CN107546112B - SiC ohmic contact structure and manufacturing method thereof - Google Patents

Abstract

The invention relates to a SiC ohmic contact structure and a manufacturing method thereof, comprising: manufacturing a SiC substrate; depositing a first Ni layer, a Ti layer, a second Ni layer, a TaSi ₂ layer and a Pt layer on the surface of the substrate in sequence; Annealing treatment is performed to complete the fabrication of the SiC ohmic contact structure. The SiC ohmic contact provided by the present invention improves the thermal stability and oxidation resistance of the ohmic contact.

Description

SiC ohmic contact structure and fabrication method thereof

technical field

The invention belongs to the field of silicon carbide device manufacturing, in particular to a SiC ohmic contact structure and a manufacturing method thereof.

Background technique

Compared with traditional germanium and silicon materials, the advantages of the third-generation wide-bandgap semiconductor silicon carbide mainly include: the electric field withstand capability is about ten times that of silicon materials, the band gap is about three times that of silicon materials, and the thermal conductivity is about silicon materials. triple etc. The above material characteristics make it show the incomparable advantages of traditional silicon-based devices under the conditions of extreme temperature (especially high temperature) and large voltage, high frequency and high power, and strong radiation.

Ohmic contact is one of the key factors for silicon carbide devices to be used in extreme environments such as high temperature and easy oxidation. Its purpose is to achieve the smallest possible voltage drop when the electrode is in a forward voltage. Guaranteed device performance. Assuming that the ohmic contact degrades or fails, it will inevitably affect the turn-on resistance of the device, and in severe cases, it will affect the performance of the device, and even cause the device to fail. Therefore, it is particularly necessary to design an ohmic contact electrode with good thermal stability and anti-oxidation.

At present, the problems of silicon carbide ohmic contact metal or alloy layer include weak oxidation resistance, which is oxidized in the air; poor thermal stability, degradation or failure at high temperature; low hardness, easy to be mechanically damaged and other shortcomings, these shortcomings will make The reliability of the ohmic contact electrode is reduced, which severely limits its application environment and scope, and further affects and limits the application scope and reliability of silicon carbide devices.

SUMMARY OF THE INVENTION

In view of the above background, the present invention aims to realize an ohmic contact structure with high temperature resistance and oxidation resistance and a manufacturing method thereof.

In one aspect, the present invention provides a method for fabricating a SiC ohmic contact structure, comprising:

(a) making SiC substrate;

(b) sequentially depositing a first Ni layer, a Ti layer, a second Ni layer, a TaSi ₂ layer and a Pt layer on the surface of the substrate;

(c) performing a first annealing treatment to complete the fabrication of the SiC ohmic contact structure.

In one embodiment of the present invention, step (a) may include:

(a1) selecting a 4H-SiC substrate and performing standard RCA cleaning on the 4H-SiC substrate;

(a2) using a plasma enhanced chemical vapor deposition (Plasma Enhanced Chemical VaporDeposition, PECVD) process to deposit an oxide layer with a thickness of 100 nm on the surface of the 4H-SiC substrate;

(a3) etching the oxide layer to form an ion implantation window, and using an ion implantation process to perform N ⁺ and P ⁺ ion implantation on the surface of the 4H-SiC substrate to form an N-type doped region and a P-type doped region;

(a4) The remaining oxide layer is etched away, and a second annealing treatment is performed.

In an embodiment of the present invention, in step (a3), the doping source of the N-type doping region is Al, and the doping concentration is 1.0×10 ²⁰ cm ⁻³ ; the doping of the P-type doping region is Al. The source was N, and the doping concentration was 3.0×10 ²⁰ cm ⁻³ .

In an embodiment of the present invention, the temperature of the second annealing treatment in step (a4) is 1700° C., and the annealing time is 30 minutes.

In one embodiment of the present invention, step (b) may include:

(b1) using a DC magnetron sputtering process to deposit the first Ni layer on the surface of the substrate; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 9.8nm/min;

(b2) using a DC magnetron sputtering process to deposit the Ti layer on the surface of the first Ni layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 2.9nm/min;

(b3) using a DC magnetron sputtering process to deposit the second Ni layer on the surface of the Ti layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 9.8nm/min;

(b4) using a radio frequency magnetron sputtering process to deposit the TaSi ₂ layer on the surface of the second Ni layer; the deposition power of the radio frequency magnetron sputtering process is 60W and the deposition rate is 2.9nm/min ;

(b5) Using a DC magnetron sputtering process to deposit the Pt layer on the surface of the TaSi ₂ layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 2.9nm/min.

