JPH0590378A - Impurity analyzing method - Google Patents

Abstract

PURPOSE:To extremely accurately perform a microanalysis of impurities of a semiconductor substrate and a thin film on the substrate. CONSTITUTION:The surface of an object such as a semiconductor substrate 1 is etched with plasma gas, and an etching residue 2 is obtained on the surface to be etched. Then, the residue 2 is decomposed with fluoric acid vapor to obtain decomposed matter 3. Further, recovery liquid 4 in which the matter 3 is recovered with recovery liquid is obtained, and analyzed by using a high sensitivity analyzer 5. Thus, the semiconductor substrate itself, a polysilicon film and a thick nitride film which were heretofore difficult to be analyzed, can be analyzed. Particularly, surface contaminant metal impurities are detected and can be reduced.

Description

Detailed Description of the Invention

[0001]

The present invention is used in a method for analyzing impurities in an object such as a semiconductor substrate and a thin film on a semiconductor substrate,
In particular, the present invention relates to an impurity analysis method improved so that the surface of an object is etched with a gas that has been turned into plasma and the etching residue is analyzed.

[0002]

2. Description of the Related Art In the electronic industry, as devices are miniaturized, wafer contamination (metal contamination) due to metal impurities caused by materials and processes becomes a problem as a cause of increased leak current and deterioration of junction breakdown voltage and oxide film breakdown voltage. ing. To improve device reliability and improve production yield,
Metal contamination must be reduced by improving the purity of materials and reducing process contamination. It is said that pollution must be reduced to a level of 10 ¹⁰ atoms / cm ² or less in the future. In reducing metal contamination, it is essential to quantitatively grasp metal impurities in a semiconductor substrate up to a concentration level of 10 ⁹ atoms / cm ² or less.

Further, a technique utilizing the characteristics of a thin film formed on a substrate is rapidly advancing, and thin films such as a polysilicon film and a nitride film are formed on the substrate and used. Along with the ultra-high integration of semiconductors, higher quality of these thin films is required, and reduction of the concentration of metal impurities such as Na and Fe is also required. In order to reduce the concentration of metal impurities, it is essential to measure the concentration of these impurities in the thin film.

As a method for analyzing impurities in a semiconductor substrate and a thin film on the semiconductor substrate, secondary ion mass spectrometry (hereinafter referred to as S
This is called the IMS method. ) And total reflection X-ray fluorescence analysis (hereinafter, T
This is called the R-XRF method. ) Was used. Further, the semiconductor substrate and the thin film on the semiconductor substrate are sprayed with hydrofluoric acid for decomposition, and the decomposed product is recovered by a recovery liquid, and a highly sensitive analysis method such as flameless atomic absorption spectrometry (hereinafter, hydrofluoric acid vapor decomposition-
This is called atomic absorption spectrometry. ) Was used. In this case, the hydrofluoric acid vapor decomposition-atomic absorption spectrometry was not pretreated.

[0005]

Among the above-mentioned conventional impurity analysis methods, the SIMS method has a drawback that sensitivity is insufficient depending on the element and quantitative analysis is difficult. Also, T
The R-XRF method also has the drawback of lacking sensitivity.

On the other hand, the hydrofluoric acid vapor decomposition-atomic absorption spectrometry method is
It is extremely quantitative, and the sensitivity is detected up to the level of 10 ⁸ atoms / cm ² depending on the element, which is effective in reducing metal contamination. However, this conventional hydrofluoric acid vapor decomposition-atomic absorption spectrometry does not require any special pretreatment, so that it can be decomposed with hydrofluoric acid vapor, a natural oxide film, a thermal oxide film, and a thin film (~ 4
00Å) Only the impurities in the nitride film and the glass film can be analyzed, and the semiconductor substrate itself, the polysilicon film, and the thick nitride film cannot be analyzed.

An object of the present invention is to eliminate the above-mentioned drawbacks, and in particular, to provide an impurity analysis method which enables ultra trace analysis of impurities in a semiconductor substrate and a thin film on a semiconductor substrate.

[0008]

According to the present invention, in a method of analyzing impurities in an object such as a semiconductor substrate and a thin film on a semiconductor substrate, the surface of the object is etched with a gas that is made into plasma, and the etching residue is analyzed. Is characterized by.

Further, the present invention provides the method for analyzing an etching residue, wherein the etching residue is decomposed with hydrofluoric acid vapor, the decomposed product is recovered with a recovery liquid, and impurities in the recovery liquid are analyzed with a high-sensitivity analyzer. It can be a method of analysis.

[0010]

When the surfaces of the semiconductor substrate and the thin film on the semiconductor substrate are etched with a gas that is made into plasma, all surface impurities are removed as etching residues. Therefore, by analyzing this etching residue, it becomes possible to carry out the trace analysis of the target impurities with high accuracy.

The etching residue is analyzed by decomposing the etching residue on the object with hydrofluoric acid vapor, recovering it with a recovery liquid, and analyzing the impurity components in the recovery liquid with a high-sensitivity analyzer. You can

[0012]

Embodiments of the present invention will be described below with reference to the drawings and tables.

FIG. 1 is a flow chart for explaining an example of the impurity analysis method of the present invention, and FIG. 2 is a schematic sectional view showing a main part of an example of the etching apparatus.

