An ohmic contact structure of a semiconductor device and a method of fabricating the same
By forming heavily doped polycrystalline SiC regions on the surface of a SiC single-crystal substrate and overcoming the grain boundary barrier using the quantum mechanical tunneling effect, the problems of SiC consumption and difficulty in reducing the barrier height in traditional methods are solved, and a simplified process and low contact resistance ohmic contact structure are realized.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SUZHOU LOONGSPEED SEMICON TECH CO LTD
- Filing Date
- 2026-06-10
- Publication Date
- 2026-07-14
AI Technical Summary
In traditional methods for fabricating ohmic contact structures for semiconductor devices, the reaction of Ni and SiC during high-temperature annealing to form Ni and Si compounds consumes SiC. This process involves numerous steps, and existing methods struggle to effectively reduce the barrier height.
An amorphous layer is formed by ion implantation on the surface of a SiC single-crystal substrate, and then transformed into a heavily doped polycrystalline SiC region by high-temperature activation annealing. A metal structure is then formed directly on the polycrystalline SiC region, and the grain boundary barrier is overcome by utilizing the quantum mechanical tunneling effect to form an ohmic contact.
It simplifies the process steps, avoids the consumption of SiC, reduces contact resistance, and improves the performance of ohmic contacts.
Smart Images
Figure CN122396024A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and more specifically, to an ohmic contact structure for a semiconductor device and a method for fabricating the same. Background Technology
[0002] Traditional methods for fabricating ohmic contact structures in semiconductor devices include the following steps: Step 1: On the Si surface of the 4H-SiC single crystal substrate 1, one of N, P, or Al is implanted by ion to form a concentration of 5 × 10⁻⁶. 19 cm -3 ~4×10 20 cm -3 The region was activated at a high temperature of 1700℃~1850℃ for 5~60 minutes, i.e., the 4H-SiC implantation region 2, as shown. Figure 1 ; Step 2: Deposit a Ni layer 31 using physical sputtering or evaporation, such as... Figure 2 ; Step 3: Annealing at 750°C completes the initial solid-state reaction: 2Ni + SiC → Ni2Si + C. Ni combines with Si to form Ni2Si, and free carbon C precipitates in the form of graphite. Ni2Si forms a uniform silicide layer, removes unreacted excess Ni, and eliminates residual Ni and free carbon C. Step 3 consumes SiC.
[0003] Step 4: Annealing at 1000°C or higher, Ni + SiC → NiSi + C, Ni combines with Si to form NiSi, free carbon C precipitates in the form of graphite, optimizing the interface structure, promoting carbon graphitization, and forming Ni Silicide layer 3, as shown. Figure 3 As shown. Step 4 reaction consumes SiC.
[0004] Step 5: Using physical sputtering or evaporation, deposit Ti layer 4, TiN layer 5, W layer 6, and AlCu layer 7 to ultimately form a low-resistivity ohmic contact, such as... Figure 4 .
[0005] In step 1: the concentration is 5×10 19 cm -3 ~3×10 20 cm -3 The region represents a conventional doping concentration. In this case, Ni Silicide layer 3 is essential. Ni Silicide layer 3 addresses the following two issues: 1. Stability of chemical bonds: The Si-C bond energy of SiC is extremely high and extremely difficult to break. When Ni is annealed at high temperature, it reacts with SiC, breaks the Si-C bond, and selectively combines with Si to form Ni2Si (nickel silicide), releasing C atoms, thereby creating a metal-rich interface layer on the SiC surface that is more conducive to conductivity.
[0006] 2. Engineering of work function: The formed Ni2Si layer has an effective work function that is more compatible with the conduction band bottom of SiC, which can effectively reduce the barrier height.
[0007] Therefore, the traditional methods for fabricating ohmic contact structures in semiconductor devices consume SiC and involve numerous process steps, which is a technical problem that urgently needs to be solved by those skilled in the art.
[0008] The information disclosed in the background section is only intended to enhance the understanding of the background of this application, and therefore may contain information that is not part of the prior art known to those skilled in the art. Summary of the Invention
[0009] This application provides an ohmic contact structure for a semiconductor device and its fabrication method, to solve the technical problems in the traditional fabrication method of ohmic contact structure for semiconductor devices, where the reaction of Ni and SiC to form Ni and Si compounds during high-temperature annealing consumes SiC, and the fabrication of Silicide involves high temperatures and numerous process steps.
