A high-voltage fast soft recovery diode with selective aluminum corrosion and its fabrication method

Abstract

This invention discloses a high-voltage fast soft recovery diode with selective aluminum corrosion and its fabrication method. The high-voltage fast soft recovery diode with selective aluminum corrosion has, from top to bottom, an anode Al layer and an anode high-concentration P layer. + Regions and low-concentration P regions, low-concentration drift N regions ‑ Zone, high-concentration cathode N + The anode region consists of an active P-type cathode AL layer; the anode region consists of an active P-type cathode AL layer. + The diode is composed of a region and a terminal P region, wherein the anode AL layer is disposed above the etching tank; the etching tank is disposed in the anode active region. This invention also discloses a method for fabricating this type of high-voltage fast soft recovery diode. The structure of this invention reduces the forward conduction voltage drop, significantly improves the surge current capability and reverse recovery softness factor, and achieves a better trade-off between forward conduction and reverse recovery characteristics.

Description

Technical Field

[0001] This invention belongs to the field of power semiconductor device manufacturing technology, and relates to a high-voltage fast soft recovery diode with selective aluminum corrosion and its manufacturing method. Background Technology

[0002] High-voltage direct current transmission uses press-fit IGBTs and IGCTs that are constantly evolving towards higher frequency, lower loss, higher reliability, and lower cost. This requires that the large-size, wafer-type freewheeling diodes connected in antiparallel have high withstand voltage, low leakage current, fast soft recovery characteristics, and a wide SOA (Safe Operating Area).

[0003] In high-voltage fast soft recovery diodes, fast and soft recovery are contradictory. Currently, fast and soft recovery characteristics are achieved through two methods: one is anode injection efficiency control technology, which controls the anode P... + The first is the doping concentration in the region; the second is carrier lifetime control technology, which combines proton irradiation and electron irradiation technology.

[0004] To improve the fast soft recovery characteristics of high-voltage diodes and minimize anode hole injection efficiency, low anode doping and a shallow junction depth are required. To achieve high blocking voltage, termination molding is necessary at the edge of the silicon wafer to reduce the surface electric field strength under reverse blocking. In high-voltage applications, beveled termination molding is widely used in high-voltage wafer diodes due to its simplicity and good high-voltage stability. However, beveled molding results in a larger termination size and requires a deep P-type junction to meet the blocking voltage requirement. Due to the high diffusion coefficient and good lattice matching of aluminum (AL) impurities, it is often used to form the deep junction P-type withstand voltage region in high-voltage, high-power applications. Therefore, the deep junction P-region requiring high withstand voltage contradicts the shallow junction P-region requiring fast soft recovery. Existing large-size, wafer-type high-voltage fast soft recovery diodes use boron and aluminum double diffusion to form the anode region, achieving high blocking voltage, although the boron-formed P-type junction... + While the diffusion concentration in the anode region is low, the hole injection efficiency is difficult to control due to the depth of the anode P-region, resulting in poor fast soft recovery characteristics. The use of a thicker anode region, lower anode injection efficiency, and lifetime control techniques leads to a relatively high forward voltage drop (2–5V) and poor surge current capability in existing fast soft recovery diodes. To meet the application requirements for low voltage drop, high surge current capability, high withstand voltage, and fast and soft electrical characteristics, the development of high-performance high-voltage fast soft recovery diodes is urgently needed. Summary of the Invention

[0005] The purpose of this invention is to provide a high-voltage fast soft recovery diode structure based on selective corrosion of aluminum and its fabrication method. This achieves high voltage withstand capability while solving the problems of high forward voltage drop, poor surge current capability, and poor reverse recovery characteristics.

[0006] The technical solution adopted in this invention is a high-voltage fast soft recovery diode with selective aluminum corrosion, wherein an anode Al layer and a high-concentration P layer are sequentially arranged from top to bottom. + Regions and low-concentration P regions, low-concentration drift N regions - Zone, high-concentration cathode N + The region and cathode AL layer also include an anode region and an etching tank, wherein the anode region is located below the anode AL layer and includes an active P + The corrosion tank, which is a pre-deposited AL corrosion zone, is located below the anolyte AL layer and at the anolyte active P zone. + Within the district.

