KR20000067108A - Highly Selective and Anisotropic Dry Etch Method of GaN - Google Patents

Abstract

PURPOSE: A method for anisotropy dry etching of GaN is provided to gain a high potentiometric selectivity coefficient between AlGaN and GaN. CONSTITUTION: An AlGaN layer and a GaN layer is laminated on a substrate to make a nitride semiconductor. The nitride semiconductor is loaded into an ICP(Inductively Coupled Plasma), ECR(Electron Cyclotron Resonance), or MRIE(Magnetically enhanced Reactive Ion Etch) machine. Inside the machine, the pressure is controlled as 10 mTorr, and the temperature is fixed on 20°C. The GaN layer is etched by changing the plasma output power(0¯3000W), RF(Radio Frequency) table output power(0¯500W), and the amount of injecting oxygen (0¯8SCCM(Standard Cubic Centimeter per Minute)). After finishing the etching process, the nitride semiconductor is washed using a mixed solution to remove the oxygen. the mixed solution is composed of deionized water, ammonium fluoride and HF.

Description

Highly Selective and Anisotropic Dry Etch Method of GaN

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a selective etching method of a nitride semiconductor including gallium and aluminum, and more particularly, to a high electron mobility transistor (HEMT) and a modulation doped field effect transistor. The present invention relates to a gallium nitride (GaN) high selectivity anisotropic dry etching method with respect to aluminum gallium nitride (AlGaN) for manufacturing electronic devices.

In order to realize electronic device fabrication using compound semiconductors, an etching process is required. However, since nitride semiconductors are chemically stable, satisfactory etching cannot be obtained by wet etching, and selective etching of each material is performed. Not. Therefore, in order to fabricate an electronic device using a nitride semiconductor, the nitride semiconductor must be etched by a dry etching method. However, due to the strong bonding force inherent in the nitride semiconductor material, the selectivity for the material to be etched is lowered, making it difficult to manufacture an electronic device such as a field effect transistor, thereby making it difficult to produce high quality devices.

Dry etching of nitride semiconductors mainly uses plasma using halogen gas such as chlorine (Cl ₂ ), bromine (Br ₂ ) and iodine (I ₂ ). At this time, the halogen gas is combined with the Group III material of the nitride semiconductor to generate a highly volatile halogenated gas such as gallium chloride (GaCl _x ), aluminum chloride (AlCl _x ), gallium bromide (GaBr) or aluminum bromide (AlBr), Nitrogen atoms (N) of Group 5 form nitrogen molecules (N ₂ ) to perform an etching process of the nitride semiconductor. In this case, when argon gas is added when using chlorine gas in halogen gas, argon (Ar) accelerates the decomposition of chlorine or collides with the surface of the nitride semiconductor in the form of ions to desorption of gallium chloride or aluminum chloride formed by etching. Increasingly, an increase in the etching rate can be achieved. However, when etching the nitride semiconductor in this way, the chemical bond between the Group 3 and Group 5 elements must be broken before the reaction can begin. Therefore, the plasma parameters must be adjusted so that the ions in the plasma state have high ion energy, and the selectivity ratio for each material is primarily limited to the chemical bonding force of each material.

Prior arts related to this selective etching method include aluminum gallium nitride containing 28% aluminum using chlorine / argon (Cl ₂ / Ar) plasma of Smith et al. (Appl. Phys. Lett. 71, 3631, 1997). A selective etching method of gallium nitride (GaN) having a selectivity of 10 with respect to (AlGaN) has been reported. They also reported a selective etching method of gallium nitride (GaN) containing 100% aluminum, that is, a selectivity of 38 with respect to aluminum nitride (AlN), and the higher the content of aluminum, the higher the selectivity. Vartuli et al. (Electrochem. Soc. Interface, 144, 2146, 1997) used a boron trichloride / argon (BCl ₃ / Ar) plasma to achieve a low selectivity of less than 5 for aluminum gallium nitride containing 31% aluminum. As reported by Smith et al., It was reported that the higher the gallium content, that is, the smaller the average binding energy, the lower the gallium nitride selectivity. On the other hand, Basak et al. (Jpn. J. Appl. Phys. 38, 42, 1999) used chlorine / methane / argon (Cl ₂ / CH ₄ / Ar) plasma in aluminum gallium nitride containing 15% aluminum. A selection ratio of 4.2 was reported, and they also reported that the selection ratio was determined by the difference in binding force.

As mentioned above, the selective etching method of gallium nitride with respect to aluminum gallium nitride currently depends only on the method by the difference of the intrinsic binding force of a material.

The present invention adds oxygen, sulfur, or selenium to halogen gas, and uses the plasma thereof, as well as the inherent bonding force in the material as compared to the conventional etching method using only halogen gas plasma, as well as the large bonding force difference on the nitride semiconductor surface. It is an object of the present invention to provide an anisotropic dry etching method having a high selectivity of gallium nitride by inducing artificial oxygen bonding such as gallium-oxygen and aluminum-oxygen.