[0010] This application provides a method for fabricating an ohmic contact structure for a semiconductor device, characterized by comprising the following steps: Step S11: In the ohmic contact region pre-defined on the surface of the SiC single crystal substrate, doping is performed by ion implantation. The doping concentration introduced by ion implantation is sufficient to damage the SiC lattice in the pre-defined ohmic contact region and form a continuous amorphous layer as an amorphous SiC region. Step S12: Perform high-temperature activation annealing to transform the heavily doped amorphous SiC region into a heavily doped polycrystalline SiC region; the doping concentration of the polycrystalline SiC region satisfies the requirement that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through the quantum mechanical tunneling effect. Step S13: A metal structure is formed directly on the heavily doped polycrystalline SiC region, wherein the contact between the polycrystalline SiC region and the metal structure is an ohmic contact.
[0011] This application also provides an ohmic contact structure for a semiconductor device, including: SiC single crystal substrate; Polycrystalline SiC region is a pre-defined ohmic contact region formed on the surface of SiC single crystal substrate. The doping concentration of the polycrystalline SiC region satisfies the requirement that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through the quantum mechanical tunneling effect. The metallic structure is formed directly on the heavily doped polycrystalline SiC region.
[0012] The embodiments of this application, by adopting the above technical solutions, have the following technical effects: The method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment has fewer steps, making the process simpler; no SiC is consumed in each step; and high-temperature activation annealing occurs only once. Attached Figure Description
[0013] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 A schematic diagram illustrating step 1 of the traditional method for fabricating ohmic contact structures in semiconductor devices; Figure 2 A schematic diagram illustrating step 2 of the traditional method for fabricating ohmic contact structures in semiconductor devices; Figure 3 A schematic diagram illustrating step 4 of the traditional method for fabricating ohmic contact structures in semiconductor devices; Figure 4 A schematic diagram illustrating step 5 of the traditional method for fabricating ohmic contact structures in semiconductor devices; Figure 5 This is a schematic diagram illustrating step S11 of the method for fabricating the ohmic contact structure of the semiconductor device according to an embodiment of this application. Figure 6 This is a schematic diagram illustrating step S12 of the method for fabricating the ohmic contact structure of the semiconductor device according to an embodiment of this application. Figure 7 This is a schematic diagram illustrating step S13 of the method for fabricating the ohmic contact structure of the semiconductor device according to an embodiment of this application. Figure 8 A TEM image with a spatial scale of 50 nm is obtained for step S21 of the method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment. Figure 9 A TEM image with a spatial scale of 100 nm is obtained for step S22 of the method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment. Figure 10 for Figure 9TEM image of the corresponding structure with a spatial frequency scale of 20 nm⁻¹ and Fast Fourier Transform (FFT); Figure 11 This is a comparison diagram of the ohmic characteristics of the ohmic contact structure of the semiconductor device prepared in Embodiment 2 of this application and the ohmic contact structure in the background art.
[0014] Figure label: SiC single crystal substrate 1, amorphous SiC region 81, polycrystalline SiC region 82. 4H-SiC implantation region 2, Ni layer 31, Ni Silicide layer 3, Ti layer 4, TiN layer 5, W layer 6, AlCu layer 7. Detailed Implementation
[0015] To make the technical solutions and advantages of the embodiments of this application clearer, the exemplary embodiments of this application will be described in further detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not an exhaustive list of all embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.
[0016] Example 1 The method for fabricating the ohmic contact structure of the semiconductor device according to embodiments of this application includes the following steps: Step S11: As Figure 5 As shown, in the ohmic contact region on the surface of the SiC single crystal substrate 1, doping is performed by ion implantation. The doping concentration introduced by ion implantation is sufficient to damage the SiC lattice in the ohmic contact region and form a continuous amorphous layer as an amorphous SiC region 81. Step S12: As Figure 6 As shown, high-temperature activation annealing is performed to transform the heavily doped amorphous SiC region into a heavily doped polycrystalline SiC region 82. The doping concentration of the polycrystalline SiC region 82 satisfies the requirement that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through the quantum mechanical tunneling effect. Step S13: A metal structure is formed directly on the heavily doped polycrystalline SiC region 82, and the contact between the polycrystalline SiC region and the metal structure is an ohmic contact.
