JPH09129693A - Method of analyzing impurities on the surface of semiconductor substrate and thin film thereon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make feasible of the analysis of impurities in a recovery solution leaving it intact with high precision and in high sensitivity by using a chemical solution containing chloric acid for a recovery solution of decomposed matter of semiconductor substrate thin film by hydrofluoric acid vapor. SOLUTION: A Teflon made sealing vessel 21 containing HF22 is heated on a hot plate 23 so that the produced HF gas 25 may be sprayed on the whole surface of a silicon wafer 26 using N2 gas 24 to decompose the thin film and impurities on the surface. Later, the whole surface of the Si wafer is scanned with recovery solution in chlorine concentration of 0.3% to be turned into 12ppm of gross chlorine concentration at the oxidization.reduction potential of 1020mV, PH3 and then the recovery solution is recovered using a micro pipet so as to measure the impurities by an atomic absorptiometric device. Through these procedures, about 90% of aqua regia recovery solution can be received by one time processing thereby enabling the analysis with high precision in high sensitivity to be performed within a short time by safety operation eliminating the melting down process in a dilute acid after evaporated solidification.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for analyzing impurities on the surface of a semiconductor substrate and a thin film on a substrate, and more particularly, to an analysis method for analyzing platinum (Pt) as an impurity on the surface of a semiconductor substrate and a thin film on the substrate.

[0002]

2. Description of the Related Art In the field of electronic industry, device miniaturization,
With the increase in density, reduction of contamination caused by materials and manufacturing processes has become an important issue. In particular, heavy metal contamination must be eliminated as much as possible because it significantly degrades the performance of semiconductor devices. In order to solve this problem, ultrasensitive analysis of the surface of the semiconductor substrate and the thin film on the substrate for detecting metal contamination is required.

As a conventional impurity analysis method, a Vapor Phase Decomposition (VPD) method, which has a high detection sensitivity, is relatively simple in operation, and easy to analyze data, is widely used (Japanese Unexamined Patent Application Publication No. Hei. No. 188,642, JP-A-4-360551).

FIGS. 5 and 6 are cross-sectional views of respective examples of the apparatus used in the above-mentioned VPD method. The apparatus shown in FIG. 5 is provided with a beef 2 for evaporating Teflon, a Teflon wafer carrier 3 and a decomposed liquid receiving tray 4 on the bottom surface of a Teflon sealed container 1 respectively. Hydrofluoric acid 6 is introduced into beaker 2 and vaporized at ambient temperature. The generated hydrofluoric acid gas reacts with an oxide film on wafer 5 to be decomposed, and the reaction-decomposed droplet 7 is subjected to a decomposed liquid receiving tray. 4. And
After the reaction decomposition droplets 7 are collected using a micropipette, they are diluted to a certain amount with pure water and used as a sample solution.

In the apparatus shown in FIG. 6, a Teflon evaporating beaker 2 and a Teflon table 8 are provided on the bottom of a Teflon sealed container 1, respectively, and mixed acid (20% hydrofluoric acid and
(0% nitric acid) 9 is put in and heated by a heater (not shown). In the apparatus shown in FIG. 6, after the wafer 5 is placed on the convex portion 81 of the table 8, the mixed acid 9 in the beaker 2 is heated to continuously generate the mixed acid gas b. While the nitrogen gas a is fed through the nitrogen gas suction port 10, the nitrogen gas in the closed container 1 is discharged through the nitrogen gas discharge port 11.

As a result, the mixed acid gas b rising from the beaker 2 is quickly guided to the wafer 5 on the table 8 by carrying the flow of the nitrogen gas a. At this time, the mixed acid gas b
The surface of the wafer 5 (the surface opposite to the convex portion 81) is efficiently guided by the downward airflow of the nitrogen gas a, causing a chemical reaction with the oxide film on the surface of the wafer 5 to decompose the oxide film. As a result, the reaction decomposition liquid 12 becomes droplets and is scattered on the surface of the wafer 5. After that, the closed container 1 is opened, and the wafer 5 is taken out.
The recovery liquid is dropped on the surface, the wafer 5 is tilted, and all the droplets of the reaction decomposition liquid 12 are recovered by the micropipette while rolling on the surface without leaking.

