Semiconductor device geometries have dramatically decreased in size since their introduction several decades ago. Modern semiconductor fabrication equipment routinely produces devices with 250 nm, 180 nm, and 65 nm feature sizes, and new equipment is being developed and implemented to make devices with even smaller geometries. The smaller sizes, however, mean device elements have to work closer together which can increase the chances of electrical interference, including cross-talk and parasitic capacitance.
To reduce the degree of electrical interference, dielectric insulating materials are used to fill the gaps, trenches, and other spaces between the device elements, metal lines, and other device features. The aspect ratio of a gap is defined by the ratio of the gap's height or depth to its width. These spaces are difficult to fill using conventional CVD methods. A film's ability to completely fill such gaps is referred to as the film's “gapfilling” ability. Silicon oxide is one type of insulation film that is commonly used to fill the gaps in intermetal dielectric (IMD) applications, premetal dielectric (PMD) applications and shallow trench isolation (STI) applications among others. Such a silicon oxide film is often referred to as a gapfill film or a gapfill layer.
Some integrated circuit manufacturers have turned to the use of high density plasma CVD (HDP-CVD) systems to deposit silicon oxide gapfill layers. HDP-CVD systems form a plasma that is approximately two orders of magnitude or greater than the density of a standard, capacitively-coupled plasma CVD system. Examples of HDP-CVD systems include inductively-coupled plasma systems and electron cyclotron resonance (ECR) plasma systems among others. HDP-CVD systems generally operate at lower pressure ranges than low density plasma systems. The low chamber pressure employed in HDP-CVD systems provides active species having a long mean-free-path and reduced angular distribution. These factors, in combination with the plasma's density, contribute to a significant number of constituents from the plasma reaching even the deepest portions of closely spaced gaps, providing a film with improved gapfill capabilities as compared to films deposited in a low density plasma CVD system.
Another factor that allows films deposited by HDP-CVD techniques to have improved gapfill characteristics as compared to films deposited by other CVD techniques is the occurrence of sputtering, promoted by the plasma's high density, simultaneous with film deposition. The sputtering element of HDP deposition slows deposition on certain features, such as the corners of raised surfaces, thereby contributing to the increased gapfill ability of IIDP deposited films. Some HDP-CVD systems introduce argon or a similar heavy inert gas to further promote the sputtering effect. These HDP-CVD systems typically employ an electrode within the substrate support pedestal that enables the creation of an electric field to bias the plasma toward the substrate. The electric field can be applied throughout the HDP deposition process to generate sputtering and provide better gapfill characteristics for a given film. One HDP-CVD process commonly used to deposit a silicon oxide film forms a plasma from a process gas that includes silane (SiH4), molecular oxygen (O2) and argon (Ar).
At very small feature sizes some HDP-CVD silicon oxide processes use inert gas or fluent gas components lighter than argon to limit the amount of sputtering so that redeposition of the sputtered material does not pinch-off the gap and form a void during the gapfill process. Still other HDP-CVD processes rely on a multi-step deposition, etch, deposition technique that is often referred to as a “dep/etch/dep” process. An HDP dep/etch/dep process divides the deposition of the gapfill layer into two or more steps separated by a plasma etch step. The plasma etch step etches the upper corners of the first deposited film more than the film portion deposited on the sidewall and lower portion of the gap, thereby widening the gap and enabling the subsequent deposition step to fill the gap without prematurely closing it off. Typically, HDP dep/etch/dep processes can be used to fill higher-aspect-ratio small-width gaps than a standard HDP deposition step for the particular chemistry would allow.
Etchant gases used in the etch portion of an HDP dep/etch/dep process include NF3, CF4, C2F6 and/or SF6. While these etchant gases can be successfully used in a number of different applications, further improvements and/or alternative approaches are desirable. Such improved processes are particularly desirable in light of the continuing decrease in minimum feature sizes achievable in IC manufacturing and the more aggressive gapfill challenges presented by integrated circuit designs employing such reduced minimum feature sizes.