[0007] The N-region thickness is 500–900 μm, and the concentration is 1 × 10⁻⁶ μm. 12 cm 3 ~2×10 14 cm 3 The active P + The depth of the zone is 5–10 μm, and the concentration is 1 × 10⁻⁶. 18 cm 3 ~5×10 18 cm 3 The depth of the terminal P region is 70–80 μm, and the concentration is 1 × 10⁻⁶. 14 cm 3 ~5×10 14 cm 3 High-concentration cathode N + The depth of the zone is 10–20 μm, and the concentration is 1 × 10⁻⁶. 20 cm 3 ~5×10 20 cm 3 ;

[0008] A method for fabricating a high-voltage fast soft recovery diode by selective etching of aluminum is implemented according to the following steps:

[0009] (1) Select original defect-free, dislocation-free, high-resistivity zone-melted irradiated single-crystal silicon wafers as N - The substrate material of the region, with a substrate concentration of 10. 12 ~10 14 cm -3 Crystal orientation <111> or <100> The silicon wafer thickness is 700-900μm, and the single crystal diameter is 4″≦6″.

[0010] (2) After standard RCA cleaning, the silicon wafer is placed into the aluminum pre-deposition process source tube, and aluminum is pre-deposited on both sides of the silicon wafer at low temperature to form a shallow junction P + N - P + structure;

[0011] (3) After coating and photolithography, and marking the silicon wafer in step (2) to distinguish between the anode and cathode, the aluminum in the active area of ​​the anode is selectively etched away, while all the pre-deposited aluminum on the entire cathode surface is etched away, with a thickness of 10-15 μm, forming a shallow junction P in the terminal area. + N - structure;

[0012] (4) After the silicon wafer is cleaned by standard RCA, the silicon wafer in step (3) is oxidized and diffused at high temperature using a special high-temperature diffusion furnace. The resulting oxide layer is used as a masking layer for subsequent phosphorus diffusion. A deep junction and low-concentration P-type withstand voltage region is formed in the terminal area. The P-type junction depth is 70-80 μm.

[0013] (5) Photoresist is applied to the silicon wafer in step (4), and after exposure and development, the cathode oxide layer is removed, exposing the cathode of the silicon wafer while the anode is protected by the oxide layer.

[0014] (6) After the silicon wafer in step (5) undergoes standard RCA cleaning, phosphorus pre-deposition is performed on its cathode surface. Then, the PSG layer, i.e., the phosphorus silicon glass layer, is removed from the surface using dilute HF acid. Next, a dedicated phosphorus-driven diffusion furnace is used for high-temperature oxidation diffusion to form N. + The junction depth is 10–20 μm;

[0015] (7) Photolithography of P on the silicon wafer in step (6) + A diffusion window is then established, followed by low-temperature pre-deposition of boron in the active region on the anode side, and then high-temperature propagation to form a surface concentration of 1e18cm⁻¹. -3 ~5e18cm -3 Low-concentration boron, junction depth 5–10 μm, yields P in the active region. + N - N + structure.

[0016] (8) Aluminum and alloy are evaporated on both sides of the silicon wafer in step (7);

[0017] (9) The silicon wafer from step (8) is laser-cut into a circular wafer with a diameter of 38-89 mm. Then, the mesa is shaped, etched, and coated with adhesive for protection. This forms a complete chip and completes the initial measurement of the reverse blocking voltage.

[0018] (10) Electronally process the chip from step (9). + Proton irradiation followed by annealing, with adjustment of the reverse recovery time t rr Reverse recovery charge Q rr And the reverse recovery softness parameter, and finally perform the final test. Final reverse recovery time t rr The time is controlled to be 5–15 μs, and the reverse recovery charge Q is obtained. rr The value is 5000–10000 μAs, and a final measurement is performed.

