Solid phase epitaxy of 3C—SiC on Si(001)

Abstract

A method of making a SiC buffer layer on a Si substrate comprising depositing an amorphous carbon layer on a Si(001) substrate, controlling the thickness of the amorphous carbon layer by controlling the time of the step of depositing the amorphous carbon layer, and forming a deposited film. A 3CSiC buffer layer on Si(001) comprising a porous buffer layer of 3CSiC on a Si substrate wherein the porous buffer layer is produced through a solid state reaction.

Claims

1. A method of making a SiC buffer layer on a Si substrate, comprising: depositing an amorphous carbon layer on a Si(001) substrate; controlling the thickness of the amorphous carbon layer by controlling the time of the step of depositing the amorphous carbon layer; forming a deposited film; annealing the deposited film and the Si(001) substrate; and forming a SiC buffer layer on the Si(001) substrate; wherein the step of depositing the amorphous carbon layer on the Si(001) substrate is by magnetron sputtering of a C target at room temperature at a rate of 0.8 nm/min.

2. The method of making a SiC buffer layer on a Si substrate of claim 1 wherein the Si(001) substrate is hydrogen passivated by chemical etching using hydrofluoric acid (HF), prior to the step of depositing a carbon layer, and wherein the deposited film has a root-mean-square roughness of about 0.3 nm.

3. The method of making a SiC buffer layer on a Si substrate of claim 2 wherein the deposited amorphous carbon film on the Si(001) substrate is annealed and wherein the step of annealing is at a temperature of from about 850 C. to about 950 C. for about 30 minutes.

4. The method of making a SiC buffer layer on a Si substrate of claim 1 wherein the magnetron sputtering comprises 15 sccm Ar flow, 3 mT pressure, and 100 W DC plasma power.

5. The method of making a SiC buffer layer on a Si substrate of claim 1 wherein the step of annealing at a temperature of about 950 C. comprises a ramp rate of about 1 C./sec and pressure below 210.sup.9 Torr.

6. The method of making a SiC buffer layer on a Si substrate of claim 1 wherein the method is via a solid state reaction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates an atomic force microscopy (AFM) image of as-deposited amorphous C film on Si(001), showing a root-mean-square (RMS) roughness of 0.3 nm.

(2) FIG. 2 illustrates an X-ray photoelectron spectroscopy (XPS) spectra for the C 1s and Si 2p signals for the 2 nm amorphous C film as-deposited, after annealing at 850 C. and 950 C. in ultrahigh vacuum (UHV) for 30 minutes.

(3) FIG. 3 illustrates a high-resolution transmission electron microscopy (HRTEM) image close to the [110] zone of Si of a 2 nm amorphous C thin film annealed at 950 C., showing the 3CSiC on top of Si(001). The HRTEM image shows the cube-on-cube orientation of Ge/SiC/Si layers. The fast Fourier transform (FFT) pattern generated from the box area shows a d-spacing between {111} planes consistent with that of 3CSiC including all three layers shows the orientation relation. An inverse fast Fourier transform image (IFFT) showing a set of misfit dislocations at the Ge/SiC interface.

(4) FIG. 4A illustrates a low-magnification multibeam image of Si, SiC and Si cap layers. The pores below the SiC epilayer in the Si substrate are indicated by white arrows. FIG. 4B illustrates an AFM image of the SiC surface showing a high density of pores.

(5) FIG. 5 illustrates a structure of the SiC/Si interface with C atoms and Si atoms. The large lattice mismatch results in dislocations at the interface that are spaced approximately every 4 Si lattice spacings and every 5 SiC lattice spacings. Planar averaged density of the acceptor band located 230 meV above the Si valence band. It is well localized at the interface.

DETAILED DESCRIPTION

(6) This invention demonstrates a new route for the synthesis of a 3CSiC buffer layer on Si(001) for the purpose of seeding subsequent epitaxial growth of 3CSiC on Si(001) for the integration of 3CSiC with Si electronic technology. The synthesis occurs by depositing and annealing an amorphous carbon film on Si(001), resulting in solid state epitaxy of a few nanometer thick crystalline 3CSiC layer on Si(001).

(7) This is a method of producing a porous SiC buffer layer on a Si substrate.

(8) This method concerns a solid state reaction with a pre-deposited amorphous C film at about 950 C. in ultrahigh vacuum (UHV).

Example 1

(9) The amorphous carbon layer is deposited on a hydrogen passivated Si(001) substrate by magnetron sputtering of a C target at room temperature at a rate of 0.8 nm/min. The layer thickness can be precisely controlled by deposition time.

Example 2

(10) The sputtering conditions were 15 sccm Ar flow, 3 mT total pressure, and 100 W DC plasma power.

(11) The deposited film exhibits a smooth surface morphology with a root-mean-square (RMS) roughness of 0.3 nm as determined by atomic force microscopy, as illustrated in FIG. 1.