In the analysis of impurities on the surface of a semiconductor substrate and a thin film on a substrate, a natural oxide film on a wafer 5 as a semiconductor substrate is removed using a device such as that shown in FIGS. A thin film such as an oxide film or a nitride film is decomposed, and metal impurities remaining on the semiconductor substrate are recovered by a recovery solution by a method as shown in FIG. 7, and impurities in the recovery solution are analyzed by an atomic absorption spectrometer (AAS: Atomic Absorption Sp
ectrometry) and inductively coupled plasma mass spectrometer (ICP)
-MS: Inductively Coupled Plasma-Mass Spectromet
ry).

The VPD-AAS method and the VP method are generally used in accordance with an analyzer which generally uses a series of operations from thin film decomposition by vapor such as hydrofluoric acid to measurement and analysis by the analyzer.
It is called the D-ICP-MS method. There are other devices having the same principle other than the device shown here, but they are omitted here. In addition, in the device that performs thin film decomposition by steam,
The device of FIG. 4 described later is also known (Kaori Watanabe et al.,
"Technique for evaluating ultra-trace impurities in semiconductor processes", IEICE Technical Committee SDM 91-159, December 1991), which will be described later.

Here, a method of recovery using a recovery liquid will be described. First, as shown in FIG. 7A, a semiconductor substrate 15 on which a thin film such as a natural oxide film, an oxide film, or a nitride film on the surface is decomposed. Then, the collected solution 16 is collected with a micropipette 17.
After dropping, the entire surface is scanned with the collecting liquid 16 and taken into the collecting liquid so that all the metal impurities on the substrate surface can be collected as shown in FIGS. I do. Finally, as shown in FIG. 7D, the recovered liquid 16 after scanning is recovered by the micropipette 17 and introduced into the analyzer.

Next, the recovered liquid will be described. Normal V
Pure water, dilute hydrofluoric acid-hydrogen peroxide mixed solution, etc. are used as the recovery liquid for the PD method. Particularly when a precious metal element with a low ionization tendency is to be measured, aqua regia is used as the recovery liquid. ing. Among the noble metal elements, Pt is particularly difficult to recover, so the substrate is heated to recover aqua regia. Noble metal elements cannot be sufficiently decomposed by hydrofluoric acid vapor, and even if they can be decomposed, they tend to re-adhere to the silicon substrate surface because their ionization tendency is smaller than that of silicon. This is because recovery is difficult with a mixed solution of hydrogen acid and hydrogen peroxide.

In short, in order to analyze the noble metal element, there is no chemical solution that can be decomposed and recovered other than the use of aqua regia, which has an extremely strong oxidizing property, and the Pt analysis can be efficiently recovered by further heating the substrate. Is known (SDM9
1-159).

In addition to the VPD method, X-rays are incident on the substrate at a very small incident angle, and impurities are quantitatively determined by fluorescent X-rays obtained from impurities such as metals existing near the substrate surface. Reflection X-ray fluorescence analysis (TR-XRF: Total Refl
Section X-Ray Florescence spectrometry, or secondary ion mass spectrometry (SIMS) in which primary ions are incident on a silicon substrate and metal ions in the substrate are sputtered to detect ionized secondary ions.
y) etc. are used for impurity analysis.

[0013]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention TR-XR
F is a non-destructive analysis and easy to measure, but VPD
The method has the drawbacks that measurement cannot be performed with high sensitivity as compared with the method, and that only the surface of the electrode can be measured.

Further, the SIMS has a problem that the sensitivity is insufficient for some elements and that quantitative analysis is difficult. Further, there are drawbacks such that a large-scale and expensive device is required and skill is required for analysis operation and data analysis.

For these reasons, the VPD method is most often used for analyzing impurities on the surface of a semiconductor substrate. Further, as described above, in the case of analyzing a noble metal element, particularly Pt, a VPD method of recovering aqua regia in a heated state of a semiconductor substrate has been conventionally used.

