JP2000035410A - Measuring method of metal deposit quantity on wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly measure the deposit quantity of metal by mixing water solution containing water soluble salt of desired metal with an organic solvent selected from lower alcohol, ketone, or the like, and using a specimen adhering with metal by soaking a virgin wafer in this mixed liquid. SOLUTION: Water soluble salt of target metal, for example water soluble salt of metal such as zinc, nickel, copper, iron, calcium, or chrome, is dissolved in pure water so as to become fixed concentration. Next, the water solution is mixed with organic solvent such as lower alcohol or ketone of high compatibility with water and high evaporation rate, so that the target quantity of metal becomes sufficient concentration to deposit on a wafer, and after soaking a virgin wafer in the mixed liquid for a fixed time, it is naturally dried to make a standard specimen uniformly deposited on the metal. The metal on the standard specimen is measured by the use of a total reflection fluorescent X-ray device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a method for analyzing metal adhering to the surface of a semiconductor substrate, and more particularly to a method for analyzing the concentration of metal adhering to a silicon wafer surface.

[0002]

2. Description of the Related Art It is known that metal impurities on a wafer surface affect the electrical characteristics of a device, even if the amount is small. Such control of impurities is increasingly required to be strict with the increase in density and integration of devices. Therefore, it is essential to analyze these trace impurities with high sensitivity and high accuracy. As a method of analyzing the concentration of the metal impurities attached to the wafer surface, for example, an acid solution is dropped on the wafer surface to dissolve the metal impurities, the acid solution containing the dissolved metal impurities is collected, and the collected solution is collected. A method of measuring the amount of metal impurities therein by using a chemical analyzer such as a flameless atomic absorption spectrometer has been used.

However, in the case of the above-described conventional method, since the impurities in the region where the acid solution is dropped for eluting the metal impurities are averaged, it is impossible to examine the distribution state of the metal impurities on the wafer surface. Met. In recent years, a method using a total reflection fluorescent X-ray apparatus has been utilized as a metal concentration measuring method for compensating the above-mentioned disadvantages. As a method for quantifying the amount of metal using the above apparatus, there is a method using a calibration curve created using a standard sample. However, a disadvantage of this method is that it is difficult to prepare a standard sample used for performing quantitative analysis. One of the requirements required as a standard sample is the problem of uniformity of the deposited metal. In order to make the adhesion amounts of various metals sufficiently uniform, the preparation method becomes complicated, and, in addition, compared to the complexity of the preparation method, it has not reached a sufficiently uniform level to be used for inspection. Therefore, it is strongly desired to provide a method that can be easily prepared at the inspection site. Although there is a commercially available standard sample, it is not always suitable for the situation of the wafer manufacturing site, so that at present, it is not always possible to increase the predetermined measurement accuracy in spite of the high cost.

[0004] Furthermore, there is a case where the gettering effect of a metal is investigated as a method of inspecting the performance of a silicon wafer. In this case, however, it is difficult to obtain a standard sample as a control for comparison. Therefore, in order to be more accurate, ICP
It is necessary to perform a cross-check using a method such as -MS, frameless atomic absorption, or the like, and at present it is not always a simple method.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a means for inspecting the distribution of metals on a wafer surface more precisely by using a total reflection X-ray fluorescence apparatus. That is, using a simpler method, prepare a standard sample to be used as a comparison control in a form corresponding to the situation of the manufacturing site and the amount of gettered metal, and use this to distribute the metal on the wafer surface. It provides a way to check the situation.

[0006]

Means for Solving the Problems The present inventors have conducted various studies to find a method for preparing a precise standard sample according to the situation at the manufacturing site and the type and amount of metal to be gettered. An aqueous solution containing a water-soluble salt of a metal is prepared, and then the aqueous solution is mixed with water such as lower alcohol or acetone, and the amount of the target metal is reduced to an organic solvent having a certain or more evaporability. The inventors have found that the above object can be achieved by mixing the mixture so as to have a concentration sufficient for adsorption to a standard sample, and using this mixed solution, thereby completing the present invention.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the amount of metal on a wafer using a total reflection X-ray fluorescence apparatus,
It is characterized by using a highly reliable standard sample. Preparation of a standard sample is performed in the following procedure. A water-soluble salt of a target metal, for example, a water-soluble salt of a metal such as zinc, nickel, copper, iron, calcium, and chromium is dissolved in pure water so as to have a certain concentration, and the obtained aqueous solution is dissolved in a lower alcohol or Highly compatible with water, such as ketones, and mixed with an organic solvent having a high evaporation rate so that the desired amount of metal has a concentration sufficient to adhere to the wafer,
Next, the virgin wafer is immersed in the mixed solution for a certain period of time and air-dried.

