JPH06337264A - Microanalytic method for aluminum - Google Patents

Abstract

PURPOSE:To provide a highly accurate microanalytic method for aluminium. CONSTITUTION:Hydrofluoric acid solution is added with a boron compound, e.g. boric acid, and a phosphorus compound, e.g. phosphoric acid, and used for dissolving silicon oxide on the surface of a silicon wafer. The dissolved liquid is then collected as a sample solution for frameless atomic absorption spectrochemical analysis of aluminum. Phosphorus functions to deposit an aluminum compound (aluminium phosphate) having lower solubility earlier than aluminium fluoride (AlF3) at the time of solidification of the sample solution through evaporation. Boron in the sample solution functions to discharge the residual fluorine in the from of boron fluoride from a high temperature furnace to the outside at the time of calcination and atomization. Since AlF3 is not present, atomization of vapor is promoted in the high temperature furnace thus enhancing the sensitivity of atomic absorption spectrometry along with the reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for microanalyzing aluminum, and more particularly to a method for analyzing a trace amount of aluminum in a hydrofluoric acid solution by using a high temperature furnace method such as a flameless atomic absorption spectrometry method. The present invention relates to a technique effectively applied to analysis of aluminum impurities in a silicon oxide film on a wafer.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, the inclusion of impurities leads to deterioration of characteristics and manufacturing yield. Therefore, it is an important technique to analyze and measure impurities in the semiconductor device manufacturing process and manage each manufacturing process based on the measurement information. For example, “Electronic Materials” issued by the Industrial Research Council, December 1990 issue, December 1, the same year, P6
And P7 describe a highly sensitive elemental analyzer for PPT levels. In the same document, "In recent years, impurities in semiconductor processes, new materials, development of highly functional materials in the materials field, environmental analysis of water quality and atmosphere, medical science, pharmacy, biochemistry, etc. It has been an important issue to analyze such trace elements. Until now, atomic absorption spectrophotometers and high-frequency induction plasma (ICP) emission spectrometers have been used. The range is ppm (10 ⁻⁶ g / ml) to ppb in the solution sample.
It is (10 ⁻⁹ g / ml) level, and it cannot be applied to the control level of impurity concentration of various reagents from sub-ppb to several ppt (10 ⁻¹² g / ml), which is required in the electronics field such as semiconductor devices. Is the reality. Is stated. "

On the other hand, JP-A-2-272359 discloses a method for measuring the amount of impurities on the surface of a wafer. In the abstract of this publication, "HF solution 3 is dropped on a semiconductor wafer having an oxide film 2 formed on a cleaned surface and then left for a certain period of time (approximately 2 to 5 minutes). The dropping solution dropped on 1 causes a chemical reaction with the oxide film 2 to gradually widen the reaction region and finally become spherical. Next, the spherical solution 3 is collected with a pipette or the like and The amount of impurities in the solution 3 is measured with a flame atomic absorption spectrophotometer. "

On the other hand, Japanese Unexamined Patent Publication No. 2-271253 discloses a surface analysis method for a silicon semiconductor substrate. In the abstract of this publication, "a vapor of a volatile substance is applied to the surface of a silicon semiconductor substrate for a certain period of time. As a result, a natural oxide film on the surface of the substrate reacts with the volatile substance and is decomposed.
Next, a certain amount of purified nitric acid or other acid is added to the surface to be measured of the silicon semiconductor substrate and dissolved so as to etch the surface of the substrate to collect the reaction product, and the solution containing the metal element is collected with a micropipette. This is used as a sample and measured by a flameless atomic absorption spectrometer. Is stated. "

Regarding the flameless atomic absorption spectrophotometer,
For example, it is disclosed in Japanese Utility Model Laid-Open No. 62-178353.

[0006]

Conventionally, in the analysis of a trace amount of aluminum in a hydrofluoric acid solution, a flameless atomic absorption spectrophotometer capable of analyzing a highly concentrated acidic solution has been used. However, in the analysis of a trace amount of aluminum in a hydrofluoric acid solution using a flameless atomic absorption spectrophotometer, the binding energy is much larger than the boiling point and the aluminum fluoride (AlF
It has been clarified by the present inventor that ₃ ) is generated, which causes chemical interference (interference), resulting in low sensitivity and low reproducibility.