[0017] The method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment has important steps, as follows: In step S11, a high-dose ion implantation is used to heavily dope the predetermined ohmic contact region on the surface of the SiC single crystal substrate. The doping concentration introduced by the ion implantation is sufficient to damage the SiC lattice in the predetermined ohmic contact region and transform it into an amorphous SiC region. The cumulative lattice damage in the predetermined ohmic contact region is the cause of amorphization. That is, step S11 transforms the SiC in the predetermined ohmic contact region into a heavily doped amorphous SiC region.
[0018] In step S12, since the doping concentration introduced by ion implantation is extremely high, for example, the doping concentration in the amorphous SiC region can be greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1×10 22 cm -3 Under the premise of this highly doped amorphous SiC region, high-temperature activation annealing is performed to transform the heavily doped amorphous SiC region into a heavily doped polycrystalline SiC region. The doping concentration of the polycrystalline SiC region satisfies the condition that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through the quantum mechanical tunneling effect.
[0019] The mechanism by which heavily doped amorphous SiC regions transform into heavily doped polycrystalline SiC regions is as follows: In step S11, the ohmic contact region pre-defined on the surface of the SiC single crystal substrate is doped by ion implantation: High-dose ion implantation exceeds the critical dose for amorphization, which first destroys the lattice structure of the SiC single crystal substrate. The ordered lattice structure at the ion implantation site in the SiC single crystal substrate is completely destroyed, resulting in lattice disorder and the formation of a continuous amorphous layer. This transforms the SiC in the preset ohmic contact region into a continuous amorphous layer, serving as a heavily doped amorphous SiC region. The presence of continuous amorphous layers in the heavily doped amorphous SiC region results in a lack of complete single-crystal templates as recrystallization guides during the high-temperature activation annealing process in step S12, thereby inducing the formation of polycrystalline phases and transforming the heavily doped amorphous SiC region into a heavily doped polycrystalline SiC region.
[0020] In step S13, the doping concentration of the heavily doped polycrystalline SiC region is greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1×10 22 cm -3 This means that the doping concentration of the polycrystalline SiC region is extremely high, sufficient to satisfy the requirement that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through quantum mechanical tunneling. With such a high doping concentration, a metal structure can be directly formed on top of the polycrystalline SiC region, and the contact between the polycrystalline SiC region and the metal structure is an ohmic contact.
[0021] The method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment has fewer steps, making the process simpler; no SiC is consumed in each step; and high-temperature activation annealing occurs only once.
[0022] In the background technology, step 1: "On the Si surface of the 4H-SiC single crystal substrate 1, one of N, P, or Al is implanted by ion implantation to form a concentration of 5×10⁻⁶." 19 cm-3~4×10 20 The region is 3 cm-3 in size and activated at a high temperature of 1700℃~1850℃ for 5~60 min, which is the 4H-SiC implantation region 2". Because the implantation dose is less than the critical threshold, it is only in the "point damage" mode. That is, the amorphous material in the 4H-SiC implantation region 2 is only distributed in a point-like manner. Therefore, during the high temperature activation at 1700℃~1850℃ for 5~60 min, the amorphous material recovers to single crystal. That is, after step 1, the 4H-SiC implantation region 2 is single crystal SiC.
[0023] Unlike the prior art, this application does not require the formation of a Ni Silicide layer 3. The reason is as follows: When the doping concentration of polycrystalline SiC regions is extremely high, the width of the space charge region at the grain boundaries of the polycrystalline SiC regions is extremely narrow, that is, the barrier layer is extremely narrow, and thus the grain boundary barrier is extremely small. At this time, majority carriers do not need to obtain thermal energy and can directly "penetrate" the grain boundary barrier (field emission) by means of the quantum mechanical tunneling effect, thereby forming an ohmic contact.
[0024] It is necessary to clarify the difference between the barrier layer of polycrystalline SiC and the macroscopic depletion region in the sense of single crystal: There is no macroscopic depletion region in polycrystalline SiC in the sense of a single crystal. The electrical behavior of polycrystalline SiC is mainly dominated by local barriers and defect states at grain boundaries. At nanoscale grain boundaries, a barrier layer similar to a "depletion region" can be observed in polycrystalline SiC. However, the barrier layer of polycrystalline SiC is caused by defects and interface states, rather than the classic PN junction formation mechanism in the sense of a single crystal.
