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APCVD (Atmospheric Pressure)
This is a relatively simple system that can operate with wafers on a
horizontal conveyor belt. Deposition rate is fast and at low temperatures. The
use of this method with ozone and TEOS is common in the industry, especially
for shallow trench and pre-metal deposition layers.
LPCVD (Low Pressure)
This technique permits either horizontal or vertical loading of the wafers
into the furnace and accommodates large numbers of wafers for processing. It
gives good conformal-step coverage with excellent purity and uniformity
(typically better than APCVD and PECVD). There is less dependence of the
resulting layer on gas flow. However, the process requires higher temperatures
and the deposition rate is low. Pressures required can be from 0.1 to 2
torr.
PECVD (Plasma Enhanced)
In this process, radio frequency (RF) is used to induce plasma in the
deposition gas. This results in a higher deposition rate at relatively low
temperatures. Step coverage is good.
ALD (Atomic Layer Deposition)
Relatively new as a commercially available technique, ALD utilizes
sequential precursor gas pulses to deposit a film one layer at a time. The
first precursor gas is introduced into the process chamber and produces a
monolayer of gas on the substrate. A second precursor gas is then introduced
into the chamber and reacts with the monolayer produced from the first gas.
Since each pair of gas pulses (which is one cycle) produces exactly one
monolayer of the desired film, the thickness of the final film is precisely
controlled by the number of deposition cycles.
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