[0019] In step (2), aluminum is pre-deposited at low temperature, at a temperature of 850℃~1050℃, for a time of 30min~120min.

[0020] In step (4), the oxidation is carried out at high temperature, with a temperature of 1200℃~1250℃ and a time of 20h~30h.

[0021] In step (6), phosphorus pre-deposition is carried out at a temperature of 1000-1050℃ for 1-2 hours; the oxidation high-temperature diffusion is carried out at a temperature of 1200-1250℃ for 3-4 hours.

[0022] In step (7), the low-temperature pre-deposition of boron is carried out at a temperature of 900-1000℃ for 60-100 min; the high-temperature propulsion is carried out at a temperature of 1100-1200℃ for 3-4 h.

[0023] The manufacturing method of the high-voltage fast soft recovery diode of the present invention involves etching away the AL in the active region after pre-deposition of AL in the anode, while retaining the AL in the terminal region; after long-term, high-temperature diffusion, a deep junction, low-concentration P-type withstand voltage region is formed in the terminal region; other process methods are the same as those of conventional high-voltage diode processes.

[0024] Compared with existing conventional large-size wafer diode structures, the present invention has the following advantages:

[0025] The anode active region of the structure of this invention contains only P with low concentration and shallow depth. + The terminal region contains only a low-concentration P-type withstand voltage region. Therefore, the hole injection efficiency in the anode active region is significantly reduced, improving the device's fast and soft recovery characteristics. Furthermore, compared to existing structures, this invention achieves high withstand voltage while significantly reducing device thickness, resulting in a markedly lower forward conduction voltage drop and a significantly improved surge current capability, thus achieving a better trade-off between forward conduction and reverse recovery characteristics. Attached Figure Description

[0026] Figure 1(a) is a cross-sectional view of an existing high-voltage fast soft recovery diode.

[0027] Figure 1(b) is a cross-sectional view of the high-voltage fast soft recovery diode with aluminum selective corrosion according to the present invention.

[0028] Figure 2 This is a schematic diagram showing the location of the space charge region broadening and local lifetime control of the high-voltage fast soft recovery diode with aluminum selective corrosion according to the present invention.

[0029] Figure 3 This is a flowchart of the key process steps of the high-voltage fast soft recovery diode with aluminum selective corrosion of the present invention.

[0030] Figure 4 This invention relates to the manufacturing process of a high-voltage fast soft recovery diode with selective aluminum corrosion.

[0031] Figure 5 This is a schematic diagram comparing the forward conduction characteristics of the high-voltage fast soft recovery diode of the present invention with those of existing high-voltage fast soft recovery diodes.

[0032] Figure 6 This is a schematic diagram comparing the surge characteristics of the high-voltage fast soft recovery diode of the present invention with those of existing high-voltage fast soft recovery diodes.

[0033] Figure 7 This is a schematic diagram comparing the reverse breakdown characteristics of the high-voltage fast soft recovery diode of the present invention with those of existing high-voltage fast soft recovery diodes.

[0034] Figure 8 This is a schematic diagram comparing the reverse recovery characteristics of the high-voltage fast soft recovery diode of the present invention with those of existing high-voltage fast soft recovery diodes. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0036] Reference Figure 2 The high-voltage fast soft recovery diode structure of the present invention comprises, from top to bottom, an anode AL layer 11 and an anode high-concentration P layer 11. + Zone 21 and low-concentration P zone 22, low-concentration drift N - Zone 3, High-concentration cathode N + Zone 4 and cathode AL layer 51, also including anodic region and corrosion tank 12, wherein the anodic region is located below the anodic AL layer and includes active P + Zone 21 and terminal P zone 22, the corrosion tank is a pre-deposited AL corrosion zone, located below the anode AL layer 11 and the anode active P zone. + Within Zone 21.

