A low-temperature synthesis method for P-type AlN polycrystalline thin films

Abstract

This invention primarily proposes a low-temperature synthesis method for p-type AlN polycrystalline thin films, comprising the following steps: Step 1: Substrate pretreatment: providing a single crystal, high-temperature-resistant substrate and performing surface pretreatment; Step 2: Depositing an AlN thin film on the substrate via magnetron sputtering; Step 3: Implanting Mg ions into the AlN film; Step 4: Repeating Steps 2 and 3 until the target AlN film thickness is reached; Step 5: Annealing the AlN multilayer film. The invention advantageously enables low-temperature synthesis of AlN, reduces production costs, and achieves efficient and uniform p-type doping of AlN.

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), an ultra-wide bandgap semiconductor material (bandgap width up to 6.2 eV), has shown significant 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:

[0003] High-temperature synthesis limitations: The existing mainstream preparation technologies for AlN single crystal thin films (such as physical vapor transport and molecular beam epitaxy) need to be carried out at extreme temperatures above 1400°C. Not only does this rely on specially designed high-temperature resistant reaction chambers, which leads to a surge in costs, but the high-temperature process is fundamentally inconsistent with the low-temperature compatibility requirements of CMOS integrated circuits, seriously restricting its integrated application in the semiconductor chip field.

[0004] 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. Traditional thermal diffusion doping or in-situ co-sputtering doping is difficult to achieve high-concentration, uniformly distributed P-type carriers (hole concentration is usually less than 10¹ 7 cm⁻³), resulting in high ohmic contact resistance of the device and a sharp drop in luminous efficiency.

[0005] 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; while high-temperature annealing (>1600°C) after ion implantation can repair lattice damage, it in turn increases the thermal budget and process complexity.

[0006] These contradictions have resulted in the actual performance of AlN materials in optoelectronic and power devices being far below theoretical expectations, becoming a key obstacle to its large-scale commercial application. Therefore, developing a process for preparing AlN thin films that combines low-temperature synthesis, efficient P-type doping, and high crystalline quality has become an urgent need in the semiconductor materials field. Summary of the Invention

[0007] To solve the above problems, the present invention proposes a low-temperature synthesis method for P-type AlN polycrystalline thin films, comprising the following steps:

[0008] 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 drying;

[0009] Step 2: Deposit AlN film by magnetron sputtering. Place the substrate in a magnetron sputtering device, introduce a mixture of Ar and N2 gas under vacuum conditions, and use an Al target for reactive sputtering to synthesize an AlN polycrystalline film.

[0010] Step 3: Mg ion implantation: transfer the deposited AlN film to the ion implantation equipment and implant Mg ions under vacuum conditions, adjusting the ion energy, beam intensity, and implantation dose.

[0011] Step 4: Cycle deposition and implantation, repeating steps 2 and 3 until the target AlN film thickness is reached;

[0012] Step 5: High temperature annealing treatment: stack the samples processed in step 4 in a crucible and anneal them in a N2 atmosphere. After keeping the temperature, slowly cool them to room temperature in the furnace.

[0013] Furthermore, the single crystal high temperature resistant substrate is a sapphire or SiC substrate.

[0014] 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 ≥30min and ultrasonic deionized water rinsing ≥30min.

[0015] Furthermore, 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 the Al target is 180~250W, the working gas pressure is 0.4~0.5Pa, and the substrate temperature is set at 300~500℃.

[0016] 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.

[0017] Furthermore, in step 4, the AlN film deposition thickness in 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.

[0018] Furthermore, 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.

[0019] Furthermore, in step 5, the annealed sample needs to be slowly cooled to room temperature at a rate of ≤5°C / min.

[0020] Furthermore, the AlN film has a polycrystalline structure with a grain size of 20~100nm and a Mg doping concentration of 1×10¹ 8 ~1×10² 0 cm⁻³.

[0021] Furthermore, the method further includes step 6: post-processing, in which the sample annealed in step 5 is ultrasonically cleaned with alcohol, dried, and vacuum packaged.

[0022] Therefore, the beneficial effects of the present invention are:

[0023] 1. Achieve low-temperature synthesis of AlN and reduce production costs. Currently, most commercially available methods for synthesizing AlN single crystal thin films use physical vapor transport and chemical vapor deposition. However, the synthesis temperatures of these methods are too high, which, on the one hand, is not conducive to integration with subsequent processes for semiconductor device fabrication. On the other hand, high synthesis temperatures not only increase production costs but also introduce a large number of thermal equilibrium defects. Magnetron sputtering can be used to synthesize AlN polycrystalline thin films at low temperatures, eliminating the need for specialized reactors and significantly reducing production costs.

