N-type carbon-based semiconductor substrate and preparation method thereof

Abstract

A method of producing a semiconductor substrate by utilizing a bulk of sp3 carbon allotropes, such as diamond or diamond-like carbon, and treating the bulk with electron donor ions to form an n-type semiconductor 5 substrate is described. The ion radius of the donor ion is not more than 15% greater than or less than the atomic ion radius of the sp3 carbon allotrope. The invention further extends to semiconductor substrates and semiconductors having substrates prepared according to the invention.

Description

Technical Field

[0001] The present invention relates to an electric conductor, and more particularly to an n-type carbon-based semiconductor, a method for preparing the carbon-based semiconductor, and a substrate suitable for the semiconductor. Background Art

[0002] Diamond is a material with semiconductor properties superior to those of silicon (Si), germanium (Ge), or gallium arsenide (GaAs) used in traditional semiconductors. Specifically, diamond offers a higher bandgap, higher breakdown voltage, and greater saturation velocity, resulting in a significant increase in cutoff frequency and maximum operating voltage compared to devices made from, for example, Si, Ge, or GaAs. Furthermore, due to the very strong sp3 carbon bonds that structure the crystal, diamond has the highest thermal conductivity of any solid at room temperature and excellent electrical conductivity (after doping) in temperatures up to and exceeding 400°C. Therefore, diamond and any carbon allotrope containing sp3 carbon bonds have the potential for efficient semiconductor operation at high powers.

[0003] Diamond's advantages as a semiconductor have not been fully realized for a variety of reasons. While natural diamonds may be of device quality, their supply and sizes are limited and they are quite expensive. Furthermore, most natural diamonds are insulators, so electrically active impurities need to be introduced, or doped, to make them useful as semiconductors. However, doping diamonds via ion implantation has proven difficult because strong carbon bonds prevent the penetration of ionic impurities.

[0004] All known prior art implantation methods for diamond doping are high-energy ion implantation, such as is routinely performed with silicon to produce semiconductors (which are widely used commercially). However, high-energy ion implantation causes lattice damage to the crystal. This damage is partially reversible because diamond annealing temperatures are below its graphitization transition point. Complete conversion of the first 20% of the diamond film to graphite material appears inevitable. This damage occurs even when the implanted atoms are smaller than carbon, such as nitrogen ions. Damage can be much greater with dopant ions such as sodium or phosphorus, which are larger than carbon.

[0005] A second approach to producing device-quality diamonds is to synthesize them on a suitable substrate via a chemical vapor deposition (CVD) process. In this technique, a gaseous mixture containing a carbon supply, typically methane and hydrogen, is pyrolyzed above the substrate surface or injected into a high-frequency plasma. In this context, the substrate is either a very thin single-crystal diamond or small diamond crystals dispersed on another host substrate. Carbon-containing free radicals react to produce diamond crystals on the substrate, while the hydrogen present is converted to atomic hydrogen, which preferentially etches away graphite, leaving a primarily diamond film. This method allows for doping by introducing electrically active impurities into the bulk environment above the substrate, which are then incorporated into the diamond lattice during lattice synthesis. However, to date, oxygen addition has only been included in small percentages and at a constant rate. Furthermore, any additional gases used in various diamond processes (e.g., boron) are always included at a constant flow rate to influence real-time doping.

[0006] Using the teachings of the prior art, boron and oxygen can be reliably grown as substitutions into the diamond lattice at low pressures. Boron has useful electrical activity, providing p-type material, while nitrogen has been found to be electrically inactive during growth. Some prior art efforts have been made to produce n-type diamond by introducing phosphorus and alkali metals. Because the chemical incorporation of the impurities appears to be strongly dependent on growth addition, and the dopant feedstock forms long-lived volatile residues in the growth chamber, control of doping levels in the prior art is very crude. No known prior art allows for the reliable production of n-type diamond doped with any desired material without substantial lattice damage (implantation).

[0007] While diamond p-type and n-type impurities and technologies do exist today, there are no complementary diamond semiconductor processes with known impurities available.

