JPH10253556A - Preparation of sample for analysis - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the reliability of a sample for analysis, to shorten the time for preparation of the sample, and to improve the accuracy of quantitative determination of contamination of the surface of a base, of which the amount of contamination is unknown, by dripping a sampling liquid by a small quantity in several times repeatedly onto one point of the surface of the base being heated. SOLUTION: A base 11 for a standard sample is set on a jig 12 and heated to a temperature of 110 deg.C, by using a temperature regulator 21, in a state wherein the shape of the base 11 is changed to a recessed one with the rear thereof kept in vacuum. A standard solution of which the atomic concentration is known is sampled by 100μl (the atomic weight is equivalent to 1×10<14> atoms/cm<2> ) by using a micropipette 22. The micropipette 22 is fixed at the center of the base 11 by using micropipette supports 23, 24 and 25 and a sampling liquid 15 is dripped by 2μl in 50 times separately to the center of the base 11. The result shows that the dimension of a trace of the dripped liquid is 2mm or less with respect to any samples. The detection efficiency of a working curve of the standard sample for the working curve is improved in values of the curve to be about three times better than that of the working curve prepared by a usual method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing an analytical sample capable of performing highly accurate measurement, and to a reduction in sample preparation time.

[0002]

2. Description of the Related Art Conventionally, a standard sample for a calibration curve of a total reflection X-ray fluorescence analyzer has been prepared by two methods, a spin coating method and a dropping liquid method. The spin coating method is used for preparing a calibration curve sample for quantifying contaminant atoms taken into the film, and the dropping liquid method is used for preparing a calibration curve sample for quantifying particle contaminant atoms.

[0003] The spin coating method is a method in which a certain amount of atoms is incorporated into an oxide film while growing a natural oxide film on the entire surface of a cleaned substrate. A method for incorporating atoms into the natural oxide film on the substrate surface is to use a mixed solution of an oxidizing agent (hydrogen peroxide, nitric acid, ammonia, etc.) of known atomic concentration and pure water by spin coating or the like on the entire surface of the substrate. This is a method in which atoms are incorporated into an oxide film while being applied and growing a natural oxide film by the oxidizing power of an oxidizing agent in a solution.

In the dropping liquid method, a predetermined amount of liquid is sampled from a standard solution having a known atomic concentration using a micropipette onto a cleaned substrate, and the liquid is dropped on the substrate.
The standard solution is pure water, a mixed solution of hydrofluoric acid and pure water, or a mixed solution of hydrofluoric acid and an oxidizing agent (hydrogen peroxide or nitric acid) and pure water.
The metal element in the dropped liquid is air-dried in the air or dried in a vacuum to prevent contamination from the air, and is left as a droplet mark on the substrate.

[0005] Two kinds of standard samples for a calibration curve prepared by the above method are measured using a total reflection X-ray fluorescence spectrometer, and the integrated intensity of the fluorescent X-rays generated from the atoms to be calibrated and the spin coat method Has prepared a calibration curve of total reflection X-ray fluorescence based on the atomic concentration in the film existing per unit area, and in the case of the dropping liquid method, the atomic concentration in the droplet mark.

There is also a sample preparation method for quantifying particles on the silicon substrate surface whose contamination amount is unknown and contamination in the substrate surface natural oxide film using a total reflection X-ray fluorescence analyzer. This is because, as described in Japanese Patent Application Laid-Open No. 5-82495, contamination on the silicon substrate surface of which the amount of contamination is unknown is determined by using pure water, hydrofluoric acid and pure water, or hydrofluoric acid and an oxidizing agent (hydrogen peroxide). , Nitric acid, ammonia, etc.) and pure water are dropped on the substrate, and the dropped liquid is moved over the entire surface of the substrate to extract contamination on the substrate surface. The dripping liquid takes in particles on the substrate and contamination in the oxide film while dissolving the oxide film into the liquid. The dropping solution from which the contamination is extracted is dried on the substrate to remain as a droplet mark, and the droplet mark is determined by using total reflection X-ray fluorescence to quantify the contamination on the silicon substrate surface whose contamination amount is unknown. is there. In this case, the contamination is quantified using a calibration curve of a sample prepared by a dropping liquid method.

