Method for producing trichloromonosilane

2 2003168 The present invention relates to a method for production of trichloromonosilane,HSiC13.

Super-pure trichloromonosilane is used as a raw material for production of silicon 5 transistors.

Trichloromonosilane is produced by reacting silicon powder with HCl-gas in a fluidized bed reactor where HCl-gas is supplied to the reactor containing silicon powder at a tell-p~,ldture between about 280C and about 300C.

Trichloromonosilane which has a boiling point of 31.8C is separated from the product gas from the fluidized bed by condensation and is sep~ted from other chlorosilanes by destill~ti-)n.

1 0 An i~ , lant parameter in the production of trichloromonosilane is the amount of nonreacted HCl-gas.

The amount of non-reacted HCl-gas is very important cost factor for the process and the amount of non-reacted HCl-gas should be as low as possible.

An increasing amount of non-reacted HCl-gas gives also an increasing amount of the 1 5 unwanted by-product SiC14 in the product gas and thus lower the amount of produced trichloromonosilane.

For production of trichloromonosilane silicon powder is used which has been produced by crushing and grinding of block cast silicon.

Due to the low cooling rate which is obtained in block casting, alloying elements and il~ ;lies in block cast silicon show a strong tendency of segregation.

During crushing and 2 0 grinding of block cast silicon an inhomogeneous powder product is obtained which shows rather big dirrt;l~;nces in chem~ co~llposi~ion between individual particles.

The quality and homogenity of the silicon powder has a marked effect on the above described method for production of trichloromonosilane, and it has now been found 2 5 that by using silicon powder which has been produced by gas atomizing of molten silicon, a surprisingly high u~ili7~tion of HCl-gas is obtained in the method for producing trichloromonosil~ne by reaction of silicon powder with HCI-gas.

The present invention thus relates to a method for production of trichlololllonosil~ne in 3 0 a fluidized bed reactor by reaction of silicon powder with HCl-gas at a ~e~ e.~ e between 280 and 300C, which method are characteri_ed in that the silicon charged to the reactor is produced by gas atomi7ing of molten silicon.

Z00~ 8 The silicon powder has a particle size ~l-.~,en l and lO00 ~m, preferably between 50 and 800 ~Lm.

By the method according to the present invention the ~ltili7~tion of HCl in the process is 5 considerably increased as the content of non-reacted HCl in the product gas is reduced from the conventional S - lO % to 2 - 3 %.

The reduction of the amount of non-reacted HCl also gives a reduced amount of produced by-products, above all SiCl4.

It hasthus been found that the amount of produced SiC14 has been reduced by 3 - 5 % by the method according to the present invention.

This again gives a higher production of 1 0 trichloromonosil~nf EXAh~LE The following tests were carried out in a fl~ li7e~1 bed reactor having an internal 15 rli~meter of 40 mm.

In all tests the same amount of silicon having a particle size between 50 and 350 llm was used. HCl-gas at a pressure of 2 bar was supplied to the bottom of the reactor.

The flow of HCl was kept constant during all the tests.

After heating and initi~li7ing of the reaction, the reaction conditions were kept con~t~nt at 290C.

Under these conditions the HCl content of the product gas was measured.

Test A was carried out with silicon powder produced in conventional way by crushing and grinding.

Test B was carried out with silicon powder produced by atomi7~tion of molten silicon by nitrogen.

2 5 The chçmic~l co~posilion of the silicon powders was as follows.

Test A Test B % by weight % by weight 3 0 Fe 0.40 Ca O.Ol 0.05 Al 0.47 0.42 rl 0.02 0.02 2003~68 It was found that the yield of HCl for test A was 92 %, while the yield of HCl for test B was 98 %.

From this it is evident that a strongly increased yield of HCl is obtained by the me~hod according to the present invention co,~ d to the conventional method.