[0025] Meanwhile, the polycrystalline SiC region structural feature in this application also brings the following key advantages: 1) The numerous grain boundaries in polycrystalline SiC act as impurity accumulation regions: The high density of grain boundaries in polycrystalline SiC provides segregation sites for dopant atoms. Under low or limited annealing conditions, impurities are enriched in the grain boundary region, thereby achieving extremely high effective carrier concentration in the local area.
[0026] Polycrystalline SiC contains a large number of grain boundaries, and the "large" number of grain boundaries is an inherent characteristic of polycrystalline SiC; while monocrystalline SiC has almost no grain boundaries.
[0027] The role of grain boundaries in polycrystalline SiC regions in providing segregation sites for doped atoms is as follows: First: Create localized high conductivity channels to reduce resistance. The segregation of doped atoms at grain boundaries is equivalent to laying out "nanoscale conductive paths" between grains with high resistivity. This effectively reduces the overall resistivity of the polycrystalline SiC region; Second: Utilize the "tunnel junction" effect to form a quasi-Ohmic contact. When the effective carrier concentration at the grain boundaries of polycrystalline SiC regions is extremely high, a very narrow barrier layer, similar to a "depletion region," is formed. Carriers can easily pass through this barrier layer via quantum tunneling, resulting in a quasi-ohmic contact with extremely low resistance. This is very useful at the interface between metals and polycrystalline SiC, facilitating the formation of good ohmic contacts.
[0028] 2) Defect-assisted tunneling: Dangling bonds and high-density defects at grain boundaries introduce abundant local states in the band gap, enabling carriers to be transported through defect-assisted tunneling, significantly enhancing interface conductivity and thus reducing contact resistance.
[0029] 3) In subsequent steps, Ti needs to be deposited on the surface of the polycrystalline SiC region. The work function of Ti is about 4.33 eV.
[0030] In the background art, a Ni layer 31 is formed in step 2. The work function of Ni is approximately 4.6 eV.
[0031] Compared to the prior art, Ti has a lower work function. Therefore, due to the lower height of the Schottky barrier formed between the Ti layer 31 and the polycrystalline SiC region, this application achieves a superior ohmic contact.
[0032] In practice, after high-temperature activation annealing in step S12, the amorphous SiC region 81 is transformed to include at least the polycrystalline SiC region 82 facing downwards from the top surface of the amorphous SiC region. In step S11, the pre-set doping concentration at position 82 of the polycrystalline SiC region during ion implantation is greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm -3 ; The thickness of the polycrystalline SiC region 82 is greater than or equal to 0.001 μm and less than or equal to 0.5 μm. The polycrystalline grain size of the polycrystalline SiC region 82 is less than or equal to 1500 μm. 2 .
[0033] In practice, after high-temperature activation annealing in step S12, the amorphous SiC region 81 is transformed and also includes a single-crystal SiC region 83 located below the polycrystalline SiC region 82. The doping concentration of the single-crystal SiC region 83 is greater than or equal to 5 × 10⁻⁶. 18 cm -3 And less than or equal to 4.0 × 10 20 cm -3 The thickness of the single-crystal SiC region 83 ranges from greater than or equal to 0.001 μm to less than or equal to 0.5 μm.
[0034] In practice, step S12, the high-temperature activation annealing step, is specifically as follows: The high temperature range is greater than or equal to 1700℃ and less than or equal to 1850℃, and the activation time range is greater than or equal to 5min and less than or equal to 60min.
[0035] In practice, SiC single crystal substrates include 4H-SiC, 6H-SiC, 3C-SiC, and 15R-SiC single crystal substrates.
[0036] In practice, in step S11, the dopant used for ion implantation is N, P, Al, Si, or Mg.
[0037] As an alternative approach, step S13 involves directly forming a metal structure on the heavily doped polycrystalline SiC region, specifically including: Ti layer, TiN layer, W layer and AlCu layer are deposited sequentially from bottom to top on the polycrystalline SiC region; Alternatively, Ni, Ti, TiN, W, and AlCu layers can be deposited sequentially from bottom to top on the polycrystalline SiC region.
