JP4524834B2 - Water quality evaluation method - Google Patents

Description

【０００８】
この時の結果を表２にまとめた。表２には、超純水中の不純物濃度を直接分析した結果も合わせて示した。水中の金属を直接分析しても分析下限値（１０ｎｇ／立）以下であったが、本発明の方法を用いればナトリウム、カルシウム、鉄が検出され、本法では超純水中に含まれる１０ｎｇ／立以下の極めて低濃度の不純物を検出することができる。
【０００９】
【表２】

【００１０】
尚、時間分析法とは、回収した溶解液を注入し、シグナル強度がベース（無検知状態）シグナルに安定したことを見計らって、それまでの時系列シグナルを、図１に示すように取り込む方法で、この方法により、回収した微少量溶解液中の極低濃度の分析が可能となる。
【００１１】
本発明による分析の結果と、従来の方法による分析の結果の比較を表３に示した。
【００１２】
【表３】

【００１３】
【発明の効果】
以上で明らかなように、本発明によれば回収した溶解液の測定装置に誘導結合プラズマ質量分析装置（ＩＣＰＭＳ）を使用するので、基板と接触した超純水中の不純物を多元素同時に１０⁸ｎｇ／立以下のレベルで検出可能となる。これは、ウエハ上での濃度に換算すると、１０⁸原子／ｃｍ²程度まで検出可能となる。そして、回収した溶解液のＩＣＰＭＳ導入部にはプラスチック製を用い、インターフェース部には白金製コーンを用いることにより、フッ酸系など回収した溶解液の組成によらずに上記検出が可能となる。又、測定に時間分析を用いることにより、１００μ立程度の微少量の回収液中の５〜１０元素を１０ｎｇ／立まで検出可能となり、分析時間は１検体（６元素）当たり３０秒程度になる。
【図面の簡単な説明】
【図１】本発明の時間分析により得られたナトリウムの時系列データ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for evaluating the quality of ultrapure water used for cleaning a semiconductor substrate (also referred to as a wafer), and in particular, analyzing a very small amount of metal elements in ultrapure water at the same time in multiple elements in a short time. It relates to a method for evaluating water quality.
[0002]
[Prior art]
A water quality evaluation method for measuring the amount of impurities contained in pure water by immersing a semiconductor substrate in pure water, then dissolving the surface of the substrate with a solution, and collecting and analyzing the solution is a patent No. 2,888,957 (Japanese Patent Laid-Open No. 4-147060), and in this evaluation method, a flameless atomic absorption method is used for analysis of the collected solution, and its detection lower limit is 0.75 to 50 × 10 ¹⁰ atoms. / Cm ² .
[0003]
[Problems to be solved by the invention]
If the solution is analyzed by the flameless atomic absorption method, there are the following problems.
{Circle around (1)} Each element must be measured, and it takes about 3 minutes to measure one element, so it takes a very long time to measure multiple elements.
(2) Considering that the amount of sample liquid required per element is about 20μ and the amount of liquid recovered from the wafer is small (about 100μ), the number of elements that can be measured on one wafer is There is a limit.
(3) The lower limit of analysis is several hundred ng / standing to several μg / standing, and an element with poor sensitivity can only detect up to about 10 ⁹ to 10 ¹¹ atoms / cm ² when converted to the amount of impurities on the wafer.
[0004]
[Means for Solving the Problems]
The present invention has been developed to solve the above-mentioned problems, and the water quality evaluation method according to claim 1 is a step of bringing the substrate into contact with ultrapure water , and then the surface of the substrate is a dissolved solution of about 100 μm. in the step of dissolving, then collected 100μ elevational about lysate in the evaluation method of water comprising a step of analyzing, by using an inductively coupled plasma mass spectrometer, introduced from the recovered 100μ elevation of about lysate By reading the signal intensity of each element until completion and integrating the signal intensity data of each element obtained in time series for each element, the recovered solution of about 100 μm was used to contact the substrate. Impurities in ultrapure water can be detected at a level of 10 ng / rise or less.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Six n-type silicon wafers having a diameter of 6 inches were prepared, and the surface of the wafer was cleaned by performing normal RCA cleaning using a quartz tank. Two of these wafers were washed and dried, and the surface metal element concentration was measured using a total reflection X-ray fluorescence spectrometer. As a result, the iron concentration on the surface of the cleaned wafer was 2 × 10 ⁹ atoms / cm ² or less. One of these was mounted on a polypropylene wafer holding container and brought into contact with ultrapure water at a flow rate of 1 standing / min for 1 hour, that is, 60 standing. Thereafter, the entire surface of the wafer was melted with 100 µ standing hydrofluoric acid to dissolve and collect deposits on the wafer.
[0006]
The recovered dissolved solution was analyzed for Fe concentration by an inductively coupled plasma mass spectrometer (ICPMS) under the measurement conditions shown in Table 1. The sample introduction system of the mass spectrometer is a cross flow type, the spray chamber is made of a polypropylene torch (inner tube), the interface sampling cone is made of platinum, and the skimmer cone is made of platinum.
[0007]
[Table 1]