However, even in the VPD method, if aqua regia is dropped onto a semiconductor substrate that is overheated even by a slight amount, the aqua regia will fly out strongly on the semiconductor substrate and the stability as an analytical method is poor. . In addition, local exhaust equipment must be installed to prevent suction of acid-based atmospheres, and work must be performed in a clean draft that is much safer than usual. Furthermore, in the above-mentioned VPD method, since the aqua regia evaporates or spatters to some extent by heating the semiconductor substrate, it is difficult to secure the amount of the recovered liquid, and the effect on the quantitative analysis result is large.

Furthermore, in the above-mentioned VPD method, aqua regia as a recovered liquid cannot be directly introduced into an analyzer such as AAS or ICP-MS for measurement. This is because the sample introduction portion is corroded due to the high acid concentration, or is affected by the matrix. In addition, since an attempt is made to measure a trace amount of impurities, it is not possible to dilute aqua regia, which is a recovered liquid, for measurement.

Therefore, the aqua regia must be evaporated to dryness, and the residue must be dissolved in a dilute acid such as hydrochloric acid or nitric acid for measurement. For this reason, the conventional method naturally has a problem that the trouble and the time until the measurement are increased, whereby contaminants are mixed in and the background is deteriorated.

The present invention has been made in view of the above points.
An object of the present invention is to provide a method for analyzing impurities on a semiconductor substrate surface and a thin film on a substrate, which can analyze impurities with high accuracy and high sensitivity as a recovered liquid.

Another object of the present invention is to provide a method of analyzing impurities on a semiconductor substrate surface and a thin film on a substrate, which can stably analyze impurities by a safe operation.

It is a further object of the present invention to provide a method for analyzing impurities on a semiconductor substrate surface and a thin film on a substrate, which is particularly suitable for Pt analysis by improving the recovery rate of Pt.

[0022]

In order to achieve the above object, the present invention decomposes a semiconductor substrate surface and a thin film on the substrate by hydrofluoric acid vapor, and recovers the decomposed product with a recovery liquid.
In the impurity analysis method for analyzing the recovered liquid, a chemical solution containing chloric acid is used as the recovered liquid. Here, the chemical solution containing chloric acid is any one of chlorine water, a mixed solution of chlorine water and ozone water, and electrolytic ionic water using hydrochloric acid as a supporting salt.

When electrolytic ionized water using hydrochloric acid is used as the supporting salt, Pt attached to the surface of the semiconductor substrate can be eluted by chloric acid generated during electrolysis. Table 1 shows P
The figure shows the metal elution amount when the semiconductor substrate on which t was deposited was treated with electrolytic ionic water.

[0024]

[Table 1] Here, in Table 1, pure water refers to water that only circulates in the apparatus, and electrolyzed off anode water refers to water that contains hydrochloric acid as a supporting salt but has not been electrolyzed, and electrolyzed on anode water. Means water which has undergone electrolysis to generate chloric acid. The oxidation-reduction potential of the anode water used was 11
05 mV, pH is 1.2.

From Table 1, it can be seen that Pt was detected in the anolyte water which was electrolyzed by adding hydrochloric acid as a supporting salt, as compared with other metals. This is because chloric acid present in the anode water reacts with Pt and elutes. Therefore, when the Pt analysis of the semiconductor substrate surface and the thin film on the substrate is performed by the VPD method, Pt can be decomposed and recovered by using a chemical solution containing chloric acid such as anode water as the recovery liquid.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the first embodiment of the method for analyzing impurities on the surface of a semiconductor substrate and a thin film on a substrate according to the present invention in comparison with the recovery rate of Pt according to a conventional method.
In this embodiment, impurities in a thin film on a semiconductor substrate decomposed by a decomposition apparatus to which the VPD method is applied are recovered using chlorine water as a recovery liquid, and analyzed by AAS.

Here, as the above-mentioned disassembling apparatus, the conventional apparatus shown in FIGS. 5 and 6 can be used, but here, the disassembling apparatus having the configuration shown in FIG. 4 disclosed in the above-mentioned document (SDM91-159) is used. Used. In the figure, a Teflon sealed container 21 containing hydrofluoric acid (HF) 22 is
It is heated by the hot plate 23, thereby generating HF vapor 25 in the Teflon sealed container 21, and sending out the HF vapor 25 into the pipe with nitrogen (N ₂ ) gas 24.