[0007]

The total reflection X-ray fluorescence spectrometer has a structure as shown in FIG. 1 and performs identification and quantitative analysis of atomic species by the following method.

First, in order to irradiate the measurement position on the surface of the sample substrate 4 with X-rays 3, the X axis, the Z axis, and the θ axis of the substrate 4 are adjusted, and the substrate 4 is moved to the measurement position. Next, the φ axis of the sample substrate is adjusted, and X-rays are incident on the surface of the measurement substrate 4 at a total reflection angle φa5. The X-rays incident on the surface of the substrate 4 at a total reflection angle excite the atoms 6 existing near the sample surface, and characteristic X-rays 7 are generated from the excited atoms. This characteristic X-ray is detected by a semiconductor detector (SSD) 8 on the substrate, passes through a signal amplifier 9,
It is converted into an electric signal proportional to the magnitude of the characteristic X-ray energy. The energy and integrated intensity of the characteristic X-rays are analyzed using the personal computer 10 to identify and quantify the atoms.

A calibration curve used for quantification by a total reflection X-ray fluorescence analyzer is obtained from the integrated intensity of characteristic X-rays generated from a standard sample having a known atomic concentration.

In particular, when quantifying particulate or particulate contamination on a silicon substrate, quantification is performed using a calibration curve obtained based on a sample prepared by a spin coating method. Since the amount of contamination per unit area is different from that of a film, the quantitative value differs from the actual value and the quantitative value is not reliable. Therefore, when quantifying particulate or particulate contamination,
A calibration curve of the sample prepared by the drop solution method must be used. Most of the contamination generated in the semiconductor manufacturing process is particle-like contamination, and it is often necessary to use a sample prepared by a dropping liquid method for preparing a calibration curve. However, preparing a sample by the dropping liquid method has the following problems.

A semiconductor detector used in a total reflection X-ray fluorescence spectrometer has a detector in-plane sensitivity characteristic as shown in FIG. As can be seen from the figure, in order to make the reliability of the measured value of the standard sample prepared by the dropping liquid method 95% or more,
The size of the droplet mark on the standard sample must be 2 mm or less, and the amount of the sampling liquid when the size of the droplet mark is 2 mm or less is 5 μl or less. However, taking into account the sampling accuracy of the standard solution and the residual solution when the sample solution is dropped, the amount of the sample solution is 50%.
More than μl is required. When 50 μl of the sampling liquid is dropped on the substrate, the size of the droplet mark becomes 5 to 6 mm and the SSD
The characteristic X-rays generated from the atoms in the droplet traces are detected in the region where the detection sensitivity is low, and the characteristic X-rays are counted down, so that the accurate atomic concentration cannot be measured. In other words, in order to increase the reliability of the calibration curve, it is necessary to reduce the amount of the sampling liquid in consideration of the sensitivity dependence in the SSD detection plane, but if the amount of liquid is reduced, the accuracy when dropping the sampling liquid decreases. Contradictory problems had occurred.
Further, after the dropping of the sampling liquid, time is spent for drying the dripping liquid.

The same problem also exists in a sample preparation method in which contamination on the surface of a substrate whose contamination amount is unknown is extracted into a solution, dried, and subjected to total reflection X-ray fluorescence analysis.

When the amount of contaminant extract is small when extracting the contaminant on the substrate surface of which the amount of contaminant is unknown into the solution, the contaminant extraction efficiency decreases in proportion to the size of the substrate when the entire surface of the substrate is moved. I do. When the amount of the contaminated extract is increased to improve the contamination extraction efficiency, the size of the droplet trace after drying the extract becomes larger than the high sensitivity area in the SSD detection surface, and the reliability of the contamination quantitative value is improved. Decrease.

