case studies discussed in this article investigate a point-of-use
(POU) liquid-chemical-concentration analysis system from Jetalon Solutions
(Campbell, CA) and were performed at two high-volume Texas Instruments
fabs. One case focuses on etch processing in the surface-preparation
area, while the other focuses on back-end processing.
of use is defined as any location in the fab where chemicals
are blended or delivered, including inside process tools and chemical
blending and delivery systems. Continuous, real-time liquid-chemical-concentration
measurements at the point of use provide many benefits to process
and equipment engineers. For example, they can be correlated to metrology
data on wafer-surface defects and yield, leading to early identification
of yield failures. In addition, they promote the development and automatic
maintenance of best-known methods for wafer processing. They enable
tools to become more process-flexible as chemical concentrations are
adjusted, controlled, and monitored at the point of use. Tool failure
modes can be identified and addressed, resulting in increased tool
uptime and productivity.
summary, POU sensors incorporated into monitor and control systems
will help process and equipment engineers to accelerate process development,
identify and eliminate tool failure modes (thereby increasing tool
productivity), reduce chemical consumption and wafer scrap (leading
to significant annual cost savings), and minimize the environmental
impact of semiconductor manufacturing. Taken together, these benefits
will improve the overall cost of ownership.
general, process tools lack POU liquid-concentration sensors. Consequently,
engineers rely on grab samples and laboratory analyses for information
on liquid-chemical concentration, a method that is neither done in
real time nor continuously. Although it is accurate, it does not provide
the benefits of POU sensors.
be of most benefit, liquid-chemical-concentration sensors must be
designed specifically for semiconductor applications. They must provide
real-time continuous data output with ≤1-second response time,
they must have a small footprint, they should have no moving parts,
they should be process transparent, and they should offer a reasonable
return on investment. In addition, liquid-chemical-concentration
sensors must be reliable, exhibiting high resolution and appropriate
dynamic range. Finally, they must be compatible with acids, bases,
solvents, oxidizers, and slurries.
the sensor in this study was used to gather data from surface-preparation
processes, it has been developed for all liquid-chemical process areas.
It can be used for blending CMP slurry at the point of use; monitoring
ECD plating baths, solvents in ultrapure water, chemical drain lines,
or process chemical baths; and performing a range of chemical spiking
applications in batch-wafer processes.
demonstrate the benefits of a POU sensor system, fab tests were performed
using a CR-288 liquid-chemical-concentration analysis system (CAS)
from Jetalon. The CAS consists of a fully integrated, miniaturized
optical reflectivity device, an optical fluidic cell, and a DSP-based
electronic circuit. It uses optical reflectivity to measure refractive
index and, therefore, concentrations of liquids. The optical reflectivity
device includes an LED light source, a mirror, a sapphire window,
and a photodiode-array detector, which measures scattered-light intensity
simultaneously over all relevant angles.
device is packaged in a compact optical fluidic cell that measures
5 X 5 X 7.5 cm. Only the sapphire window and Teflon components make
contact with the liquid chemical under analysis. The sensor measures
temperature using a thermocouple placed inside the optical fluidic
cell. Capable of achieving data output rates of 100 points per second,
it has a temperature range of 10°–70°C, sensitivity
of 0.01% of concentration, a response time of 10 milliseconds (1 second
in practice), and a pressure range of 0–50 psi.
the reflectivity geometry, light is incident on an optically transparent
sapphire window (index of refraction n1),
which is in contact with a liquid under analysis (index of refraction
For reflectance angles (θs)
smaller than the critical angle (θc),
light is predominantly reflected off the window (total external reflection).
For reflectance angles greater than θc,
light is both reflected off the window and transmitted through it.
By measuring the change in scattered-light intensity as a function
can be determined. From Snell's Law, θc
is related to a liquid's index of refraction. It follows that by accurately
liquid concentration can be determined accurately.
1: Index-of-refraction measurements from the liquid-chemical-concentration
sensor plotted as a function of measurement time for different
performance results, obtained under controlled laboratory conditions,
are shown in Figures 1 and 2. To conduct the tests, the optical fluidic
cell was inserted into a chemical delivery system that can be operated
in either closed-loop or open-loop control flow modes. The delivery
system included a piston pump, temperature control bath, and an autotitrator.
Initial laboratory measurements for testing and calibration using
hydrogen peroxide (H2O2)
are presented in Figure 1, which shows index of refraction plotted
as a function of time. Measurements were taken for H2O2
concentrations of 1.0, 1.1, 1.13, and 1.141%. H2O2
concentrations were spiked into the delivery system, which operated
in closed-loop mode in doses of 0.1, 0.03, and 0.011%, and were verified
using an autotitrator. For convenience, data were acquired every 5
seconds over a 9-hour period. Figure 2 shows similar results obtained
from a comparable laboratory setup for dilutions of SC-1 from 1:1:20
to 1:1:50 and ultrapure water (UPW).