In an embodiment of the present invention, the vacuum degree in the magnetron sputtering chamber during deposition is ≤5e ^-6 mTorr.

In one embodiment of the present invention, the thickness of the first Ni layer is 30 nm, the thickness of the Ti layer is 100 nm, the thickness of the second Ni layer is 30 nm, the thickness of the TaSi ₂ layer is 300 nm, and the thickness of the Pt layer is 30 nm. The thickness is 200nm.

In an embodiment of the present invention, the annealing temperature in the first annealing process in step (c) is 975° C., and the annealing time is 2 min.

In yet another aspect, the present invention provides a SiC ohmic contact structure, comprising: a SiC substrate, and a first Ni layer, a Ti layer, a second Ni layer, a TaSi ₂ layer and a Pt layer that are sequentially arranged on the SiC substrate Floor.

Compared with the prior art, the present invention provides a method for making an ohmic contact by using a Pt/TaSi ₂ /Ni/Ti/Ni/SiC structure, which improves the thermal stability and oxidation resistance of the ohmic contact; In air, it exhibits good IV characteristics at 500 °C, and no degradation occurs after 300 h of aging at 500 °C.

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the following briefly introduces the accompanying drawings used in the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

1 is a process flow diagram of a SiC ohmic contact provided by an embodiment of the present invention;

Fig. 2 is the XRD element diagram of a kind of Pt/Ti/SiC structure before and after annealing provided by the embodiment of the present invention;

3 is a scanning electron microscope image of a device surface after annealing provided by an embodiment of the present invention;

4 is an XRD elemental diagram of a Pt/TaSi ₂ /Ni/Ti/Ni/SiC structure before and after annealing provided by an embodiment of the present invention;

5 is an IV curve diagram of a Pt/TaSi ₂ /Ni/Ti/Ni/SiC, Ti/Pt structure N, P-type ohmic contact provided by an embodiment of the present invention after annealing at 975°C;

Fig. 6 is a kind of Pt/TaSi ₂ /Ni/Ti/Ni/SiC, Ti/Pt structure N, P-type ohmic contact characteristic on-resistance variation curve diagram with aging time provided by the embodiment of the present invention;

FIG. 7 is a layout of a CTLM structure provided by an embodiment of the present invention;

FIG. 8 is a microscope picture of a metal structure after peeling provided by an embodiment of the present invention; and

FIG. 9 is a cross-sectional view of a SiC ohmic contact structure according to an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

Please refer to FIG. 1. FIG. 1 is a process flow diagram of a SiC ohmic contact provided by an embodiment of the present invention, including:

(a) making SiC substrate;

(b) sequentially depositing a first Ni layer, a Ti layer, a second Ni layer, a TaSi ₂ layer and a Pt layer on the surface of the substrate;

(c) performing a first annealing treatment to complete the fabrication of the SiC ohmic contact structure.

Preferably, step (a) may comprise:

(a1) selecting a 4H-SiC substrate and performing standard RCA cleaning on the 4H-SiC substrate;

(a2) Utilize PECVD process to deposit an oxide layer with a thickness of 100 nm on the surface of the 4H-SiC substrate;

(a3) etching the oxide layer to form an ion implantation window, and using an ion implantation process to perform N ⁺ and P ⁺ ion implantation on the surface of the 4H-SiC substrate to form an N-type doped region and a P-type doped region;

(a4) The remaining oxide layer is etched away, and a second annealing treatment is performed.

Wherein, in step (a3), the doping source of the N-type doping region is Al, and the doping concentration is 1.0×10 ²⁰ cm ⁻³ ; the doping source of the P-type doping region is N, and the doping concentration is N is 3.0×10 ²⁰ cm ^-3 .

Further, the temperature of the second annealing treatment in step (a4) is 1700° C., and the annealing time is 30 min.

Preferably, step (b) may comprise:

(b1) using a DC magnetron sputtering process to deposit the first Ni layer on the surface of the substrate; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 9.8nm/min;

(b2) using a DC magnetron sputtering process to deposit the Ti layer on the surface of the first Ni layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 2.9nm/min;

(b3) using a DC magnetron sputtering process to deposit the second Ni layer on the surface of the Ti layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 9.8nm/min;

(b4) using a radio frequency magnetron sputtering process to deposit the TaSi ₂ layer on the surface of the second Ni layer; the deposition power of the radio frequency magnetron sputtering process is 60W and the deposition rate is 2.9nm/min ;

(b5) Using a DC magnetron sputtering process to deposit the Pt layer on the surface of the TaSi ₂ layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 2.9nm/min.