1 (a) is a schematic diagram showing a nitride semiconductor,

(b) is a schematic diagram which shows after the gallium nitride layer etching of a nitride semiconductor by this invention.

Figure 2 (a) is a graph showing the etching rate of gallium nitride and aluminum gallium nitride according to the present invention according to the inflow amount of oxygen introduced into the plasma---silver gallium nitride etching rate,---silver aluminum 5% Etch rate of aluminum gallium nitride contained, -Δ- is the etching rate of aluminum gallium nitride containing 10% aluminum,

(b) is a graph showing the relative etching rate of gallium nitride with respect to aluminum gallium nitride, that is, selectivity as shown in (a), and-?-to aluminum gallium nitride containing 10% of silver aluminum. Is a selectivity ratio of gallium nitride to aluminum gallium nitride containing 10% of aluminum.

3 is a graph showing the selectivity ratio of gallium nitride to aluminum gallium with respect to the plasma output.-■-is the selectivity ratio of gallium nitride to aluminum gallium nitride containing 10% of aluminum. % Is the selectivity ratio of gallium nitride to the contained aluminum gallium nitride.

FIG. 4 is a graph showing the selectivity of gallium nitride to aluminum gallium nitride on the RF table output,-■-is the selectivity ratio of gallium nitride to aluminum gallium nitride containing 10% of aluminum; Is the selectivity ratio of gallium nitride to aluminum gallium nitride containing 5% aluminum.

The basic structure of high-speed electron transfer transistor (HEMT), modulation doped field effect transistor (MODFET) and other electronic devices using compound semiconductor is n-type or p-type binary gallium compound (GaAs, GaN, etc.) Ternary compounds including aluminum used as a channel layer and a charge supply layer or a cladding layer of Al _x Ga _1-x As, Al _x Ga _{1 -x} N, etc.) layer, a binary gallium compound layer as a capping layer for passivation and ohmic contact. Therefore, for gate contact, the binary gallium compound layer must be etched to expose the charge supply layer. At this time, the thickness of the capping layer and the charge supply layer is hundreds of angstroms (Å), so the binary gallium compound layer must be etched at a high selectivity.

The present invention has a binding energy (511 kJ / mol) that is larger than the binding energy of aluminum-nitrogen (297.96 kJ / mol), which is an etched material, using a plasma added with oxygen, sulfur or selenium, and is non-volatile aluminum. -Oxygen bonds are induced on the surface of aluminum gallium nitride so that they can exhibit significantly higher selectivity even at lower aluminum content than the selective etching method using the conventional inherent difference in bonding strength. In addition, by controlling the plasma generation conditions during the etching process it can be applied flexibly according to the type of semiconductor device used. The method of selectively etching the nitride layer of the nitride semiconductor of the present invention is as follows.

A nitride semiconductor in which an aluminum gallium nitride layer and a gallium nitride layer are sequentially stacked on a substrate may be inductively coupled plasma (hereinafter referred to as ICP), electron resonance plasma (hereinafter referred to as ECR), or plasma enhanced by a magnetic field. (Magnetically Enhanced Reactive Ion Etch, hereinafter referred to as MRIE) Placed in a reactor with oxygen, sulfur or selenium gas with halogen gas, pressure in the reactor 10 mTorr, temperature 20 ℃, plasma output 0 ~ 3,000 W, RF ( The gallium nitride layer of the nitride semiconductor is etched by changing the radio-frequency table output from 0 to 500 W, changing the oxygen inflow from 0 to 8 sccm (Standard Cubic Centimeter per Minute).

On the other hand, when the gallium nitride layer of the nitride semiconductor is etched using an oxygen plasma, deionized water: ammonium fluoride (NH ₄ F) to remove oxygen remaining on the aluminum gallium nitride surface after the etching process is completed: 1 to 100% of hydrofluoric acid (HF) is washed for 1 to 300 seconds using a solvent mixed at a volume ratio of 0 to 1: 0 to 1: 0.01 to 1.

Hereinafter, the present invention will be described in more detail with reference to Examples and Test Examples. However, these do not limit the technical scope of the present invention.

<Example 1>

The thin film growth method used metalorganic chemical vapor deposition (MOCVD) and the substrate (0001) sapphire was used. Trimethylgallium (TMGa), trimethylaluminum (TMAl), and ammonia (NH ₃ ) were used as gallium, aluminum, and nitrogen sources, respectively. First, a gallium nitride nucleation layer of 300 500 was grown on a substrate at 500 ° C, and an n-type gallium nitride epitaxial layer having a thickness of 1.8 µm was grown at 1,020 ° C for 1 hour. The aluminum gallium nitride thin film containing 5% and 10% aluminum was grown to 5,000 mm thick.