An object of the present invention is to provide an aluminum trace analysis method capable of analyzing a trace amount of aluminum in a hydrofluoric acid solution with high sensitivity and reproducibility in a high temperature furnace analysis method such as a flameless atomic absorption spectrometry method. To do. The above and other objects and novel features of the present invention will be apparent from the description of the present specification and the accompanying drawings.

[0008]

The outline of the representative ones of the inventions disclosed in the present application will be briefly described as follows. That is, in the aluminum microanalysis method of the present invention, after adding a boron compound such as boric acid and a phosphorus compound such as phosphoric acid to a hydrofluoric acid solution, the silicon oxide film on the surface of the silicon wafer is melted using this hydrofluoric acid solution. . After that, the melt is collected to obtain a solution sample,
This solution sample is analyzed by a flameless atomic absorption spectrophotometer to analyze the content of aluminum.

In another embodiment of the present invention, after the silicon oxide film on the surface of the silicon wafer is melted by a hydrofluoric acid solution, the melt is recovered as a solution sample, and then a boron compound such as boric acid is added to the solution sample. And a phosphorus compound such as phosphoric acid are added, and the solution sample is analyzed by a flameless atomic absorption spectrophotometer to analyze the content of aluminum.

[0010]

According to the above-mentioned means, in the method for microanalyzing aluminum of the present invention, since phosphorus and boron are added to the hydrofluoric acid solution which is a solvent for collecting a solution sample, the solution is formed by the action of phosphorus. When the sample is evaporated to dryness, an aluminum compound (aluminum phosphate: AlPO ₄ ) having a low solubility is deposited before aluminum fluoride. Further, due to the action of boron in the solution sample, the fluorine remaining in the high temperature furnace at the time of ashing and atomization is discharged outside the furnace as boron fluoride. Therefore, in the sample in the high temperature furnace, aluminum fluoride which is difficult to be atomized, which has been generated conventionally, does not exist, and both become atomic vapors, so that the atomic absorption sensitivity is increased and the analysis can be performed with good reproducibility. .

In the aluminum microanalysis method according to another embodiment of the present invention, since phosphorus and boron are added to the solution sample, the solubility of the solution sample is smaller than that of aluminum fluoride when the solution sample is evaporated to dryness by the action of phosphorus. An aluminum compound (aluminum phosphate) is deposited. Further, due to the action of boron in the solution sample, the fluorine remaining in the high temperature furnace at the time of ashing and atomization is discharged outside the furnace as boron fluoride. Therefore, in the sample in the high temperature furnace, aluminum fluoride which is difficult to be atomized, which has been generated conventionally, does not exist, and both become atomic vapors, so that the atomic absorption sensitivity is increased and the analysis can be performed with good reproducibility. .

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1 is a flow chart showing a method for microanalyzing aluminum according to an embodiment of the present invention, FIG. 2 is a flow chart showing a method for obtaining a solution sample by melting a silicon oxide film on the surface of a silicon wafer, and FIG. 3 is also a frame. FIG. 4 is a flow chart-like explanatory view showing the analysis state by a RES atomic absorption spectrophotometer, FIG. 4 is a graph showing the correlation between the absorbance and the boron concentration in the aluminum microanalysis method of the present invention, and FIG. 5 is the correlation between the absorbance and the phosphorus concentration. FIG. 6 is a graph showing the correlation between the detection limit of aluminum and the phosphorus or boron concentration in the aluminum microanalysis method of the present invention.

In this embodiment, an example of analyzing aluminum (Al) contained in a silicon oxide film of a silicon wafer and Al ₂ O ₃ attached to the surface of the silicon wafer by a flameless atomic absorption spectrophotometer will be described. As shown in FIG. 1, aluminum microanalysis is carried out by adding phosphorus (P) and boron (B) to phosphoric acid (H ₃ P
O ₄ ), boric acid (H ₃ BO ₃ ) in a predetermined amount, a step of dropping the hydrofluoric acid solution onto the surface of the silicon wafer to melt the silicon oxide film, and a hydrofluoric acid solution on the silicon wafer. And the like, and a step of obtaining a solution sample by collecting the molten solution and a step of analyzing the solution sample by a flameless atomic absorption spectrophotometer to analyze aluminum.