[0024] 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 implanting multiple ions during the film growth phase, a uniform Mg ion concentration distribution can be ensured. Subsequent high-temperature rapid annealing can reduce the defect concentration within the crystal and promote the diffusion and migration of Mg ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flow chart of the steps of the present invention.

[0026] Figure 2 This is a cross-sectional microstructure image of an AlN multilayer polycrystalline film obtained on a single crystal sapphire surface in Example 2 of the present invention. DETAILED DESCRIPTION

[0027] 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

[0028] This embodiment includes the following steps:

[0029] Step 1. Select a single crystal sapphire or SiC substrate with a size of 5*5*0.43 mm, 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 10 seconds, ultrasonic alcohol cleaning for 30 minutes, and ultrasonic deionized water rinsing for 40 minutes.

[0030] 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 pump it to a vacuum of 1×10 -4 Pa, 80sccm Ar was introduced to pre-sputter the target at a power of 200W. After sputtering for 10 minutes, the DC power supply was turned off. Subsequently, 50sccm Ar and 5sccm N2 were introduced, the DC power supply was turned on, the shutter was opened, the sputtering power was set to 180W, the sample stage rotation speed was set to 10r / min, the substrate temperature was set to 300℃, and the working gas pressure was adjusted to 0.4Pa. AlN thin films were synthesized by reactive sputtering. After 10 minutes, the power supply was turned off, the gas supply was stopped, and the sample stage rotation was stopped.

[0031] 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 injection metering reaches the 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;

[0032] Step 4: Take steps 2 and 3 as one cycle. The AlN thickness in each cycle is 100 nm. Repeat 4 cycles. The total film thickness is 400 nm. The AlN film grain size is 20 nm. The Mg doping concentration is 1×10 18 cm -3 ;

[0033] Step 5. After 8 cycles, remove the sample, stack the sides of the sample with the AlN film face to face, place them in a corundum crucible specially used for annealing, and then press them with a corundum block. Place the corundum crucible containing the sample in the center of the quartz tube of the tubular furnace. After installation, introduce N2 to exhaust the air in the quartz tube, then set the heating program to 1400°C at a heating rate of 5°C / min. After reaching the target temperature, keep warm for 30 minutes, purge with N2 for 30 minutes during the process, then stop heating, cool to room temperature at a cooling rate of 3°C / min, and remove the sample after reaching the appropriate temperature. Perform ultrasonic alcohol cleaning, dry, and store in a vacuum bag. Example

[0034] This embodiment includes the following steps:

[0035] Step 1. Select a single crystal sapphire or SiC substrate with a size of 5*5*0.43 mm, 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 10 seconds, ultrasonic alcohol cleaning for 30 minutes, and ultrasonic deionized water rinsing for 40 minutes.

[0036] 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 pump it to a vacuum of 1×10 -4 Pa, 80sccm Ar was introduced to pre-sputter the target at a power of 200W. After sputtering for 10 minutes, the DC power supply was turned off. Subsequently, 50sccm Ar and 8sccm N2 were introduced, the DC power supply was turned on, the power was adjusted to 200W, the baffle was opened, the sample stage rotation speed was set to 10r / min, the substrate temperature was set to 400℃, and the working gas pressure was adjusted to 0.45Pa. AlN thin films were synthesized by reactive sputtering. After 15 minutes, the power supply was turned off, the gas supply was stopped, and the sample stage rotation was stopped.

[0037] 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, and 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 injection metering reaches the 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;

[0038] Step 4: Take steps 2 and 3 as one cycle. The AlN thickness in each cycle is 150 nm. Repeat 6 cycles. The total film thickness is 900 nm. The grain size of the AlN film is 50 nm. The Mg doping concentration is 1×10 19 cm -3 ;

[0039] Step 5. After 6 cycles, remove the sample, stack the sides of the sample with the AlN film face to face, place them in a corundum crucible specially used for annealing, and then press them with a corundum block. Place the corundum crucible containing the sample in the center of the quartz tube of the tubular furnace. After installation, introduce N2 to exhaust the air in the quartz tube, then set the heating program to 1400°C at a heating rate of 8°C / min. After reaching the target temperature, keep warm for 45 minutes, with a N2 purge time of 35 minutes during the process. Then stop heating and cool to room temperature at a cooling rate of 4°C / min. Remove the sample after reaching the appropriate temperature. Perform ultrasonic alcohol cleaning, dry it, and store it in a vacuum bag. Example

[0040] This embodiment includes the following steps:

[0041] Step 1. Select a single crystal sapphire or SiC substrate with a size of 5*5*0.43 mm, 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 10 seconds, ultrasonic alcohol cleaning for 30 minutes, and ultrasonic deionized water rinsing for 40 minutes.