Wherein, the vacuum degree in the magnetron sputtering chamber during deposition in step (b) is ≤5e ^-6 mTorr.

Preferably, the thickness of the first Ni layer is 30 nm, the thickness of the Ti layer is 100 nm, the thickness of the second Ni layer is 30 nm, the thickness of the TaSi ₂ layer is 300 nm and the thickness of the Pt layer is 200 nm.

Preferably, the annealing temperature in the first annealing process in step (c) is 975° C., and the annealing time is 2 min.

Among them, the first Ni layer reacts with SiC, and the Ti layer can combine the C generated by the reaction between Ni and SiC, so as to prevent free C atoms from agglomerating on the surface, causing the surface to be rough or ineffective. As shown in FIG. 2 , FIG. 2 is an XRD element diagram of a Pt/Ti/SiC structure before and after annealing provided by an embodiment of the present invention. After annealing, the proportion of Ti is significantly reduced, while the proportion of TiC alloy is significantly increased.

The second Ni layer acts as the adhesion layer between the Ti layer and the TaSi ₂ layer, which can effectively reduce the annealing temperature so that the N/P type annealing can be performed at the same time, and at the same time, it can improve the contact surface appearance; as shown in Fig. 3, Fig. 3 is a scanning electron microscope image of the device surface after annealing provided in the embodiment of the present invention. It can be seen that the Ni layer also blocks the upward diffusion of Ti.

Further, the TaSi ₂ layer is the key to prevent the oxidation of the ohmic contact electrode, which can effectively block the downward diffusion of O. After annealing at 500 °C for 300 h in air, the proportion of O below the TaSi ₂ layer did not increase, indicating that The blocking effect of TaSi ₂ layer on O is remarkable. In addition, the decomposition of TaSi ₂ conforms to the exponential form, which makes the structure effective for a long time, and therefore, allows the structure to be exposed to air for aging tests. As shown in FIG. 4 , FIG. 4 is the XRD element diagram of a Pt/TaSi ₂ /Ni/Ti/Ni/SiC structure before and after annealing provided by the embodiment of the present invention, and each element basically maintains the original alloy structure, that is, the TaSi ₂ The slow decomposition keeps the structure of each metal layer basically unchanged.

The pure Ni/Pt and Ti/Pt structures in the present invention will fail in a short period of time in a high-temperature air environment. Ni/TaSi ₂ /Pt and Ti/TaSi ₂ /Pt structures are difficult to form a good P-type ohmic contact electrode. The Pt/TaSi ₂ /Ni/Ti/Ni/SiC structure achieves ohmic contact properties on both N and P substrates. Compared with the Ti/Pt structure with better performance in the vacuum or inert range, its properties are shown in Figure 5. 5 is an IV curve diagram of a Pt/TaSi ₂ /Ni/Ti/Ni/SiC, Ti/Pt structure N, P-type ohmic contact after annealing at 975°C provided by an embodiment of the present invention; the ohmic contact characteristics are good. The structure was subjected to high temperature and aging tests in the air, and no serious degradation occurred after 300 hours. At the same time, as shown in FIG. 6 , FIG. 6 is the characteristic on-resistance of a Pt/TaSi ₂ /Ni/Ti/Ni/SiC, Ti/Pt structure N, P-type ohmic contact provided by an embodiment of the present invention with aging time Change curve diagram; at room temperature and 500 ℃ high temperature conditions, measure its characteristic on-resistance and compare with Ti/Pt structure. That is, Pt/TaSi ₂ /Ni/Ti/Ni/SiC has good performance under high temperature and aging conditions, and has great advantages compared with the other structures above.

Embodiment 2

The present invention proposes a method for making SiC ohmic contact by utilizing a Pt/TaSi ₂ /Ni/Ti/Ni/SiC structure, including:

S201, selecting a 4H-SiC substrate, and performing standard RCA cleaning on the 4H-SiC substrate;

S202, using a PECVD process to deposit an _SiO2 oxide layer with a thickness of 100 nm on the 4H-SiC substrate;

S203, etching the oxide layer to form an ion implantation window, and implanting N ⁺ or P ⁺ ions into the 4H-SiC substrate to form a highly doped N region or P region and perform high temperature annealing;

S204, etching the remaining oxide layer;

S205, depositing a metal layer on the 4H-SiC substrate, the metal layer sequentially includes a first Ni layer, a Ti layer, a second Ni layer, a TaSi ₂ layer and a Pt layer from bottom to top;

S206, rapid annealing to form an ohmic contact.

