CN116864379B - Method for preparing ohmic contact electrode - Google Patents
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- CN116864379B CN116864379B CN202311137558.XA CN202311137558A CN116864379B CN 116864379 B CN116864379 B CN 116864379B CN 202311137558 A CN202311137558 A CN 202311137558A CN 116864379 B CN116864379 B CN 116864379B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/0445—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising crystalline silicon carbide
- H01L21/048—Making electrodes
- H01L21/0485—Ohmic electrodes
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Abstract
The application relates to the field of semiconductors and discloses a preparation method of an ohmic contact electrode. The preparation method of the application uses Ti/Ni bimetal to deposit in turn, and then forms ohmic contact electrode after three independent anneals. Because Ti can react with C, carbon film or carbon cluster formed by C atoms accumulated near the interface and on the surface of metal is avoided, the surface morphology of the ohmic contact electrode is smooth, the specific contact resistance is lower, and the ohmic contact performance of SiC is improved. The three independent anneals enhance the adhesion of the contact interface and the use temperature is lower, so that the occurrence probability of point defects and expansion defects is reduced, and the performance and the reliability of the device are improved.
Description
Technical Field
The application relates to the field of semiconductors, in particular to a preparation method of an ohmic contact electrode.
Background
Silicon carbide (SiC) is one of wide-bandgap semiconductor materials rapidly developed in recent decades, and compared with widely-used semiconductor materials Si, gc and GaAs, siC materials have many advantages of wide-bandgap, high breakdown electric field, high carrier saturation drift rate, high thermal conductivity, high power density and the like, and are ideal materials for preparing high-temperature, high-power and high-frequency devices, but there are still many problems and difficulties in the manufacturing process of SiC devices, and the development of SiC devices is severely restricted. The ohmic contact electrode is an important process for preparing the SiC device, and the quality of the ohmic contact electrode directly influences the indexes such as device efficiency, gain, switching characteristics and the like when the device is applied under high-temperature high-power conditions.
For the ohmic contact electrode of the device, low specific contact resistivity and high stability are two important factors that determine the device performance. Therefore, in order to fully exert the advantages of the SiC material, the manufacturing process of the Europe contact electrode has very important positions in the device process. For N-type SiC, an alloy system based on Ni is deposited on heavily doped SiC and is subjected to one-time high-temperature rapid annealing, wherein the annealing temperature is generally higher than 900 ℃. However, the ohmic contact electrode prepared by the prior art has the problems of rough contact interface, poor adhesion and easy formation of carbon aggregation, and affects the quality and the characteristics of ohmic contact; moreover, because high-temperature rapid annealing is used, the SiC epitaxial layer is easy to excite to generate a large number of point defects and expansion defects, and the performance and the reliability of the device are affected.
Disclosure of Invention
Therefore, the application aims to provide a preparation method of an ohmic contact electrode, which can prevent a carbon film or a carbon cluster from being formed near an ohmic contact interface and on the surface of metal, so that the surface morphology of the ohmic contact electrode is smooth, the specific contact resistance is lower, and the performance of the ohmic contact electrode is improved; meanwhile, the occurrence probability of point defects and expansion defects is reduced, the performance and reliability of the semiconductor device are improved, and the method can be applied to the field of preparing metal oxide semiconductor field effect transistors (metal oxide semiconductor field effect transistors, MOSFETs).
In order to achieve the above object, as a first aspect of the present application, there is provided a method of manufacturing an ohmic contact electrode, comprising:
obtaining a SiC semiconductor device;
removing an interlayer dielectric (ILD: inter-Layer Dielectrics) layer on the SiC semiconductor device to expose an N+ region of the source region;
sequentially depositing a Ti metal layer and a Ni metal layer on the surface of the N+ region of the source region;
independent annealing is carried out for more than three times in a protective gas atmosphere, so that an ohmic contact electrode is formed; wherein the temperature of each independent annealing is not higher than 800 ℃, the temperature of the first independent annealing is lower than the highest value in all independent annealing temperatures, and the temperature of the last annealing is the lowest value in all independent annealing temperatures.
Optionally, the preparation method is carried out for 3-5 times in a protective gas atmosphere; further optionally, performing primary annealing in a protective gas atmosphere at 500-600 ℃, and cooling to room temperature after annealing; then carrying out secondary annealing in a protective gas atmosphere at 700-800 ℃, cooling to room temperature after annealing, and removing impurities precipitated on the surface; and then carrying out third annealing in a protective gas atmosphere at 400-500 ℃, and cooling to room temperature after annealing.
Optionally, the thickness of the Ti metal layer is 200-400 angstroms, and the thickness of the Ni metal layer is 500-1000 angstroms.