As the organic solvent to be used, lower alcohols and ketones having high compatibility with water and having a high evaporation rate are used. As lower alcohols, methanol,
Alcohols having 3 or less carbon atoms such as ethanol, isopropanol and propanol are preferably used. Acetone is preferably used as the ketone. Above all, isopropanol is preferred because uniform metal deposition can be easily achieved in relation to the evaporation rate.

The metal salt used is not particularly limited as long as it is a water-soluble salt such as zinc, nickel, copper, iron, calcium and chromium. Note that a virgin wafer manufactured under strict conditions is used. The mixing ratio between the aqueous solution containing the metal and the organic solvent may be appropriately selected depending on the desired amount of the metal to be attached. Usually, the amount of the organic solvent is in the range of 1 to 99 in volume ratio to the aqueous solution 1. is there.

The immersion time of the wafer in the mixed solution is usually about 1 minute to 10 minutes. After immersion, excess immersion liquid is dried in a clean room at room temperature (about 22 ° C.). Since the drying speed of the organic solvent is high, there is no need for forced drying by ventilation or the like. The total reflection X-ray fluorescence apparatus used for the measurement is not particularly limited. For example, TREX610T manufactured by Technos (Osaka) may be used.

Hereinafter, preparation examples of the standard sample according to the present invention will be described, but of course, the present invention is not limited to these examples.

(Preparation Example of Standard Sample) Fe, Cu, Ni,
Each of 10 ppm standard solutions of Zn, Cr and Ca was
Measure exactly 200cc each with a graduated cylinder, add isopropanol to each, add 1000c
c. After thoroughly stirring this mixed solution, put it into an immersion tank, immerse a sufficiently washed 6-inch wafer in the immersion tank for 3 minutes, remove excess immersion liquid after immersion, and dry at room temperature in a clean room. To prepare a standard sample.

The amount of Ni deposited on the above standard sample is determined by the TREX610T manufactured by Technos Co., Ltd.
Are used to select nine arbitrary points on the wafer, measurement is performed for each point, and the integrated adhesion amount is shown in FIG. 1 using a histogram. In addition, the amount of Ni deposited on a commercially available standard sample prepared by the spin coating method was measured in the same manner.
Shown in As is clear from the results shown in these two drawings, the Ni adhesion amount of the standard sample prepared by the above method is higher in uniformity than that prepared by the spin coating method which is a commercially available product, It can be seen that the product is sufficiently practical for use as a standard product for preparing a calibration curve.

The amount of metal adhered on the standard sample prepared by the above method and a standard sample manufactured by using a commercially available spin coating method was measured using a total reflection fluorescent X-ray apparatus manufactured by Technos, and the following was measured. The results shown in Table 1 were obtained.

[0015]

[Table 1]

From the results shown in Table 1 above, it is clear that the method according to the present invention is excellent as a standard sample for measuring the amount of metal adhesion on a wafer. When this was used for actual measurement, a highly reproducible measurement result was obtained.

[0017]

Effect of the Invention As described above, zinc, nickel, copper, iron,
Using a standard sample in which calcium and chromium are adhered to a virgin wafer, the amount of adhered metal is measured by total reflection X-ray fluorescence. The effect is obtained that product inspection and quality inspection can be performed more easily.

[Brief description of the drawings]

FIG. 1: N tested as representative of metal on a reference wafer prepared by the method used in the present invention.
It is the figure which showed the distribution state of the adhesion amount of i by the histogram.

FIG. 2 is a histogram showing a distribution state of an attached amount of Ni inspected as a representative of metal on a reference wafer prepared by a spin coating method.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Norio Nakamura 11-2 Kiyohara Industrial Park, Utsunomiya City, Tochigi Prefecture F-term in MMC Corporation (reference) 2G001 AA01 BA04 CA01 FA02 GA01 GA13 KA01 LA11 NA09 NA10 NA11 NA13 NA17 RA02 RA03 RA20 4M106 AA01 AA07 AB16 AB17 CB01 DH25 DJ18

Claims (2)

[Claims] In a method for measuring the amount of metal adhered on a wafer using total reflection X-ray fluorescence, an aqueous solution containing a water-soluble salt of a desired metal is selected from lower alcohols or ketones as a standard sample. The above-mentioned method, wherein the mixture is mixed with an organic solvent, a virgin wafer is immersed in the mixed solution for a certain period of time, and then dried and used. 2. The method according to claim 1, wherein isopropanol is used as the organic solvent.