A Study on Contamination Control of Oxygen Analyzer By Applying Purifier

Rapid thermal annealing(RTA) has been widely used to anneal Si wafer via rapid thermal process chamber. RTA helps the doped ions be activated and reduces the defects in Si lattices by restructuring the bonding [1]. However, when atmospheric air permeates the chamber during RTA process due to the chamber leakage, it generates unwanted silicide on the Si substrate and reduces the electrical properties. It degrades device performance and reliability. For those reasons, oxygen analyzer always monitors the oxygen density in processing chamber during RTA process to prevent any further damage of product quality owing to chamber leakage. However, when oxygen analyzer is contaminated by processed gases, it causes signal delay or low signal which makes it difficult to sense the real oxygen density of chamber [2]. In this paper, to prevent the contamination of oxygen analyzer due to the processed gas, the oxygen purifier was adopted at the inner part of processed gases flow line.

Fig.1 shows various kinds of oxygen density profiles during RTA process depending on normal / delay / low signals, respectively.

Fig.2 shows secondary electron microscope (SEM) image of unused and used for 180 days of porous thimble type oxygen sensor. In mass analysis experiment, O, Si, C, P were detected as contaminants on surface of the used oxygen sensor.

Fig.3 is the gas flow diagram of oxygen analyzer with oxygen purifier.

Fig.4 is average oxygen density during RTA process for 180 days with and without purifier.

 In experimental results, oxygen purifier selectively eliminated the contaminants in processed gas which passes through oxygen sensor. We obtained dramatic improvement of sensor sensitivity deviation nearly 71% than before.

 As a result, More accurate oxygen density monitoring of RTA chamber is possible than before. In addition, oxygen purifier in RTA chamber prevents the quality degradation of semiconductor device immediately when the wafer is exposed to atmospheric air caused by chamber leakage.

Reference

[1]] O.Flament and J.L.Leray, IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 42 NO. 6, DECEMBER 1995

[2]R.RAMADOORTHY,P. K. DUTTA, S. A. AKBAR, JOURNAL OF MATERIALS SCIENCE 38(2003)4271-4283