In the aluminum microanalysis, as shown in FIG. 2, the extraction liquid 2 is dropped on the surface of a silicon wafer (Si wafer) 1 with a micropipette 3. The extraction liquid 2 is composed of a hydrofluoric acid solution, and phosphorus (P) and boron (B) are added thereto as described later. P
Is added about 0.1 mol / l in the state of phosphoric acid (H ₃ PO ₄ ), and B is added about 0.06 mol / l in the state of boric acid (H ₃ BO ₃ ).

A silicon oxide film (SiO ₂ film) 4 exists on the surface of the wafer (silicon wafer) 1. The silicon oxide film 4 is melted by the hydrofluoric acid solution which is the extraction liquid 2. The melt 5 formed by the silicon oxide film 4 dissolving in the extract liquid 2 becomes spherical due to the surface tension when the silicon oxide film 4 disappears and silicon is exposed. Therefore, the melt 5 is sucked up by a micropipette 3 (not shown) to form a solution sample 7. This solution sample 7 is a flameless atomic absorption spectrophotometer (FL-AAS
Analysis). As a method for obtaining the solution sample 7 by melting the silicon oxide film 4 on the surface of the silicon wafer 1, there is also the following method. The silicon wafer is placed in hydrofluoric acid vapor to decompose the natural oxide film on the surface, and then the extract is dropped on the silicon wafer and a guide is set on the extract. The guide moves in an arc in the radial direction of the wafer. The wafer is rotated in synchronization with this movement. This structure is similar to that of a polishing device for polishing a wafer, and a molten liquid in which a silicon oxide film is melted is accumulated under the guide. Therefore, this melt is sampled with a micropipette or the like to obtain a solution sample.

As shown in FIG. 3, the solution sample 7 is dropped from the micropipette 3 and put in the cuvette 11 of the graphite furnace 10 in the flameless atomic absorption spectrophotometer. In the graphite furnace 10, the solution sample 7 was steam dried (dried to dryness) at about 100 ° C., and then about 1000 ° C.
The sample is ashed to ash 12 and 3000 ° C.
Atomic vapor 13 is made to some extent. Further, a lamp (atomic spectrum light source) arranged on one side of the graphite furnace 10
Light 15 emitted from 14 is irradiated from one side of the graphite furnace 10, and transmitted light 16 transmitted through the atomic vapor layer is detected by a detector 17. Then, the irradiation intensity I _{0 of the} light 15 is
From the detected intensity I of the transmitted light 16 to the absorbance (absorbance = lo
gI ₀ / I) is obtained. This absorbance corresponds to the number of atoms. Therefore, if the correlation between the absorbance and the number of atoms is obtained in advance, the number of atoms, that is, the aluminum content (contamination amount) can be easily known from the absorbance obtained by analysis.

In such an aluminum microanalysis method, since a desired amount of phosphorus and boron are added to the solution sample 7, the action of phosphorus causes the solution sample 7 to be heated before aluminum fluoride (AlF ₃ ) during evaporation to dryness. An aluminum compound (aluminum phosphate) having a low solubility is deposited on the surface. Further, due to the action of boron in the solution sample, the fluorine remaining in the high temperature furnace at the time of ashing and atomization is discharged outside the furnace as boron fluoride. Therefore, in the high temperature furnace, aluminum fluoride which has been difficult to be atomized and which has been conventionally generated does not exist. As a result, all the samples become atomic vapors, so the atomic absorption sensitivity becomes high.

Here, the result of aluminum analysis in the hydrofluoric acid solution in the case of the conventional method in which phosphorus and boron are not added will be described with reference to FIG. 20 microliters of a sample containing Al at a concentration of 50 ppb was prepared, the hydrofluoric acid concentration (wt%) of this sample was changed, this was atomized, and the absorbance was measured. The hydrofluoric acid used was 46.8 wt%. The absorbance (relative value) is a relative value of the measured values when the absorbance in pure water is 100. As is clear from the graph, the absorbance of aluminum in hydrofluoric acid is lower than about 40% at a hydrofluoric acid concentration of 10% and 20% at a concentration of 20% as compared with the absorbance of pure water. To do.

