A method for PECVD thin film deposition to enhance dielectric film adhesion of gallium nitride devices

Abstract

The present invention discloses a method for PECVD thin film deposition for enhancing the adhesion of a dielectric film of a gallium nitride device: (1) alternately turning on / off the dielectric film to deposit a dielectric film to obtain a dielectric film thickness of 10-40nm; (2) then using N2O and SiH4 continuous gas flow to deposit the dielectric film, the gas flow ratio is 1:2 to 1:10, the deposition time is 8-15 minutes, and the SiO2 thickness is 300-600nm, and then repeating step (1) to pulse deposit a dielectric film thickness of 10-40nm; (3) adding a Pd metal layer with a thickness of 20-50nm on the metal electrode, the Pd metal layer is combined with the dielectric film to form PdO, which is used to increase the quality and viscosity of the dielectric film. The present invention can reduce film stress, improve film quality, reduce interlayer leakage current, and improve the stability and reliability of the device on the basis of the existing process.

Description

Technical Field

[0001] The invention relates to the field of microelectronic technology, in particular to a PECVD thin film deposition method for enhancing the adhesion of a dielectric film of a gallium nitride device. Background Art

[0002] Compared with silicon (Si), gallium nitride (GaN) material has a larger bandgap width. At the same time, GaN heterojunction has higher electron mobility and two-dimensional electron gas density. Therefore, GaN materials are currently widely used in electronic devices or optoelectronic devices such as high electron mobility transistors (HEMT), LEDs, and light detection. Thin film deposition has two main uses, one is surface passivation and the other is interlayer insulation. Surface passivation and interlayer insulation are key technologies for achieving high-performance GaN devices. The insulating dielectric film of gallium nitride devices is mainly SiO2 and Si3N4, which are mainly achieved by PECVD, ALD, LPCVD and other methods. PECVD is favored because of its fast growth rate, low growth temperature, good controllability and excellent film quality.

[0003] Taking GaN HEMT as an example, the widely adopted preparation method is PECVD. SiH4+N2O is used to react and deposit SiO2 under heating and plasma atmosphere, and SiH4+NH3 is used to react and deposit Si3N4 under heating and plasma atmosphere. However, the stress of PECVD dielectric film is generally very large, easy to break or peel off, and the adhesion to the metal electrode is very poor. How to grow a dielectric film with low stress and strong adhesion has always been a key problem that plagues the gallium nitride device process. The present invention proposes a thin film deposition method based on PECVD technology. The present invention deposits high-quality low-stress dielectric films by alternating pulse deposition and continuous deposition. Pd metal is used as a transition layer between the metal electrode and the dielectric film, which can effectively enhance the adhesion of the film. The prepared device can be used in high-voltage and high-power applications. Summary of the invention

[0004] The object of the present invention is to provide a method for enhancing the dielectric film adhesion of a gallium nitride device using a PECVD film to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for PECVD thin film deposition to enhance the adhesion of a dielectric film of a gallium nitride device comprises the following steps:

[0007] (1) The epitaxial layer structure of the GaN device is composed of a substrate layer, a buffer layer, a GaN channel material layer, an AlN isolation layer, an AlGaN barrier layer and a cap layer. The AlGaN barrier layer is provided with a metal electrode. A dielectric film is deposited on the surface of the cap layer and the metal electrode by pulsed PECVD, and then the gas is alternately turned on / off to obtain a dielectric film with a thickness of 10-40 nm.

[0008] (2) then depositing a dielectric film by continuous gas flow to obtain a dielectric film thickness of 300-600 nm, and then repeating step (1) to perform pulse deposition of the dielectric film to obtain a dielectric film thickness of 10-40 nm;

[0009] (3) Adding a Pd metal layer on the metal electrode, Pd combines with the dielectric film to form PdO, which is used to increase the quality and viscosity of the dielectric film, wherein the metal electrode layer is a metal electrode Ti and a metal electrode Au.

