SU1530981A1 - Mass-spectrometry method of determining methyl iodide content in dimethylcadmium - Google Patents

Abstract

This invention relates to the analytical chemistry of organic compounds and can be used to control the production of semiconductor elements. The method includes ionization of dimethylcade vapors by electron impact, recording the mass spectrum and calculating the concentration of lithium iodide from the heights of the peaks of the mass spectrum. A feature of the method is the enrichment of the sample to be analyzed before ionization using an exchange reaction with mercury, which results in the formation of metallic cadmium deposited on the walls of the inlet tube and dimethyl mercury. The use of the exchange reaction allowed a 50-fold reduction in the detection limit of methyl iodide in dimethylcadmium. 1 zp 1 dw., 2 tab.

Description

SP

WITH

The invention relates to analytical chemistry, in particular to mass spectrometric methods for the analysis of cadmium alkyl compounds, in particular to the determination of methyl iodide content in dimethylcadmium.

Dimethyl cadmium (DMC) is the starting component in the preparation of many complex semiconductors. Methyl iodide (IM), used in the synthesis of DMK, is difficult to detect impurity, is always present in it, and often its concentration determines the quality of LMC; therefore, a sensitive and rapid method is necessary to determine the IM content along with other impurities. .

The purpose of the invention is to reduce the detection limit of methyl iodide in dimethylcadmium.

The drawing shows a graph of the height of the peaks from time to time.

The proposed method for mass spectrometric analysis is the introduction of sample vapors into an ion source, their ionization by electron impact, the registration of the mass spectrum and the calculation of concentrations by dimethylcad

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methyl iodide at peak heights, taking into account the relative sensitivity factors, prior to introducing the vapors of the sample to be analyzed, saturates the surface of the tube between the ionization chamber and the mercury leak, then establishes a constant flow of vapors of the sample, records its mass spectrum and determines the ratio of dimethylcadium from ratios

LI1A 11 Y1

- h 14-4 0.83

h. ,, / 0,71 + h, 44 / 0,24

iodide concentration

methyl, kg / m,

dimethylcadium concentration, kg / m;

 gp

- heights of peaks with mass

numbers 142, 144, 217, respectively.

Mercury saturation is carried out by introducing mercury vapor from an ampoule with metallic mercury at room temperature, the inlet tube being cooled with liquid nitrogen for 5-15 minutes.

The proposed method is carried out as follows.

A part of the inlet tube (10 cm) of the MI 1201 mass spectrometer is wrapped with a cloth that is moistened with liquid nitrogen. From the inlet system, a stream of mercury vapor is supplied from a metal ampoule, which contains liquid mercury at room temperature. The accumulation of mercury in the tube is carried out for a time t, after which the tube is heated to room temperature and a stream of dimethylcadium intensity usually used during anapism is supplied through it (the vapor pressure in the ionization chambers increases to 10 - 10 Pa). When colliding with a wall, DMK molecules react with an exchange with mercury, which results in the formation of metallic cadmium deposited on the wall and dimethyl mercury (DMR). With a high degree of filling of the adsorption layer on the surface of the mercury inlet tube, the degree of DMQ and DMR at room temperature can reach 95-98% and higher. The intensity of the lines of the mass spectrum of DMK, on

d

five

0

5 Q

5 55

40

MIs on the MI line (with c - mass numbers 127, 142) are reduced by 50 times or more, which allows the MI detection limit to be reduced by the same number of times. As a characteristic peak for determining the amount of MI, it is most advisable to choose the peak of CH1 ions with a mass number of 142. The intensity of the ion peak imposing on it is 1,2) + is 0.83 times the intensity of the peak of n4cci ions (. With a mass number of 144, i.e. The part of the intensity of the peak with the mass number 142 attributable to the CH ion is equal to iiVOj a

In the transalkylation reaction, one DMR molecule is obtained from one DMK molecule. Therefore, to determine the concentration of DMK supplied from the inlet system, one of the peaks of the mass spectrum of dimethyl mercury (characterizing the amount of DQMs that passed the perealkylation reaction) and the mass spectrum of DMS, on which the peak of MI is applied, can serve. As such peaks, peaks with mass numbers of 217 and 144, respectively, are used.