2: Index-of-refraction measurements from the sensor plotted as
a function of measurement time for different SC-1 dilutions and
case studies presented here focus on a concentration analysis of SC-1
in immersion wet benches. In both studies, the optical fluidic cell
was connected directly with the SC-1 bath recirculation system using
a 1/4-in. connection. Figure 3 shows the sensor head installed at
the point of use (the recirculation line of the SC-1 bath) inside
a 200-mm wet tool from Dainippon Screen (Kyoto, Japan). The tool operated
in full production mode during the case studies. In the first case
study, which involved an etch process and open-loop H2O2
spiking, the initial SC-1 bath concentrations were 1:1:5. In the second
case study, which involved a back-end process with no chemical spiking,
0.75% ammonia hydroxide, and 98.5% water were used. In both studies,
concentration data were collected continuously for more than a month.
The data presented here represent a small fraction of the total data
that were collected and analyzed.
3: The sensor head (circled) installed at the point of use (in
the air-bleed line of the filter) inside the SC-1 bath recirculation
line of a 200-mm wet tool.
Study 1: Etch Process. Figures 4–7 present concentration
measurements for the first case study. Figure 4 shows SC-1 concentration
and process bath temperature plotted as a function of time during
a 24-hour wafer production run. It also shows three bath life cycles.
Figure 5 shows the same data as Figure 4 over a 5-hour period, illustrating
concentration behavior between two SC-1 bath dump/fill cycles. In
both tests, concentration and temperature data were collected simultaneously
every second. Within each bath life cycle, 40 ml of H2O2
were spiked into the 27-L bath each time a batch of wafers was introduced
into the tank.
4: SC-1 concentration and bath temperature plotted as a function
of time during a 24-hour wafer production period.
concentration data reveal several key bath characteristics, including
the effectiveness of H2O2
spikes to maintain chemical concentration; SC-1 concentration changes
as a function of time and wafers processed; bath change-out properties
and conditions; variations in SC-1 concentration from bath to bath;
and the effectiveness of the bath's temperature-control system and
various tool failure modes related to pumps, valves, etc. As illustrated
in Figure 5, the concentration data between 5 and 10 hours revealed
several things about the etch process. First, immediately following
spike, the SC-1 concentration increased beyond the initial bath concentration.
Second, the overall concentration of the bath increased from 9.09%
to 9.24%. Third, the sensor detected the H2O2
5: The same data as in Figure 4 plotted for one bath lifetime,
which was approximately 4 hours.
6 highlights an H2O2
spike. Initially, SC-1 concentration increased to approximately 9.38%
during injection and then receded to 9.16% after mixing was completed.
Overall, the difference in SC-1 concentration before and after the
spike was 0.03%. As shown in Figures 4 and 5, the cumulative effect
of the H2O2
spikes was to increase the SC-1 bath concentration, indicating that
the spike concentrations were too high and that spiking frequency
was too frequent.
6: Close-up of a 40-ml H2O2
spike in the 27-L SC-1 process bath.
7 presents a close-up view of SC-1 process bath concentration and
temperature during a bath change plotted as a function of time. The
steep drop in concentration occurred when the sensor was exposed to
air during the SC-1 bath drain (dump). The data also show a significant
variation in SC-1 concentration before and after the bath change.
While the concentration before the bath change was 9.15%, it was 9.06%
after the bath change, a 0.09% drop.
7: SC-1 concentration plotted as a function of time for an SC-1
Study 2: Back-End Process. Figures 8 and 9 illustrate SC-1
concentration measurements for the second case study. Figure
8a shows SC-1 concentration plotted as a function of time, focusing
on a bath change during which the diaphragm pump used to circulate
the SC-1 bath unexpectedly turned on and off several times. The pump
shutoff contributed to the accumulation of static chemical residues
in the recirculation line and extended refill times. After the pump
and refill-delay issues were corrected, the process returned to normal,
as indicated in Figure
9: SC-1 concentration and bath temperature plotted as a function
of time for the second case study. The data were collected continuously
for 45 hours.
9 shows concentration data plotted as a function of time during 45
hours of continuous operation. The data reveal that there was a smooth
transition between bath changes and initial SC-1 concentration values,
which varied by less than 0.05% from bath change to bath change. However,
the data also show a decrease of 0.7% in SC-1 bath concentration during
wafer processing. This relatively large and unexpected change in concentration
led to an investigation of the SC-1 bath, which determined that the
bath was automatically being filled with UPW during wafer processing
because of a leak.
ongoing work, the sensor has been incorporated into a closed-loop-control
spiking system to maintain SC-1 concentration and extend SC-1 bath
lifetime. This change will lead to reduced chemical consumption, greater
cost savings, and increased tool productivity.
article has presented two case studies demonstrating the performance
of a compact real-time liquid-chemical-concentration analysis system.
In both studies, SC-1 used in immersion baths was analyzed at the
point of use and in real time during wafer production. Concentration
data were used to diagnose the efficiency of H2O2
spiking, determine appropriate bath lifetimes, and identify and eliminate
tool failure modes.
studies will investigate the use of the sensor in chemical spiking,
delivery, control, and monitoring systems, which are expected to have
a significant impact on cost of ownership because they will reduce
chemical consumption; identify and eliminate tool failure modes; maintain
best-known methods for chemical delivery, spiking, and blending; and
increase tool uptime and productivity.