[0010] Furthermore, in the step (1), the dielectric film is SiO2, the N2O gas is turned on and then turned off, the SiH4 gas is turned on and then turned off, and the N2O and SiH4 gas are alternately turned on / off in sequence to deposit SiO2.

[0011] Furthermore, in step (1), the time for starting the N2O gas and starting the SiH4 gas is 5-10 seconds.

[0012] Furthermore, in step (1), the flow ratio of N2O gas to SiH4 gas is 1:2 to 1:10, the alternating switching operation is repeated 10-20 times, and the plasma RF power is 20w-100w.

[0013] Furthermore, in the step (2), the plasma radio frequency power is 50W-150W, and the deposition time is 8-15 minutes.

[0014] Furthermore, in the step (1), the dielectric film is Si3N4, the gas flow ratio is 1:2 to 1:10, and the alternating switching operation is repeated 10-20 times to obtain a Si3N4 thickness of 10-40nm, wherein the time for turning on the NH3 gas and the SiH4 gas is 5-10s.

[0015] Furthermore, in the step (2), Si3N4 can be deposited by continuous gas flow of NH3 gas and SiH4 gas, with a gas flow ratio of 1:2 to 1:10 and a deposition time of 16-30 minutes to obtain a Si3N4 thickness of 300-600nm, and then the pulse deposition Si3N4 operation is repeated 10-20 times to obtain a thickness of 10-40nm.

[0016] Furthermore, the substrate layer is silicon or sapphire or silicon carbide.

[0017] Furthermore, the buffer layer is aluminum nitride or gallium nitride.

[0018] Furthermore, the cap layer is silicon nitride or gallium nitride.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention is mainly used for surface passivation and metal interlayer insulation of gallium nitride HEMT devices and deep ultraviolet LED devices. The thin film deposition technology proposed by the present invention can reduce film stress, improve film quality, reduce interlayer leakage current, and correspondingly improve the stability and reliability of the device, as well as the device operating current and output power. The process of the present invention is simple and has good repeatability, and can give full play to the characteristics of high frequency, high breakdown voltage, high current density, etc. of gallium nitride power devices. The present invention will be applied to the production and manufacturing of gallium nitride power devices, radio frequency devices and deep ultraviolet LED devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of alternately depositing dielectric films by pulsed PECVD / conventional PECVD according to the present invention;

[0022] Figure 2 A schematic diagram of conventional PECVD deposition of silicon dioxide on the metal surface of the gallium nitride device of the present invention;

[0023] Figure 3 A schematic diagram of first depositing a thin layer of high-density silicon dioxide on the metal surface of the gallium nitride device of the present invention by pulsed PECVD;

[0024] Figure 4 It is a schematic diagram of the epitaxial layer structure of the gallium nitride HEMT device of the present invention;

[0025] Figure 5 It is a schematic diagram of the Ti / Au / Pd metal electrode structure of the present invention. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0027] Embodiment 1, as Figure 4 , Figure 5As shown: the epitaxial layer structure of the device of the present invention is: silicon or sapphire or silicon carbide substrate layer 1, aluminum nitride or gallium nitride buffer layer 2, gallium nitride channel layer 3, aluminum nitride isolation layer 4, aluminum gallium nitride barrier layer 5, silicon nitride or gallium nitride cap layer 6. In the device manufacturing process, it is necessary to first go through cleaning, photolithography and etching processes, and evaporate metal electrodes. Generally, the metal electrode structure is Ti / Au multilayer metal, but because SiO2 or Si3N4 film is repellent to gold, the film has poor adhesion on the electrode and is very easy to fall off and peel off, causing device failure. The pulsed interactive deposition and Pd interlayer of the present invention can effectively solve the above problems.

[0028] Among them, the quality of the dielectric film of the GaN device directly affects the insulation performance and current collapse effect of the device, thereby affecting the saturation current and output power of the device.

