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Determination of Chlorine Ion Contamination on Integrated Circuit Substrates

IP.com Disclosure Number: IPCOM000078176D
Original Publication Date: 1972-Nov-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 3 page(s) / 31K

Publishing Venue

IBM

Related People

Yao, CK: AUTHOR

Abstract

A microdeposition technique coupled with x-ray fluorescence analysis has been developed, to determine microgram chloride ion levels on substrates or modules. This technique is rapid and precise and it requires three minutes to analyze each sample. There are three steps in this analysis: sodium chloride solution preparation, deposition of standard solution on substrates, and measurement of the intensity of chloride K(Alpha)1 fluorescence produced by the sodium chloride deposited on the substrates.

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Determination of Chlorine Ion Contamination on Integrated Circuit Substrates

A microdeposition technique coupled with x-ray fluorescence analysis has been developed, to determine microgram chloride ion levels on substrates or modules. This technique is rapid and precise and it requires three minutes to analyze each sample. There are three steps in this analysis: sodium chloride solution preparation, deposition of standard solution on substrates, and measurement of the intensity of chloride K(Alpha)1 fluorescence produced by the sodium chloride deposited on the substrates.

The chloride radiation was measured with a Siemens SRS-1 X-Ray Sequential Spectrometer. The source employed was a chromium target x-ray tube operated at 32KV and 60 mA. A graphite analyzer crystal with the vacuum path was used and the goniometer was set at the proper angle (2 Theta = 89.29 degrees) for the chloride K(Alpha 1) radiation. A flow proportional counter operated at 1571 volts, base line at 0.8 volt, and window at 0.7 volt was used to determine the chloride radiation. The intensity of the C1(K(Alpha 1)) fluorescence was measured directly from the sodium chloride deposited on the center of the substrates (standardization).

The x-ray measurement of trace amounts of chloride on substrates is best performed by using a set of reference standards.

The reference standards were prepared by dissolving 0.165 gm. of sodium chloride (NaCl) in deionized water and diluted to 100 ml. 10 ml of this solution was diluted to 50 ml. The final solution contained 200 ppm of Cl/-/ in the deionized water. Various amounts of the sodium chloride solution were then added on the substrates. Sodium chloride is soluble in deionized water, and the mixtures were homogeneous with the following amounts added onto the center of each substrate. Drops of NaCl Solution Added Added Chloride

Standard No. onto the Substrate (5Vl/drop) (Mu gm) 1 0 0

2 1 1

3 2 2

4 3 3

5 4 4

6 5 5

7 6 6

8 7 7

9 8 8

10 9 9

11 10 10.

The composition of chloride present is expressed in Mu gms per drop as added on the substrates. Every drop of NaCl solution contains 1.0 Mu gm f Cl in deionized water. Since the aluminum sample holder inside hole diameter is 8 mm, the irradiated area on substrate is 50.3 mm/2/.

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Standards and samples were prepared for x-ray fIuorescence analysis by using identical procedures. A calibration curve of net intensity (counts per 40 seconds from the Cl(K(Alpha 1)) radiation) plotted against the amount of chloride added to the substrate in Mu gm per drop was generated. The net intensity was obtained by subtracting the background intensity from the total counts. The background intensity was counted from an empty sample holder at the 2 Theta angle of Cl(K(Alpha 1)) (89.29 degrees). The slope of the calibration, intensity vs. gm of Cl added, is a linear function of the amount of chloride deposited on the substrates up to 8 Mu gm level. Thus, the calibration was constructed in increm...