High-speed diamond growth using a microwave plasma in pulsed mode
Disclosed is a method for manufacturing a diamond film of electronic quality at a high rate using a pulsed microwave plasma. The plasma that has a finite volume is formed near a substrate (in a vacuum chamber) by subjecting a gas containing at least hydrogen and carbon to a pulsed discharge. The pulsed discharge has a succession of low-power states and of high-power states and a peak absorbed power P C , in order to obtain carbon-containing radicals in the plasma. These carbon-containing radicals are deposited on the substrate in order to form a diamond film. Power is injected into the volume of the plasma with a peak power density of at least 100 W/cm 3 , while maintaining the substrate to a substrate temperature of between 700° C. and 1000 ° C.
1. A method for manufacturing a diamond film comprising:
forming a plasma of finite volume near a substrate by subjecting a gas containing at least hydrogen and carbon in a vacuum chamber to periodic pulsed discharges using a pulsed microwave plasma by applying only a repeated succession of a low-power state and a high-power state, in which the ratio of the duration of the high-power state to the duration of the low-power state is between 1/9 and 1, and having a peak absorbed power P C so as to obtain at least carbon-containing radicals in the plasma, and depositing the said carbon-containing radicals on the substrate in order to form a diamond film thereon;
wherein the power being injected into the volume of the plasma with a peak power density of at least 100 W/cm 3 while maintaining the substrate to a substrate temperature of between 700° C. and 1000° C. and also wherein the pressure of the plasma is maintained between 100 mbar and 350 mbar.
2. The method according to claim 1 , in which a plasma having at least one of the following features is generated near the substrate:
the peak power density of the plasma is between 100 W/cm 3 and 250 W/cm 3 ,
the maximum temperature of the plasma is between 3500 K and 5000 K,
the temperature of the plasma in a boundary region of the plasma located less than 1 cm from the surface of the substrate is between 1500 K and 3000 K and
the plasma contains hydrogen atoms having a maximum concentration in the plasma of between 1.7×10 16 and 5×10 17 cm −3 .
3. The method according to claim 1 or claim 2 , in which said gas contains carbon and hydrogen in a carbon/hydrogen molar ratio of between 1% and 12%.
4. The method according to claim 1 , in which said gas contains at least one hydro-carbon, and a plasma having a concentration of the carbon-containing radicals of between 2×10 14 cm −3 and 1×10 15 cm −3 is generated.
5. The method according to claim 1 , in which at least one of the following parameters is estimated:
a substrate temperature,
a temperature of the plasma,
a temperature of the plasma in said boundary region, located less than 1 cm from the surface of the substrate,
a concentration of atomic hydrogen in the plasma,
a concentration of carbon-containing radicals in the plasma,
a concentration of carbon-containing radicals in said boundary region close to the plasma,
a pressure of the plasma and
a power density of the plasma,
and the power emitted as a function of time is adapted according to at least one of these parameters.
6. The method according to claim 1 , in which the plasma is contained in a cavity with at least one of the following properties:
the periodic pulsed discharges have a peak power of at least 5 kW at 2.45 GHz and
the gas containing hydrogen and carbon is emitted with a ration of the flow rate to the volume of plasma of between 0.75 and 7.5 sccm/cm 3 .
7. The method according to claim 1 , in which the plasma is contained in a cavity with at least one of the following properties:
the periodic pulsed discharges have a peak power of at least 10 kW at 915 MHz and
the gas containing hydrogen and carbon is emitted with a ratio of the flow rate to the volume of the plasma of between 0.75 and 7.5 sccm/cm 3 .