On the other hand, the inventor has found that the addition of B and P improves the absorbance. The graphs of FIGS. 4 and 5 are graphs showing how the absorbance is improved. Figure 4
Is a graph showing the correlation between the boron concentration and the Al absorbance, and the graph in FIG. 5 is a graph showing the correlation between the phosphorus concentration and the Al absorbance. These graphs were obtained by changing the boric acid concentration or phosphoric acid concentration of 20 microliters of a sample containing 50 ppb of aluminum in a 9.5% hydrofluoric acid solution as a sample solution. When changing the concentration of boric acid, fix the concentration of phosphoric acid at 0.06 mol / l,
When changing the phosphoric acid concentration, adjust the boric acid concentration to 0.06 mol / l.
Fixed to. From the graph, it was confirmed that the sensitivity was not improved by adding boric acid alone or phosphoric acid alone, and the sensitivity of aluminum in the hydrofluoric acid solution was improved for the first time only when phosphoric acid and boric acid were present at the same time. . The absorption of both boric acid and phosphoric acid is improved from the addition of 0.005 mol / l or more, and the absorption is restored to the level of aluminum in pure water by the addition of 0.02 mol / l or more. Further, in order to improve reproducibility, it is desirable to add 0.05 mol / l or more of boric acid and phosphoric acid at the same time. Since the boron concentration and the phosphorus concentration to be added are known, it is clear that the change in the absorbance due to the addition of boron and phosphorus can be canceled out by only measuring the absorbance of a solution having the same composition in advance.

FIG. 6 shows the detection limit of aluminum element in the hydrofluoric acid solution obtained from the results of FIGS. 4 and 5. From the graph, it is several tens pp in the conventional method without adding boric acid or phosphoric acid.
It was confirmed that the detection limit, which was varied in b, could be reduced to 0.3 ppb, and the sensitivity was improved about 10 times or more as compared with the conventional method. Also, due to the improved reproducibility,
The reliability of the analysis result can be improved.

In this example, the analysis of aluminum in a 9.5% hydrofluoric acid solution is shown.
Similar results were obtained for the analysis of aluminum in% hydrofluoric acid solution.

[0022]

【The invention's effect】

(1) According to the aluminum microanalysis method of the present invention, it was an interfering element in the trace aluminum analysis in the hydrofluoric acid solution in the high temperature furnace method by simultaneously adding the boron solution and the phosphoric acid solution to the sample solution. It is possible to prevent the formation of aluminum fluoride and obtain an effect that the analysis can be performed with high sensitivity. That is, according to the aluminum microanalysis method of the present invention, the detection limit of the aluminum element in the hydrofluoric acid solution is about 0.3 ppb as compared with several tens ppb by the conventional method, and the sensitivity is about the same as the conventional method. It has improved more than 10 times.

(2) According to the aluminum microanalysis method of the present invention, by simultaneously adding the boron-based solution and the phosphoric acid-based solution to the sample solution, an interfering element is present in the trace aluminum analysis in the hydrofluoric acid solution in the high temperature furnace method. It is possible to prevent the formation of aluminum fluoride, which was a problem with the conventional method, and obtain an effect that the analysis can be performed with good reproducibility.

(3) From the above (2), according to the aluminum microanalysis method of the present invention, it is possible to obtain the effect that the reliability of the analysis result can be improved by improving the reproducibility of the analysis.

(4) According to the present invention, it is possible to provide an aluminum microanalysis method capable of analyzing the detection of elemental aluminum in a hydrofluoric acid solution at a higher level and with good reproducibility.