[0008] Purpose of the invention

[0009] It is therefore an object of the present invention to produce n-type substrates from single crystal and polycrystalline diamond, and any other allotropic form of carbon containing sp3 carbon bonds, for use in the manufacture of electronic and optical devices, particularly semiconductor devices in diamond and diamond-based carbon (DLC). Summary of the Invention

[0010] According to the present invention, there is provided a method for producing a semiconductor substrate, comprising the following steps:

[0011] - Utilizes a host of sp3 carbon allotropes; and

[0012] - treating the body with electron donor ions, wherein the ionic radius of the donor ions is within 15% larger or smaller than the atomic ionic radius of the sp3 carbon allotrope to operatively form an n-type semiconductor substrate.

[0013] The body of sp3 carbon allotrope may be diamond; and the step of treating the body may comprise growing diamond by a chemical vapor deposition (CVD) process while intermittently adding a dopant (preferably oxygen) to hydrogen and methane gases during the CVD process, such that the oxygen dopant in the diamond grows as a layer through the bulk of the substrate during the CVD process.

[0014] Oxygen dopant may be added intermittently at less than 1:200 of the total introduced gas volume; and the ratio of methane to hydrogen may be 1:10 or less.

[0015] The treatment may be provided such that the temperature of the substrate on which diamond is deposited is between 900 and 1100 degrees Celsius, preferably between 950 and 1000 degrees Celsius.

[0016] The present invention further comprises the step of producing an n-type epitaxial layer using diamond.

[0017] According to another aspect of the present invention, the body of the sp3 carbon allotrope can be a diamond-like carbon (DLC) film; and the step of treating the body can include: growing the DLC film by a chemical vapor deposition (CVD) process in the presence of oxygen ions, so that oxygen is incorporated in the formation of sp2 and sp3 bonds, and an n-type dopant is generated through the bulk phase of the DLC.

[0018] The present invention further comprises the step of producing an n-type epitaxial layer using DLC.

[0019] According to another aspect of the present invention, a body of sp3 carbon allotrope may be treated by implanting an impurity (preferably either oxygen or nitrogen) into the body such that the implanted impurity acts as an n-type active impurity.

[0020] The present invention also provides that the step of implanting is provided at low energy with simultaneous annealing.

[0021] The implantation step may take place during a chemical vapor deposition (CVD) process, wherein the process alternates between growth and implantation, such that the grown layer reaches a thickness equal to the depth of the implant to be applied, and then the implant is applied.

[0022] The host of the sp3 carbon allotrope may be diamond or diamond-like carbon (DLC).

[0023] The present invention also provides the following step: using diamond or DLC to produce an n-type epitaxial layer.

[0024] According to another aspect of the present invention, there is provided a semiconductor substrate prepared according to any one of the aforementioned aspects.

[0025] According to yet another aspect of the present invention, a semiconductor is provided, comprising a substrate prepared according to any one of the above aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0027] Figure 1 Shown is a diode created with boron p-type and nitrogen n-type impurities in a diamond crystal. DETAILED DESCRIPTION

[0028] The present invention describes a method for producing a semiconductor substrate, which generally comprises the steps of utilizing a host of an sp3 carbon allotrope and treating the host by growing or implanting electron donor ions into the host to form an n-type semiconductor substrate. These donor ions include dopant ions that are considered defects in the sp3 carbon allotrope solid and have an ionic radius that is within 15% larger or smaller than the atomic ionic radius of the sp3 carbon allotrope solid. These dopant ions are also electron donors operable to form the n-type semiconductor substrate. Typical examples of suitable donor / dopant ions herein include, but are not limited to, oxygen and nitrogen. Therefore, any suitable electron donor ion may be used in accordance with the present invention, provided that the donor ion meets the aforementioned characteristics associated with the sp3 carbon allotrope used (which can be identified and is within the skill of one skilled in the art).

[0029] The semiconductor substrate can then be further processed and used as is known in the semiconductor art.The present invention therefore also includes semiconductor substrates prepared according to the present invention and semiconductors incorporated into these substrates.

[0030] In an embodiment of the present invention, the sp3 carbon allotrope includes diamond and diamond-like carbon (DLC), but can be further extended to other suitable sp3 carbon allotropes.