To account for the different ionization efficiencies of IM, DMK, DMR, mixtures of IM with DMK and IM with DMR were accurately prepared, and according to the results of the analysis, the coefficients to relative sensitivity shown in Table 1 were measured.

Thus, the concentration of DMK in the sample can be characterized by the sum (0.71 + h) of 0.24 and the ratio of the concentrations of IM and DMK can be determined by the indicated formula

Him

h 14 g - h

144

0.83

35 55

45

50

HAMK LP, 7 / 0.71 + h, 44 / 0.24

The drawing shows the time dependences of t from the moment the DMK vapor was supplied through the inlet tube covered with mercury for t 5, 10 and 15 min (curves 1, 2, 3, respectively). As can be seen, the degree of conversion of DMK to DMR in the first 5 minutes from the start of the overlap is close to 100%. An increase in T to 15 min increases the time for the complete decomposition of DMC by only 1.5 times. In the future, our work uses 7–10 min. The almost complete absence of the DMS mass spectrum lines for 5 min allows several times to register the mass spectrum in the range

the mass numbers are 140-145 and 215-220, i.e. get average values of magnitudes.

To verify the correctness of the method and eliminate the possibility of losing myocardial infarction during the passage of the inlet tube, we analyzed the mixtures of DMK with IM, prepared with an accuracy of 2%, from IM brand HC and rectified DMK containing, according to gas chromatographic analysis, 7.240 mol.% IM.

Example I. A 200 ml glass ampoule containing a mixture of 90.5% DMC and 9.6 × IM at 1000 Pa pressure is added to the metering valve of the inlet system of the mass spectrometer Yi 1201 via a covort junction. Part of the inlet tube (10 cm long, 8 mm inner diameter) is wrapped with a cloth that is moistened with liquid nitrogen. The valve, which cuts off the inlet system from a metal ampoule containing a drop of mercury (room ampoule temperature), is opened for 10 min. For 5 min, the inlet tube is heated to room temperature. The mass spectrometer is tuned to the peak of the ion peak with a mass number of 217/202 and the sample vapor flow is set using a metering valve of such an intensity that the height of the controlled peak is half of the coarsest scale of the amplifier (150 V). After that, for 5 minutes, the picn of ions with mass numbers 142, 144, 217 are alternately recorded, from which heights are calculated using the formula indicated.

The results of analyzes of a mixture of DMK and IM are given in table 2.

The proposed method can be implemented without constructive alterations on mass-produced mass spectrometers.

0

having both a double inlet system, and a single one. In the latter case, mercury vapor is introduced into the system, and then the sample to be analyzed. The extension of the analysis procedure is not more than 30-40 minutes.

Claims (2)

1. Mass spectrometry method for determining the content of methyl iodide in dimethylcadmium, which consists in introducing sample vapors into the ion source of the mass spectrometer, their ionization by electron impact, recording the mass spectrum and calculating methyl iodide concentrations and dimethylcadiums by peak heights taking into account coefficients relative sensitivity, characterized in that, in order to reduce the detection limit of methyl iodide, the surface of the tube between the ionization chamber and the leak is pre-saturated with 5 mercury, then rehydrating a constant flow of vapor sample at room temperature, the tube register its mass spectrum and determining the ratio of the concentration of methyl iodide X, five 0 0 E5 MI and dimethylcadium concentrations KGH (ml relations JM- .t.Oi§3 XA “LC h. ,,, / 0.71 + h, / 0.24 where L, h, d and hj are the heights of the peaks with mass numbers 142, 144, 217, respectively. 2. A method according to P1, characterized in that the saturation with mercury is carried out by introducing mercury vapor from an ampoule with metallic mercury at room temperature, the inlet tube being cooled with liquid nitrogen for 5-15 minutes 237.6 13 1510 240,8 17 1520 308.1 63 1480 O, 104 9.4-0,11,1 0.1025 9.3 -0.22.1 0.109 9.8 + 0.33.1 ge 500500100Table 1 table 2 thirty 35 0 it Ning