[0029] Therefore, the present invention proposes to deposit a high-quality low-stress dielectric film by alternating pulse deposition and continuous deposition to improve device performance, and the method is as follows:

[0030] A dielectric film is deposited on the cap layer and the metal electrode surface by pulse PECVD. The gas valve switch and plasma RF power are controlled by computer programming. N2O and SiH4 are alternately turned on / off to deposit SiO2. The gas flow ratio is 1:2 to 1:10. The alternating switch operation is repeated 10-20 times. The plasma RF power is 20w-100w. A high-quality pulse-deposited dielectric film with a thickness of 10-40nm is obtained. Then, SiO2 is deposited by continuous gas flow of N2O and SiH4. The gas flow ratio is 1:2 to 1:10. The deposition time is 8-15 minutes. The plasma RF power is 50w-150w. A conventional dielectric film with a thickness of 300-600nm is obtained.

[0031] Then pulsed alternating deposition is used to obtain a high-quality dielectric film with a thickness of 10-40nm;

[0032] A Pd metal layer 9 is added on the metal electrode Ti7 / metal electrode Au8, and the thickness of Pd is 20-50nm. Since Pd has good adhesion to SiO2 and Si3N4, Pd / SiO2 is a widely used automobile exhaust treatment catalyst. Pd combines with SiO2 to form PdO, and Pd has good adhesion to SiO2. Adding Pd to the metal electrode can enhance the quality and adhesion of the dielectric film, greatly improving the yield and device reliability.

[0033] Embodiment 2:

[0034] A dielectric film is deposited on the cap layer and the metal electrode surface by pulsed PECVD. The gas valve switch and plasma RF power are controlled by computer programming. NH3 and SiH4 are alternately turned on / off to deposit Si3N4. The gas flow ratio is 1:2 to 1:10. The alternating switch operation is repeated 10-20 times. The plasma RF power is 20w-100w. A high-quality pulsed deposited dielectric film with a thickness of 10-40nm is obtained. Then, Si3N4 is deposited by continuous gas flow of NH3 and SiH4. The gas flow ratio is 1:2 to 1:10. The deposition time is 8-15 minutes. The plasma RF power is 50w-150w. A conventional dielectric film with a thickness of 300-600nm is obtained.

[0035] Then pulsed alternating deposition is used to obtain a high-quality dielectric film with a thickness of 10-40nm.

[0036] The main deposition methods for dielectric films such as SiO2 and Si3N4 are PECVD, ALD, and PVD. PECVD decomposes gas molecules into ions through plasma ionization, and the ion chemical reaction combines to deposit dielectric films. The step coverage is good. The deposition rate of PECVD is fast, about 20-40nm / min, but the film stress needs to be adjusted according to the process conditions. ALD is a CVD technology that alternately introduces two reactive gases in a pulsed manner. Since the gas is input in pulses, there is no chemical reaction between the gases. Only a single gas reacts with the wafer each time, and each pulse can only deposit a single atomic layer. The ALD deposition speed is very slow, the step coverage is very good, and the film layer is very dense, but the deposition rate is about 0.05-0.5nm / min. PVD is a method of depositing dielectric films through physical bombardment of high-energy ions. The deposition rate is 10-20nm / min, the material is dense, but the step coverage is poor, which is suitable for planar sputtering.

[0037] The dielectric film of gallium nitride devices requires good coverage, and the film layer is relatively thick, so PVD or ALD is not suitable. PECVD is more commonly used, but the density and coverage of PECVD dielectric film are not as good as ALD. The PEALD equipment recently launched on the market is expected to combine the rapid deposition of PECVD and the dense coverage of ALD. However, since PECVD and ALD are two different deposition principles, PEALD cannot give full play to the advantages of both, and the process cannot achieve alternating deposition of PECVD and ALD. According to the deposition principle of ALD, it is proposed to use pulsed PECVD to deposit SiO2 / Si3N4 films, which can not only obtain good coverage similar to ALD, but also be compatible with conventional PECVD deposition, and obtain a deposition rate close to that of conventional PECVD, refer to Table 1 below.

