Low-frequency bias power in hdp-cvd processes

This patent application is a divisional of U.S. patent application Ser. No. 11/034,515, entitled “LOW-FREQUENCY BIAS POWER IN HDP-CVD PROCESSES,” filed Jan. 10, 2005, the disclosure of which is hereby incorporated by reference in its entirety for all purposes.

One of the primary steps in the fabrication of modern semiconductor devices is the formation of a film, such as a silicon oxide film, on a semiconductor substrate. Silicon oxide is widely used as an insulating layer in the manufacture of semiconductor devices. As is well known, a silicon oxide film can be deposited by a thermal chemical-vapor deposition (“CVD”) process or by a plasma-enhanced chemical-vapor deposition (“PECVD”) process. In a conventional thermal CVD process, reactive gases are supplied to a surface of the substrate, where heat-induced chemical reactions take place to produce a desired film. In a conventional plasma-deposition process, a controlled plasma is formed to decompose and/or energize reactive species to produce the desired film.

Semiconductor device geometries have decreased significantly in size since such devices were first introduced several decades ago, and continue to be reduced in size. This continuing reduction in the scale of device geometry has resulted in a dramatic increase in the density of circuit elements and interconnections formed in integrated circuits fabricated on a semiconductor substrate. One persistent challenge faced by semiconductor manufacturers in the design and fabrication of such densely packed integrated circuits is the desire to prevent spurious interactions between circuit elements, a goal that has required ongoing innovation as geometry scales continue to decrease.

Unwanted interactions are typically prevented by providing spaces between adjacent elements that are filled with an electrically insulative material to isolate the elements both physically and electrically. Such spaces are sometimes referred to herein as “gaps” or “trenches,” and the processes for filling such spaces are commonly referred to in the art as “gapfill” processes. The ability of a given process to produce a film that completely fills such gaps is thus often referred to as the “gapfill ability” of the process, with the film described as a “gapfill layer” or “gapfill film.” As circuit densities increase with smaller feature sizes, the widths of these gaps decrease, resulting in an increase in their aspect ratio, which is defined by the ratio of the gap\'s height to its depth. High-aspect-ratio gaps are difficult to fill completely using conventional CVD techniques, which tend to have relatively poor gapfill abilities. One family of electrically insulating films that is commonly used to fill gaps in intermetal dielectric (“IMD”) applications, premetal dielectric (“PMD”) applications, and shallow-trench-isolation (“STI”) applications, among others, is silicon oxide (sometimes also referred to as “silica glass” or “silicate glass”).

Some integrated circuit manufacturers have turned to the use of high-density plasma CVD (“HDP-CVD”) systems in depositing silicon oxide gapfill layers. Such systems form a plasma that has a density greater than about 10¹¹ ions/cm³, which is about two orders of magnitude greater than the plasma density provided by a standard capacitively coupled plasma CVD system. One factor that allows films deposited by such HDP-CVD techniques to have improved gapfill characteristics is the occurrence of sputtering simultaneous with deposition of material. Sputtering is a mechanical process by which material is ejected by impact, and is promoted by the high ionic density of the plasma in HDP-CVD processes. The sputtering component of HDP deposition thus slows deposition on certain features, such as the corners of raised surfaces, thereby contributing to the increased gapfill ability.

Biasing of the substrate may attract the charged ionic species in the plasma, resulting in an interaction anisotropy that promotes bottom-up gapfill. One drawback to biasing the substrate is that an electrical discharge may result, causing arcing within the chamber. Even when such discharges are relatively small, they may result in microcontamination of the substrate and produce defects. Such discharge is typically avoided by setting lower limits on chamber pressure and/or upper limits on the bias power. Such limits act to constrain the way in which substrates may be processed. Although lower chamber pressures and higher bias powers may be useful in achieving desired film characteristics, such as substantially void-free gapfill for certain aggressive structures, they both tend to increase the occurrence of undesirable bias discharge.

There is accordingly a need in the art for improved systems that reduce the tendency for bias application to cause electrical discharges in HDP systems.