[0031] Using currently known methods for doping diamond with oxygen, oxygen is introduced in the gas phase in a microwave plasma in a manner that allows electrical conductivity only in the terminal layer of the diamond. Alternative methods of oxygen doping are also in practice. However, with this second ion implantation method, the oxygen achieves a limited implantation depth and a much lower conductivity than with the doping method of the present invention. For semiconductors, a high conductivity during forward bias is very important.

[0032] In a first exemplary embodiment of the present invention, the present invention has been developed to provide a method whereby the oxygen concentration in diamond can be precisely controlled during the synthesis of oxygen-doped diamond by a microwave plasma method, thereby increasing the bulk conductivity of the diamond. During this doping process, oxygen is doped into the diamond lattice, and the conductivity is generated not by oxygen and hydrogen terminated bonds in the bulk phase, but rather by oxygen donor electrons as described below.

[0033] During diamond synthesis, oxygen is introduced into the diamond body as an impurity in the gas phase to produce n-type semiconductor properties in the diamond. During the synthesis of oxygen-doped diamond by chemical vapor deposition (CVD) process, oxygen is introduced into the volatile reaction gas including hydrogen and methane. As a starting point, oxygen accounts for about 0.5% of the total of hydrogen, methane and oxygen. Oxygen is injected at a variable concentration flow rate. In the CVD chamber, the oxygen is decomposed into ions in the plasma. Subsequently, physics determines how the oxygen ions are incorporated into the diamond lattice as the crystal grows. A single crystal film or polycrystalline film of diamond containing oxygen atoms is grown on a diamond seed crystal substrate placed in a reactor, and an array of doping sites is produced as the crystal grows. Sometimes silicon wafers are also used as a substrate covered with nanodiamonds to allow the growth of polycrystalline thin film diamond over the entire wafer area.

[0034] The oxygen percentage used in the synthesis of this embodiment of the invention is preferably less than 1:200 of the total introduced gas volume. As described above, the introduced gases are oxygen, methane, and hydrogen. The ratio of methane to hydrogen in the reaction gas is preferably 1:10 or less. The temperature of the substrate on which the diamond is deposited is typically 900°C to 1100°C, preferably 950°C to 1000°C.

[0035] It should also be understood that, as mentioned above, the ratio of oxygen to the other two gases is important. First, there is a solid solubility limit, which limits the amount of oxygen that can naturally be incorporated into the diamond lattice. Violating this limit during CVD can affect the CVD process. More likely, it will form other molecules that are pumped out. Forcing more oxygen into the lattice using different methods may disrupt the structure, causing the characteristics of the diamond to change. Furthermore, if the oxygen impurity concentration is too high, the semiconductor properties will be replaced by metallic conductive properties. When performed correctly, the oxygen will form an epitaxial layer of n-type diamond material, which will facilitate semiconductor processing near the surface and also allow the creation of vertical BJT structures in the bulk phase.

[0036] To grow a single crystal film of single-crystal diamond, it is preferable to use a heteroepitaxially grown diamond or single-crystal diamond substrate. Any of the {111}, {110}, and {100} planes can be used, with the latter being preferred. As mentioned above, polycrystalline diamonds are also effective.

[0037] This will produce an n-type epitaxial diamond wafer, which serves as the basis (i.e., substrate) for diamond semiconductor processing.

[0038] In a second embodiment of the present invention, by expanding upon the aforementioned process of adding oxygen impurities to diamond synthesis, the present invention further provides for the inclusion of oxygen impurities in the synthesis of diamond-like carbon (DLC), a well-known allotrope of carbon containing sp3 bonds, to provide a cheaper alternative to "diamond electronics" and the flexibility to create transistor circuits with it. Because DLC production is a low-temperature process, it offers the potential and advantage of being able to sputter semiconductor coatings onto a wide range of surfaces. DLC has never before been used for anything other than coatings.

[0039] It should be understood that a critical parameter during DLC ​​production is the background pressure. Incorrect oxygen addition can negatively impact the background pressure, interfering with the formation of the desired sp3 carbon bonds. sp3 carbon bonds typically contribute at least 60% to the production of most DLCs. These bonds are responsible for diamond formation and the strength of DLC. The remainder is made up of sp2 bonds, which are weak and form graphite. By preventing the formation of sp3 bonds, DLC will not form. Therefore, controlling the background pressure is crucial.

