JPH01167644A - Activation analysis of trace oxygen and nitrogen impurities in high-purity material - Google Patents

Abstract

PURPOSE:To improve analysis sensitivity by converting an oxygen impurity to <13>N and a nitrogen impurity to <11>C by proton irradiation, separating nitrogen and carbon and making determination of the oxygen impurity and the nitrogen impurity. CONSTITUTION:A measuring sample is activated by projecting the proton thereon. The following nuclide forming reaction takes place: <16>O+P <13>N+alpha, <14>N+P <11>C+alpha. The activated sample is heated to 1,400 deg.C to oxidize the carbon and to gasify the nitrogen. The trace gas for analysis gasified in a heating furnace 1 is carried by a carrier gas and is introduced into a lime packed column 3 where C is absorbed and separated. The remaining gas passes a disoxidizing column 4 where the oxygen is removed and thereafter, the gas is carried to a molecular sieve 5 where the nitrogen is captured. The determination of the oxygen impurity and the nitrogen impurity is executed. The analysis sensitivity is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for activation analysis of oxygen and nitrogen trace impurities in materials that require high purity, such as silicon, aluminum, gallium, and arsenic.

[Prior art] With the advancement of science and technology, materials with extremely high purity are being developed. For example, in semiconductor materials such as silicon, aluminum, gallium, arsenic, etc., one impurity around pI) b is a problem. Become. Activation analysis is an indispensable analytical technique for the development of these materials. In other words, in order to guarantee the purity of materials, it is important to accurately measure the amount of extremely small amounts of impurities, but in order to quantify extremely small amounts of substances, the target element to be measured is activated, and the target element is determined from the radiation dose. Activation analysis, which determines the amount, is highly sensitive and is evaluated as a method for obtaining absolute amounts. In this method, the sample to be analyzed is often irradiated with an accelerated particle beam to convert the target element into a radionuclide, which is then separated using various techniques and its radiation dose measured.

However, in this series of procedures, chemical methods have conventionally been used as separation techniques, but these methods are extremely complicated and require skill.

For example, oxygen contained in the semiconductor material described above is an impurity that requires the most attention, and when looking at this oxygen, 16Q is converted into a radionuclide of 18F by irradiation with sH8. To separate this 18p, first, a sample is dissolved in a heated solution of hydrochloric acid and nitric acid containing hydrofluoric acid as a carrier. Next, boric acid is added to the mixture while keeping the mixture heated, and potassium chloride is further added to dilute the mixture. When the mixture is cooled, a precipitate of potassium borofluoride (KBF4) is obtained. The solution is filtered to separate the precipitate, which is again dissolved in an aqueous nitric acid solution containing potassium bromide, silver nitrate is added and heated, and the precipitate formed is filtered to remove interfering elements. At this point, F is dissolved in the filtrate, so boric acid and nitric acid are added to the filtrate again, and after keeping it warm, potassium chloride is added and cooled to obtain a precipitate of KBF4 (for example, J of Radio
anal, Chem.

Vo72. No. 1-2.1982. p527-53
5> The obtained precipitate is washed and subjected to measurement, but the time required for this series of separation operations is more than - hours, and other impurities, which are equal to the half-life of lap (70 minutes), are C, N, etc. are similarly separated using chemical operations. For example, C is oxidized to carbon dioxide, then absorbed into lithium hydroxide, and separated as a precipitate of lithium carbonate, and N is absorbed into hydrochloric acid. It is converted into ammonia with soda, and is precipitated and separated as ammonium, tetraphenyl, and boron.

[Problems to be Solved by the Invention] As described above, in order to separate the elements to be measured, the conventional method requires the use of complicated techniques, requiring skill and time. For this reason, not only is there a delay in the measurement information, but there are also problems such as a decrease in measurement sensitivity in the case of short half-lives.

The present invention was made to solve these problems, and therefore aims to easily and quickly perform activation analysis of trace impurities of oxygen and nitrogen in high-purity materials.

[Means for Solving the Problems] The invention for achieving this object is achieved by the following steps.

(b) The first step is to irradiate the measurement sample with protons to make it radioactive. (b) The second step is to heat the activated sample to 1400°C to oxidize carbon and gasify nitrogen. (b) Lime The third step is passing the gas through a column packed with oxygen, the fourth step is passing the gas through an oxygen removal column, and the fifth step is passing the gas through a cooled molecular sieve.

[Action co- When irradiated with protons, the following nuclide production reaction occurs.

