CN1272835C - Dry etching method for gallium nitride materials - Google Patents

Abstract

The invention discloses a gallium nitride material dry etching method belonging to the technical field of gallium nitride material etching, which is characterized in that the gas is mixed with chlorine gas, nitrogen gas and oxygen Cl ₂ /N ₂ /O ₂ The plasma generated by the formed reaction gas is etched to obtain a high etching selectivity and a high GaN etching rate. The mixed gas can also be Cl ₂ /He/O ₂ or Cl ₂ /Ne/O ₂ or Cl ₂ /N ₂ O/O ₂ . Since the present invention uses a combination of three gases as reaction gases in the dry etching gallium nitride material system, a high etching selectivity ratio and a high GaN etching rate can be obtained. At the same time, a residue-free, scratch-free and smooth etching surface can be obtained. By adjusting the relative content of oxygen in the three mixed gases, the selective etching ratio and etching rate can be adjusted. The experimental results show that the selective etching ratio of GaN and Al _0.28 Ga _0.72 N is 60:1, The etch rate of GaN reaches 320nm/min.

Description

A dry etching method for gallium nitride material

technical field

The present invention relates to a gallium nitride compound used in devices such as light-emitting diodes (LEDs), laser diodes (LDs), high electron mobility transistors (HEMTs), heterojunction bipolar transistors (HBTs), and photodetectors The invention relates to a semiconductor dry etching method, which belongs to the technical field of gallium nitride material etching.

Background technique

In the process of making light-emitting diodes, laser diodes, high electron mobility transistors, heterojunction bipolar transistors, photodetectors and other devices based on gallium nitride-based materials, it is necessary to use gallium nitride-based materials (including GaN, InN, AlN, AlGaN, InGaN, AlInGaN, etc.) for etching. If wet etching is used to etch III-V compound semiconductors, hydrochloric acid, sulfuric acid, hydrofluoric acid or their mixtures are generally used. Due to the high bonding energy and stable chemical properties of gallium nitride materials, gallium nitride materials are used in their It is difficult to dissolve in the solution, so the etching of gallium nitride generally uses dry etching instead of wet etching technology. Among them, plasma-based dry etching has the advantages of high etching rate, uniform etching rate on a large area, good controllability, and low cost, so plasma dry etching technology Research and development is very popular.

The so-called plasma dry etching refers to the use of dry etching equipment to turn the reactive gas into the plasma, and the atoms and high-energy ions with high chemical activity contained in the plasma are closely related to the surface of the etched sample. reaction, forming volatile gases that are pumped away by the system, causing etching of the sample. It can be seen that the selection of the reactive gas species is very important to the etching effect.

In the device etching process, it is very important to obtain a higher etching selectivity ratio and a higher etching rate at the same time, and it is also a problem that people are eager to solve. The so-called etching selectivity refers to the ratio of the etching rate for etching a certain material (such as GaN) to the etching rate for another material (such as AlGaN). In particular, in devices such as high electron mobility transistors, heterojunction bipolar transistors, and photodetectors, it is particularly important to obtain a high etching selectivity and a high etching rate: for example, in high electron mobility field effect In the tube, there is a GaN layer with a thickness of tens of nanometers covering the AlGaN layer. The thickness of the AlGaN layer is also tens of nanometers. The dry etching should have a large etching rate for GaN, but a small etching rate for AlGaN, that is, the selected dry etching should have a high etching selectivity ratio, so that the GaN can be etched away at the same time. , Try not to etch away the AlGaN layer.

In plasma dry etching, the composition of the reactive gas is very important in determining the etching rate and etching selectivity. Different reaction gases are used to obtain different etching rates and etching selectivity ratios. The composition of the disclosed reactive gas with etching selectivity mainly includes:

(1) Cl ₂ /Ar combination, the etching selectivity ratio of GaN and AlN is 7-8.5:1, see literature RJShul, GAVawter, CGWillison, MMBridges, JWLee, SJPearton and CRAbernathy, Solid-State Electronics 42(1998) 2259. and RJ Shul, CG Willison, MMB Bridges, J. Han, JW Lee, SJ Pearton, CRAbernathy, JD Mackenzie and SM Donovan, Solid-State Electronics 42 (1998) 2269. The etch selectivity ratio of GaN and Al _0.28 Ga _0.72 N is 10:1, see literature SASmith, CA Wolden, MDBremser, AD Hanser, RF Davis, and WV Lampert, Appl. Phys. Lett.71 (1997) 3631. The etch selectivity of this method is not high enough.