Embodiments of the invention reduce the risk of bias discharge by using a lower frequency for the bias and additionally enhance tuning speed for the bias system with electronic frequency sweeping. In a first set of embodiments, a substrate processing system is provided. A housing defines a process chamber. A substrate holder is disposed within the process chamber and configured to support a substrate during substrate processing. A gas-delivery system is configured to introduce a gas into the process chamber. A pressure-control system maintains a selected pressure within the process chamber. A high-density plasma generating system is operatively coupled with the process chamber for forming a plasma having a density greater than 10¹¹ ions/cm³ within the process chamber. A radio-frequency bias system is electrically coupled with the substrate holder to generate an electrical bias on the substrate at a frequency less than 5 MHz. A controller controls the gas-delivery system, the pressure-control system, the high-density plasma generating system, and the radio-frequency bias system.

In some instances, frequency of the electrical bias may be less than 3 MHz. The pressure-control system may maintain the selected pressure less than 2 mtorr or less than 1 mtorr in different embodiments. The radio-frequency bias system may generate a bias having a power greater than 5000 W. In one embodiment, the radio-frequency bias system comprises a radio-frequency generator electrically coupled with an impedance matching network. The radio-frequency generator is adapted to electronically sweep cyclically through a frequency range to determine the frequency that minimizes a power reflected from the process chamber. The radio-frequency generator may also be adapted to change the frequency in response to a change in the power reflected from the process chamber. The radio-frequency generator may be adapted to electronically sweep with a period substantially between 50 and 100 ms. The frequency range may be approximately 2.7-3.3 MHz in one embodiment.

In a second set of embodiments, a substrate processing system is also provided. A housing defines a process chamber. A substrate holder is disposed within the process chamber and configured to support a substrate during substrate processing. A gas-delivery system is configured to introduce a gas into the process chamber. A pressure-control system maintains a selected pressure within the process chamber. A high-density plasma generating system is operatively coupled with the process chamber for forming a plasma having a density greater than 10¹¹ ions/cm³ within the process chamber. A radio-frequency bias system is electrically coupled with the substrate holder and comprises a radio-frequency generator electrically coupled with an impedance matching network. The radio-frequency generator is adapted to electronically sweep cyclically through a frequency range to determine a frequency that minimizes a power reflected from the process chamber. A controller controls the gas-delivery system, the pressure-control system, the high-density plasma generating system, and the radio-frequency bias system. In various specific embodiments, the pressure, bias power, frequency range, sweeping period, and the like may be as noted above.

In a third set of embodiments, a method is provided for depositing a silicon oxide film on a substrate disposed in a substrate processing chamber. A process gas is flowed into the substrate processing chamber. The process gas comprises a silicon source, an oxygen source, and a fluent gas. A plasma having an ion density greater than 10¹¹ ions/cm³ is formed from the process gas. An electrical bias is applied to the substrate at a frequency less than 5 MHz. The silicon oxide film is deposited over the substrate with the plasma in a process that has simultaneous deposition and sputtering components. In some instances, the substrate may have a gap formed between adjacent raised surfaces, with the film also being deposited within the gap. In various specific embodiments, the pressure, bias power, frequency range and sweeping period of a sweeping frequency, and the like may be as noted above.

In a fourth set of embodiments, a method is provided for depositing a silicon oxide film on a substrate disposed in a substrate processing chamber. A process gas is flowed into the substrate processing chamber. The process gas comprises a silicon source, an oxygen source, and a fluent gas. A plasma having an ion density greater than 10¹¹ ions/cm³ is formed from the process gas. An electrical bias is applied to the substrate. The electrical bias is swept through a frequency range to determine a frequency that minimizes a power reflected from the substrate processing chamber. The silicon oxide film is deposited over the substrate with the plasma in a process that has simultaneous deposition and sputtering components. In some instances, the substrate may have a gap formed between adjacent raised surfaces, with the film also being deposited within the gap. In various specific embodiments, the pressure, bias power, frequency range, sweeping period, and the like may be as noted above.

A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a simplified diagram of one embodiment of an HDP-CVD system according to the present invention;

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