Optionally, starting from the first independent annealing, the time of each independent annealing is sequentially decreased; further alternatively, the time for each independent anneal is 180-400s.
Optionally, the protective gas atmosphere concentration of the three anneals is the same.
Optionally, the protective gas includes nitrogen and an inert gas.
Optionally, the obtaining the SiC semiconductor device includes: electrode patterns for ohmic contact are made on SiC wafers using photolithographic processes.
Compared with the existing preparation technology of the SiC ohmic contact electrode, the preparation method has at least the following beneficial effects:
the Ti/Ni double-layer metal is used for deposition and annealing treatment in turn, when the metal Ti reacts with the SiC alloy, a large number of C vacancies are easily formed on the surface of the SiC, the net electron concentration is increased, the specific contact resistance is reduced, and the ohmic contact performance is greatly improved finally;
the metal added with the Ti layer can react with C atoms decomposed by SiC, so that the phenomenon that the C atoms can accumulate near an interface and form a carbon film or a carbon cluster on the surface of the metal is avoided, and the surface morphology of an ohmic contact electrode is smooth;
the three independent rapid anneals are introduced to enhance the adhesion of a contact interface and reduce the contact resistance, and simultaneously, the metal and SiC are fully reacted, so that the surface morphology of the formed ohmic contact electrode is smoother, and the contact resistance is lower;
the rapid annealing temperature is reduced, the epitaxial defects caused by a high-temperature process are reduced, and the yield and the performance of the device are improved.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a undue limitation;
FIG. 1 is a schematic diagram showing the structure of an N-type SiC ohmic contact electrode prepared by the application;
fig. 2 is a schematic view showing the structure of a SiC semiconductor device for making an ohmic contact electrode according to the present application;
FIG. 3 is a schematic diagram of a structure of an isolation layer etched away from an ohmic contact electrode region;
FIG. 4 is a schematic diagram showing the structure after sequentially depositing a Ti metal layer and a Ni metal layer;
FIG. 5 is a schematic diagram showing the structure of a stable Ti/Ni/Si/TiC alloy formed in the ohmic contact electrode region by a first pre-annealing.
Detailed Description
The application discloses a preparation method of an ohmic contact electrode, and a person skilled in the art can properly improve the technological parameters by referring to the content of the text. It is expressly noted that all such similar substitutions and modifications will be apparent to those skilled in the art, and are deemed to be included in the present application. While the products and processes of the present application have been described in terms of preferred embodiments, it will be apparent to those skilled in the relevant art that the application can be practiced and practiced with modification and alteration and combination of the processes described herein without departing from the spirit and scope of the application. It will be apparent that the described embodiments are some, but not all, embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" and the like, if any, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element. Meanwhile, the embodiments of the present application and features in the embodiments may be combined with each other without collision.
In a first aspect of the present application, there is provided a method for manufacturing an ohmic contact electrode, comprising:
obtaining a SiC semiconductor device;
removing the interlayer dielectric layer on the SiC semiconductor device to expose the N+ region of the source region;
sequentially depositing a Ti metal layer and a Ni metal layer on the surface of the N+ region of the source region;
independent annealing is carried out for more than three times in a protective gas atmosphere, so that an ohmic contact electrode is formed; wherein the temperature of each independent annealing is not higher than 800 ℃, the temperature of the first independent annealing is lower than the highest value in all independent annealing temperatures, and the temperature of the last annealing is the lowest value in all independent annealing temperatures.
In the specific embodiment of the present application, the method for preparing the ohmic contact electrode of the present application will be described by taking SiCMOSFET as an example, and the description is used for further understanding of the preparation method of the present application, and does not constitute undue limitation of the present application;
the structural schematic diagram of the ohmic contact electrode formed by the SiCNMOSFET is shown in FIG. 1, wherein N+ represents an N-type heavily doped region, N-represents an N-type lightly doped region, and P+ represents a P-type heavily doped region; the first N+ region is a SiC substrate layer, the second N+ region and the P+ region are part of an active region of the semiconductor device, and the N-region is a SiC epitaxial layer.
In some embodiments of the present application, the obtaining a SiC semiconductor device includes: an electrode pattern of ohmic contact is made on the SiC wafer using a photolithographic process, which can be determined according to practical requirements, such as an electrode pattern for SiCMOSFET.
When a SiCMOSFET is taken as an example, the structural schematic diagram of the SiC semiconductor device is shown in fig. 2, where a first n+ region is taken as a substrate layer, and an N-region and an ILD layer as an epitaxial layer are sequentially disposed above the first n+ region; wherein, the epitaxial layer is adjacent to the upper surface and provided with a P+ region; and a second N+ region is arranged adjacent to the upper surface of the P+ region, and the P+ region and the second N+ region jointly form a part of the active region.