[0040] This background pressure is the reason why ion guns are not suitable for simultaneous use during DLC ​​formation, as these ions will impact the target, thus disturbing the pressure and no sp3 bonds will form. Therefore, a uniform pressure is required throughout the DLC formation chamber.

[0041] According to a third embodiment of the present invention, an impurity such as oxygen or nitrogen is implanted into the bulk, allowing the implanted impurity to act as an n-type impurity. In this regard, the only remaining implantation method capable of growing oxygen-containing n-type epitaxial DLC layers (without interfering with sp3 bond formation) is by alternating oxygen implantation with DLC growth. In this case, a certain thickness is grown, and then an equivalent depth of a specific thickness is implanted using an appropriate implant voltage, minimizing damage so that the next growth cycle (deposition) can continue unimpeded. This n-type epitaxial DLC layer is an integral component in producing DLC ​​electronics. For certain structures, producing semiconductors without a prepared epitaxial layer foundation becomes more complex and expensive.

[0042] Now, using epitaxial layer wafers formed in diamond or DLC, this aspect will address the precise processing required to form n-channel FET or BJT types. Implantation is a surface technique that lends itself to creating shallow semiconductor circuits in the chosen semiconductor material (in this case, diamond). Because it is cubic, the diamond lattice presents similar problems to silicon, as implanting perpendicular to the surface would allow channels to form, and the implanted ions would end up being too deep or passing through the material.

[0043] Another aspect to consider is the size of the nitrogen ions. Since they are nearly identical in size to carbon in diamond crystals, these implanted particles easily fit between carbon atoms in the crystal lattice and pass directly through the diamond. Furthermore, as a lightweight ion, nitrogen does not readily affect the bound carbon. This lower weight cannot be overcome by greater momentum, as that would ensure the particles would pass through the diamond. Since nitrogen's ionic radius is within 15% larger or smaller than the atomic ionic radius of diamond or DLC, it is a suitable donor ion for the present invention.

[0044] Therefore, the present invention uses angled implantation (along with thermodynamic lattice distortion (vibration)) to create a better chance for nitrogen ions to strike diamond carbon atoms and enter the lattice as electrically active impurities with acceptable activation energy. 7 degrees from vertical, used in the silicon semiconductor field, is a good starting point. However, at this angle, at the implant voltage used by those skilled in the art of implantation, and in the absence of lattice distortion, acceptable results will not be provided. The desired result, determined by the design, should lead to the optimal choice of implant angle, implant energy, and target temperature.

[0045] An example might be an implant angle of 30 degrees from vertical, an implant energy of 10 kEV, and the diamond heated to 300 degrees Celsius.

[0046] Thus, exemplary embodiments one to three described above form an n-type semiconductor substrate that can be further processed according to the following examples. However, it should be understood that the specific design can vary depending on the specific purpose and will be well within the capabilities of those skilled in the art.

[0047] For example, an n-type epitaxial layer with a high concentration of n-type nitrogen implanted (paired with the known technique of boron p-type impurity implantation in the diamond lattice) will be used in a similar manner to other semiconductor processes to create wells, bias specific regions, create vertical BJT structures (for reference) or power circuits and horizontal structures to create the entire body of the entire semiconductor device. Figure 1 Shown is a diode created with boron p-type and nitrogen n-type impurities in a diamond crystal.

[0048] When using DLC ​​instead of diamond as the basis for semiconductor circuits, those skilled in the art don't necessarily favor successful impurity implantation due to its low implantation energy and lack of lattice structure. This is because DLC lacks a crystalline structure, so channeling is not an issue. DLC consists of regions that may have a nanocrystalline structure at one point, but is generally amorphous. This DLC structure requires higher implantation energies to achieve greater penetration due to the greater material disorder.

[0049] Semiconductors are made from crystals free of impurities, allowing precise control over the creation of electronic circuits. Like diamond, it is also a crystal. DLC consists of varying ratios of sp2 and sp3 bonds. The purest form, Ta-C (tetrahedral amorphous carbon), consists exclusively of sp3 CC bonds and is best suited for semiconductor processing. As long as the DLC material is an insulator, it can be implanted to create electronic circuits. However, if the DLC has a low conductivity level, it is not suitable for semiconductor processing because leakage and short circuits in the structure would render it unusable.