In FIG. 1, first, the surface of the semiconductor substrate 1 is etched with a gas made into plasma by the etching apparatus of FIG. 2 to obtain an etching residue 2 on the surface of the semiconductor substrate. Next, the etching residue 2 is decomposed with hydrofluoric acid vapor to obtain a decomposition product 3. Then, the decomposed product 3 is recovered with a recovery liquid to obtain a recovery liquid 4. Finally, the recovered liquid 4 is analyzed using the high sensitivity analyzer 5. Although the target object is the semiconductor substrate 1 in FIG. 1, the same applies to a thin film on a semiconductor substrate.

Specific embodiments will be described in detail below.

Example 1 Example 1 shows an example of analysis of a polysilicon thin film on a silicon substrate.

The silicon substrate 1a on which the polysilicon thin film (3000Å) was formed was set on the susceptor 7 provided in the etching chamber 6, and the polysilicon thin film was etched under the following etching conditions.

Power: 200 W Gas: CF ₄ 100SCCM, O ₂ 100SC
CM pressure: 1 Torr temperature: 50 ° C. Etching time: 6 minutes After etching, the surface of the silicon wafer is decomposed by the generated vapor of hydrofluoric acid, and the decomposed product is recovered with 200 μl of dilute hydrofluoric acid-hydrogen peroxide solution, and the recovered liquid is used. Was analyzed by a flameless atomic absorption spectrometer. The results are shown in Table 1.

[0019]

[Table 1] In Table 1, the pretreatment background is the background level of the etching apparatus itself, and contamination of metal impurities is not seen at a very low level. As for the measured impurities in the polysilicon film, Al is about 30 times as much as the pretreatment background, and Fe, Cu, and Na are about 2 to 5 times as much. From this, it is understood that the present invention makes it possible to grasp the metal contamination of the polysilicon thin film on the silicon substrate at the level of 10 ⁹ atoms / cm ² .

Also, with respect to a silicon substrate, if a polysilicon thin film is processed under substantially the same conditions, a certain amount of decomposition and analysis can be performed.

The etching apparatus used in the present invention is
As long as there is no metal contamination from the etching apparatus itself like the downstream type shown in FIG.

[Embodiment 2] In Embodiment 2, an example in which a nitride film is analyzed by the method of the present invention is shown. In Example 2 as well, the process shown in FIG. 1 was performed and analyzed.

The silicon substrate 1a having the nitride film (1000 Å) formed thereon was etched by the etching apparatus shown in FIG. 2 as in Example 1 under the following etching conditions.

Power: 200 W Gas: CF ₄ 100SCCM, O ₂ 100SC
CM pressure: 1 Torr temperature: 50 ° C. Etching time: 2.5 minutes After etching, the surface of the silicon wafer is decomposed with hydrofluoric acid generated vapor, and the decomposed product is recovered with 200 μl of a dilute hydrofluoric acid-hydrogen peroxide solution, The recovered liquid was analyzed by a flameless atomic absorption spectrometer. The results are shown in Table 2.

[0025]

[Table 2] Al was detected about 60 times more in the measured impurities in the nitride film on the silicon substrate, and Fe and Cu contained 4 to 2 times.
About 0 times is detected. The pretreatment background is at a very low level so there is no contamination from the etching equipment. Therefore, according to the present invention, 400 Å on a silicon substrate
The metal impurities in the thick nitride film having the above thickness are 10 ⁹ atoms /
It can be seen that analysis can be performed at the cm ² level.

[0026]

As described above, the substrate or the thin film is decomposed by the generated vapor of hydrofluoric acid, the decomposed product on the substrate is recovered by the recovery liquid, and the impurity component in the recovery liquid is analyzed by the high sensitivity analyzer. Before, by etching the substrate or thin film with a gas that turned into plasma, and analyzing the etching residue,
There is an effect that a semiconductor substrate itself, a polysilicon film or a nitride film having a thickness of 400 Å or more, which cannot be analyzed conventionally, can be analyzed. Therefore, by using the analysis method of the present invention, it is possible to reduce metal contamination and manufacture a semiconductor product of high quality and high production yield, and the effect is great.

[Brief description of drawings]

FIG. 1 is a flowchart for explaining an example of an impurity analysis method of the present invention.

FIG. 2 is a schematic cross-sectional view showing a main part of an example of the etching apparatus.

[Explanation of symbols]

 1 Semiconductor Substrate 1a Silicon Substrate 2 Etching Residue 3 Decomposition Product 4 Recovery Liquid 5 High Sensitivity Analyzer 6 Etching Chamber 7 Susceptor

Claims (2)

[Claims] 1. A method for analyzing impurities in an object such as a semiconductor substrate and a thin film on a semiconductor substrate, wherein the surface of the object is etched with a gas that is made into plasma,
A method for analyzing impurities, which comprises analyzing the etching residue. 2. The method for analyzing the etching residue comprises decomposing the etching residue with hydrofluoric acid vapor, recovering the decomposed product with a recovery liquid, and analyzing impurities in the recovery liquid with a high-sensitivity analyzer. The method for analyzing impurities according to claim 1.