HF vapor 25 delivered by N ₂ gas 24
Is sprayed on the entire surface of the silicon wafer 26 fixed by the vacuum tweezers 27 to decompose thin films and contaminants on the surface of the wafer 26.

Thereafter, the method shown in FIG.
The entire surface of the wafer 26 is scanned with a recovery solution that is chlorine water unique to the present embodiment, and then the recovery solution is recovered by a micropipette, and impurities are measured by an atomic absorption spectrometer (AAS).

Here, the chlorine water has a chlorine concentration of 0.3%.
Was adjusted so that the total chlorine concentration was 12 ppm. The oxidation-reduction potential is 1020 mV and the pH is 3. FIG. 1 shows VPD processing (a series of disassembly and recovery operations).
The recovery rate was obtained by repeating 5 times. At this time, the analysis substrate is intentionally subjected to Pt contamination at 1 × 10 ¹³ atoms / cm ² .

As a result, as shown by white circles in FIG. 1, the conventional method of recovering aqua regia while heating the semiconductor substrate has a recovery rate of about 70% in the first recovery, but the chlorine recovery of the present embodiment is about 70%. In the method of recovering water, as shown by the black circle in FIG. 1, 90% can be recovered by one recovery operation, and the recovery rate is improved by about 20% as compared with the conventional method.

Further, conventionally, a recovery liquid (aqua regia) having a recovery rate of about 70% must be evaporated to dryness and dissolved in a dilute acid, so that contamination during that time becomes a problem. On the other hand, in the present embodiment, measurement can be performed in the state of the recovered chlorine water, and the conventional problem of contamination and the like is solved.

At this time, the lower limit of quantification is 3 × 10 ⁸ atoms.
s / cm ² , and there is no problem in measurement because data reproducibility is good. The conventional lower limit of quantification is 1 × 10 ⁹ atom
Since it was s / cm ² , it can be seen that the lower limit of quantification of the analysis of the present embodiment was improved by about one digit, and the sensitivity was increased.

The concentration of chlorinated water as the recovery liquid is 5 to
20 ppm is preferred. At a concentration of 5 ppm or less, chloric acid is too dilute to collect all of Pt on the semiconductor substrate, and at a concentration of 20 ppm or more, chlorine is too concentrated and cannot be directly measured by a measuring device.

Next, a second embodiment of the present invention will be described. FIG. 2 is a diagram comparing the second embodiment of the method of the present invention with the Pt recovery rate of the conventional method. In this embodiment, a mixed solution of chlorine water and ozone water is used as the recovery liquid. The recovered liquid at this time has a chlorine concentration of 0.3%.
Was adjusted to pH 3 by mixing chlorine water having a total chlorine concentration adjusted to 12 ppm and ozone water obtained by bubbling a gas having an ozone concentration of 6 g / Nm ³ at 60 liters / hour for 40 minutes.

The characteristic shown in FIG. 2 is different from that of the first embodiment shown in FIG.
Intentionally 1 × 10¹³ atoms / cm²
The substrate surface contaminated with Pt is repeatedly processed 5 times,
The recovery rate was determined. As a result, the black circles in Figure 2
As shown, in the present embodiment, chlorine water-ozone water mixing
Recovered in liquid, present on substrate surface in one recovery operation
93% of Pt can be recovered, which is less than the recovery of chlorine water alone.
It turned out that the recovery rate is good.

The lower limit of quantification at this time is 7.8 × 10 ⁸ at.
It was oms / cm ² . The pH of the recovered liquid of the chlorinated water / ozone water mixed liquid is adjusted to 4 or less. If the pH is 4 or more, the acid is too weak to obtain a recovery effect. In this embodiment, the same effect as that of the first embodiment can be obtained.

Next, a third embodiment of the present invention will be described. FIG. 3 is a diagram showing a comparison between the third embodiment of the method of the present invention and the Pt recovery rate of the conventional method. This embodiment is an example in which anode water of electrolytic ion water with hydrochloric acid as a supporting salt is used as the recovery liquid. The recovered liquid (anode water) at this time was obtained by electrolyzing pure water using a three-layer electrolytic layer, and 40 mM hydrochloric acid was used as a supporting salt. The oxidation-reduction potential of the produced anode water is 1100 mV, and the pH is 1.30.

