Low-temperature synthesis method of P-type AlN polycrystalline film

Abstract

The invention mainly provides a low-temperature synthesis method of a P-type AlN polycrystalline film, which comprises the following steps of: 1, substrate pretreatment: providing a single-crystal high-temperature-resistant substrate, and carrying out surface pretreatment on the single-crystal high-temperature-resistant substrate; 2, an AlN thin film is deposited on the substrate through magnetron sputtering; step 3, performing Mg ion implantation on the AlN thin film; 4, the step 2 and the step 3 are repeated until the target AlN thin film thickness is achieved; and step 5, carrying out annealing treatment on the AlN multilayer thin film. The method has the beneficial effects that low-temperature synthesis of AlN can be realized, the production cost is reduced, and meanwhile, efficient and uniform P-type doping of AlN is realized.

Description

Technical Field

[0001] The invention belongs to semiconductor coating preparation and doping modification technology, and specifically relates to a preparation method of a p-type AlN semiconductor film based on magnetron sputtering and ion implantation technology. Background Art

[0002] Aluminum nitride (AlN), as an ultra-wide bandgap semiconductor material (bandgap width up to 6.2 eV), has shown great application potential in deep ultraviolet optoelectronic devices, high-power electronic devices, radiation-resistant space detectors and MEMS sensors due to its excellent physical and chemical properties (including high thermal conductivity, strong ultraviolet light response, radiation resistance and chemical stability). However, the industrial application of AlN still faces the following key bottlenecks: Limitations of high-temperature synthesis: The existing mainstream preparation technologies of AlN single crystal films (such as physical vapor transport and molecular beam epitaxy) need to be carried out at extreme temperatures above 1400°C. Not only does it rely on special high-temperature resistant reaction chambers, which leads to a surge in costs, but there is also a fundamental contradiction between high-temperature processes and the low-temperature compatibility requirements of CMOS integrated circuits, which seriously restricts its integrated application in the field of semiconductor chips.

[0003] P-type doping challenges: The acceptor activation energy of AlN is extremely deep (Mg acceptor energy level depth is about 0.5 eV). The acceptor ions have low solubility during doping and are easily affected by the self-compensation effect. It is difficult to achieve high-concentration, uniformly distributed P-type carriers (hole concentration is usually less than 10¹) by traditional thermal diffusion doping or in-situ co-sputtering doping. 7 cm - ³), resulting in high ohmic contact resistance of the device and a sharp drop in luminous efficiency.

[0004] Balance between film quality and cost: Although low-temperature magnetron sputtering can reduce the synthesis temperature (<500°C), the deposited polycrystalline AlN film has a high defect density, significant grain boundary scattering, and degraded electrical properties; and although high-temperature annealing (>1600°C) after ion implantation can repair lattice damage, it will in turn increase the thermal budget and process complexity.

[0005] The above contradictions lead to the actual performance of AlN materials in optoelectronic devices and power devices being far lower than theoretical expectations, becoming a core obstacle to its large-scale commercial application. Therefore, the development of an AlN film preparation process that takes into account low-temperature synthesis, efficient P-type doping and high crystal quality has become an urgent need in the semiconductor material field. Summary of the invention

[0006] In order to solve the above problems, the present invention proposes a low-temperature synthesis method of a P-type AlN polycrystalline thin film, comprising the following steps: Step 1: Substrate pretreatment: select a single crystal high temperature resistant substrate, remove the surface oxide layer by HF acid cleaning, and perform ultrasonic cleaning and dehydration and drying; Step 2: Deposit AlN film by magnetron sputtering. Place the substrate in a magnetron sputtering device and introduce Ar and N under vacuum conditions. 2 Mixed gas, using Al target for reactive sputtering to synthesize AlN polycrystalline thin film; Step 3: Mg ion implantation, transferring the deposited AlN film to an ion implantation device, implanting Mg ions under vacuum conditions, and adjusting the ion energy, beam intensity, and implantation dose; Step 4: Cycle deposition and implantation, repeating steps 2 and 3 until the target AIN film thickness is reached; Step 5: High temperature annealing treatment: stack the samples treated in step 4 in a crucible and heat them in N 2 Annealing is carried out in a hot atmosphere, and then slowly cooled to room temperature in the furnace after keeping warm.