In some embodiments of the present application, the interlayer dielectric layer may be made of ILD materials conventional in the art, for example, LPTEOS (low pressure tetraethoxysilicate glass) +bpsg (borophosphosilicate glass) film structure.
In some embodiments of the present application, the isolation layer for removing the ohmic contact electrode region on the SiC semiconductor device may be removed by a wet process, for example, by using an etchant, and more specifically, using a BOE (Buffered Oxide Etch, buffer oxide etchant) that is typically mixed with water or ammonium fluoride and water to etch away the ILD film layer of the ohmic contact electrode region and expose the n+ region of the source region. In other embodiments of the present application, the exposed electrode area is cleaned after the isolation layer is removed, and the natural oxide layer on the surface is removed to prepare for subsequent metal deposition, and the schematic structure is shown in fig. 3.
In some embodiments of the application, when the Ti metal layer and the Ni metal layer are deposited, the deposition can be performed by adopting modes of direct current magnetron sputtering, reactive magnetron sputtering and the like, and the structural schematic diagram is shown in fig. 4; the metal Ni and the C atoms do not react with low efficiency, the metal Ti and the C atoms react with high efficiency, firstly, the Ti layer metal is deposited to react with the C atoms decomposed by SiC, so that the phenomenon that the C atoms accumulate near an interface and form a carbon film or a carbon cluster on the surface of the metal is avoided, the surface morphology of an ohmic contact electrode is smooth, a large number of C vacancies are formed on the surface of the SiC, the net electron concentration is increased, the specific contact resistance is reduced, and the ohmic contact performance is greatly improved finally; if the Ni layer is deposited first, the reaction efficiency with C atoms is lowered, and the expected effect cannot be achieved.
Meanwhile, the thicknesses of the Ti metal layer and the Ni metal layer also influence the ohmic contact performance; when the ohmic contact resistance is too thin, the ohmic contact resistance is increased, so that the on-resistance is further increased, and the performance of the device is affected; when too thick, the surface reaction is insufficient, the interface may be severely roughened, and ohmic contact resistance may be increased. Thus, the Ti layer thickness may be optimally 200-400 angstroms, e.g., 200 angstroms, 250 angstroms, 300 angstroms, 350 angstroms, 400 angstroms, etc., and the Ni layer thickness may be optimally 500-1000A, e.g., 500 angstroms, 550 angstroms, 600 angstroms, 650 angstroms, 700 angstroms, 750 angstroms, 800 angstroms, 850 angstroms, 900 angstroms, 950 angstroms, 1000 angstroms, etc.
In some embodiments of the present application, the first independent anneal is performed in a protective gas atmosphere at a temperature of 500 ℃ to 600 ℃, e.g., 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃, 560 ℃, 570 ℃, 580 ℃, 590 ℃, 600 ℃, etc., for a time T1, and after the anneal is completed, the temperature is reduced to room temperature. The first pre-annealing can soften the Ti layer and the Ni layer, the Ni and the Ti can mutually diffuse, and stable Ti/Ni/Si/TiC alloy is formed in the ohmic contact electrode area. After the first independent annealing is completed, unreacted metal on the surface of the ILD layer is stripped by using mixed solution of hydrofluoric acid and nitric acid (1:3), and preparation is carried out for the second independent annealing, and the structure diagram is shown in fig. 5.
In some embodiments of the present application, the second independent anneal is performed in a protective gas atmosphere at a temperature of 700 ℃ to 800 ℃, e.g., 710 ℃, 720 ℃, 730 ℃, 740 ℃, 750 ℃, 760 ℃, 770 ℃, 780 ℃, 790 ℃, 800 ℃, etc., for a time T2, and after annealing is completed, the temperature is reduced to room temperature. The second annealing promotes the Ti/Ni/Si/TiC alloy formed by the first pre-annealing to react sufficiently to generate more C vacancies on the SiC surface and at the same time generate ohmic alloy (including Ni 2 Si and NiSi, the main component being Ni 2 Si, less NiSi content), forming ohmic contact electrodes; after the second independent annealing is completed, impurity substances such as Ti/TiC and the like precipitated on the surface of the ILD layer are removed by using mixed solution of hydrofluoric acid and nitric acid (1:3), and the structural schematic diagram is shown in figure 1.
