KR20010006514A - Process for obtaing diamond layers by gaseous-phase synthesis - Google Patents

Abstract

The present invention provides a method for obtaining a diamond layer by vapor phase synthesis comprising generating a glow discharge of direct current at a discharge gap between a cathode and an anode in hydrogen flow. The substrate is heated at a temperature of 700-900 ° C. and the diamond layer is 0.3-2 Deposited on dielectric and conductor substrate at discharge current density. The deposition takes place to synthesize the carbon-containing gas and hydrogen. At this time, the carbon-containing gas has a concentration of 3 to 10% in the flow of gas. Graphite surplus of the discharge in the hydrogen stream is removed for 5-10 minutes. The carbon-containing gas is composed of methane at a concentration of 3 to 8% and the substrate is grounded or insulated from the discharge gap 0.1 to 5 mm away from the anode. The anode is made by arranging 0.1 to 1 mm of molybdenum wire with a gap of 1 to 3 mm. During the deposition of the diamond layer on the conductor substrate, the substrate is placed on the anode. In the case of the deposition of the diamond layer on the silicon substrate, the pure silicon oxide is 0.3 to 2 The hydrogen is first removed from the substrate for 10-20 minutes at a hydrogen flow of.

The silicon carbide layer is made of a substrate made by feeding 7-12% methane in the gas stream for 10 to 20 minutes. The diamond layer is made using a process with a nanocrystalline structure, which is 3-4 Radiation threshold of 100 Current density exceeding

This property enables diamond layers to be used in the manufacture of flat panel displays, as well as in electron microscopy, microwave electronics and many other applications.

Description

PROCESS FOR OBTAING DIAMOND LAYERS BY GASEOUS-PHASE SYNTHESIS}

It is known to laser melt carbon and deposit it with amorphous diamond on a low temperature substrate. However, this method is very complicated and expensive, and there are many limitations in the measurement.

It also provides a low density emission area (at 20V / micron area) Per 1000 ratings), which is obviously not enough to make a color monitor with 256 brightness levels.

Chemical vapor deposition methods for making diamond films are known. This method maintains DC glow emission from the hydrogen flowing between the cathode and the anode, heats the substrate to the deposition temperature, allows the gas containing carbon to flow The deposition of diamond films in a mixture with hydrogen and the removal of graphite surpluses in the flow of hydrogen. The intensity of this emission current is about 1 And the substrate temperature reaches about 1000 ° C. The deposition takes place in a mixed gas stream of hydrogen and methane and the methane concentration is in the range of 0.3 to 3%. Under these conditions, the diamond film has a polycrystalline structure of micrometer-sized crystals. The basis for using diamond material as an electron emitter in low temperature operation is negative electron affinity, which is a property of diamond. However, the diamond film mentioned above does not have sufficient emission properties to make the cathode for color monitors. Because the density of emission area is 1,000 per Because it is not higher. Level required is 100,000 per That's it.

So far, no attempt has been made to develop an effective electron emitter based on polycrystalline diamond film. This is especially due to the low level of emission area density.

In the present invention, improved (degree) emission current intensity, emission level and We have developed a method for producing diamond films with emission area density.

The present invention relates to a method of making a film that can be used very effectively for field emission, which can be used in the manufacture of flat panel displays in electron microscopes, microwave electronic devices and other applications.

1 is a configuration diagram of an apparatus for performing the method of the present invention;

2 and 3 are detailed views of main parts of the apparatus;

Figure 4 is an electron microscope scanning image of the diamond film surface formed by the method of the present invention.

Explanation of symbols on the main parts of the drawings

DESCRIPTION OF SYMBOLS 1 cathode 2 substrate 3 anode 4 chamber actor

5 gas flow rate meter 6 spectrum analyzer 7 pump device

8: optical thermometer

Experiments were performed in the installation environment as shown in FIG.

The discharge chamber is cylindrical and preferably made of stainless steel

It is broken. Through an isolator on one side of the cylinder, a cathode made of molybdenum is installed. The cathode has a lot of small holes through which gas such as hydrogen or hydrogen mixed with methane enters the chamber. The anode is also made of molybdenum. This positive (+) structure allows the emitter chamber to vary the distance between electrodes while maintaining pressure. The anode and cathode have separate cooling systems. The diameter of the anode and cathode is 1 to 5 Can be changed within the range of 1 to 5 to be.

The chamber is vacuum pumped to reach the desired vacuum. Then hydrogen or a mixture of hydrogen and methane is fed through the cathode. The flow rate of each gas is controlled by the flow rate controller, which is a suitable gas flow rate (100 to 1,000 per minute for hydrogen). ) And control the percentage rate between hydrogen and methane. The gases are mixed in a buffer volume, which is then sent to the emitter chamber. The proper air pressure (50 to 100 Torr) inside the chamber is maintained by the vacuum pump.

DC power supplies the voltage to the cathode through a ballast resistor. The anode (+) has a grid structure as shown in FIG. 2. The grid is net-shaped and is preferably made of molybdenum wire of 0.3 mm. The net includes a plurality of openings of 1-2 mm diameter. A substrate holder is placed with the substrate at a distance of 1 to 3 mm from the lattice anode (+). The grid and substrate holder are grounded. As a substrate, silicon was used as the starting medium in one of the standard processes to increase the concentration in the core area. DC power supplies 1 to 10 amps (A) at 500 to 1000 volts (V). Deposition temperature is 700 to 1000 ° C. The system can be fully measured

The deposition process on a silicon substrate involves the following steps:

1. The pressure inside the chamber To Vacuum pump to Torr. Hydrogen is then placed in the chamber to a pressure between about 50 and about 300 Torr. Supply the voltage required for breakdown and sustaining discharge. The substrate is heated to the desired temperature (600-1000 ° C.).