[0037] N-region 3 thickness 500–900 μm, concentration 1×10 12 cm 3 ~2×10 14 cm 3 The anode active P + Zone 21 has a depth of 5–10 μm and a concentration of 1 × 10⁻⁶. 18 cm 3 ~5×10 18 cm 3 The depth of terminal P region 22 is 70–80 μm, and the concentration is 1 × 10⁻⁶. 14 cm 3 ~5×10 14 cm3 High-concentration cathode N + Zone 4 has a depth of 10–20 μm and a concentration of 1 × 10⁻⁶. 20 cm 3 ~5×10 20 cm 3 The N-region of the substrate has a concentration of 10. 12 ~10 14 cm -3 The thickness is 500–900 μm.

[0038] Compared with the existing high-voltage fast soft recovery diode structure in Figure 1(a) of the embodiment of the present invention, the high-voltage fast soft recovery diode structure of the embodiment in Figure 1(b) has only P in the active region on the anode side. + The region can reduce the overall thickness of the device and lower the forward voltage drop; at the same time, it significantly reduces the anode hole injection efficiency and improves the fast soft recovery characteristics.

[0039] refer to Figure 2 The working principle of the high-voltage fast soft recovery diode of the present invention is as follows:

[0040] During the reverse cutoff period, the terminal region is controlled by PN. - The junction has a breakdown voltage and can withstand the reverse cutoff electric field. Due to the bending effect of the PN junction, two additional electric field peaks are generated at the junction bend at the termination edge. In the active region, P... + N - Junction breakdown voltage, electric field passes through P + Within the region, but far from the anode surface area. During reverse recovery, due to the very low P-doping in the anode terminal region, the holes injected in the through-state are negligible, thus the anode has active P-type p ... + The region provides the primary hole injection, which significantly alleviates the current concentration effect at the terminal edge during reverse recovery, improving device reliability; due to the extremely low hole injection efficiency of the anode, N - The base region achieves a flipped carrier distribution, and the fast soft recovery characteristics are significantly improved.

[0041] The method for preparing the high-voltage fast soft recovery diode by selective aluminum corrosion of the present invention is carried out according to the following steps, the relevant process steps are as follows: Figure 3 , 4 As shown:

[0042] (1) Select original defect-free, dislocation-free, high-resistivity zone-melted irradiated single-crystal silicon wafers as N - The substrate material of the region, with a substrate concentration of 10. 12 ~10 14 cm -3 Crystal orientation <111> or <100> The silicon wafer thickness is 700-900μm, and the single crystal diameter is 4″≦6″.

[0043] (2) After standard RCA cleaning, the silicon wafer is placed into the aluminum pre-deposition process source tube, and aluminum is pre-deposited on both sides of the silicon single crystal wafer at a low temperature of 850℃~1050℃ for 30min~120min to form a shallow junction P + N - P + structure;

[0044] (3) After coating and photolithography, the silicon wafer from step (2) is marked to distinguish between the anode and cathode. The aluminum in the active region of the anode is selectively etched away, while all the pre-deposited aluminum on the entire cathode surface is etched away, with a thickness of 10-15 μm, forming a shallow junction P in the terminal region. + N - structure;

[0045] (4) After the silicon wafer is cleaned by standard RCA, the silicon wafer in step (3) is subjected to high-temperature oxidation diffusion in a special high-temperature diffusion furnace at a temperature of 1200℃~1250℃ for 20h~30h. The resulting oxide layer is used as a masking layer for subsequent phosphorus diffusion. A deep junction and low-concentration P-type withstand voltage region is formed in the terminal area. The junction depth of the P-type region is 70~80μm.

[0046] (5) Photoresist is applied to the silicon wafer in step (4), and after exposure and development, the cathode oxide layer is removed, exposing the cathode of the silicon wafer while the anode is protected by the oxide layer.