Example 3

(12) The samples were then mounted on a Ta holder and transferred into an ultrahigh vacuum (UHV) system with a high-temperature heating stage. To form the SiC layer, samples were annealed at temperatures up to 950 C. for 30 minutes, with a ramp rate of 1 C./sec and pressure below 210.sup.9 Torr. The temperature was monitored by a thermocouple embedded in the heating stage.

(13) The formation of SiC is monitored by in situ x-ray photoelectron spectroscopy (XPS). Shown in FIG. 2 are XPS spectra for the C 1s and Si 2p signals for the as-deposited amorphous carbon film, and upon annealing at 850 and 950 C. The as-deposited C film exhibits a single carbon peak at 284 eV and doublet Si 2p peak at 99.5 eV with a broad hump at 102 eV. The feature at 102 eV is indicative of the formation of suboxides, which typically forms during or after the carbon deposition. For annealing below 850 C., no changes in the C 1s or Si 2p peaks were observed, indicating no reactions between the C and Si substrate.

(14) Upon annealing at 850 C., we observe the presence of a shoulder on the C 1s peak at 282.5 eV and the onset of a peak at 101.5 eV in the Si 2p spectra. These emerging features with shifts in binding energy are consistent with the formation of SiC bonds. The O 1s peak (not shown) is nearly absent indicating that the suboxide has either decomposed or desorbed at this temperature.

(15) Upon annealing at 950 C., a single C peak is observed at 282.5 eV, indicating a complete conversion of CC bonds to CSi bonds. Similarly, the Si 2p peak is now composed of two peaks; a doublet at 99.5 eV characteristic of the substrate, and a peak at 101.5 eV indicative of the SiC bond. These results indicate that initial SiC formation occurs at 850 C., and a complete SiC layer is formed at 950 C.

(16) FIG. 3 shows a high-resolution transmission electron microscopy (TEM) image of a sample annealed at 950 C. A 5 nm thick SiC is seen on top of the Si(001) with a high density of fine faults along {111} planes. The fast Fourier transform (FFT) close to the [110] zone axis generated from the box area containing a portion of Si and SiC is shown as an inset. The d-spacing of {111} planes of SiC, calibrated with respect to Si(111), is 2.51 , consistent with that of 3CSiC. The angle between two sets of SiC {111} planes is 70.5, confirming that it is fcc type. It exhibits a cube-on-cube orientation relationship that can be written as (1-11).sub.Si(1-11).sub.SiC and [110].sub.Si[110].sub.SiC. Note that the streaks seen along the [1-11] direction in the FFT pattern are due to the fine faults, which help relieves the strain due to the large lattice mismatch between SiC and Si.

(17) Pores tens of nanometers in diameter and 20 nm deep are also observed below the SiC epilayer in the Si substrate for samples annealed at 950 C., as illustrated in FIG. 4A. AFM observations also show pits spaced hundreds of nanometers apart on the surface of the SiC, where areas between pores exhibit a smooth morphology, consistent with the crystallization of the SiC. These observations of the pores are similar to those due to reactions with CO gas, which has been shown to help relieve strain and improve epilayer quality, and are formed here as a result of the outward diffusion of Si atoms to react with the C that are on the surface to form SiC.

(18) The structure and electronic properties of the SiC/Si interface is calculated by density functional theory (DFT). Many interfaces were examined with varying stoichiometries. The interface with the lowest free energy is shown in FIG. 5, which contains less than a monolayer of C at the interface. The large lattice mismatch results in dislocations at the interface that are spaced approximately every 4 Si lattice spacings and every 5 SiC lattice spacings. The Si valence band is found to be at 1.27 eV above the SiC valence band. Thus the conduction bands are nearly identical across the interface. One mid-gap state, an acceptor band 230 meV above the Si valence band, appears and is well localized at the interface. The planar averaged charge density is also shown.

(19) This all-solid thin film route offers a new approach for the solid phase epitaxy of a single crystalline 3CSiC buffer layer to seed the growth of high quality 3CSiC epilayer for the integration with Si MOS technology.

(20) The use of a pre-deposited amorphous C layer as the carbon source in place of gaseous species such as CO offers significant advantages that the SiC buffer layer is single cubic phase, works at a much lower temperature (950 C.) than those with gaseous species (1100-1300 C.), is compatible with MBE and with CVD.

(21) This new process also produces a porous SiC buffer layer which will relieve strain and improve crystallinity of the SiC epilayer. In addition, the SiC buffer layer can be much more precisely controlled down to the nanometer scale, by controlling the thickness of the amorphous carbon layer.

(22) Many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that the claimed invention may be practiced otherwise than as specifically described. Any reference to claim elements in the singular, e.g., using the articles a, an, the, or said is not construed as limiting the element to the singular.