The characteristic shown in FIG. 3 is deliberately 1 × 10 ¹³ atoms / cm ² , as in the embodiments shown in FIGS.
The substrate surface contaminated with Pt is repeatedly processed 5 times,
The recovery rate was determined. Here, the amount of Pt already contained in the anode water was excluded when calculating the data. As a result, when the anode water was used as the recovery liquid, a recovery rate of 85% was obtained in one recovery operation.

Since the amount of chloric acid in the anode water can be increased depending on the amount and concentration of the supporting salt and the conditions of the electrolysis, the recovery rate can be further increased. At this time, the lower limit of quantification was 2.1 × 10 ⁸ atoms / cm ² . The anode water as the recovery liquid has an oxidation-reduction potential of 10
It is preferably at least 00 mV and at most pH 2.

As described above, according to the above embodiment,
By using a chemical solution containing chloric acid, such as anode water, for the recovery liquid, Pt attached to the semiconductor substrate can be eluted, and a large recovery rate can be obtained. it can. For this reason, compared to the conventional method using aqua regia as the recovery liquid, the time and labor required for measurement can be eliminated, and contaminants can be prevented from entering and the background can be prevented from lowering, so that high accuracy and high sensitivity can be achieved. Can analyze impurities containing Pt. Furthermore, the recovery rate of Pt can be improved and the lower limit of quantification can be improved by about one digit as compared with the related art.

In the above embodiment, the measurement is performed by AAS, but the same result can be obtained by measurement by ICP-MS.

[0043]

As described above, according to the present invention,
When the impurity analysis of the semiconductor substrate surface and the thin film on the substrate is performed by the VPD method, a noble metal element, particularly Pt, reacts with chloric acid to form a recovered solution by using a chemical solution containing chloric acid such as anode water as the recovered solution. Since Pt is eluted, Pt can be decomposed and recovered as a recovery solution, and chemical solutions containing chloric acid have low danger and require special equipment, which is extremely dangerous and requires a special facility. Impurity analysis that could not be performed can be measured with the recovered liquid in a safe operation without using special equipment, high accuracy by preventing contamination, high sensitivity by lowering background, analysis Time can be reduced.

According to the present invention, the recovery rate of Pt can be greatly improved (for example, 21%) and the lower limit of quantification can be improved by about one digit compared with the conventional method. It can greatly reduce the contamination of semiconductors and contribute to the production of semiconductor products with high quality and high production yield.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of the method of the present invention and P
It is a figure which shows the collection rate of t in comparison.

FIG. 2 shows a second embodiment of the method of the present invention and P of the conventional method.
It is a figure which shows the collection rate of t in comparison.

FIG. 3 shows a third embodiment of the method of the present invention and P of the conventional method.
It is a figure which shows the collection rate of t in comparison.

FIG. 4 is a configuration diagram of an example of a decomposition apparatus used in the method of the present invention.

FIG. 5 is a cross-sectional view of an example of an apparatus used for a conventional analysis method.

FIG. 6 is a cross-sectional view of another example of a device used in a conventional analysis method.

FIG. 7 is an explanatory diagram of a collecting method using a collecting liquid.

[Explanation of symbols]

 Reference Signs List 15 semiconductor substrate 16 recovery liquid 17 micropipette 21 sealed container made of Teflon 22 hydrofluoric acid (HF) 23 hot plate 24N _TwoGas 25 HF vapor 26 Semiconductor silicon wafer 27 Vacuum tweezers

Claims (2)

[Claims] 1. An impurity analysis method for decomposing a semiconductor substrate surface and a thin film on a substrate by hydrofluoric acid vapor, recovering the decomposed product with a recovery liquid, and analyzing the recovery liquid, wherein the recovery liquid is chloric acid. A method for analyzing impurities on the surface of a semiconductor substrate and a thin film on a substrate, characterized by using a chemical solution containing: 2. The chemical solution containing chloric acid is any one of chlorine water, a mixed solution of chlorine water and ozone water, and electrolytic ionic water using hydrochloric acid as a supporting salt. The method for analyzing impurities on a surface of a semiconductor substrate and a thin film on the substrate according to claim 1.