Thermal gradient enhanced CVD deposition at low pressure

Abstract

A method wherein a thermal gradient over a substrate enhances Chemical Vapor Deposition (CVD) at low pressures. An upper heat source is positioned above the substrate and a lower heat source is positioned below the substrate. The upper and lower heat sources are operated to raise the substrate temperature to 400-700° and cause a heat gradient of 100-200° C. between the upper and lower heat sources. This heat gradient causes an increase in the deposition rate for a given reactant gas flow rate and chamber pressure. The preferred parameters for implementation of the present invention for poly crystalline silicon deposition include the temperature of the upper heat source 100-200° C. above the lower heat source, a substrate temperature in the range of 400-700° C., a reactant gas pressure between 250 and 1000 mTorr, and a gas flow rate of 200-800 sccm. The substrate is rotated, with 5 RPM being a typical rate. A deposition rate of 2000 angstroms per minute deposition of poly crystalline silicon is achieved with a 200° C. temperature differential, substrate temperature of 650° C., pressure of 250 mTorr and silane flow of 500 sccm.

Description

[0001] This application is a continuation in part of U.S. application Ser. No. 09 / 396,588 filed Sep. 15, 1999 (which claims the benefit of U.S. Provisional Application Ser. No. 60 / 100,594 filed Sep. 16, 1998), which is a continuation in part of (a) U.S. application Ser. No. 08 / 909,461 filed Aug. 11, 1997, (b) U.S. application Ser. No. 09 / 228,835 filed Jan. 12, 1999 (which claims the benefit of U.S. Application Ser. No. 60 / 071,572 filed Jan. 15, 1998), and (c) U.S. Application Ser. No. 228,840 filed Jan. 12, 1999 (which claims the benefit of U.S. Provisional Application Ser. No. 60 / 071,571 filed Jan. 15, 1998). The disclosures of the foregoing applications are hereby incorporated by reference.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to methods and apparatus for chemical vapor deposition onto a substrate, and more particularly to a method that deposits silicon at a high rate due to enhanced mass transport by thermal diffusion, i...

AI Technical Summary

Benefits of technology

[0011] It is therefore an object of the present invention to provide a method and apparatus for the Chemical Vapor Deposition (CVD) of various materials at a high rate.

[0012] It is a further object of the present invention to provide a method and apparatus for the CVD of various materials at a high deposition rate with improved uniformity.

[0013] It is another object of the present invention to provide a method and apparatus for the CVD of various materials at a high rate, with improved uniformity and reduced surface roughness.

[0015] An advantage of the present invention is that it provides a higher deposition rate CVD method with good film quality.

[0016] A further advantage of the present invention is that it provides a CVD deposition method with a deposition rate five times more rapid than prior art methods providing comparable film quality.

Problems solved by technology

A disadvantage of this process is that it causes gas reactions that deplete the supply of available reactants which partially defeats the effect of pre-activation in increasing the deposition rate.

Silicon deposition rates over 10,000 angstroms per minute have been reported, however these high deposition rates do not produce poly crystalline silicon films that are useful in manufacturing semiconductor devices because the resulting poly crystalline silicon has undesirable features such as large grain size, non uniform thickness, etc.

Operation at higher concentrations of the reactant gases results in non-uniform deposition across the substrates, as well as large differences in the deposition rate from substrate to substrate.

Increasing the gas flow rate in the chamber of FIG. 1 can improve deposition uniformity at higher pressures, but has the disadvantage of increasing the gas pressure resulting in gas phase nucleation causing particles to be deposited on the substrate.

There are other problems associated with the reactor of FIG. 1, such as film deposition on the interior surfaces of the quartz tube 14 causing a decrease in the partial pressure of the reactive feed gas concentration near the substrate surface.

This results in a reduced deposition rate and potential contamination due to film deposited on the wall of tube 14 flaking off and falling on the substrate 20 surfaces.

Another problem occurs due to the introduction of a temperature gradient applied between the injector end and exhaust end of the tube to compensate for the depletion of reactive chemical species from the entrance to the exit.

This variation in grain size from substrate to substrate can result in variations of poly crystalline silicon resistivity and difficulties with the subsequent patterning of the poly crystalline silicon resulting in variations in the electrical performance of the integrated circuits produced.

Two major problems are associated with the apparatus of FIG. 2.

The other major problem is that the substrates 32 are not at the same temperature due to the method of heating the substrates from heater 42 with no heater below the substrates.

The major problem associated with the reactor of FIG. 3 is the limited throughput, i.e. the number of substrates processed per hour.

This problem can be addressed by increasing the operating pressure to 10 Torr or greater resulting in high deposition rates exceeding 1000 angstroms per minute, however operating the reactor at such high pressures can result in a gas phase reaction where silicon particles are formed in the gas and deposited on the substrate.

Another problem associated with the reactor is the tendency for silicon deposition on the quartz walls 64, 66 resulting in loss of radiant energy transmission from the lamps 62, 63.

This causes non-uniform heating of the substrate resulting in non-uniform film deposition on the substrate 56.

In addition, the time the substrate is above 600° C. must be held to a minimum, as heating the substrate to elevated temperatures, i.e. greater than 600° C. results in unwanted diffusion of dopants.

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