Method of controlling the uniformity of PECVD-deposited thin films

Abstract

We have discovered that controlling a combination of PECVD deposition process parameters during deposition of silicon-containing thin film provides improved control over surface standing wave effects. By minimizing surface standing wave effects, the uniformity of film properties (particularly film thickness) across a substrate surface onto which the films have been deposited is improved. The process parameters which have the greatest effect on surface standing wave effects include: the spacing between the upper and lower electrodes in the plasma reactor; the RF frequency of the plasma source; the amount RF power to the plasma source; the process chamber pressure; the relative concentrations of the various components in the precursor gas composition; and the precursor gas overall flow rate relative to the substrate processing volume.

Description

RELATED APPLICATIONS [0001] This application is a continuation-in-part of U.S. application Ser. No. 10 / 829,016, filed Apr. 20, 2004, which is currently pending.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention pertains to a method of controlling surface standing wave effects during PECVD deposition of a silicon-containing thin film. By controlling surface standing wave effects during film deposition, the uniformity of a silicon nitride film deposited by PECVD (plasma-enhanced chemical vapor deposition) can be tightly controlled over a large surface area. [0004] 2. Brief Description of the Background Art [0005] Current interest in thin film transistor (TFT) arrays is particularly high because these devices are used in liquid crystal active matrix displays of the kind often employed for computer and television flat panels. The liquid crystal active matrix displays may also contain light emitting diodes for back lighting. Further, organic light e...

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Benefits of technology

[0032] An a-SiNx:H gate dielectric film exhibiting the physical characteristics listed above provides excellent performance capabilities, and the uniformity of the film across the substrate enables the production of flat panel displays having dimensions in the range of 1900 mm×2200 mm, and possibly even larger.

[0046] The width of the plasma sheath can be increased, for example (and not by way of limitation), by decreasing the spacing between the upper and lower electrodes in a parallel plate processing chamber.

[0048] As mentioned above, a reduction in the RF power to the plasma source to within the range of about 0.2 W / cm2 to about 0.6 W / cm2 can aid in improving film thickness uniformity. Although a decrease in RF power also decreases the film deposition rate, we have found, that for a silicon-containing PECVD deposited film, this range of RF power typically provides an acceptable film deposition rate of at least 1,000 Å / min, by way of example and not by way of limitation).

[0049] The PECVD process parameters described above, when used in combination, provide better control over surface standing wave effects and film thickness uniformity for silicon-containing films such as silicon nitride and silicon oxide. Our initial indications are that PECVD-deposited a-Silicon films are not as significantly affected by standing wave effects.

Problems solved by technology

However, we discovered that when the substrate size was increased to dimensions of 1500 mm to 1800 mm, this precursor source gas produced a non-uniform film thickness which varied by as much as about 25%; produced film structures where the Si—H bonded content exceeded 23 atomic %; and, produced films where the wet etch rate in HF solution (normalized to thermal oxide 1000 Å / min) exceeded 2400 Å / min in some instances.

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