Preferably, in step S203, the doping source of the N-type doping region is Al, and the doping concentration is 1.0×10 ²⁰ cm ⁻³ ; the doping source of the P-type doping region is N, and the doping concentration is 3.0×10 ²⁰ cm ^-3 . The high temperature annealing temperature was 1700° C. and the time was 30 min.

Preferably, in step S205, in the deposition method used, the first Ni layer, the Ti layer, the second Ni layer and the Pt layer are deposited by DC magnetron sputtering; the TaSi ₂ layer is deposited by radio frequency magnetron sputtering ;

The deposition power of the first Ni layer, the Ti layer, the second Ni layer and the Pt layer is 100W; the deposition power of the TaSi ₂ layer is 60W;

The deposition rate of Ti layer, TaSi ₂ layer and Pt layer is 2.9nm/min, and the deposition rate of the first Ni layer and the second Ni layer is 9.8nm/min; the vacuum degree of the chamber during deposition is ≤5e ^-6 mTorr;

The deposition gas flow rate of the first Ni layer and the second Ni layer is 24Ar/sccm, the deposition gas flow rate of the Ti layer and the Pt layer is 16Ar/sccm, and the deposition gas flow rate of the TaSi ₂ layer is 20Ar/sccm.

Further, the thickness of the first Ni layer is 30 nm, the thickness of the Ti layer is 100 nm, the thickness of the second Ni layer is 30 nm, the thickness of the TaSi ₂ layer is 300 nm, and the thickness of the Pt layer is 200 nm.

Wherein, the method for performing performance test on the ohmic contact structure in this embodiment is as follows:

Step 1: Select a 4H-SiC substrate, and perform standard RCA cleaning on the 4H-SiC substrate;

Step 2: deposit an oxide layer of SiO ₂ with a thickness of 100 nm on the 4H-SiC substrate by using the PECVD process;

Step 3: etching the oxide layer to form an ion implantation window, implanting N ⁺ or P ⁺ ions into the 4H-SiC substrate, forming a highly doped N region or P region and performing high temperature annealing;

Step 4: Use the mask to perform photolithography, form CTLM patterns, remove the primer, and use HF to remove the natural oxide layer and other impurities.

Further, the CTLM graph formed in step 4 is shown in FIG. 7 , and FIG. 7 is a layout of a CTLM structure provided by an embodiment of the present invention;

Preferably, in step 4, the HF ratio is HF:H ₂ O=1:20. Immerse in HF for 2 min, then rinse with water to remove the HF solution, and dry with N ₂ .

Step 5: sequentially depositing the first Ni layer, the Ti layer, the second Ni layer, the TaSi ₂ layer and the Pt layer on the SiC material;

Step 6: metal stripping and rapid annealing to form an ohmic contact structure and perform a performance test on the ohmic contact structure.

Further, the specific steps of metal stripping in step 6 are: placing the entire substrate material including the 4H-SiC substrate and the metal layer in acetone, soaking for about 10 hours until the metal layer on the photoresist layer is lifted, and then performing ultrasonic waves for about 3 minutes. Until the lifted metal completely falls off. As shown in FIG. 8 , FIG. 8 is a microscope picture of a metal structure after peeling according to an embodiment of the present invention; the metal ring is observed under a microscope without adhesion. The annealing conditions are a temperature of 975° C., in a protective atmosphere of an inert gas, and an annealing time of 2 min.

The present invention utilizes Pt/TaSi ₂ /Ni/Ti/Ni/SiC structure to make SiC ohmic contact. First, Ni reacts with SiC. The Ti layer can combine the C generated by the reaction between Ni and SiC, so as to avoid the accumulation of free C atoms on the surface, which may cause the surface to be rough or fail. After annealing, the proportion of Ti decreased significantly, while the proportion of TiC alloy increased significantly. The second Ni layer acts as the adhesion layer between the Ti metal layer and the TaSi ₂ metal layer, which can effectively reduce the annealing temperature so that N/P type annealing can be performed at the same time, and at the same time, it can improve the contact surface appearance, and the nickel layer also It has a blocking effect on the upward diffusion of Ti. The TaSi ₂ layer is the key to preventing the oxidation of the ohmic contact electrode. It can effectively block the downward diffusion of O. After 300h aging test, the proportion of O below the TaSi ₂ layer does not increase, indicating that the TaSi ₂ layer has a significant blocking effect on O.