[0047] (6) After the silicon wafer from step (5) undergoes standard RCA cleaning, phosphorus pre-deposition is performed on its cathode surface at a temperature of 1000–1050°C for 1–2 hours. Then, the PSG (phosphosilicate glass) layer on the surface is removed using dilute HF acid. Following this, a dedicated phosphorus-propelled diffusion furnace is used for high-temperature oxidation diffusion at a temperature of 1200–1250°C for 3–4 hours, forming N… + The junction depth is 10–20 μm;

[0048] (7) In step (6), P is photolithographically patterned on the silicon wafer. + A diffusion window is established, followed by low-temperature pre-deposition of boron in the active region on the anode side at 900–1000 °C for 60–100 min, followed by high-temperature deposition at 1100–1200 °C for 3–4 h, resulting in a surface concentration of 1e18 cm⁻¹. -3 ~5e18cm -3 Low-concentration boron, junction depth 5–10 μm, yields P in the active region. + N - N + Structure. At this point, all high-temperature processes are complete, resulting in the device structure shown in Figure 1(b).

[0049] (8) Aluminum and alloy are evaporated on both sides of the silicon wafer in step (7);

[0050] (9) The silicon wafer from step (8) is laser-cut into a circular wafer with a diameter of 38-89 mm. Then, the mesa is shaped, etched, and coated with adhesive for protection. This forms a complete chip and completes the initial measurement of the reverse blocking voltage.

[0051] (10) Electronally process the chip from step (9). + Proton irradiation followed by annealing, with adjustment of the reverse recovery time t rr Reverse recovery charge Q rr And the reverse recovery softness parameter, and finally perform the final test. Final reverse recovery time t rr The time is controlled to be 5–15 μs, and the reverse recovery charge Q is obtained. rr The value is 5000–10000 μAs, and a final measurement is performed.

[0052] This invention relates to a high-voltage fast soft recovery diode. Taking a 4.5kV withstand voltage rating as an example, its various electrical characteristics were simulated using professional simulation software, and compared with the various electrical characteristics of existing high-voltage fast soft recovery diodes. The evaluation of each device characteristic is as follows:

[0053] 1) Forward conduction characteristics

[0054] Figure 5 This is a schematic diagram comparing the forward conduction characteristics of an existing high-voltage fast soft recovery diode with those of the high-voltage fast soft recovery diode of this invention. (At J = 50 A / cm) 2 At that time, the forward voltage drops of existing high-voltage fast soft recovery diodes and the high-voltage fast soft recovery diodes of the present invention were 1.82V and 2.19V, respectively, and the voltage drop of the structure of the present invention was reduced by 16.9%. Therefore, the high-voltage fast soft recovery diode of the present invention has lower conduction losses.

[0055] 2) Surge characteristics

[0056] Figure 6 This diagram illustrates a comparison of the surge characteristics of existing high-voltage fast soft recovery diodes and the high-voltage fast soft recovery diode of this invention. At both low and high current levels, the on-state voltage drop of the high-voltage fast soft recovery diode of this invention is significantly smaller than that of existing high-voltage fast soft recovery diodes, and the voltage change amplitude when the curve bends back clockwise is also smaller, indicating stronger surge current resistance.

[0057] 3) Reverse breakdown characteristics

[0058] Figure 7This diagram illustrates a comparison of the reverse breakdown characteristics of existing high-voltage fast soft recovery diodes and the high-voltage fast soft recovery diode of this invention. The reverse breakdown voltages of the present invention and the existing high-voltage fast soft recovery diodes are 5690V and 6010V, respectively, representing a 5.3% reduction. It is evident that although the voltage of the structure of this invention is slightly lower, it still fully meets the blocking voltage requirements.

[0059] 4) Reverse recovery characteristics

[0060] Figure 8 This diagram illustrates a comparison of the reverse recovery characteristics of existing high-voltage fast soft recovery diodes and the high-voltage fast soft recovery diode of this invention. Under the same test conditions, the reverse peak current density J of the present invention and existing high-voltage fast soft recovery diodes are shown. RM 290A / cm 2 and 320A / cm 2 The reverse recovery softness factors are 1.4 and 1, respectively. Compared with existing high-voltage fast soft recovery diodes, the reverse peak current density of the high-voltage fast soft recovery diode of this invention is reduced by about 6.5%, and the reverse recovery softness factor is increased by 40%, showing a significant improvement in soft recovery characteristics.