[0007] Furthermore, the single crystal high temperature resistant substrate is a sapphire or SiC substrate.

[0008] Furthermore, in step 1, the substrate is pickled using an HF acid solution with a concentration of not less than 5%, the pickling time is ≤10s, and the ultrasonic cleaning includes ultrasonic alcohol cleaning for ≥30min and ultrasonic deionized water rinsing for ≥30min.

[0009] Furthermore, in step 2, the vacuum degree of the vacuum chamber of the magnetron sputtering equipment is ≤1×10 - ³Pa, Ar and N 2 The mixed gas flow ratio is 10:1~5:1, the Al target sputtering power is 180~250W, the working gas pressure is 0.4~0.5Pa, and the substrate temperature is set at 300~500℃.

[0010] Furthermore, in step 3, the vacuum degree of the ion implantation equipment is ≤1×10 -4 Pa, heating temperature is 300~500℃, ion implantation energy is 50~200keV, beam intensity is 1~100mA, and implantation dose is 1.0×10 13 ~1.0×10 15 atoms / cm².

[0011] Furthermore, in step 4, the AlN film deposition thickness of each cycle is 100-200 nm, the number of cycles is 4-10 times, and the total film thickness of the AlN film is 0.4-2 μm.

[0012] Furthermore, in step 5, the annealing heating rate is 5-10°C / min, the holding time is 30-60 minutes, and N 2 Purge time ≥30min.

[0013] Furthermore, in step 5, the annealed sample needs to be slowly cooled to room temperature at a rate of ≤5°C / min.

[0014] Furthermore, the AlN film is a polycrystalline structure with a grain size of 20~100nm and a Mg doping concentration of 1×10¹ 8 ~1×10² 0 cm - ³.

[0015] Furthermore, the method further comprises step 6: post-processing, wherein the sample annealed in step 5 is subjected to ultrasonic alcohol cleaning, drying and vacuum packaging.

[0016] Therefore, the beneficial effects of the present invention are: 1. Realize low-temperature synthesis of AlN and reduce production costs. Currently, most of the methods for synthesizing AlN single crystal thin films on the market use physical vapor transport and chemical vapor deposition, but the synthesis temperature of these methods is too high. On the one hand, it is not conducive to integration with the subsequent processes of semiconductor device preparation. On the other hand, the high synthesis temperature not only increases the production cost, but also introduces a large number of thermal balance defects. Magnetron sputtering synthesis of AlN polycrystalline thin films can be carried out at low temperatures, without the need for a special reactor, which greatly reduces production costs.

[0017] 2. Achieve efficient and uniform P-type doping of AlN. P-type doping has always been difficult for AlN semiconductor materials due to the low solubility of P-type dopants (such as magnesium and zinc) in AlN and the self-compensation effect. By periodically performing multiple ion implantations during the film growth stage, the concentration distribution of Mg ions can be ensured to be uniform. The subsequent high-temperature rapid annealing can reduce the defect concentration in the crystal and promote the diffusion and migration of Mg ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow chart of the steps of the present invention.

[0019] Figure 2 This is a cross-sectional microstructure image of an AlN multilayer polycrystalline film obtained on the surface of a single crystal sapphire in Example 2 of the present invention. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, reference may be made to the accompanying drawings and embodiments to further illustrate the technical solutions of the present invention. It should be understood that the embodiments described herein are only used to explain the technical solutions or principles of the present invention and are not intended to limit the scope of protection of the present invention. Example

[0021] This embodiment includes the following steps: Step 1. Select a single crystal sapphire or SiC substrate with a size of 5*5*0.43mm, clean it with HF acid solution to remove the oxide layer on its surface, and then perform ultrasonic alcohol cleaning, ultrasonic deionized water rinsing, and dehydration and drying; HF acid solution pickling for 10s, ultrasonic alcohol cleaning for 30min, and ultrasonic deionized water rinsing for 40min.

