on the diamond surface by a known method such as ion plating or spattering is preferable. Al ₂ O is a particularly preferable mask.
There is at least one metal compound coating selected from ₃ , Or ₂ O ₃ , TiO ₂ , TiN, TiC, SiO ₂ , Si ₃ N ₄ , SiC, MgO and GeO ₂ .

[Action]

In order to etch diamond, it is necessary to physically or chemically remove carbon, which is a constituent element that is bonded very strongly, from the surface.

According to the method of the present invention, active species such as oxygen ions and oxygen radicals generated from oxygen rapidly react with carbon atoms constituting diamond, and become molecular species such as CO and CO ₂ and diffuse into the gas phase. Therefore, the diamond can be etched at a very high etching speed. For example, when using only oxygen as the reaction gas, 130 Å / min under the condition of ion beam current of 50 μA / cm ² and energy of 3 KeV.
Etching speed of is obtained.

When diamond is heated by etching in an oxygen atmosphere, the graphitization phenomenon of diamond easily occurs. In that case, hydrogen, carbon monoxide, carbon dioxide, water vapor, halogen gas, carbonization of 2 or less carbon atoms is generated. By using a mixed gas in which at least one of hydrogen gas and halogenated hydrocarbon gas having one carbon atom is mixed with oxygen, graphitization can be prevented.

Further, in the selective etching method of diamond using the oxygen plasma of the present invention, it is also possible to use a conventional polymer resist as a mask, but since the polymer resist is etched at a faster speed than diamond, 1000 Å or less It can only be used for very shallow etching. On the other hand, in the present invention, the etching rate of the mask can be made equal to or less than that of diamond by using the mask of the metal oxide which is resistant to the oxidation of oxygen plasma, and the etching rate of the diamond is 10 μm or more. It is possible to perform deep selective etching. In particular, Al ₂ O ₃ , SiO ₂ , and Cr ₂ O ₃ are extremely excellent as masks for the method of the present invention because they have an etching rate that is less than half that of diamond.

〔Example〕

Example 1 Using a parallel plate electrode type plasma etching apparatus,
Etching was performed on a single crystal diamond having a mask in which a film of a metal compound was vapor-deposited to a film thickness of 5 μm.

That is, the above mask is partially provided on one plate electrode.
Place a single crystal diamond plate of 2.5 × 1.5 × 0.3 mm,
The reaction gas (O ₂ : CF ₄ : Ar = 2: 1: 1) was introduced into the device and the pressure was maintained at 0.03 torr, and a high frequency of 50 W at 13.56 MHz was used to generate a discharge between the electrodes and the diamond was left for 15 minutes. Etching.

The etching depths of single crystal diamond (abbreviated as DM) and each mask used are listed in the table below together with the etching depth of polymer resist (abbreviated as PR) under the same conditions shown for reference.

From this table, the polymer resist is
Although etching is performed at a speed three times higher, the metal compound coating film has a smaller etching speed than diamond, and it can be seen that it can be sufficiently used as an etching mask.

Example 2 On the surface of a single crystal diamond plate similar to that in Example 1,
A resist pattern having a width of 10 μm was formed by photolithography. After SiO ₂ was coated thereon to a thickness of 3 μm by a high frequency sputtering method, the resist was peeled off to form a SiO ₂ pattern mask having an opening with a width of 10 μm.

Next, using an ion beam type plasma etching system that uses O ₂ : CF ₄ : Ar = 2: 1: 1 as a reaction gas,
Etching was performed for 30 minutes using an ion beam of 0 μA / cm ² . The other conditions were the same as in Example 1.
After that, the SiO ₂ mask was dissolved and removed with hydrofluoric acid, and an etching pattern having a width of 10 μm and a depth of 2.5 μm was obtained on the diamond surface.

When etching was performed under the same conditions as above except that Ar: O ₂ = 1: 1 was used as the reaction gas, the depth of the etching pattern obtained on the diamond surface was 1.5 μm.

〔The invention's effect〕

According to the present invention, the diamond semiconductor element can be selectively etched at a high etching speed.

Therefore, since it is possible to subject the diamond semiconductor to fine processing by selective etching according to the present invention, it becomes possible to easily produce a heat-resistant small large-power element or high-speed element using diamond as a semiconductor material, It is expected that the development of new semiconductor devices will progress.

Claims (2)

(57) [Claims] 1. A method of selectively etching with a plasma of oxygen or a reaction gas containing oxygen, wherein a mask of a metal compound is applied to a portion other than an etched portion of a semiconductor surface made of diamond, and the reaction gas contains hydrogen or hydrogen. At least one kind of carbon oxide, carbon dioxide, water vapor, halogen gas, hydrocarbon gas having 2 or less carbon atoms, and halogenated hydrocarbon gas having 1 carbon atom is used as a mixture. Etching method. 2. The mask is Cr ₂ O ₃ , TiO ₂ , TiC, SiC, MgO.
And at least one metal compound film selected from GeO _2, and the etching method for a diamond semiconductor according to claim (1).