<Example 2>

A gallium nitride layer and an aluminum gallium nitride semiconductor grown on a substrate were subjected to chlorine / argon (Cl ₂ / Ar) inflow rate of 30/10 sccm, pressure 10 mTorr, temperature 20 ° C., and ICP output in an inductively coupled plasma (ICP) reactor. 1,000 W and RF (Radio-Frequency) table (table) outputs are fixed at 100 W, respectively, oxygen inflow is changed from 0 to 8 sccm, and the etching rate and selectivity of gallium nitride to aluminum gallium nitride are measured and this is shown in FIG. a) (b) shows a graph of distilled water: ammonium fluoride (NH ₄ F): 1 to 100% hydrofluoric acid (HF) in order to remove oxygen remaining on the surface of aluminum gallium nitride after etching. The solvent was mixed at a volume ratio of 1 to 1 to 300 seconds.

FIG. 2 (a) shows changes in the etch rate of gallium nitride, aluminum gallium nitride containing 5% aluminum, and aluminum gallium nitride containing 10% aluminum, and used chlorine / argon (Cl ₂ / Ar) plasma. It can be seen that the etching rate of each is smaller by different ratios. FIG. 2 (b) is a graph showing the relative etching rate of gallium nitride with respect to aluminum gallium nitride, that is, selectivity in (a), and gallium nitride with respect to aluminum gallium nitride containing 5% aluminum. The selectivity of gallium nitride was about 3, and the selectivity of gallium nitride to aluminum gallium nitride containing 10% of aluminum was a maximum increase of 22.2.

<Example 3>

The gallium nitride (GaN) layer and the aluminum gallium nitride (AlGaN) layer grown in the same manner as in Example 1 were the same except that the ICP output was 500 to 2,000 W under the oxygen flow rate of 2 sccm optimized in Example 2. The selectivity was measured by etching under the conditions, and the results thereof are shown in FIG. 3 and washed in the same manner as in Example 2 using hydrofluoric acid (HF) to remove oxygen remaining on the aluminum gallium nitride surface after etching. .

As shown in the graph of FIG. 3, as the ICP output increases, the selectivity gradually increases, so that the selectivity of gallium nitride to aluminum gallium nitride having a 5% aluminum content is 13.1 at maximum, and gallium nitride to aluminum gallium nitride having a 10% aluminum content. The selectivity of was up to 24.2.

<Example 4>

Except for using the gallium nitride (GaN) and aluminum gallium nitride (AlGaN) layers grown in the same manner as in Example 1, the RF table output was 100 to 250 W under the optimized 2 sccm oxygen inflow conditions found in Example 2. Was etched under the same conditions as in Example 2 to measure the selectivity ratio of gallium nitride to aluminum gallium nitride, and the results are shown in FIG. 4, and Example 2 was used to remove oxygen remaining on the aluminum gallium nitride surface after etching. It was washed with hydrofluoric acid (HF) in the same manner. As shown in the graph of FIG. 4, as the RF table output increased, the selectivity gradually decreased, so that the selectivity of gallium nitride to aluminum gallium nitride having a 10% aluminum content was reduced to 13. However, the etch rate increased significantly, and when the selectivity was 13, gallium nitride was 5,500 Å / min, aluminum gallium nitride with 5% aluminum content was 1,850 Å / min, and aluminum gallium nitride with 10% aluminum content was 425 Å /. The high etch rate was shown as min, and as the output of the table increased, the self bias induced in the specimen increased, so that the ions present in the plasma strongly collided with the surface, resulting in large etching in the direction perpendicular to the surface of the specimen. Occurred and anisotropy increased.

Selective etching method of gallium nitride in the nitride semiconductor according to the present invention can increase the selectivity to more than 10 to 23 or more compared with the conventional gallium nitride etching method using a halogen plasma can greatly contribute to the development of electronic devices and application range .

Claims (6)

In the method of etching a nitride semiconductor, oxygen (O), sulfur (S) or selenium (Se) gas and halogen gas is introduced into the reactor and the gallium nitride layer characterized in that the gallium nitride layer is etched using plasma. Anisotropic dry etching method with high selectivity. The gallium nitride high selectivity anisotropic dry etching method according to claim 1, wherein the oxygen is etched using 0 to 50% of the total gas. The method of claim 1, wherein the gallium nitride high selectivity anisotropic dry etching method using an oxygen plasma, characterized in that the plasma power is adjusted to 0 to 3,000 W. The method of claim 1, wherein the plasma RF table power is adjusted to 0 to 500 W. The gallium nitride high selectivity anisotropic dry etching method using oxygen plasma. 4. The gallium nitride as claimed in claim 1 or 3, wherein the plasma generator uses any one selected from electron resonance plasma (ECR), inductively coupled plasma (ICP), and magnetic field enhanced plasma (MRIE). Anisotropic dry etching method with high selectivity. The method of claim 1 or 2, wherein the ionized water: ammonium fluoride (NH ₄ F) is used to remove oxygen remaining on the aluminum gallium nitride surface after etching the gallium nitride layer using an oxygen plasma. Gallium nitride, characterized in that the cleaning is performed for 1 second to 300 seconds using a solvent mixed with 1 to 100% of hydrofluoric acid (HF) at a volume ratio of 0 to 1: 0 to 1: 0.01 to 1. Anisotropic dry etching method of selectivity.