(2) Br ₃ , the etching selectivity ratio of GaN and AlN is 13:1, and the etching rate of GaN is 180nm/min, see literature H.Cho, J.Hong, T.Maeda, SMDonovan, CRAbernathy, SJPearton and RJ Shul, Materials Science and Engineering B 59 (1999) 340. The etch selectivity ratio of this method is not high enough, and the etch rate is low.

(3) Cl ₂ /Ar/O ₂ , the etching selectivity ratio of GaN and AlN is 48:1, see literature SASmith, WVLampert, P.Rajagopal, ADBanks, D.Thomson, and RFDavis, J.Vac.Sci. & Technol. A 18, (2000) 879. The etch selectivity ratio of GaN and Al _0.1 Ga _0.9 N is 24:1, and the etch rate of GaN is 60nm/min, see literature JMLee, KMChang, IHLee, and SJPark, J.Vac.Sci. 18 (2000) 1409. The etching selectivity of GaN and AlGaN is not high enough for this method, and the etching rate of GaN is very low.

(4) Cl2/C _x H _y Cl _z (x, y, z are integers), refer to the literature Chinese patent, application number: 0310423.37, the etching selectivity ratio of this gas component to GaN and AlGaN is relatively low.

The physical and chemical properties of AlN and AlGaN are quite different. AlN is a binary compound semiconductor composed of Al and N atoms; while AlGaN is a ternary compound semiconductor composed of Al, Ga, and N atoms. AlGaN It can also be regarded as the formation of a part of Ga atoms in GaN replaced by Al atoms, such as Al _0.28 Ga _0.72 N, which can be regarded as the formation of 28% of the total number of Ga atoms in GaN replaced by Al atoms. Generally speaking, under the same etching conditions, the lower the Al content in AlGaN, the lower the etching selectivity between GaN and AlGaN. That is to say, when the Al content in AlGaN is lower, it is more difficult to obtain a high etching selectivity ratio between GaN and AlGaN.

Increasing the etching rate and etching selectivity ratio means that the etching rate of GaN should be increased as much as possible, while the etching rate of AlGaN should be reduced as much as possible.

An important reason for affecting the etching rate of AlGaN is that when etching AlGaN, the oxygen (O) in the reaction chamber reacts with Al to form Al oxides, which are very hard and not easy to be etched, so they will Slow down the etch rate of AlGaN. Therefore, if some measures are taken during the etching process to make it easier to form Al oxides on the surface of AlGaN, the etching rate of AlGaN will be effectively reduced.

Contents of the invention

The invention provides a dry etching method in order to solve the two problems of etching selectivity and etching rate in dry etching.

A dry etching method for gallium nitride material proposed by the present invention is characterized in that: the method is generated by a reaction gas containing chlorine, nitrogen, and oxygen Cl ₂ /N ₂ /O ₂ mixed with these three gases. Etching with plasma can obtain high etching selectivity and high etching rate of GaN.

In the above-mentioned dry etching method, etching is performed by plasma generated by a reaction gas containing chlorine, helium, and oxygen Cl ₂ /He/O ₂ mixed with three gases.

In the above-mentioned dry etching method, etching is carried out by plasma generated by a reaction gas containing chlorine gas, neon gas, and oxygen gas Cl ₂ /Ne/O ₂ mixed.

In the above-mentioned dry etching method, etching is performed by plasma generated by a reaction gas formed by mixing three gases including chlorine, nitrogen monoxide, and oxygen Cl ₂ /N ₂ O/O ₂ .

Since the present invention uses a combination of three gases as reaction gases in the dry etching gallium nitride material system, a high etching selectivity ratio and a high GaN etching rate can be obtained. At the same time, a residue-free, scratch-free, smooth etch surface can be obtained. By adjusting the relative content of oxygen in these three mixed gases, the selective etching ratio and etching rate can be adjusted. The experimental results show that when the flow rate of oxygen is 2 sccm, the selectivity to GaN and Al _0.28 Ga _0.72 N The etching ratio is 60:1, and the etching rate of GaN reaches 320nm/min.

Description of drawings

Figure 1 shows that when an inductively coupled plasma device is used, the substrate temperature is 20°C, the flow rates of chlorine gas and nitrogen gas are 40 sccm and 10 sccm respectively, the ICP power is 1750W, the DC bias voltage is -220V, and the reaction chamber pressure is 20mTorr. The relationship between flow rate, etching rate and etching selectivity ratio.