[0038] As an alternative approach, step S13 involves directly forming a metal structure on the heavily doped polycrystalline SiC region, specifically including: An ohmic contact metal layer is deposited on the polycrystalline SiC region; wherein the ohmic contact metal layer includes one or more of ytterbium hexaboride, aluminum, silver, magnesium, scandium, indium, hafnium, uranium, cesium, potassium, and sodium; Ti layer, TiN layer, W layer, and AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer, or Ni layer, Ti layer, TiN layer, W layer, and AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer.
[0039] During implementation, physical sputtering or evaporation processes are used to deposit the various layers in the metal structure.
[0040] Example 2 TEM images are visualizations of microscopic structures or analytical data obtained through transmission electron microscopy (TEM). TEM images are physical images directly acquired from actual samples using TEM. These images are formed by irradiating the sample with a high-energy electron beam and capturing electrons that penetrate or are scattered by the sample, revealing the true structure and characteristics of materials at the nanoscale or even atomic scale.
[0041] The method for fabricating the ohmic contact structure of the semiconductor device in this application is a specific implementation of Embodiment 1.
[0042] Figure 8 A TEM image with a spatial scale of 50 nm is obtained for step S21 of the method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment. Figure 9 A TEM image with a spatial scale of 100 nm is obtained for step S22 of the method for fabricating the ohmic contact structure of the semiconductor device in this application embodiment. Figure 10 for Figure 9 TEM image of the corresponding structure with a spatial frequency scale of 20 nm⁻¹ and Fast Fourier Transform (FFT).
[0043] like Figure 8 As shown, after completing step S21, an amorphous SiC region 81 is formed.
[0044] like Figure 9 As shown, after completing step S22, a polycrystalline SiC region 82 and a single-crystal SiC region 83 are formed.
[0045] like Figure 10 As shown, Figure 9 The FFT diffraction pattern 122 corresponds to region 82 of the polycrystalline SiC. The FFT diffraction pattern 122 exhibits typical polycrystalline diffraction ring characteristics.
[0046] The method for fabricating the ohmic contact structure of the semiconductor device according to embodiments of this application includes the following steps: Step S21: As Figure 8 As shown, in the predetermined ohmic contact region of the Si surface on the surface of a 4H-SiC single crystal substrate, N ions are implanted for doping. The doping concentration of the amorphous SiC region introduced by ion implantation is greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm-3 ; Step S22: As Figure 9 and Figure 10 As shown, high-temperature activation annealing is performed to transform the heavily doped amorphous SiC region into a heavily doped polycrystalline SiC region 82; the doping concentration of the polycrystalline SiC region ranges from greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm -3 The extremely high doping concentration in the polycrystalline SiC region is sufficient to allow majority carriers to overcome the grain boundary barrier directly through quantum mechanical tunneling; the doping concentration of the single-crystal SiC region 83 ranges from greater than or equal to 5 × 10⁻⁶. 18 cm -3 And less than or equal to 4.0 × 10 20 cm -3 ; Step S23: Form a metal structure directly on the heavily doped polycrystalline SiC region.
[0047] Figure 11 This is a comparison diagram of the ohmic characteristics of the ohmic contact structure of the semiconductor device prepared in Embodiment 2 of this application and the ohmic contact structure in the background art.
[0048] Figure 11 The horizontal axis represents the conduction voltage, and the vertical axis represents the conduction current. The steeper the slope of the curve, the smaller the contact resistance. For example... Figure 11 As shown, the curve of the ohmic contact structure of the semiconductor device of this application has a higher slope and a lower contact resistance.
[0049] Example 3 like Figure 7 As shown, the ohmic contact structure of the semiconductor device in this application embodiment includes: SiC single crystal substrate 1; Polycrystalline SiC region 82 is formed on the surface of a SiC single crystal substrate in a predetermined ohmic contact region. The doping concentration of the polycrystalline SiC region satisfies the requirement that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through the quantum mechanical tunneling effect. The metallic structure is formed directly on the heavily doped polycrystalline SiC region.