Claims

1. A method for fabricating a high-voltage fast soft recovery diode using selective aluminum corrosion, characterized in that, Includes the following steps: (1) Select original defect-free, dislocation-free, high-resistivity zone-melted single-crystal silicon wafers as N - The substrate material of the region, with an N-region concentration of 10. 12 ~10 14 cm -3 Crystal orientation <111> or <100> The silicon wafer thickness is 700~900um, and the single crystal diameter is 4″≦6″; (2) After standard RCA cleaning, the silicon wafer is placed into the aluminum pre-deposition process source tube, and aluminum is pre-deposited on both sides of the silicon wafer at low temperature to form a shallow junction P + N - P + structure; (3) After coating and photolithography, the aluminum in the active region of the anode is selectively etched away, while all the pre-deposited aluminum on the entire cathode surface is etched away, with a thickness of 10~15um, forming a shallow junction P in the terminal region. + N - structure; (4) After the silicon wafer is cleaned by standard RCA, the silicon wafer in step (3) is subjected to high-temperature oxidation diffusion in a special high-temperature diffusion furnace at a temperature of 1150℃~1250℃ for 15~20h. The resulting silicon dioxide layer is used as a masking layer for subsequent phosphorus diffusion, with a thickness of 1~2um. A deep junction and low-concentration P-type withstand voltage region is formed in the terminal area, with a junction depth of 70~80um. (5) Photoresist is applied to the silicon wafer in step (4), and after exposure and development, the cathode oxide layer is removed, exposing the cathode of the silicon wafer, while the anode is protected by the oxide layer. (6) After the silicon wafer in step (5) is cleaned using standard RCA, phosphorus pre-deposition is performed on its cathode surface. Then, the PSG, i.e., the phosphorus silicon glass layer, on the surface is removed with dilute HF acid. Next, a special phosphorus-driven diffusion furnace is used for high-temperature oxidation diffusion to form N + The junction depth is 10~20um; (7) P is photolithographically etched onto the silicon wafer in step (6). + A diffusion window is then established, followed by low-temperature pre-deposition of boron in the active region on the anode side, and then high-temperature propagation to form a surface concentration of 1e18cm⁻¹. -3 ~5e18cm -3 Low-concentration boron, junction depth 5~10 μm, P is obtained in the active region. + N - N + structure; (8) In step (7), aluminum is evaporated on both sides of the silicon wafer with a thickness of 10~25um, and then metallized at a temperature of 400~600℃; (9) The silicon wafer from step (8) is laser-cut into a circular wafer with a diameter of 38~89mm. Then, the mesa is shaped, etched and coated with adhesive for protection. This forms a complete chip and completes the initial measurement of the reverse blocking voltage. (10) Irradiate the chip from step (9) with electrons and adjust the reverse recovery time t. rr The reverse recovery charge Q is 5~15µs. rr The value is 5000~10000 uAs, and a final test is performed.

2. The method for fabricating a high-voltage fast soft recovery diode by selective corrosion of aluminum as described in claim 1, characterized in that: In step (2), aluminum is pre-deposited at low temperature, with a temperature of 850℃~1050℃ and a time of 30min~120min.

3. The method for fabricating a high-voltage fast soft recovery diode by selective corrosion of aluminum as described in claim 1, characterized in that: In step (4), the oxidation is carried out at high temperature, with a temperature of 1200℃~1250℃ and a time of 20h~30h.

4. The method for fabricating a high-voltage fast soft recovery diode by selective corrosion of aluminum as described in claim 1, characterized in that: In step (6), phosphorus pre-deposition is carried out at a temperature of 1000~1050℃ for 1h~2h; the oxidation high-temperature diffusion is carried out at a temperature of 1200℃~1250℃ for 3~4h.

5. The method for fabricating a high-voltage fast soft recovery diode by selective corrosion of aluminum as described in claim 1, characterized in that: In step (7), the low-temperature pre-deposition of boron is carried out at a temperature of 900~1000℃ for 60~100 min; the high-temperature propulsion is carried out at a temperature of 1100~1200℃ for 3~4 h.

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