Embodiment 3

Please refer to FIG. 9, which is a cross-sectional view of a SiC ohmic contact structure provided by an embodiment of the present invention; the SiC ohmic contact structure includes: a SiC substrate 1, and a first Ni layer 2 sequentially disposed on the SiC substrate , Ti layer 3 , second Ni layer 4 , TaSi ₂ layer 5 and Pt layer 6 .

To sum up, the principles and implementations of the present invention are described with specific examples in this paper, and the descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention; meanwhile, for those of ordinary skill in the art, According to the idea of the present invention, there will be changes in the specific embodiments and application scope. In summary, the contents of this specification should not be construed as limitations to the present invention, and the protection scope of the present invention should be based on the appended claims. .

Claims (8)

1. a preparation method of SiC ohmic contact structure, is characterized in that, comprises: (a) Fabrication of SiC substrate; including: (a1) selecting a 4H-SiC substrate and performing standard RCA cleaning on the 4H-SiC substrate; (a2) Utilize PECVD process to deposit an oxide layer with a thickness of 100 nm on the surface of the 4H-SiC substrate; (a3) etching the oxide layer to form an ion implantation window, and using an ion implantation process to perform N+ and P+ ion implantation on the surface of the 4H-SiC substrate to form an N-type doped region and a P-type doped region; (a4) etching away the remaining oxide layer, and performing a second annealing treatment; (b) photolithography is performed on the surface of the substrate shown by the mask to form a CTLM pattern; the first Ni layer, the Ti layer, the second Ni layer, the TaSi ₂ layer and the Pt layer are sequentially deposited on the substrate surface; Wherein, the first Ni layer, the Ti layer and the second Ni layer are all deposited by a DC magnetron sputtering process; (c) performing a first annealing treatment to complete the fabrication of the SiC ohmic contact structure. 2 . The manufacturing method according to claim 1 , wherein the doping source of the N-type doping region in step (a3) is Al, and the doping concentration is 1.0×10 ²⁰ cm ⁻³ ; the P The doping source of the type doped region is N, and the doping concentration is 3.0×10 ²⁰ cm ^-3 . 3 . The manufacturing method according to claim 1 , wherein the temperature of the second annealing treatment in step (a4) is 1700° C., and the annealing time is 30 min. 4 . 4. The manufacturing method according to claim 1, wherein in step (b), successively depositing the first Ni layer, the Ti layer, the second Ni layer, the TaSi layer and the Pt layer on the surface of the substrate comprises: (b1) using a DC magnetron sputtering process to deposit the first Ni layer on the surface of the substrate; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 9.8nm/min; (b2) using a DC magnetron sputtering process to deposit the Ti layer on the surface of the first Ni layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 2.9nm/min; (b3) using a DC magnetron sputtering process to deposit the second Ni layer on the surface of the Ti layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 9.8nm/min; (b4) using a radio frequency magnetron sputtering process to deposit the TaSi ₂ layer on the surface of the second Ni layer; the deposition power of the radio frequency magnetron sputtering process is 60W and the deposition rate is 2.9nm/min ; (b5) Using a DC magnetron sputtering process to deposit the Pt layer on the surface of the TaSi ₂ layer; the deposition power of the DC magnetron sputtering process is 100W and the deposition rate is 2.9nm/min. 5 . The manufacturing method according to claim 4 , wherein, the vacuum degree in the magnetron sputtering chamber during deposition is less than or equal to 5e ^-6 mTorr. 6 . The manufacturing method according to claim 1 or 4, wherein the thickness of the first Ni layer is 30 nm, the thickness of the Ti layer is 100 nm, the thickness of the second Ni layer is 30 nm, and the thickness of the TaSi2 layer is 30 nm. The thickness is 300 nm and the thickness of the Pt layer is 200 nm. 7 . The manufacturing method according to claim 1 , wherein the annealing temperature in the first annealing process in step (c) is 975° C., and the annealing time is 2 min. 8 . 8. A SiC ohmic contact structure, comprising: a SiC substrate, and a first Ni layer, a Ti layer, a second Ni layer, a TaSi layer and a Pt layer that are sequentially arranged on the SiC substrate; wherein , the ohmic contact structure is fabricated and formed by the method according to any one of claims 1 to 7 .

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