Supporting Information:
A Tool for Uniform Coating of 300 mm Wafers with Nanoparticles
Dean M. Holunga, Nicholas A. Brunelli, and Richard C. Flagan
Summary of Included Figures
The supporting information comprises a many figures that provide additional insight into
the underlying dynamics and subtleties of the thermodeposition device. The supplemental figures
describe the overall solution to the heat transfer throughout the device, as shown in Fig. S1. In
this figure, the temperature contours demonstrate the uniform heating that is achieved through
heating with the band heaters on top and cooling with water recirculated in the bottom plate. The
uniform temperature profile is key to obtaining uniform particle deposition.
The second contribution to the uniform deposition of non-agglomerated nanoparticles is
the flow field, demonstrated with a contour plot in Fig S2 for different aerosol inlet flow rates.
As the four contour plots demonstrate, the aerosol inlet design allows for a smooth transition
from axial to radial flow to enable uniform deposition for flow rates of 30 SLM and below. At
the highest flow rate (60 SLM), a low velocity zone is observed near the heated top plate,
indicating flow separation. This low velocity zone would hinder uniform deposition of pristine
particles as it would allow particle agglomeration.
Uniform deposition is important over the entire surface of the wafer and is particularly
challenging in the center of the device near the stagnation point of the flow. This requires heating
the aerosol gas in the inlet region to less than 15°C of the heated top plate; this facilitates
thermophoretic deposition in the flow stagnation zone. Without heating, the cold aerosol inlet
gas encounters a warmed substrate, resulting in an adverse temperature gradient, shown in Fig.
S3, which may prevent nanoparticle deposition in the center of the device, as shown in Fig. S4
(1) and (2). Too much heating may enhance deposition beyond uniformity as shown in Fig. S4
(4). The optimal inlet temperature, Fig S4 (3), is a process variable that requires tuning for each
change in temperature gradient and flowrate.
Finally, additional surface plots demonstrating the deposition patterns at low aerosol inlet
flow rates (1.6 and 2.4 SLM) are presented in Figs. S5-S6 to supplement Figs. 2 and 3 of the
main text. The low flow rates allow longer residence times in the deposition zone leading to
high deposition rates in the center of the wafer and no deposition at the outer edges. These
results are summarized in Fig. 4 and demonstrate the importance of judiciously choosing the
aerosol inlet flow rate and the temperature gradient across the device.
Figure S1. Schematic of Thermophoretic Depositor with Isotherms.
Isotherms of deposition chamber modeled in Fluent. Components of chamber: 1. Inner ring
heater. 2. Outer ring heater. 3. Band heater and mount. 4. Top MDC stainless steel Flange. 5.
Bottom MDC stainless steel Flange. 6. Water cooling chamber. 7. Aerosol inlet. 8. Gas outlet. 9.
Viton Gasket. Modeled average current supplied to the heaters (with listed power capacity) as
follows: 1. Inner ring heater, 0.4 A/1000 W, middle ring heater, 2. 0.6 A/1500 W, 3. Outer band
heater 7.5 A/1500 W.
A
B
C
D
Figure S2. Modeled Velocity Contours for Flow Rates.
Velocity contour plots for flow rates (A) 1.5, (B) 15, (C) 30, and (D) 60 SLM without separation
as modeled in Fluent.
Figure S3. Modeled Inlet Temperature Distribution without Inlet Heating.
Model predicts an unfavorable temperature gradient at the wafer surface when the aerosol is not
preheated.
Surface Plot: Temperature
Arrows: Thermophoretic Flux
Surface Plot: Temperature
A
Surface Plot: Temperature
Arrows: Thermophoretic Flux
B
Arrows: Thermophoretic Flux
Surface Plot: Temperature
C
Arrows: Thermophoretic Flux
D
Figure S4. Deposition Profile without Inlet Heating.
Model predicts (A) the lack of deposition when the inlet is not heated (i.e., inlet temperature of
315 K), (B) less than average coverage at the wafer center when the inlet is heated to 455 K, (C);
uniform coverage at the wafer center when the inlet is heated to 465 K and (D) excessive
deposition at the wafer center if the aerosol is overheated to 480 K. The arrows are proportional
to the relative magnitude of thermophoretic particle flux.
Figure S5. Modeled Deposition Profile.
Normalized particle deposition and concentration at 1.6 SLM modeled in Femlab. Arrows
indicate particle flux rate at the surface of the wafer.
Figure S6. Modeled Deposition Profile.
Normalized particle deposition and concentration at 2.4 SLM modeled in Femlab. Arrows
indicate particle flux rate at the surface of the wafer.