In other words, in order to increase the reliability of the quantitative value of the contamination on the substrate surface of which the amount of contamination is unknown, the amount of the contaminated extract must be increased. There is a contradictory problem that droplet traces become large and characteristic X-rays generated from atoms in droplet traces are detected in a region where SSD detection sensitivity is low, and characteristic X-rays are counted down.

The present invention solves the problems of the conventional method for preparing a sample for analysis using a total reflection X-ray fluorescence analyzer as an example, improves the reliability of the sample for analysis, shortens the time for preparing the sample, and reduces contamination. It is an object of the present invention to improve the accuracy of quantification of contamination on the surface of a substrate whose amount is unknown, and to shorten the sample preparation time.

Further, the present invention provides an X-ray photoelectron spectroscopy (X
PS) or an analysis sample of an analyzer such as Auger electron spectroscopy.

[0017]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for sampling a predetermined amount of a solution from a solution using a micropipette and dropping the sample solution several times little by little while heating the substrate. This is achieved by repeatedly dropping one point on the surface of the substrate.

Using this method, when the sampling solution is repeatedly dropped on a single point on the substrate in small batches of several times, a small amount (5 μl or less) of the dropping solution is deposited on the substrate within a few seconds because the substrate is in a heated state. Dries to form droplet marks of 2 mm or less. By repeating this many times, the size of the droplet trace can be reduced to 2 mm or less even when the amount of the sampling liquid is large. Further, since the drying time of the droplet trace is very short, it is possible to suppress the contamination from the atmosphere.

When the substrate is heated, if the substrate heating temperature is low, it takes a long time to dry the droplets. Therefore, at least 50 ° C. or more is required. In addition, if the substrate heating temperature is too high, the dropped droplets scatter on the substrate, so that the temperature needs to be 150 ° C. or less at most.

Further, the sampling liquid is dropped in a state where the back surface of the substrate is evacuated and the substrate is warped in a concave shape. Since the substrate is warped in a concave shape, the dripping liquid can be collected at the center of the substrate, and the drop position error of the dripping liquid can be reduced.

[0021]

FIG. 3 shows an embodiment of the present invention. FIG. 3 (a) is a front view and FIG. 3 (b) is a plan view. The standard sample silicon substrate 11 whose substrate surface has been cleaned in advance,
The substrate is set on a jig 12 capable of heating the substrate while keeping the back surface of the substrate in a vacuum state.

The inside of the jig 12 can be evacuated from a vacuuming valve 13 provided on the side of the jig by using a rotary pump or the like. The jig 1 is fixed by a rubber O-ring 14 between the substrate 11 and the jig 12.
The degree of vacuum inside 2 is maintained, and by setting the back surface of the substrate to a vacuum state, the standard sample substrate 11 can be deformed into a concave shape. When the substrate 11 becomes concave, the sampling liquid 1
When 5 is dropped on the surface of the substrate 11, the dropped liquid can be collected at the center of the substrate.

The jig 12 has a Peltier element 16 for heating the substrate 11 and a copper 17 for transmitting heat to the substrate 11. The Peltier element 16 and the copper 17 are integrated into a Peltier element. 16 jig 1 by spring 18 on the lower surface
It is fixed to 2. Thermocouple 19 is used for copper 17 for heat conduction.
Is installed, and the wiring of the thermocouple 19 is
The Peltier device 16 is connected to the side
And is connected to a substrate temperature controller 21 outside the jig 12. The temperature controller 21 can constantly monitor the temperature of the substrate 11 and can change the voltage applied to the Peltier element 16 in accordance with the temperature to maintain the substrate temperature at the set temperature.

