US Patent 7981763 Atomic layer removal for high aspect ratio gapfill

Methods of filling high aspect ratio, narrow width (e.g., sub-50 nm) gaps on a substrate are provided. The methods provide gap fill with little or no incidence of voids, seams or weak spots. According to various embodiments, the methods depositing dielectric material in the gaps to partially fill the gaps, then performing multi-step atomic layer removal process to selectively etch unwanted material deposited on the sidewalls of the gaps. The multi-step atomic layer removal process involves a performing one or more initial atomic layer removal operations to remove unwanted material deposited at the top of the gap, followed by one or more subsequent atomic layer removal operations to remove unwanted material deposited on the sidewalls of the gap. Each atomic layer removal operation involves selectively chemically reacting a portion of the fill material with one or more reactants to form a solid reaction product, which is then removed.