In some embodiments of the present application, the third independent annealing is performed in a protective gas atmosphere at a temperature of 400-500 ℃, such as 410 ℃, 420 ℃, 430 ℃, 440 ℃, 450 ℃, 460 ℃, 470 ℃, 480 ℃, 490 ℃, 500 ℃, etc., for a time T3, and the annealing is completed with a temperature reduction to room temperature. The third annealing is used for further reaction, so that the reaction is complete, the adhesiveness of an ohmic alloy contact interface is enhanced, the surface morphology of the formed ohmic contact electrode is smoother, the ohmic contact performance is improved, and the structural schematic diagram is shown in figure 1.
In some embodiments of the application, the protective gas atmosphere concentration is the same in the three independent annealing processes, which is to consider that the gas atmosphere concentration has little influence on the annealing effect, and the gas atmosphere concentration of each independent annealing is kept consistent for facilitating the process operation; in certain embodiments of the present application, the protective gas includes nitrogen and an inert gas including, but not limited to, argon, xenon, neon, radon, and the like.
In certain embodiments of the application, the preparation method is performed 3-5 independent anneals in a protective gas atmosphere; further optionally, performing primary annealing in a protective gas atmosphere at 500-600 ℃, and cooling to room temperature after annealing; then carrying out secondary annealing in a protective gas atmosphere at 700-800 ℃, cooling to room temperature after annealing, and removing impurities precipitated on the surface; and then carrying out third annealing in a protective gas atmosphere at 400-500 ℃, and cooling to room temperature after annealing.
In certain embodiments of the present application, the time for each independent anneal is sequentially decreased from the first independent anneal, i.e., T1> T2> … … > Tn, which can reduce high temperature damage to the device; taking three independent anneals as an example, the semiconductor device can be given a certain adaptation time by using a longer time of preheating (first annealing), so that the SiC wafer is prevented from warping due to temperature rise during the second annealing; and adding a third short annealing time can ensure the reaction to be complete. In other embodiments of the application, the time for each independent anneal is 180-400 seconds.
In the three annealing processes, the whole temperature is lower than the annealing temperature of the prior art, the annealing temperature is reduced, the process is easier to realize, the adhesion of a contact interface is enhanced, and the contact resistance is reduced. Meanwhile, the metal and SiC are fully reacted, and the formed ohmic contact electrode has smoother surface morphology and lower contact resistance.
The ohmic contact electrode prepared by the process of the application has the electric shock resistivity of less than 10 -6 Ω·cm 2 Compared with the surface morphology after annealing in the traditional Ni-based ohmic contact process, the surface morphology is smooth and has no carbon film or carbon clusters.
The foregoing is only a specific embodiment of the application to enable those skilled in the art to understand or practice the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A method of making an ohmic contact electrode, comprising:
obtaining a SiC semiconductor device;
removing the interlayer dielectric layer on the SiC semiconductor device to expose the N+ region of the source region;
sequentially depositing a Ti metal layer and a Ni metal layer on the surface of the N+ region of the source region;
performing three independent anneals in a protective gas atmosphere to form an ohmic contact electrode; wherein the temperature of each independent annealing is not higher than 800 ℃, the temperature of the first independent annealing is 500-600 ℃, and the annealing is followed by cooling to room temperature; then, carrying out secondary independent annealing in a protective gas atmosphere at 700-800 ℃, cooling to room temperature after annealing, and removing impurities precipitated on the surface; and then, performing third independent annealing in a protective gas atmosphere at 400-500 ℃, cooling to room temperature after annealing, wherein the temperature of the last annealing is the lowest value of all independent annealing temperatures.
2. The method of claim 1, wherein the Ti metal layer has a thickness of 200-400 angstroms.
3. The method of claim 1, wherein the Ni metal layer has a thickness of 500-1000 angstroms.
4. The method of claim 1, wherein the time for each independent anneal decreases in sequence from the first independent anneal.
5. The method of claim 4, wherein each independent anneal is performed for a period of 180 to 400 seconds.
6. The method of claim 1, wherein the protective gas atmosphere concentration is the same for the three anneals.
7. The method of claim 1 or 6, wherein the protective gas comprises nitrogen and an inert gas.
8. The method of manufacturing according to claim 1, wherein the obtaining a SiC semiconductor device comprises: electrode patterns for ohmic contact are made on SiC wafers using photolithographic processes.
9. The method of claim 1, wherein the temperature of the first independent anneal is: 510 ℃, 520 ℃, 530 ℃, 540 ℃, 550 ℃, 560 ℃, 570 ℃, 580 ℃, 590 ℃, or 600 ℃.
10. The method of claim 1, wherein the third independent annealing is performed at a temperature of: 410 ℃, 420 ℃, 430 ℃, 440 ℃, 450 ℃, 460 ℃, 470 ℃, 480 ℃, 490 ℃, or 500 ℃.
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