CR-288 Application Note For Beol Semiconductor Processing

APPLICATION NOTE
CR-288 APPLICATION NOTE FOR
BEOL SEMICONDUCTOR PROCESSING
Authors: Christopher Wacinski and Wiley Wilkinson
Introduction
CR-288 improves process efficiency for BEOL
because tighter process control increases wafer
throughput, reduces chemical cost and decreases
wafer scrap. As an in-line, real time, highly accurate
concentration monitor, manufacturers can now:
•Precisely monitor and control the chemical
dilution and blending
•Increase chemical bath lifetime, reducing
chemical usage and disposal costs
•Monitor for chemical excursions, such as when
mechanical components fail
•Have real-time data for optimizing a process
or tool, e.g., the actual homogenization within
a chemical blend
Business Need
HVMs and OEMs want to reduce chemical costs
and prevent wafer scrap, which they could do
with a more precise monitor for BEOL processing
chemicals like oxide/metal etchants, post-CMP
cleaners, photo-resist strippers, and surface
preparation solutions. However, they will only
replace current technology when the monitor
offered meets two criteria:
CR-288’s IoR Technology Answers this Need
•CR-288 differs from other products
because it measures concentration based
on the fluid’s index of refraction (IoR)
•Measuring by IoR offers real-time in-situ
concentration measurements with a high
degree of accuracy, precision and resolution
•CR-288 can be calibrated in the field,
eliminating the need to have proprietary
chemistry sent to the factory
•There is little to no maintenance because
it has no consumable parts
•CR-288 offers wide dynamic range that is
insensitive to bubbles and color
•There is a shorter return of investment
•The monitor is significantly better than
current technology
•It is cost-effective to implement
Figure 1. CR-288 liquid chemical concentration monitor
shown with two flow cells.
ENTEGRIS, INC.
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CR-288 APPLICATION NOTE FOR BEOL SEMICONDUCTOR PROCESSING
Typical Installation
The illustration below shows a typical blending
application. In general, the concentrated chemical
is diluted using DIW before it is either placed
directly on the wafer, or it is diverted to a holding
tank where the chemistry is being recirculated
in process.
Concentrated
chemistry
DI water
Recirculation
loop
Process
tool
CR-288
Figure 2. Typical blending application.
Case Studies
HF Dilutions
This graph compares CR-288 with conductivity's
capability to measure concentration of HF dilutions from 1:100 to 1:1000. The conductivity signal
saturates at approximately 5000 ppm. CR-288 can
measure the entire range (0 – 49 wt%). Furthermore, CR-288 can measure the signal with more
resolution and has the potential for measuring
dilutions lower than 1:1000.
2500 mL/min; 1:100; 1:500; 1:750; 1:1000; HF:DI
6000
HF Concentration (ppm)
CR-288
Conductivity sensor
1:100
5000
4000
3000
2000
1:500
1000
0
13:16:19
13:17:02
13:17:46
1:750
13:18:29
1:1000
13:19:12
13:19:55
Time (hour/min/sec)
Figure 3. HF dilutions.
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APPLICATION NOTE
ENTEGRIS, INC.
CR-288 APPLICATION NOTE FOR BEOL SEMICONDUCTOR PROCESSING
Photoresist Strip Dilutions
CR-288 offers continuous precision where conductivity cannot. Conductivity cannot measure
photoresist strip in solution correctly because
photoresist strip is often a non-conductive
chemical.
The plot shows CR-288 IoR compared to a conductivity sensor output, both plotted as a function of
time. The x-axis is the percentage of water added
to the photoresist strip.
Note that the CR-288 measures photoresist strip
correctly throughout the process range.
In contrast, the conductivity sensor is completely
insensitive to the changes in concentration. It
is only once the water concentration reaches a
sufficient level that the conductivity sensor can
measure anything at all.
CR-288 inherently outperforms conductivity in this
critical metric.
4.00
1.458
1.456
3.80
Index of refraction @ 20°C
3.60
1.452
1.450
3.40
1.448
3.20
Conductivity (mS/cm)
loR @ 20°C
1.454
1.446
Conductivity
3.00
1.444
1.442
2.80
0
2
4
6
8
10
12
14
16
18
Concentration of Added H2O (%)
Figure 4. CR-288 index of refraction vs. conductivity.
ENTEGRIS, INC
APPLICATION NOTE 3
CR-288 APPLICATION NOTE FOR BEOL SEMICONDUCTOR PROCESSING
IoR Precision of Measurement for
Post-CMP Cleaner, ESC-784
This study used the CR-288 kit2, installed at the
point-of-use (POU) on a post-CMP cleaning tool
that dilutes the post-CMP cleaner at POU using two
flowmeters. One sensor head was installed in each
cleaning tank. The results show that CR-288 precisely monitored the POU dilution of the post-CMP
cleaner in real time to at least the resolution of
the flow meters (0.1 wt%) with measurement
resolution for even greater dilutions.
NOTE:
Incoming chemical is highly concentrated
and diluted to the target concentration of
2.78 wt%.
CR-288 monitors POU blend to insure
target concentration of 2.78 wt% is met
before wafer cleaning.
3.50
19.35
19.15
Fluid temperature
3.08%
3.10
2.98%
18.75
2.88%
2.90
2.78%
18.95
18.55
New concentration
2.70
Temperature (°C)
Concentration (wt%)
3.30
18.35
2.50
18.15
2.30
17.95
0
1000
2000
3000
4000
5000
6000
Time (seconds)
Figure 5. CR-288 measurements of ESC-‐784 post-CMP cleaning chemistry.
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APPLICATION NOTE
ENTEGRIS, INC.
CR-288 APPLICATION NOTE FOR BEOL SEMICONDUCTOR PROCESSING
CR-288 Millisecond Measurement in
HF/SC1 in Single Wafer Tool
While the OEM used CR-288 in an FEOL environment, the example applies equally to BEOL.
The monitor shows three wafers being processed.
A single flow cell was installed at POU and measured premixed concentrations of distilled water,
dilute HF, and SC1. The data demonstrate that:
•Using a single sensor, CR-288 can monitor
the chemical dispensed at POU as it switches
between RCA cleaning chemistry
•CR-288 near-instantaneous measurement
allows users to measure the chemistry on each
wafer. The NIR measurement takes two minutes
to achieve the required resolution while production continues
•Conductivity could only be tuned for one of the
chemicals, not all three
1.3350
CR-288 loR
1.3345
Index of Refraction
1.3340
1:2:50 SC1
1.3335
1.3330
DIW
1.3325
DIW
1:50 HF
1.3320
1.3315
0
30
60
90 120 150 180 210 240 270 300 330 360 390 420 450 480 510 540
Time (seconds)
Note: Fluid Temperature Compensation (Tcc) optimized for both HF and SC1. Recommend for tool
manufacturer to allow Tool PLC to “swap” individual Tcc values for the two blends.
Figure 6. Three wafer cycles of HF, DIW and SC1 dispense: 30-second chemical dispense; 0.1 sec CR-288 response time.
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