Particle Removal In Post Chemical-Mechanical Planarization (Cmp) Cleaning Process: Experimental And Modeling Studies
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Date
2009-06
Authors
Lok Yian, Han
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
The post chemical mechanical planarization (CMP) cleaning became very
important in wafer technology as one of its objectives was to manufacture high
quality surfaces of fine dimensions. This study comprises of an experimental as well
as a theoretical study on particle removal efficiency mainly silicon dioxide (SiO2)
particles from wafer surface after chemical mechanical planarization (CMP) cleaning.
The particle removal capacity from wafer surface in buffing (cleaning) disk was
studied using de-ionized water and citric acid at different flow rates (200 ml/min to
400 ml/min) buffing disc pressure (1psi, 2psi and 3psi) and relative buffing disc
speeds setting (0rpm, 1rpm and 2rpm). The removal efficiency in each case was
evaluated using a particle count based on measurements with a laser scattering
equipment (SP1 KLA Tenor). Particle removal efficiency was found to be increased
with flow rates, buffing disc pressure and buffing disc speeds.
A Response Surface Methodology (RSM) couple with central composite
design (CCD) was used in order to study the particle removal efficiency in the
buffing disc for citric acid and de-ionized water. Both citric acid and de-ionized
water showed satisfactory correlation with experimental value with correlation
coefficient ³ 0.92. The significant factors affecting the particle removal efficiency
were buffing disc pressure, relative buff rotational speed setting and chemical flow
rate. A mathematical model was also developed to correlate the particle removal
efficiency in buffing disk with flow rate of chemical, buffing disc pressure and
relative buffing disc rotational speed. In this case, the individual forces acting on a
particle, namely frictional force, hydrodynamic fluid drag force, adhesion force and
capillary force acting on a particle were analyzed. A theoretical model was
developed taking into account the resultant forces on the particle and the toppling
moments on a particle embedded in a wafer at varying depths. Simulations were also
carried out using the model based on the physical variables such as fluid properties,
frictional properties and operational parameters (flow rates, buff pressure and disc
speeds). The evaluation of particle removal efficiency in this simulation was
compared with experimental results. The experimental data and the model fitted well
with a correlation coefficient of 0.97 and 0.85 for de-ionized water and citric acid,
respectively.
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Keywords
Particle Removal In Post Chemical-Mechanical Planarization (Cmp) Cleaning Process , Experimental And Modeling Studies