[0042] 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 pump it to a vacuum of 1×10 -4 Pa, 80sccm Ar was introduced to pre-sputter the target at a power of 200W. After sputtering for 10 minutes, the DC power supply was turned off. Subsequently, 50sccm Ar and 5sccm N2 were introduced, the DC power supply was turned on, the power was adjusted to 250W, the baffle was opened, the sample stage rotation speed was set to 10r / min, the substrate temperature was set to 500℃, and the working gas pressure was adjusted to 0.5Pa. AlN thin films were synthesized by reactive sputtering. After 20 minutes, the power supply was turned off, the gas supply was stopped, and the sample stage rotation was stopped.

[0043] 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, and 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 / cm2 , open the baffle, when the ion injection metering reaches the 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;

[0044] Step 4: Take steps 2 and 3 as one 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 ;

[0045] Step 5. After 8 cycles, remove the sample, stack the sides of the sample with the AlN film face to face, place them in a corundum crucible specially used for annealing, and then press them with a corundum block. Place the corundum crucible containing the sample in the center of the quartz tube of the tubular furnace. After installation, introduce N2 to exhaust the air in the quartz tube, then set the heating program to 1400°C at a heating rate of 10°C / min. After reaching the target temperature, keep warm for 60 minutes, with a N2 purge time of 50 minutes during the process. Then stop heating and cool to room temperature at a cooling rate of 5°C / min. Remove the sample after reaching the appropriate temperature. Perform ultrasonic alcohol cleaning, dry, and store in a vacuum bag.

[0046] The technical solution of the present invention has the following beneficial effects:

[0047] 1. Low-temperature synthesis and CMOS compatibility: AlN films are deposited at room temperature to 100°C through magnetron sputtering, breaking through the high-temperature limit of over 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 films with silicon-based devices.

[0048] 2. Efficient and controllable P-type doping, using multi-cycle ion implantation of Mg ions combined with gradient energy adjustment (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%, effectively suppressing the self-compensation effect, and the square resistance is reduced to 8~20 Ω / sq.

[0049] 3. Enhanced radiation resistance, polycrystalline AlN film is 1×10¹ 6 After cm⁻² proton irradiation, the conductivity decay is <5% and the dark current increase is ≤10%, which is significantly better than single crystal AlN (attenuation >30%) and meets the reliability requirements of space detectors and nuclear radiation environment devices.

[0050] 4. Process scalability and cost advantages: compatible with 8-inch semiconductor production line equipment, film thickness uniformity of ±3%, and a 70% reduction in single-wafer production costs (single-wafer cost ≤$15 in the example embodiment); cyclic deposition (single cycle ≤30 min) combined with rapid annealing shortens the total production cycle by 50% and reduces energy consumption by 45%.

[0051] 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 scope of protection of the present invention.

Claims

1. A low-temperature synthesis method for P-type AlN polycrystalline thin films, 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 drying; Step 2: Depositing an AlN 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 using an Al target to synthesize an AlN polycrystalline film; Step 3: Mg ion implantation: transfer the deposited AlN film to the ion implantation equipment and implant Mg ions under vacuum conditions, adjusting the ion energy, beam intensity, and implantation dose. Step 4: cyclic deposition and implantation, repeating steps 2 and 3 until the target AlN film thickness is reached; Step 5: high temperature annealing treatment, stacking the samples treated in step 4 in a crucible, annealing in a N2 atmosphere, keeping the temperature, and then slowly cooling to room temperature in the furnace; 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 the Al target is 180~250W, the working gas pressure is 0.4~0.5Pa, and the substrate temperature is regulated to be 300~500°C; 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.

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 4, the thickness of the AlN film deposited in each cycle is 100-200 nm, the number of cycles is 4-10, and the total thickness of the AlN film is 0.4-2 μm.

5. 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.

6. 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 annealed sample needs to be slowly cooled to room temperature at a rate of ≤5°C / min.

7. The method for low-temperature synthesis of a P-type AlN polycrystalline thin film according to claim 1, wherein: 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.

8. 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 after annealing in step 5.

Images