160 + p → 13N + α ... (1) 14N
+p→mouth C+α... (2) 14N + p+41
5Q+γ... (3) Turtle2C+ p →
C+d... (4) In proton irradiation, 160 is converted to ISN, so there is no need to separate 18p as in the case of 3H irradiation. In reaction (3), the activation cross section is very small, and the amount of converted material can be ignored. The activation cross section of 12C is also small and reaction (4) can be ignored. Therefore, when there are no other nuclide impurities that are transmuted into 11N or tic, such as in a high-purity silicon substrate, trace impurities of oxygen and nitrogen can be determined by quantifying 13N and IIC.

This activated sample was heated to around 14'OO℃ and H
When e-gas is used as a carrier and mixed with oxygen,
tic and t2C are oxidized to carbon dioxide gas, and 13N becomes nitrogen gas. When these mixed gases are brought into contact with lime, the carbon dioxide gas reacts and becomes calcium carbonate, which is absorbed by the lime and separated. What remains is nitrogen gas, unreacted oxygen gas, and helium carrier, which are
After being passed through an oxygen removal column to remove oxygen, it is passed through a molecular sieve made of synthetic zeolite with a pore size of 5 mm while being cooled with liquid nitrogen, and only nitrogen gas is collected and separated.

[Example of the Invention 0 and N contained in this sample were measured by irradiating cosilicon with protons, separating 13N and IIC, and measuring the radiation intensity of the separated product.

The sample material had an oxygen content of 45 spppb and a nitrogen content of 13.5 p.
A plate-shaped silicon containing PB was irradiated with protons at 10 μA and 11 MeV for 30 minutes using a cyclotron.
2 g of this was used after etching and cleaning.

The separation method carried out will be explained using FIG. 1.

1 is a heating furnace, 2 is a test material, 3 is a lime-filled column, 4 is a deoxidizing column, 5 is a molecular sieve, and 6 is a cooling tank. The trace amount of analysis target gas gasified in the heating furnace 1 is
Carried by a carrier gas, it is led to a lime-filled column 3, where C is absorbed and separated. The remaining gas passes through a deoxygenation column 4, where oxygen is removed and then transported to a molecular sieve 5, where nitrogen is collected, forming a series of separation systems. Lime packed column 3 has a diameter of 8a
A quartz glass tube with a diameter of 25 mm and a length of 450 m is filled with granular lime.
+*a quartz glass tube filled with a reducing agent, and is a commercially available product that can remove up to 2 ppb of residual oxygen. A commercially available molecular sieve 5 for gas chromatography was used while being placed in a cooling tank 6 and cooled with liquid nitrogen. First, the inside of the separation system was thoroughly cleaned in advance and replaced with He gas. Next, while flowing He gas as a carrier gas at a flow rate of about 80 m1/min, the temperature of the heating furnace 1 was raised to 1400°C, and the He gas was replaced with He gas.
The gas was mixed with 1100 pp of oxygen, and heating was continued for 35 minutes. 35 minutes is sufficient time to gasify the entire amount of impurities. After the heating was completed, the radiation dose of the lime-filled column 3 and molecular sieve 5 was measured and converted into impurity content. Table 1 shows the results of repeating this separation operation five times and the converted content values.

As seen in Table 1, the repeat accuracy was very good, and the oxygen and nitrogen contents also matched well when compared with the reference values. The impurities contained in high-purity silicon include oxygen and carbon, followed by nitrogen. As mentioned above, in proton irradiation, the conversion of 14N into ts This shows that the method is accurate and reliable.

[Effect of the invention] As described above, in this invention, oxygen impurities are converted to 13N and nitrogen impurities to 11C by proton irradiation, nitrogen and carbon are separated by a simple separation method, and then these are quantified. Since oxygen impurities and nitrogen impurities are quantified, no special skill is required, and there is no need to spend time on separation. As described above, the contribution of the present invention to improving analytical anger and speeding up information acquisition is significant.

[Brief explanation of the drawing]

FIG. 1 is a separation process diagram for explaining an example. DESCRIPTION OF SYMBOLS 1... Heating furnace, 2... Test material, 3... Lime packed column, 4... Oxygen removal column, 5... Molecular sieve.

Claims (1)

[Claims] A method for activation analysis of trace impurities of nitrogen and oxygen in a high-purity material comprising the following steps: (a) a first step of irradiating a measurement sample with protons to activate it; The second step is to heat the sample to approximately 1,400°C to oxidize carbon and gasify nitrogen. (a) The third step is to pass the gas through a lime-filled column. (The second step is to pass the gas through an oxygen removal column.) Step 4: (H) Step 5: pass the gas through the cooled molecular sieve.