POU chemical-concentration data can be correlated to wafer-surface
metrology data and catastrophic wafer-failure events, providing opportunities
for determining the effects of chemical concentration on wafer-surface
defects and yield. That knowledge is especially important in applications
with narrow process windows, such as hydrofluoric acid etch, CMP,
photolithography, and ECD.
article is an edited, revised version of a presentation from the Semiconductor
Pure Water and Chemicals Conference (SPWCC), held February 14–16,
2005, in Santa Clara, CA. Copyrights reserved by SPWCC. Reprinted
with permission of SPWCC.
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Chiarello, PhD, is president of Jetalon Solutions (Campbell,
CA). With more than 15 years of experience in high-tech R&D at
Stanford University and the University of Chicago, he has consulted
for the world's largest high-tech manufacturers in the semiconductor,
data-storage hardware, flat-panel display, and other industries. Chiarello
has published more than 50 articles in the areas of semiconductor
device processing, solid-state physics, biophysics, surface science,
electrochemistry, and geochemistry. A NATO fellow, he has won the
Depart- ment of Energy Award for Excellence in Research and the University
of Chicago Pace Setter Award for Outstanding Contributions in Synchrotron
X-ray Techniques. He received a BS in physics from the University
of California at Santa Barbara and an MS and PhD in physics from Northeastern
University in Boston. (Chiarello can be reached at 408/866-6318 or
Eric Boyd is solutions engineer at Jetalon. Before joining
the company, he participated in other high-tech start-ups. He received
a degree in applied science (engineering) from Queens University (Kingston,
ON, Canada), graduating with first-class honors. His education included
extensive mathematical training and numerous hands-on application
courses in mechanical and electrical design. (Boyd can be reached
at 408/866-6318 or firstname.lastname@example.org.)
Wacinski is a lead engineer at Jetalon. His work as a control
systems specialist in the semiconductor industry has focused primarily
on the area of liquid flow and monitoring. As a certified LabVIEW
developer, he has consulted on projects ranging from real-time wet-chemical
dispensing to gas flow control. Wacinski spent three years as a lead
engineer in the biomedical field working for Navigant Biotechnologies,
where he developed spectrometer-based irradiance measurement and calibration
instruments. He received a BS in electrical engineering technology
from the Metropolitan State University of Denver, CO. (Wacinski can
be reached at 408/866-6319 or email@example.com.)
Kiez is an equipment engineering technician in the projects
group at Texas Instruments' DMOS5 wafer fab in Dallas, where he has
worked since 1995. The group supports all equipment engineering groups,
including photolithography, plasma, thin films, diffusion, wet etch,
implant, and CMP. Previously, Kiez worked for Pratt and Whitney Canada
as a test cell technician and served in the Canadian Forces for 10
years as an aircraft technician. He has been a member of the Alberta
Society of Engineering Technologists for 10 years. He received an
associates degree in semiconductor manufacturing technology from Texas
State Technical College in Waco and an associates degree in IC design
layout from Eastfield College in Mesquite, TX. (Kiez can be reached
at 972/927-7479 or firstname.lastname@example.org.)
Elkind, PhD, is a senior member of the technical staff at
Texas Instruments in Dallas, where he manages the company's analytical
sensors branch. With almost 17 years of experience at TI, he has worked
in both the central research laboratory and the Houston wafer fab.
He received BA and MA degrees in chemistry from Brandeis University
in Waltham, MA, and a PhD in physical chemistry from the University
of California at Berkeley. (Elkind can be reached at 972/995-1214
Presley is an equipment engineer in the assembly group at
Texas Instruments' DMAT fab in Dallas, where he has worked since 1999.
The group supports back-end equipment engineering projects and process
support, including plasma ash, wet cleans, passivation, die attach,
bonding, and welding. With 14 years of experience in the semiconductor
industry, Presley worked for Ball Semiconductor as a project leader
in the development of single-crystal silicon spheres and at a semiconductor
equipment manufacturer as an equipment design engineer and process
engineer. He received a BS in industrial engineering from the University
of Texas in Arlington and an associates degree in science at Richland
College in Dallas. (Presley can be reached at 972/927-3060 or email@example.com.)
McDermott has been a senior equipment specialist at Texas
Instruments for 19 years. For 14 of those years, he has been involved
in equipment engineering at the company's DMOS4 and DMOS5 fabs. His
areas of specialty include diffusion and wet processes. He received
an AAS in electrical engineering technology from ITT Technology Institute.
(McDermott can be reached at 972/995-1518 or
Harakas, PhD, is a member of the diffusion/wet team at Texas
Instruments' DMOS5 fab. His primary responsibilities include metal
silicide and metal nitride wet etch processes. Before joining the
group, he spent three years in the photolithography group at TI. He
received a PhD in inorganic chemistry from Texas Tech University in
Lubbock. (Harakas can be reached at 972/995-1241 firstname.lastname@example.org.)