[0050] During implementation, such as Figure 9 As shown, the ohmic contact structure also includes: A single-crystal SiC region 83 is formed between the polycrystalline SiC region 82 and the single-crystal SiC substrate; The doping concentration of the single-crystal SiC region 83 is greater than or equal to 5 × 10⁻⁶. 18 cm -3And less than or equal to 4.0 × 10 20 cm -3 The thickness of the single-crystal SiC region 83 ranges from greater than or equal to 0.001 μm to less than or equal to 0.5 μm.
[0051] In practice, the doping concentration in the polycrystalline SiC region ranges from greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm -3 ; The thickness of the polycrystalline SiC region 82 is greater than or equal to 0.001 μm and less than or equal to 0.5 μm. The polycrystalline grain size of the polycrystalline SiC region 82 is less than or equal to 1500 μm. 2 .
[0052] As an alternative, the metal structure includes: An ohmic contact metal layer is formed on the polycrystalline SiC region; wherein the ohmic contact metal layer includes one or more of ytterbium hexaboride, aluminum, silver, magnesium, scandium, indium, hafnium, uranium, cesium, potassium, and sodium; Ti layer, TiN layer, W layer, AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer, or Ni layer, Ti layer, TiN layer, W layer, AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer.
[0053] Alternatively, the metal structure includes: like Figure 7 As shown, Ti layer, TiN layer, W layer and AlCu layer are deposited sequentially from bottom to top on the polycrystalline SiC region; Alternatively, Ni, Ti, TiN, W, and AlCu layers can be deposited sequentially from bottom to top on the polycrystalline SiC region.
[0054] The ohmic contact structure of the semiconductor device in this application embodiment can be prepared using the method for preparing the ohmic contact structure of the semiconductor device in this application embodiment, or it can be prepared using other methods.
[0055] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.
[0056] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.
Claims
1. A method for fabricating an ohmic contact structure for a semiconductor device, characterized in that, Includes the following steps: Step S11: In the ohmic contact region pre-defined on the surface of the SiC single crystal substrate, doping is performed by ion implantation. The doping concentration introduced by ion implantation is sufficient to damage the SiC lattice in the pre-defined ohmic contact region and form a continuous amorphous layer as an amorphous SiC region. Step S12: Perform high-temperature activation annealing to transform the heavily doped amorphous SiC region into a heavily doped polycrystalline SiC region; wherein, the doping concentration of the polycrystalline SiC region satisfies the condition that the majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region by means of the quantum mechanical tunneling effect. Step S13: A metal structure is formed directly on the heavily doped polycrystalline SiC region, wherein the contact between the polycrystalline SiC region and the metal structure is an ohmic contact.
2. The method for preparing the ohmic contact structure according to claim 1, characterized in that, In the step of doping via ion implantation in the pre-defined ohmic contact region on the surface of a SiC single crystal substrate: When the ion implantation dose exceeds the critical dose for amorphization, the lattice-ordered structure at the ion implantation site in the SiC single crystal substrate is completely destroyed, resulting in lattice disorder and the formation of a continuous amorphous layer, which serves as the amorphous SiC region.
3. The method for preparing the ohmic contact structure according to claim 1, characterized in that, In step S12, after high-temperature activation annealing, the amorphous SiC region (81) is transformed to include at least the polycrystalline SiC region (82) from the top surface of the amorphous SiC region downwards. In step S11, the doping concentration at the preset position of the polycrystalline SiC region (82) during ion implantation is greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm -3 ; The thickness of the polycrystalline SiC region (82) is greater than or equal to 0.001 μm and less than or equal to 0.5 μm. The polycrystalline grain size of the polycrystalline SiC region (82) is less than or equal to 1500 μm. 2 .
4. The method for preparing the ohmic contact structure according to claim 3, characterized in that, In step S12, after high-temperature activation annealing, the amorphous SiC region (81) is transformed to include a single-crystal SiC region (83) located below the polycrystalline SiC region (82). The doping concentration of the single-crystal SiC region (83) is greater than or equal to 5 × 10⁻⁶. 18 cm -3 And less than or equal to 4.0 × 10 20 cm -3 The thickness of the single-crystal SiC region (83) is greater than or equal to 0.001 μm and less than or equal to 0.5 μm.