The micropipette 22 above the standard sample substrate 11 has micropipette supports 23, 24,
25. Micro pipette support 2
3, 24 and 25 fix the tip of the micropipette 22 accurately at any position on the surface of the substrate 11 by the ruler memory 26 specified on the surface of the jig 12 and the ruler memory 27 specified on the support 24. It is possible to

The standard sample substrate 11 is set on the jig 12, and the substrate 11 is deformed into a concave shape while the back surface of the substrate 11 is kept in a vacuum state. Heat to ° C. In this state, a standard solution having a known atomic concentration (iron 0.0925 ppm, nickel 0.097 ppm)
5ppm, copper 0.155ppm, platinum 0.3240ppm)
100 μl using a micropipette 22 (atomic weight is 1
× 10 ¹⁴ atoms / cm ² ). After sampling, the micropipette 22 is fixed to the center of the substrate 11 using the micropipette supports 23, 24, 25. After the fixation, the sampling liquid 15 is applied to the center of the surface of the standard sample
The solution was added dropwise in 50 portions each.

Similarly, the atomic weight is 1 × 10 ¹¹ , 1 × 1
Samples of 0 ¹² and 1 × 10 ¹³ (atoms / cm ² ) were also prepared. The size of the droplet trace after dropping was 2 mm or less in each case.

FIG. 4 shows a calibration curve measured using a total reflection X-ray fluorescence analyzer. It can be seen from the figure that the detection efficiency of the calibration curve of the standard sample for the calibration curve prepared by using the present invention is approximately three times higher than the value of the calibration curve prepared by the conventional method.

As described above, if a standard sample for a calibration curve of a total reflection X-ray fluorescence analyzer was prepared using the present invention, the accuracy of the calibration curve could be improved.

Another embodiment of the present invention will be described with reference to FIGS. 5, 6, and 7. FIG.

FIG. 5 shows another embodiment of the present invention. This embodiment is an example of a method for measuring particles and metal contamination existing on the surface of a silicon substrate and a natural oxide film on the surface using a total reflection X-ray fluorescence analyzer.

FIG. 5 shows a method for extracting contamination on the substrate surface. Since the surface of the silicon substrate 28 whose contamination amount is unknown is not cleaned, there are particles and foreign substances on the surface of the substrate 28, and metal contamination exists in the surface native oxide film. On the surface of the substrate, a sampling solution 30 for extracting contamination is provided.
Add 0 μl dropwise. The components of this sampling solution were nitric acid: hydrofluoric acid: pure water = 1: 5: 1000 and nitric acid was
8 Added to extract copper existing near the surface.

After dropping the contaminated extraction droplet, the extraction liquid 29 is applied to the substrate 28.
It is moved without any gaps on the surface, and the particles on the surface, metal contamination in the native oxide film, and copper existing near the substrate surface are taken into the extract 29. After the extraction of the substrate surface contamination, the extraction liquid 29 is moved to the center of the substrate, and the substrate is set on the jig 12 as shown in FIG. After setting the substrate 28, the back surface of the substrate is evacuated to deform the substrate into a concave shape.

Next, the tip of the micropipette 22 is fixed to the center of the substrate using the same micropipette holder (not shown) as in FIG. 3 of the above embodiment, and the contaminated extract 29 is collected. When the contaminated extract 29 is collected by using the micropipette 22, the collection efficiency can be empirically recovered to 99% or more. After the collection, the residual liquid 31 of the contaminated extract slightly remains on the substrate surface (in this case, 2 μl or less). The substrate temperature is heated to 110 ° C. while leaving the back surface of the substrate 28 in a vacuum as in the embodiment, with the residual liquid 30 that could not be recovered by the micropipette 22 remaining on the substrate surface. In this state, the recovered liquid 31 recovered by the micropipette 22 was dropped on the residual liquid 30 on the surface of the substrate 28 in 2 μl portions 150 times.

Similarly, the amount of the contaminated extract was set to 200, 100,
By changing to 50 and 30 μl, contamination on the silicon substrate surface was extracted.