[0038] Table 1. Comparison of SiO2 / Si3N4 films deposited by PECVD, ALD, and pulsed PECVD

[0039]

[0040] Based on the above results, a pulse alternating deposition method similar to ALD is used in PECVD equipment to combine the advantages of fast deposition and dense coverage. Similar to ALD / PECVD alternating deposition to obtain a low leakage and high breakdown electric field dielectric film, the present invention uses pulse deposition PECVD / conventional deposition PECVD alternating deposition to obtain a low leakage and high breakdown electric field dielectric film. Pulse PECVD deposition draws on the ALD deposition method. During the PECVD deposition process, the silicon source SiN4 gas reacts alternately with the N source NH3 gas or the O source O2 gas to obtain a high-quality and high-density thin film material. The rapidly deposited medium-quality thin film material obtained by conventional PECVD is wrapped by the high-quality dielectric film 10 deposited by pulse PECVD. The film structure is as shown in FIG. Figure 1 shown.

[0041] Conventional PECVD deposition of silicon dioxide on the metal surface of GaN devices, due to the insufficient density of PECVD surface coverage, the silicon dioxide film is corroded by acid during the subsequent process and causes it to fall off, such as Figure 2 shown.

[0042] A thin layer of high-density silicon dioxide is first deposited on the metal surface of the GaN device using pulsed PECVD, and then a thick layer of silicon dioxide is deposited using conventional PECVD. The pulsed PECVD and conventional PECVD depositions are used alternately. Since the pulsed PECVD surface coverage is very dense, the silicon dioxide film remains intact during the subsequent process. Figure 3 shown.

[0043] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for PECVD thin film deposition to enhance the adhesion of dielectric films of gallium nitride devices, characterized in that: The epitaxial layer structure of the GaN device is composed of a substrate layer, a buffer layer, a GaN channel material layer, an AlN isolation layer, an AlGaN barrier layer and a cap layer from bottom to top. The AlGaN barrier layer is provided with a metal electrode. The cap layer is made of silicon nitride or GaN. A dielectric film is deposited on the surface of the cap layer and the metal electrode. The dielectric film is SiO2. The following steps are involved: (1) Depositing a dielectric film by pulsed PECVD. The pulsed PECVD dielectric film deposition is to turn on the N2O gas, then turn off the N2O gas, turn on the SiH4 gas, then turn off the SiH4 gas, alternately turn on / off the N2O and SiH4 to deposit SiO2, and the plasma RF power is 20w-100w to obtain a dielectric film with a thickness of 10-40nm; (2) Then, a dielectric film is deposited by continuous gas flow of N2O and SiH4, with a plasma RF power of 50w-150w to obtain a dielectric film with a thickness of 300-600nm; (3) then repeating step (1) to perform pulsed PECVD deposition of a dielectric film to obtain a dielectric film with a thickness of 10-40 nm; Wherein, a Pd metal layer is added on the metal electrode, and Pd is combined with the dielectric film to form PdO, which is used to enhance the quality and viscosity of the dielectric film, wherein the metal electrode is a metal electrode Ti or a metal electrode Au.

2. A method for PECVD thin film deposition for enhancing the adhesion of a dielectric film of a gallium nitride device as claimed in claim 1, characterized in that: The deposition time in step (2) is 8-15 minutes.

3. A method for PECVD thin film deposition for enhancing the adhesion of a dielectric film of a gallium nitride device as claimed in claim 2, characterized in that: In the step (1), the time for starting the N2O gas and starting the SiH4 gas is 5-10 seconds.

4. A method for PECVD thin film deposition for enhancing the adhesion of a dielectric film of a gallium nitride device as claimed in claim 2, characterized in that: In the step (1), the flow ratio of N2O gas to SiH4 gas is 1:2 to 1:10, and the alternating on-off operation is repeated 10-20 times.

5. The method for PECVD thin film deposition for enhancing the adhesion of the dielectric film of a gallium nitride device according to claim 1, characterized in that: The substrate layer is silicon, sapphire or silicon carbide.

6. The method for PECVD thin film deposition for enhancing the adhesion of the dielectric film of a gallium nitride device according to claim 1, characterized in that: The buffer layer is aluminum nitride or gallium nitride.

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