[0008]
The results at this time are summarized in Table 2. Table 2 also shows the results of direct analysis of the impurity concentration in ultrapure water. Even if the metal in water was directly analyzed, it was below the lower limit of analysis (10 ng / stand), but sodium, calcium and iron were detected by using the method of the present invention. In this method, 10 ng contained in ultrapure water. It is possible to detect very low concentrations of impurities below / stand.
[0009]
[Table 2]

[0010]
The time analysis method is a method in which the recovered lysate is injected, and the signal intensity is stabilized at the base (no detection state) signal, and the time series signals up to that time are taken as shown in FIG. By this method, it becomes possible to analyze a very low concentration in the collected micro- dissolved solution .
[0011]
Table 3 shows a comparison between the results of the analysis according to the present invention and the results of the analysis by the conventional method.
[0012]
[Table 3]

[0013]
【The invention's effect】
As apparent from the above, according to the present invention, since an inductively coupled plasma mass spectrometer (ICPMS) is used as a measuring device for the recovered lysate, impurities in ultrapure water in contact with the substrate can be simultaneously mixed with 10 ⁸ Detection is possible at a level below ng / rise. This can be detected up to about 10 ⁸ atoms / cm ² in terms of the concentration on the wafer. The plastic can be used for the ICPMS introduction part of the collected solution and a platinum cone is used for the interface part, so that the detection can be performed regardless of the composition of the collected solution such as hydrofluoric acid. In addition, by using time analysis for measurement, it becomes possible to detect 5 to 10 elements in a small amount of collected liquid of about 100 μ up to 10 ng / stand, and the analysis time is about 30 seconds per sample (6 elements). Become.
[Brief description of the drawings]
FIG. 1 shows time series data of sodium obtained by time analysis of the present invention.

Claims (3)

In a method for evaluating water quality comprising a step of contacting a substrate with ultrapure water , a step of dissolving the surface of the substrate with a dissolving solution of about 100 μl , and then collecting and analyzing the dissolving solution of about 100 μm ,
Using an inductively coupled plasma mass spectrometer, the signal intensity of each element from the introduction of the recovered 100 μL standing lysate to the completion of the introduction is read, and the signal intensity data of each element obtained in time series is read The method for evaluating water quality is characterized in that the impurities in ultrapure water in contact with the substrate can be detected at a level of 10 ng / standby or less using the collected solution of about 100 μ standing by integrating each time. .   The water quality evaluation method according to claim 1, wherein impurities in ultrapure water in contact with the substrate are measured in an analysis time of about 30 seconds. The water quality evaluation method according to claim 1 or 2, wherein the inductively coupled plasma mass spectrometer uses a plastic introduction portion for the recovered solution and a platinum cone for the interface portion. Characteristic water quality evaluation method.

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