FIG. 7 shows the results of measuring the contamination on the surface of the silicon substrate using the total reflection X-ray fluorescence spectrometer with varying amounts of contamination extraction. In order to improve the accuracy of the silicon substrate surface contamination amount on the vertical axis, only 30 to 300 μl of the extract for contamination extraction is collected using a micropipette 22 in advance, and the extract is collected on the substrate cleaned by the above method. Then, different collected liquids were dropped in the same manner as in the above example, and traces of the dropped liquid after dropping were quantified using a total reflection X-ray fluorescence analyzer. The quantitative value of the contamination in the collected liquid for the contaminated extract was subtracted from the quantitative value of the surface contamination of the silicon substrate having a different amount of the contaminated extract, and the value obtained by dividing the subtracted value by the surface area of the substrate 28 was used as the silicon substrate on the vertical axis. The surface contamination was determined.

FIG. 7 shows that the quantitative value of the surface contamination of the silicon substrate does not change even when the amount of the contaminated extract increases. In particular, if the substrate surface contamination is extracted with 100 μl or more of the extract, the accuracy of the contamination quantification is improved. It can also be seen that the contamination extraction time becomes shorter as the amount of the contaminated extract increases. This is because, when the amount of the contaminated extract is large, the movement time when the entire surface of the silicon substrate is moved becomes short.

As described above, if the present invention is applied to the silicon substrate surface contamination extraction method, it is possible to perform the extraction in a short time without reducing the quantitative accuracy of the substrate surface contamination.

As can be seen from the two examples, when a sample for total reflection X-ray fluorescence analysis is prepared using the present invention, the reliability of the standard sample for the calibration curve of the total reflection X-ray fluorescence analyzer and the sample preparation are improved. It is possible to shorten the time, improve the accuracy of quantifying contamination on the surface of the silicon substrate whose contamination amount is unknown, and shorten the sample preparation time.

[0039]

According to the present invention, a sample for an analytical line can be produced with high reliability and in a short time, so that the reliability of the atomic quantification of the analyzer can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a total reflection fluorescent X-ray apparatus.

FIG. 2 is a sensitivity characteristic diagram in a detection plane of a semiconductor detector.

FIGS. 3A and 3B are a front view and a plan view showing a sample preparation jig and a micropipette according to an embodiment of the present invention. FIGS.

FIG. 4 is a diagram showing a calibration curve showing the effect of the present invention.

FIG. 5 is an explanatory view of a sample manufacturing method according to another embodiment of the present invention.

FIG. 6 is an explanatory view of a sample manufacturing method according to another embodiment of the present invention.

FIG. 7 is a measurement diagram showing the effect of the present invention.

[Explanation of symbols]

11 silicon substrate, 12 jig, 13 valve, 14
... O-ring, 15 ... Sampling liquid, 16 ... Peltier element, 17 ... Copper, 18 ... Spring, 19 ... Thermocouple, 20 ... Connector, 21 ... Substrate temperature controller, 22 ... Micropipette, 23 ... Post and its base, 24: Pipette lifting and position adjuster, 25: Pipette fixture, 26: Pipette position memory jig surface, 27: Pipette position memory pipette support surface.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Okura 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside Central Research Laboratory, Hitachi, Ltd.

Claims (6)

[Claims] 1. A method for preparing a sample for analysis by sampling a predetermined amount of a solution from a solution and drop-drying the sample on a substrate surface, wherein the sample solution is dropped while the substrate is heated. . 2. A sample preparation method according to claim 1, wherein, when dropping the sampling liquid, the sampling liquid is dropped a plurality of times in small amounts on the same point. 3. The method for preparing a sample according to claim 1, wherein the amount of the liquid dropped at a time is 20 μl or less, and the diameter of the liquid trace after drying is 3 mm or less. 4. The method according to claim 1, wherein the heating temperature range of the substrate is 50 ° C. to 150 ° C. 5. A method according to claim 1, wherein the back surface of the substrate is evacuated and the sample is dropped while the substrate is warped into a concave shape. 6. A method for preparing a sample in which contamination on the surface of a substrate whose contamination amount is unknown is taken into a solution, and this solution is collected using a micropipette and dropped onto the surface of the substrate. A sample preparation method of dropping on the surface