FIG. 2 is a basic structural diagram of HEMT in Example 1.

FIG. 3 is a basic structural diagram of a photodiode in Embodiment 2. FIG.

FIG. 4 is a basic structural diagram of a laser diode in Embodiment 3. FIG.

Detailed ways

The present invention is realized according to the following technical scheme:

The research results of the present invention show that (see literature YJHan, S.Xue, WPGuo, CZSun, ZBHao and Y.Luo, to be published in Jpn.J.Appl.Phys), Cl ₂ /Ar and Cl ₂ /N ₂ plasma The effect of etching on the material properties, especially the oxidation of the material surface, is essentially different. When using the combination of Cl ₂ and N ₂ to dry GaN for dry etching, the content of O atoms on the sample surface It is much higher than the result of dry etching using the combination of Cl ₂ and Ar. This shows that if the combination of Cl ₂ and N ₂ is used for dry etching of AlGaN, Al oxides are more likely to be formed on the surface of the sample, thereby reducing the etching rate of AlGaN and increasing the gap between GaN and AlGaN. The etch selectivity ratio. Therefore, in order to reduce the etch rate of AlGaN, the amount of O added in the two gas combinations has an essential difference. That is to say, the amount of O ₂ added to the plasma composed of Cl ₂ and N ₂ is much smaller than the amount of oxygen added to the Cl ₂ , Ar plasma to reduce the etching rate of AlGaN. At the same time, the minimum O ₂ content in Cl ₂ /N ₂ can ensure that the etching rate of GaN is maintained at a high level. Therefore, if the combination of Cl ₂ , N ₂ , and O ₂ is used for the etching reaction Gas, its effect is much better than Cl ₂ , Ar, O ₂ (the third of the four combined gases listed above).

Further research results show that when three combinations of Cl ₂ /He, Cl ₂ /Ne, and Cl ₂ /N ₂ O are used for dry etching of GaN, the effect obtained is the same as that of etching with Cl ₂ and N ₂ The results are the same, and it is detected that the content of O atoms on the surface of the sample is higher than the result of dry etching using the combination of these two gases, Cl ₂ and Ar. Therefore, if (Cl ₂ , He, O ₂ ) is selected, The three combinations of (Cl ₂ , Ne, O ₂ ), (Cl ₂ , N ₂ O, O ₂ ) are respectively used as etching reaction gases, and their effects are better than those of Cl ₂ , Ar, O ₂ (listed above). The 3rd of 4 combinations) is much better.

The inventors of the present invention have found that by using a reaction gas mixed with three gases (Cl ₂ /N ₂ /O 2 ) of chlorine gas, nitrogen gas, and oxygen gas (Cl 2 /N 2 /O ₂ ) when performing dry etching of gallium nitride-based compound semiconductors by generating plasma, A high selective etching ratio of GaN/AlGaN can be obtained, a high rate of etching GaN can be obtained, and a residue-free, scratch-free, and smooth etching surface can be obtained at the same time. By adjusting the relative content of oxygen in these three mixed gases, the selective etching ratio and etching rate can be adjusted. Figure 1 shows the flow rates of chlorine and nitrogen when using an inductively coupled plasma device with a substrate temperature of 20°C. When the ICP power is 1750W, the DC bias voltage is -220V, and the reaction chamber pressure is 20mTorr, the relationship between the flow rate of oxygen and the etching rate and etching selectivity ratio is 40 and 10 sccm respectively. It can be seen that when the flow rate of oxygen is 2 sccm, The selective etching ratio of GaN and Al _0.28 Ga _0.72 N is 60:1, and the etching rate of GaN reaches 320nm/min.

The method disclosed in the present invention can be used in all types of plasma etching devices. When using different plasma etching devices, the relative flow ratio between the components in the reaction gas should be adjusted to achieve the best etching effect.