(5) From the above (1) to (4), according to the aluminum microanalysis method of the present invention, Al contamination analysis of a semiconductor wafer can be easily carried out with high sensitivity.
The synergistic effect of enabling early detection of characteristic deterioration of the device due to Al contamination and quality control is obtained.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say, for example,
As a method of adding boric acid and phosphoric acid in the above-described examples, the sample was directly added to the analysis sample (solution sample) as a pretreatment, but after the analysis sample (solution sample) was placed in a high-temperature furnace such as a flameless atomic absorption spectrophotometer, Even if boric acid and phosphoric acid are added and mixed in a high-temperature furnace, the same effect as in the above-mentioned embodiment can be obtained. Further, as a method of adding boric acid or phosphoric acid to a solution sample, in addition to the method of adding an extract solution (hydrofluoric acid-based solution or the like) for extracting the analyte as in the above-mentioned embodiment, the extract solution is added to the analyte. The same effect as in the above embodiment can be obtained by the method in which boron or phosphoric acid is added to the recovered liquid that is recovered after the attachment.

As has been confirmed from the results of the present invention, when the Si oxide film contains boron or phosphorus as in a BPSG (Boronphosphosilicate Glass) film,
By decomposing the Si oxide film with a hydrofluoric acid solution and measuring the solution, the same effect as adding boron and phosphorus to the hydrofluoric acid solution can be obtained. As a result, high-sensitivity analysis of aluminum in the BPSG film is possible by the direct high temperature furnace analysis method.

In the above description, the silicon oxide film on the surface of the silicon wafer and the aluminum adhering to the surface of the silicon wafer in the manufacturing of semiconductor devices, which is the field of application of the invention mainly made by the present inventor, have been described. I explained about applying it to analysis technology,
It is not limited to that. INDUSTRIAL APPLICABILITY The present invention can be applied to at least aluminum microanalysis technology for aluminum contamination and substances containing aluminum.

[Brief description of drawings]

FIG. 1 is a flow chart showing an aluminum trace analysis method according to an embodiment of the present invention.

FIG. 2 is a flow chart-like explanatory view showing a method of collecting a solution sample in the aluminum microanalysis method according to one embodiment of the present invention.

FIG. 3 is a flow chart-like explanatory view showing an analysis state by a flameless atomic absorption spectrophotometer in the aluminum trace analysis method according to the embodiment of the present invention.

FIG. 4 is a graph showing the correlation between the absorbance and the boron concentration in the aluminum microanalysis method according to an example of the present invention.

FIG. 5 is a graph showing the correlation between the absorbance and the phosphorus concentration in the aluminum microanalysis method according to one example of the present invention.

FIG. 6 is a graph showing the correlation between the detection limit of aluminum and the concentration of phosphorus or boron in the method for microanalyzing aluminum according to one embodiment of the present invention.

FIG. 7 is a graph showing the analytical sensitivity of a trace amount of aluminum in a hydrofluoric acid solution according to a conventional method.

[Explanation of symbols]

1 ... Wafer (silicon wafer), 2 ... Extraction liquid, 3 ... Micropipette, 4 ... Silicon oxide film (SiO ₂ film), 5
... Melt liquid, 7 ... Solution sample, 10 ... Graphite furnace (high temperature furnace), 11 ... Cuvette, 12 ... Ash, 13 ... Atomic vapor,
14 ... Lamp, 15 ... Light, 16 ... Transmitted light, 17 ... Detector.

Claims (3)

[Claims] 1. A method of melting a substance which may contain aluminum with a hydrofluoric acid-based solution to obtain a solution sample, and an aluminum microanalysis method of evaporating and drying the solution sample to analyze the content of aluminum. A method for microanalyzing aluminum, characterized in that a predetermined amount of phosphorus and boron are added to a hydrofluoric acid-based solution for melting the substance. 2. A step of dissolving a substance that may contain aluminum in a hydrofluoric acid-based solution to obtain a solution sample, and storing the solution sample in an analyzer by a high-temperature furnace method to store a trace amount of aluminum in the solution sample. A method for microanalyzing aluminum, which comprises ashing and atomizing an element to analyze the content of aluminum, wherein a predetermined amount of phosphorus and boron are added to the solution sample for analysis. 3. The aluminum trace analysis method according to claim 1 or 2, wherein the solution sample is analyzed by a flameless atomic absorption spectrophotometer.