2. Remove the Silicon Oxide Layer over 10-20 minutes. If possible, the emission current intensity is 0.3-1A per With hydrogen in a chamber filled with hydrogen.

3. Then, when methane is injected into the gas stream so that the methane concentration is about 7% to 12%, a silicon carbide layer is formed for 10 to 20 minutes. This layer increases the adhesion that allows the diamond film to be deposited on the silicon substrate. This layer also improves electron injection from silicon substrates to diamond films.

4. Reduce the methane concentration in the mixed gas to between about 3% and 6%. At this stage, the growth of diamond films is about 10 to 20 microns per hour.

5. If the film is deposited over a predetermined thickness (about a few microns), the gas is injected only with hydrogen. This is a treatment step to remove the graphite layer from the substrate surface.

Figure 4 shows an electron microscope image of the surface shape of a sample of a diamond film composed of nanoscale crystals deposited by the method of the present invention. This fact was also confirmed by the study by the turnneling microscope scanning method. The X-ray projection data of the nanocrystalline sample made by the method of the present invention shows that the individual crystals are about 10 to 50 nm in size.

The emission characteristics of the films made by the process of the invention have a low voltage at "on". (There is a sample of an on-field that is about 3-4 V / micron). The emission area is located under the anode wire. To ensure better spatial emission homogeneity, the anode or substrate is moved back and forth at a frequency of 1 to 100 hertz (Hz). As a result, a film with a homogeneous distribution of emission currents is obtained.

The deposition process on metals has a slightly different step, due to the different chemistry of metals and silicon:

1. Pressure chamber To Vacuum pump until Torr. Then, hydrogen is injected into the chamber to bring the pressure between about 50 and 300 Torr. Apply the voltage required for breakdown and maintenance of discharge. The substrate is heated to the required temperature (600-1000 ° C.). No step for oxide removal is required.

2. Then, methane is injected into the gas stream so that the methane concentration is about 5% to 8%. At this stage, the diamond film is grown on the surface. The deposition rate of the film amounts to about 20 microns per hour. Due to the high carbide layer formation rate of metals such as Mo, W, and Ta, no separate step for forming the carbide layer is necessary.

3. After the film is deposited to the required thickness (a few microns), only hydrogen is injected. This is a treatment step to remove the graphite layer from the substrate surface.

In this way, a diamond film having characteristics close to those described above is produced.

The present invention can be used in the manufacture of flat panel displays in electron microscopes, microwave electronic devices and other applications using field emission.

Reference

1. Field emission flat panel display based on diamond.

Solid State Tech, 1995/4 p.71

2. Field emission characteristics for field emission display

Int.Display Res.conf., 1994/10

3. Application of A.Feldman Diamond Film and Correlated Materials

NIST Publication 885, S11,

4. F. J. Himpsel Phys. rev. B, 20 (2) 624,1979

5. Ibid. [3], p. 37, p. 61

6.Polushkin V.M. Diamond and Correlates, 1994, 3, 531

Claims (5)

Maintain breakdown and direct light emission in hydrogen flowing between cathode and anode (+), heat substrate to deposition temperature, inject carbon mixture gas to inject diamond film in mixture gas of carbon-containing gas and hydrogen A method of forming a diamond film by chemical vapor deposition on a substrate comprising depositing and removing graphite surplus in hydrogen flow, The substrate is heated to a temperature in the range of about 700 ° C. to 900 ° C. for the deposition of the diamond film of nano-unit crystals having high electron emission properties. A method of obtaining a diamond layer by vapor phase synthesis, wherein the concentration of the carbon-containing gas is in the range of 3 to 10% in the gas flow. The method of claim 1 wherein the carbon-containing gas is methane having a concentration of 3 to 8% in the gas stream. The substrate according to claim 1 or 2, wherein the substrate is made of a conductive material, located at the anode (+), and the diamond film is deposited to the required thickness in a gas flow of 3 to 8% of methane concentration, and 5 to 10. The graphite surplus is removed in a minute. 3. The substrate of claim 1 or 2, wherein the substrate is an electrical insulator and is isolated from a substrate holder that is grounded or external to the discharge volume at a distance of 0.1 to 5 mm from the grid anode. Made of 0.1 to 1 mm molybdenum wires with 1 to 3 mm spacing, the diamond film is deposited to the required thickness in a gas flow of methane concentration of 3 to 8%, and 5 to 10 is sufficient to remove graphite surplus on the film surface. Contacting hydrogen for a range of minutes. 5. The method of claim 1, 2, 3, and 4, wherein the substrate is silicon, and the substrate has a discharge current of 0.3 to 2 for a time of 10 to 20 minutes sufficient to remove the oxide layer on the silicon surface. Injecting the first mixed gas of methane and hydrogen containing methane at a concentration of 7 to 12% into a gas stream which is in contact with the silicon surface for 10 to 20 minutes sufficient to contact hydrogen under hydrogen and form a silicon carbide layer on the substrate, And then injecting a second mixture of methane and hydrogen containing methane at a concentration of 3 to 8%, allowing the second mixture to contact the silicon surface for a time sufficient to grow a diamond film of the required thickness. Characterized in that the method.