September, 2016
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Page 65
Advancements in RH Measurements in Wafer and Reticle Environments
By Allyn Jackson, CyberOptics Corp.
for characterizing and minimizing the exposure to relative humidity (RH) has become critical in all 29 nm geometry fabs and below. These RH control requirements create a need for a wireless wafer- like humidity sensor which simultaneously meas- ures RH at several points across the wafer as well as throughout the entire IC manufacturing envi- ronment.
C
Characterizing FOUPs Current methods for character-
izing nitrogen (N2) purge front-open- ing unified pods (FOUPs) have prob-
lems. These methods are typically not real-time, are time-consuming, are difficult to use and are not able to take RH measurements under pro- duction conditions. In addition, wired handheld RH meters and single- trace handheld meters are limited to one area and cannot move through- out the process environment. Other options are handmade alternatives, such as a wafer with RH sensors sim- ply taped on. Lastly, they are often limited without generating data files, and as a result, statistics and quality standards cannot be established. In one customer test, an RH
meter was put inside the FOUP around slot 13. The goal of the test was to repeat the RH meter profile for testing the FOUP on one load port without the need to open it. Starting at 40 percent RH
(cleanroom environment), the first step was to run a high-purity, high-
volume N2 pre-purge for four or five minutes and then take the reading. The second step was to conduct
a maintenance purge to five percent and measure the results in five loca- tions across the wafer.
ertain IC fabrication steps are very sensitive to moisture in semiconductor wafer environ- ments. As the technology advances, the need
Bluetooth with the company’s Multi View™ appli- cation and can be moved like a wafer to any loca- tion in the wafer process environment, providing a
true characterization of the N2 purge uniformity in the FOUP. The WaferSense AMS is a multi-func- tional device that also measures vibration and can be used for leveling to ensure proper wafer han- dling.
Geometry fabs, 29 nm and smaller, require
WaferSense wafer-shaped AMS measurement device for FOUP characterization.
well-controlled N2 and XCDA purge environments to prevent defects and yield loss. The company’s
Continued on page 68
Figure illustrating the the
WaferSense in position during N2 purge.
After that, the next step was to
run a process purge to 20 percent and take sample readings across various locations. The goal of the testing was
to test the efficiency of the N2 purge FOUP diffusers to ensure that uni- form purge levels are maintained.
WaferSense AMS In response to the need for a
reliable and easy method of qualify-
ing N2 and XCDA® environments, CyberOptics developed its Wafer - Sense® auto multi-sensor (AMS). The WaferSense AMS is a wireless wafer- like device with five RH sensors that measure the RH profile across its entire surface. The device communicates by
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