Example 1

The gallium nitride-based HEMT is subjected to an etching experiment using the dry etching method disclosed in the present invention. The basic structure of the HEMT is shown in Figure 2: a sapphire substrate 1 covered with a GaN layer 2 (thickness 2000nm), AlGaN layer 3 (thickness 20nm), and GaN layer 4 (thickness 20nm). When making the device, it is necessary to cover the mask 5 on the top to form the required pattern. The purpose of etching is to remove a part of the uppermost GaN layer 4 to expose the AlGaN layer 3, and use the gas combination (Cl ₂ /N ₂ /O ₂ ) plasma 6 formed by dry etching, the etching conditions are as in Figure 1, the flow rate of oxygen is 2 sccm, and the obtained etching rates for GaN and AlGaN are respectively 320nm /min, 5nm/min. After etching for 4s, the HEMT was taken out, and it was observed that the AlGaN layer was exposed on the surface. There was no residue, no scratches on the surface, and it was extremely smooth, and the sidewall of the etched GaN layer 4 was basically vertical, indicating that the etching was carried out with a high degree of anisotropy. etch.

Example 2

An etching test is carried out on a gallium nitride-based photodiode (photodiode) by using the dry etching method disclosed in the present invention. The basic structure of a photodiode is shown in Figure 3: a sapphire substrate 1 covered in turn with an n-type GaN layer 2 (thickness 3600nm), an unintentionally doped GaN absorption layer 3 (thickness 800nm), a p-type AlGaN layer 4 (thickness 250nm ), and a p-type GaN contact layer 5 (thickness 20nm). When making the device, it is necessary to cover the mask 6 above to form the required pattern. The purpose of etching is to remove a part of the uppermost GaN layer 5 to expose the AlGaN layer 4, and use the gas combination (Cl ₂ /He/O ₂ ) formed plasma 7 for dry etching, the flow rates of chlorine gas, helium gas and oxygen gas were 40, 20 and 2 sccm respectively, the ICP power was 1750W, the DC bias voltage was -220V, and the reaction chamber pressure was At 20mTorr, the obtained etching rates for GaN and AlGaN are 300nm/min and 5nm/min, respectively. After etching for 4s, take out the photodiode, and observe that the AlGaN layer is exposed on the surface. The surface is extremely smooth without residues and scratches, and the sidewall of the etched GaN layer 5 is basically vertical, indicating that the etching is based on a highly anisotropic Etching is performed.

Example 3

The gallium nitride-based laser diode is etched by the dry etching method disclosed in the present invention. The basic structure of the laser diode is shown in Figure 4: sapphire substrate 1, covered with n-type GaN layer 2 (thickness 3000nm), n-type InGaN layer 3 (thickness 100nm), n-type AlGaN layer 4 (thickness 500nm), n Type GaN layer 5 (thickness 100nm), then InGaN/GaN quantum well active layer 6, p-type AlGaN layer 7 (thickness 20nm), p-type GaN layer 8 (thickness 100nm), p-type AlGaN layer 9 (thickness 500nm) , p-type GaN layer 10 (thickness 200nm). When making the device, it is necessary to cover the mask 11 above to form the required pattern. The purpose of etching is to remove a part of the uppermost GaN layer 10 to expose the AlGaN layer 9, and use the gas combination (Cl ₂ /Ne/O ₂ ) formed plasma 11 for dry etching, the flow rates of chlorine gas, neon gas and oxygen gas were 40, 20 and 2 sccm respectively, the ICP power was 1750W, the DC bias voltage was -220V, and the reaction chamber pressure was At 20mTorr, the obtained etching rates for GaN and AlGaN are 310nm/min and 5nm/min respectively. After etching for 4 seconds, the laser diode was taken out, and it was observed that the AlGaN layer was exposed on the surface, and the surface was extremely smooth without residues and scratches, and the sidewall of the etched GaN layer 10 was basically vertical, indicating that the etching was performed by highly anisotropic Etching is performed.

Claims (4)

1, a kind of dry etching method of gallium nitride material, it is characterized in that: described method is by containing chlorine, nitrogen, these three kinds of gases of oxygen mix and plasma that the reacting gas that forms generates and carry out etching, obtain the etch rate of high GaN and AlGaN etching selection ratio and high GaN.

2, dry etching method according to claim 1 is characterized in that: described method is by containing chlorine, and helium, these three kinds of gases of oxygen mix and plasma that the reacting gas that forms generates and carry out etching.

3, dry etching method according to claim 1 is characterized in that: described method is by containing chlorine, and neon, these three kinds of gases of oxygen mix and plasma that the reacting gas that forms generates and carry out etching.

4, dry etching method according to claim 1 is characterized in that: described method is by containing chlorine, and nitric oxide, these three kinds of gases of oxygen mix and plasma that the reacting gas that forms generates and carry out etching.

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