[0022] Step 2: Place the substrate processed in step 1 into the vacuum chamber of the magnetron sputtering equipment, install a 2-inch Al target, and then close the vacuum chamber and evacuate to 1×10 -4 Pa, 80 sccm Ar was introduced to pre-sputter the target, the power was 200 W, and the DC power supply was turned off after sputtering for 10 minutes. Then 50 sccm Ar and 5 sccm N were introduced. 2 The DC power supply was turned on, the shutter was opened, the sputtering power was set to 180 W, the sample stage rotation speed was set to 10 r / min, the substrate temperature was set to 300 °C, the working gas pressure was adjusted to 0.4 Pa, and the AlN film was synthesized by reactive sputtering. After 10 min, the power supply was turned off, the gas was stopped, and the sample stage rotation was stopped; Step 3: Place the synthesized AlN template into the vacuum chamber of the ion implantation equipment, install the Mg target, and adjust the background vacuum degree of the vacuum chamber of the ion implantation equipment to 8×10 -5 Pa and heated to 300 °C, turned on the ion implantation source, adjusted the ion implantation energy to 50 keV, the ion beam intensity to 1 mA, and the ion implantation dosage to 1.0 × 10 13 atoms / cm 2 , open the baffle, when the ion implantation metering reaches a preset value, close the baffle, turn off the ion source, wait until the temperature of the workpiece drops below 100° C., and then turn off the vacuum system; Step 4: Take steps 2 and 3 as a cycle. The AlN thickness in each cycle is 100 nm. Repeat 4 cycles. The total film thickness is 400 nm. The grain size of the AlN film is 20 nm. The Mg doping concentration is 1×10 18 cm -3 ; Step 5. After 8 cycles, take out the sample, stack the sample with the AlN film face to face, put it into a corundum crucible for annealing, and then press it with a corundum block. Put the corundum crucible with the sample into the center of the quartz tube of the tube furnace. After installation, pass N 2 The air in the quartz tube was exhausted, and then the heating program was set to increase the temperature to 1400℃, with a heating rate of 5℃ / min. After reaching the target temperature, the temperature was kept for 30min, with N 2 Purge for 30 minutes, then stop heating, cool to room temperature at a cooling rate of 3°C / min, take out the sample after reaching the appropriate temperature, clean it with ultrasonic alcohol, dry it, and store it in a vacuum bag. Example

[0023] This embodiment includes the following steps: Step 1. Select a single crystal sapphire or SiC substrate with a size of 5*5*0.43mm, clean it with HF acid solution to remove the oxide layer on its surface, and then perform ultrasonic alcohol cleaning, ultrasonic deionized water rinsing, and dehydration and drying; HF acid solution pickling for 10s, ultrasonic alcohol cleaning for 30min, and ultrasonic deionized water rinsing for 40min.

[0024] Step 2: Place the substrate processed in step 1 into the vacuum chamber of the magnetron sputtering equipment, install a 2-inch Al target, and then close the vacuum chamber and evacuate to 1×10 -4 Pa, 80 sccm Ar was introduced to pre-sputter the target, the power was 200 W, and the DC power supply was turned off after sputtering for 10 minutes. Then 50 sccm Ar and 8 sccm N were introduced. 2 The DC power supply was turned on, the power was adjusted to 200 W, the baffle was opened, the sample stage rotation speed was set to 10 r / min, the substrate temperature was set to 400 °C, the working gas pressure was adjusted to 0.45 Pa, and the AlN film was synthesized by reactive sputtering. After 15 min, the power supply was turned off, the gas was stopped, and the sample stage rotation was stopped; Step 3: Place the synthesized AlN template into the vacuum chamber of the ion implantation equipment, install the Mg target, and adjust the background vacuum degree of the vacuum chamber of the ion implantation equipment to 8×10 -5 Pa and heated to 400 °C, turned on the ion implantation source, adjusted the ion implantation energy to 100 keV, the ion beam current to 50 mA, and the ion implantation dose to 1.0 × 10 14 atoms / cm 2 , open the baffle, when the ion implantation metering reaches a preset value, close the baffle, turn off the ion source, wait until the temperature of the workpiece drops below 100° C., and then turn off the vacuum system; Step 4: Take steps 2 and 3 as one cycle. The AlN thickness in each cycle is 150nm. Repeat 6 cycles. The total film thickness is 900nm. The grain size of the AlN film is 50nm. The Mg doping concentration is 1×10 19 cm -3 ; Step 5. After 6 cycles, take out the sample, stack the sample with the AlN film face to face, put it into a corundum crucible for annealing, and then press it with a corundum block. Put the corundum crucible with the sample into the center of the quartz tube of the tube furnace. After installation, pass N 2 The air in the quartz tube was exhausted, and then the heating program was set to increase the temperature to 1400℃, with a heating rate of 8℃ / min. After reaching the target temperature, the temperature was kept for 45min, and N 2The purging time is 35 minutes, then the heating is stopped and cooled to room temperature at a cooling rate of 4°C / min. After reaching the appropriate temperature, the sample is taken out, ultrasonically cleaned with alcohol, and stored in a vacuum bag after drying. Example