5. The method for preparing the ohmic contact structure according to any one of claims 1 to 4, characterized in that, In step S12, the high-temperature activation annealing step is specifically as follows: The high temperature range is greater than or equal to 1700℃ and less than or equal to 1850℃, and the activation time range is greater than or equal to 5min and less than or equal to 60min.
6. The method for preparing the ohmic contact structure according to any one of claims 1 to 4, characterized in that, The SiC single crystal substrate is a 4H-SiC single crystal substrate; In step S11, the dopant used for ion implantation is N, and the doping concentration introduced by ion implantation is greater than or equal to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm -3 .
7. The method for preparing the ohmic contact structure according to any one of claims 1 to 4, characterized in that, SiC single crystal substrates include 4H-SiC, 6H-SiC, 3C-SiC, and 15R-SiC single crystal substrates; In step S11, the dopant used for ion implantation is N, P, Al, Si, or Mg.
8. The method for preparing the ohmic contact structure according to any one of claims 1 to 4, characterized in that, Step S13 involves directly forming a metal structure on the heavily doped polycrystalline SiC region, specifically including: An ohmic contact metal layer is deposited on the polycrystalline SiC region; wherein the ohmic contact metal layer includes one or more of ytterbium hexaboride, aluminum, silver, magnesium, scandium, indium, hafnium, uranium, cesium, potassium, and sodium; Ti layer, TiN layer, W layer, and AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer, or Ni layer, Ti layer, TiN layer, W layer, and AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer.
9. The method for preparing the ohmic contact structure according to any one of claims 1 to 4, characterized in that, Step S13 involves directly forming a metal structure on the heavily doped polycrystalline SiC region, specifically including: Ti layer, TiN layer, W layer and AlCu layer are deposited sequentially from bottom to top on the polycrystalline SiC region; Alternatively, Ni, Ti, TiN, W, and AlCu layers can be deposited sequentially from bottom to top on the polycrystalline SiC region.
10. An ohmic contact structure for a semiconductor device, characterized in that, include: SiC single crystal substrate; Polycrystalline SiC regions are formed on the surface of a SiC single-crystal substrate through pre-defined ohmic contact regions. Among them, the doping concentration of the polycrystalline SiC region satisfies the requirement that majority carriers can directly overcome the grain boundary barrier of the polycrystalline SiC region through the quantum mechanical tunneling effect. The metallic structure is formed directly on the heavily doped polycrystalline SiC region.
11. The ohmic contact structure according to claim 10, characterized in that, Also includes: A single-crystal SiC region (83) is formed between the polycrystalline SiC region (82) and the single-crystal SiC substrate; The doping concentration of the single-crystal SiC region (83) is greater than or equal to 5 × 10⁻⁶. 18 cm -3 And less than or equal to 4.0 × 10 20 cm -3 The thickness of the single-crystal SiC region (83) is greater than or equal to 0.001 μm and less than or equal to 0.5 μm.
12. The ohmic contact structure according to claim 11, characterized in that, The doping concentration in the polycrystalline SiC region ranges from 4.0 × 10⁻⁶ to 4.0 × 10⁻⁶. 20 cm -3 And less than or equal to 1.0 × 10 22 cm -3 ; The thickness of the polycrystalline SiC region (82) is greater than or equal to 0.001 μm and less than or equal to 0.5 μm. The polycrystalline grain size of the polycrystalline SiC region (82) is less than or equal to 1500 μm. 2 .
13. The ohmic contact structure according to claim 10 or 11, characterized in that, The metal structure includes: An ohmic contact metal layer is formed on the polycrystalline SiC region; wherein the ohmic contact metal layer includes one or more of ytterbium hexaboride, aluminum, silver, magnesium, scandium, indium, hafnium, uranium, cesium, potassium, and sodium; Ti layer, TiN layer, W layer, AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer, or Ni layer, Ti layer, TiN layer, W layer, AlCu layer are formed sequentially from bottom to top on the ohmic contact metal layer.
14. The ohmic contact structure according to claim 10 or 11, characterized in that, The metal structure includes: Ti layer, TiN layer, W layer, and AlCu layer are deposited sequentially from bottom to top on the polycrystalline SiC region; Alternatively, Ni, Ti, TiN, W, and AlCu layers can be deposited sequentially from bottom to top on the polycrystalline SiC.