Etch
Figure 5 – Resistance variation of polysilicon line a) after HPM for various RTA1. b) after hot SPM SE
process for various RTA1
SPM under these standard conditions is not able sulfuric acid to 1 part 30 wt% hydrogen peroxide
to remove Pt residues. was used in this work for the selective etching of
Ni(Pt) films with 5%Pt.
Selective Etching Spray
Process Advantages Benefits of Hot SPM
High temperature SPM selective etching was Polysilicon line resistance (Rs), increases
20
carried out in the ZETA Batch Spray Cleaning associated with silicide oxidation, are affected by
System. A batch spray system offers several both formation anneal temperature and line
www
advantages for the selective metal etch step in width. The line resistance increase is higher for
.eur salicide integration. Because batch spray makes lower formation anneal temperature (below
oasiasemiconductor
very efficient use of the chemical, it is 300°C) and for narrower polysilicon lines. This is
economical to employ a fresh dispense, single shown in Figure 5a for the case of unreacted
pass approach with point of use mixing. Point of NiPt stripping with the HCl based HPM solution.
use mixing with SPM provides a higher For higher formation anneal temperature
temperature by taking advantage of the (350°C), one can observe a decrease in Rs with
exothermic mixing reaction of sulfuric acid and small dimensions caused by the well known
.com
hydrogen peroxide allowing a much higher on reverse narrow line width effect
[18]
. For narrower
wafer chemical temperature. In addition to silicided structures, the total amount of Ni
higher reactivity, the single pass approach available is larger than wide lines due to Ni(Pt)
square4
Issue III 2009
minimizes metallic recontamination by etched presence on sidewalls, so Rs decreases.
material. For a given RTA, silicidation on small lines
Figure 4 shows the temperature rise
measured when mixing room temperature 96
wt% sulfuric acid and room temperature 30 wt%
hydrogen peroxide in a beaker. The heat
generated during mixing equal volumes raises
the temperature by almost 90ºC. In the batch
spray cleaning system, 96 wt% sulfuric acid is
first preheated to 150ºC in a flow through infra
red heater and 30 wt% hydrogen peroxide is
mixed into the flow stream just before
dispensing to prevent thermal degradation of
the hydrogen peroxide and provide maximum
reactivity. Mixing of room temperature hydrogen
peroxide with the pre heated sulfuric acid
increases the temperature from 150ºC to about Figure 6 – Silicide phase formation for a same
180ºC. A volume mixing ratio of 2 parts 96 wt% RTA but two different Ni(Pt) thickness deposited
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