[0050] Using the DLC after adding oxygen as described above to produce a DLC n-type epitaxial layer wafer, it will be possible to inject n-type nitrogen by controlling the time and injection energy, and it will also be possible to inject p-type boron by controlling the time and injection energy to produce the desired semiconductor circuit. Wells and vertical circuits, not just horizontal circuits, can also be produced using known semiconductor technology. It should be understood that producing DLC ​​is a "cold" process. In order to perform nitrogen injection layer by layer (grating method) or only on the top layer, the DLC must be at an elevated temperature (above 300 degrees Celsius). Injection is only effective when the DLC material is heated.

[0051] Therefore, it can be asserted that the present invention overcomes or at least mitigates the shortcomings of the prior art. Thus, the present invention provides the ability to produce n-type substrates of sp3 carbon allotropes, such as diamond and DLC, for use in the fabrication of electronic and optical devices, particularly semiconductor devices of diamond and DLC. This provides applications such as higher operating frequencies for central processing units. The present invention also offers the benefit of semiconductors with reduced cooling requirements; they can operate at higher temperatures and are significantly smaller than conventional semiconductor circuits.

[0052] In order to provide what is believed to be the most useful and most easily understood description of the principles and conceptual aspects of the present invention, the description is presented by way of example only. In this regard, no attempt is made to show the structural details of the present invention in more detail than is necessary for a basic understanding of the present invention. The words used herein are words of description and illustration, not words of limitation.

Claims

1. A method for producing a semiconductor substrate, the method comprising the following steps: - Utilizes a host of sp3 carbon allotropes; as well as - treating the body with electron donor ions, wherein the ionic radius of the donor ions is within 15% larger or smaller than the atomic ionic radius of the sp3 carbon allotrope to operatively form an n-type semiconductor substrate.

2. The method according to claim 1, wherein The body of the sp3 carbon allotrope is diamond; and the step of treating the body includes: growing the diamond by a chemical vapor deposition (CVD) process while intermittently adding a dopant, preferably oxygen, to hydrogen and methane gases during the CVD process, such that the oxygen dopant in the diamond grows as a layer through the bulk of the substrate during the CVD process.

3. The method according to claim 2, wherein: The oxygen dopant is intermittently added at less than 1:200 of the total introduced gas volume; and wherein the ratio of the methane to the hydrogen is 1:10 or less.

4. The method according to claim 2 or 3, wherein: The treatment is provided such that the temperature of the substrate on which the diamond is deposited is between 900 and 1100 degrees Celsius, preferably between 950 and 1000 degrees Celsius.

5. The method according to claim 1, comprising the steps of: The diamond is used to create an n-type epitaxial layer.

6. The method according to claim 1, wherein The body of the sp3 carbon allotrope is a diamond-like carbon (DLC) film; and the step of treating the body includes: growing the DLC film by a chemical vapor deposition (CVD) process in the presence of oxygen ions, so that oxygen is incorporated in the formation of sp2 and sp3 bonds, generating n-type dopants through the bulk phase of the DLC.

7. The method according to claim 6, comprising the steps of: The DLC is used to produce an n-type epitaxial layer.

8. The method according to claim 1, wherein The body of the sp3 carbon allotrope is prepared by implanting an impurity, preferably either oxygen or nitrogen, into the body such that the implanted impurity serves as an n-type active impurity.

9. The method according to claim 8, wherein The implantation step is provided at low energy with a simultaneous annealing.

10. The method according to claim 8 or 9, wherein: The implantation step occurs during a chemical vapor deposition (CVD) process, wherein the process alternates between growth and implantation, so that the grown layer reaches a thickness equal to the depth of the implant to be applied, and then the implant is applied.

11. The method according to claim 10, wherein: The host of the sp3 carbon allotrope is diamond or diamond-like carbon (DLC).

12. The method according to claim 11, comprising the steps of: An n-type epitaxial layer is produced using the diamond or the DLC.

13. A semiconductor substrate prepared according to claim 1.

14. A semiconductor comprising a substrate prepared according to claim 1.

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