Method of reducing micromasking during plasma etching of a silicon-comprising substrate

#1. Field of the Invention

#The present invention relates to plasma etch processes and more specifically to plasma etch processes conducted on silicon substrates and films with mask patterns having large open areas.

#2. Description of Related Art

#The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:

#FIGS. 1A, 1B, 1C, 1D, 1E and 1F depict various high open area patterns;

#FIG. 2 is a schematic, cross section view of a semiconductor process chamber in which embodiments of the inventive method of FIG. 3 can be performed; and

#To facilitate understanding, identical reference numbers are used, where possible, to designate identical elements that are common to the figures.

#Embodiments of the present invention provide a fluorine, oxygen, and fluorocarbon based plasma etch method capable of anisotropically etching silicon in high percentage open area etch patterns without forming silicon spikes (i.e., black silicon). Generally the total surface area of the silicon substrate to be etched includes etched area and masked area. The percentage of open area refers to the ratio of the etched area to the total area of the silicon substrate. Design parameters for some devices, such as for example, DRAM memory, deep trench isolation and high frequency silicon on insulator devices, maintain open area percentage below about 20 percent and in most cases less than 15 percent.

#In a silicon etch context, high open area percentages (i.e., open area percentages above 50 percent) result in an increasing availability of silicon and an increasing likelihood of silicon spike or black silicon formation. As the percentage of open area increases, the likelihood also increases that sputtered mask material or etch reaction byproducts may redeposit on the substrate surface and act as a micro mask. The directional etch component needed for vertical sidewalls and anisotropic etching of desired features also results in directional etching around the micromask. As a result of the directional etch component, the micro mask produces spikes. A spike consists of a silicon body with a thin passivating siliconoxyfluoride skin. When viewed by an observer, light with a wavelength less than the length of the spikes will be reflected and caught between spikes thereby making the area with spikes appear dark. Spike formation as a result of directional etching around the micromask is commonly referred to as ‘black silicon’ because of this observed darkening of the silicon surface. The redeposition of mask material and etch byproducts that result in micromasking and subsequent spike formation is not acceptable because areas which should stay clean become contaminated reducing the useful area of the substrate or structure. While the formation of black silicon is more pronounced at higher open area percentages, black silicon formation has been observed in patterns having 25 percent open area.