The RCA Standard Clean, developed by W. Kern and D. Puotinen in 1965 and
disclosed in 1970 [1] is extremely effective at removing contamination from
silicon surfaces and is the defacto industry standard.[2]. The RCA clean
consists of two sequential steps: the Standard Clean 1 (SC-1) followed by
the Standard Clean 2 (SC-2). The SC-1 solution, consisting of a mixture of
ammonium-hydroxide, hydrogen-peroxide, and water, is the most efficient
particle removing agent found to date. This mixture is also referred to as
the Ammonium- Hydroxide/Hydrogen-Peroxide Mixture (APM). In the past, SC-1
solutions had the tendency to deposit metals on the surface of the wafers,
and consequently treatment with the SC-2 mixture was necessary to remove
metals. Ultra-clean chemicals minimize the need for SC-2 processing. SC-I
solutions facilitate particle removal by etching the wafer underneath the
particles; thereby loosening the particles, so that mechanical forces can
readily remove the particles from the wafer surface. The ammonium hydroxide
in the solution steadily etches silicon dioxide at the boundary between the
oxide and the aqueous solution (i.e., the wafer surface). The hydrogen
peroxide in SC-I serves to protect the surface from attack by OH" by
re-growing a protective oxide directly on the silicon surface (i.e., at the
silicon/oxide interface). If sufficient hydrogen peroxide is not present in
the solution, the silicon will be aniostropically etched and surface
roughening will quickly occur. On the other hand, hydrogen peroxide readily
dissociates and forms water and oxygen. If the concentration of the
resulting oxygen is too high, bubbles will appear in the solution. The gas
liquid interfaces that result from the bubble formation act as a “getter”
for particles that can re-deposit on the wafer surface if a bubble comes in
contact with the wafer.
Interface Roughness Effects in Ultra-Thin Tunneling Oxides
