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: The monitor is significantly better than current technology It is cost-effective to implement 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 Figure 1. CR-288 liquid chemical concentration monitor shown with two flow cells. ENTEGRIS, INC. 1
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. DI water Recirculation loop Concentrated chemistry 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. 6000 2500 ml/min; 1:100; 1:500; 1:750; 1:1000; HF:DI 5000 1:100 CR-288 Conductivity sensor HF Concentration (ppm) 4000 3000 2000 1000 1:500 1:750 1:1000 0 13:16:19 13:17:02 13:17:46 13:18:29 13:19:12 13:19:55 Time (hour/min/sec) Figure 3. HF dilutions. 2 APPLICATION NOTE ENTEGRIS, INC.
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. 1.458 4.00 lor @ 20 C 1.456 1.454 1.452 1.450 1.448 1.446 1.444 Index of refraction @ 20 C Conductivity 3.80 3.60 3.40 3.20 3.00 Conductivity (ms/cm) 1.442 2.80 0 2 4 6 8 10 12 14 16 18 Concentration of Added H 2 O (%) Figure 4. CR-288 index of refraction vs. conductivity. ENTEGRIS, INC APPLICATION NOTE 3
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 3.30 Fluid temperature 19.15 Concentration (wt%) 3.10 2.90 2.70 2.78% 2.88% New concentration 2.98% 3.08% 18.95 18.75 18.55 18.35 Temperature ( C) 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. 4 APPLICATION NOTE ENTEGRIS, INC.
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 1.3340 Index of Refraction 1.3335 1.3330 1.3325 DIW 1:2:50 SC1 DIW 1.3320 1:50 HF 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. Entegris, the Entegris Rings Design and Creating a Material Advantage are registered trademarks of Entegris, Inc. ENTEGRIS, INC. Corporate Headquarters 129 Concord Road Billerica, MA 01821 USA Customer Service Tel. +1 952 556 4181 Customer Service Fax +1 952 556 8022 In North America 800 394 4083 www.entegris.com 2014 Entegris, Inc. All rights reserved Printed in USA 3965-7601ENT-0314