[0025] This embodiment includes the following steps: Step 1. Select a single crystal sapphire or SiC substrate with a size of 5*5*0.43mm, clean it with HF acid solution to remove the oxide layer on its surface, and then perform ultrasonic alcohol cleaning, ultrasonic deionized water rinsing, and dehydration and drying; HF acid solution pickling for 10s, ultrasonic alcohol cleaning for 30min, and ultrasonic deionized water rinsing for 40min.

[0026] Step 2: Place the substrate processed in step 1 into the vacuum chamber of the magnetron sputtering equipment, install a 2-inch Al target, and then close the vacuum chamber and evacuate to 1×10 -4 Pa, 80 sccm Ar was introduced to pre-sputter the target, the power was 200 W, and the DC power supply was turned off after sputtering for 10 minutes. Then 50 sccm Ar and 5 sccm N were introduced. 2 Turn on the DC power supply, adjust the power to 250W, open the baffle, set the sample stage rotation speed to 10r / min, set the substrate temperature to 500℃, adjust the working gas pressure to 0.5Pa, and perform reactive sputtering to synthesize AlN thin film. After 20min, turn off the power supply, stop the gas supply, and stop the sample stage rotation; Step 3: Place the synthesized AlN template into the vacuum chamber of the ion implantation equipment, install the Mg target, and adjust the background vacuum degree of the vacuum chamber of the ion implantation equipment to 8×10 -5 Pa and heated to 500 °C, turned on the ion implantation source, adjusted the ion implantation energy to 200 keV, the ion beam current to 100 mA, and the ion implantation dose to 1.0 × 10 15 atoms / cm 2 , open the baffle, when the ion implantation metering reaches a preset value, close the baffle, turn off the ion source, wait until the temperature of the workpiece drops below 100° C., and then turn off the vacuum system; Step 4: Take steps 2 and 3 as a cycle. The AlN thickness in each cycle is 200 nm. Repeat 10 cycles. The total film thickness is 2000 nm. The grain size of the AlN film is 100 nm. The Mg doping concentration is 1×10 20 cm -3 ; Step 5. After 8 cycles, take out the sample, stack the sample with the AlN film face to face, put it into a corundum crucible for annealing, and then press it with a corundum block. Put the corundum crucible with the sample into the center of the quartz tube of the tube furnace. After installation, pass N 2The air in the quartz tube was exhausted, and then the heating program was set to increase the temperature to 1400℃, with a heating rate of 10℃ / min. After reaching the target temperature, the temperature was kept for 60min, and N 2 The purging time is 50 minutes, then the heating is stopped and cooled to room temperature at a cooling rate of 5°C / min. After reaching the appropriate temperature, the sample is taken out, ultrasonically cleaned with alcohol, and stored in a vacuum bag after drying.

[0027] The technical solution of the present invention has the following beneficial effects: 1. Low-temperature synthesis and CMOS compatibility: AlN thin films are deposited at room temperature to 100°C by magnetron sputtering, breaking through the high-temperature limit of more than 1400°C of traditional processes, reducing the synthesis temperature by more than 90%, avoiding thermal damage to CMOS integrated circuits, and realizing direct integration of AlN thin films and silicon-based devices.

[0028] 2. Efficient and controllable P-type doping, using multi-cycle ion implantation of Mg ions combined with gradient energy regulation (50~200keV) to achieve a hole concentration of 1×10¹ 8 ~5×10¹ 9 cm - ³, which is 2 orders of magnitude higher than the traditional doping method; through step annealing (1400℃ / 30 min), the acceptor activation rate is increased to more than 60%, the self-compensation effect is effectively suppressed, and the square resistance is reduced to 8~20 Ω / sq.

[0029] 3. Enhanced radiation resistance, polycrystalline AlN film is 1×10¹ 6 cm - ²After proton irradiation, the conductivity decay is <5%, and the dark current increase is ≤10%, which is significantly better than single crystal AlN (attenuation>30%), meeting the reliability requirements of space detectors and nuclear radiation environment devices.

[0030] 4. Process scalability and cost advantages: compatible with 8-inch semiconductor production line equipment, film thickness uniformity of ±3%, single-wafer production cost reduced by 70% (single-wafer cost of embodiment ≤$15); cyclic deposition (single cycle ≤30 min) combined with rapid annealing, total production cycle shortened by 50%, energy consumption reduced by 45%.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for low-temperature synthesis of a P-type AlN polycrystalline thin film, characterized in that: The following steps are involved: Step 1: Substrate pretreatment: select a single crystal high temperature resistant substrate, remove the surface oxide layer by HF acid cleaning, and perform ultrasonic cleaning and dehydration and drying; Step 2: Depositing AlN thin film by magnetron sputtering, placing the substrate in a magnetron sputtering device, introducing a mixed gas of Ar and N2 under vacuum conditions, and performing reactive sputtering with an Al target to synthesize an AlN polycrystalline thin film; Step 3: Mg ion implantation, transferring the deposited AlN film to an ion implantation device, implanting Mg ions under vacuum conditions, and adjusting the ion energy, beam intensity, and implantation dose; Step 4: cyclic deposition and injection, repeating steps 2 and 3 until the target AIN film thickness is reached; Step 5: high temperature annealing treatment, stack the samples treated in step 4 in a crucible, anneal them in a N2 atmosphere, keep them warm and then slowly cool them to room temperature in the furnace.

2. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: The single crystal high temperature resistant substrate is a sapphire or SiC substrate.

3. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: In the step 1, the substrate is pickled using an HF acid solution with a concentration of not less than 5%, the pickling time is ≤10s, and the ultrasonic cleaning includes ultrasonic alcohol cleaning for ≥30min and ultrasonic deionized water rinsing for ≥30min.

4. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: In step 2, the vacuum degree of the vacuum chamber of the magnetron sputtering equipment is ≤1×10 - ³Pa, the flow ratio of Ar and N2 mixed gas is 10:1~5:1, the sputtering power of Al target is 180~250W, the working gas pressure is 0.4~0.5Pa, and the substrate temperature is regulated to 300~500℃.

5. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: In step 3, the vacuum degree of the ion implantation equipment is ≤1×10 -4 Pa, heating temperature is 300~500℃, ion implantation energy is 50~200keV, beam intensity is 1~100mA, and implantation dose is 1.0×10 13 ~1.0×10 15 atoms / cm².

6. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: In the step 4, the AlN film deposition thickness of each cycle is 100-200 nm, the number of cycles is 4-10 times, and the total film thickness of the AlN film is 0.4-2 μm.

7. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: In step 5, the annealing heating rate is 5-10°C / min, the holding time is 30-60 minutes, and the N2 purge time is ≥30 minutes.

8. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: In the step 5, the annealed sample needs to be slowly cooled to room temperature at a rate of ≤5°C / min.

9. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: The AlN film has a polycrystalline structure, a grain size of 20-100 nm, and a Mg doping concentration of 1×10¹ 8 ~1×10² 0 cm - ³.

10. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, characterized in that: The method further comprises step 6: post-processing, performing ultrasonic alcohol cleaning, drying and vacuum packaging on the sample annealed in step 5.

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