CO-PYROLYSIS OF DIPSBH AND TMIN

The reaction mechanisms for the pyrolysis of diisopropylantimonyhydrid e (DIPSbH, (C3H7)(2)SbH) alone and for the co-pyrolysis df DIPSbH and trimethylindium (TMIn, (CH3)(3)In) in D-2 and H-2 ambients have been s tudied in an isothermal flow-tube, ''ersatz'' reactor using mass spect rometry to analyze the reaction products. The rate limiting step in th e pyrolysis of DIPSbH alone is the reductive coupling reaction, produc ing C3H8. Additional products are C3H6 and C6H14 produced by dispropor tionation and recombination reactions, respectively, of C3H7 radicals produced during the second stage of DIPSbH pyrolysis. The mixture of D IPSbH with TMIn produces a nonvolatile adduct on the quartz walls imme diately after mixing in the reactor even at room temperature. No produ cts were evolved at room temperature. However, for reactor temperature s between 100 and 200 degrees C, an alkane elimination reaction occurs , producing CH4. The remaining solid product is postulated to be [(CH3 )(2)InSb(C3H7)(2)](n) (n = 2 or 3). For temperatures greater than 200 degrees C, the DIPSbH begins to pyrolyze independently. This temperatu re for the onset of DIPSbH pyrolysis is considerably above the. temper ature (125 degrees C) at which pyrolysis begins for DIPSbH alone. This suggests that during co-pyrolysis formation of the adduct retards pyr olysis of DIPSbH. Apparently, dissociation of the adduct is necessary before the DIPSbH can pyrolyze independently. Co-pyrolysis of DIPSbH a nd TMIn between 250 and 375 degrees C produces (C3H7)Sb(CH3)(2) and (C H3)(3)Sb. Neither is found for the pyrolysis of DIPSbH alone. Consider ably larger amounts of C2H6 are also detected at low temperatures (les s than or equal to 300 degrees C). The ethane may come from the [(CH3) (2)InSb(C3H7)(2)](n) via an intramolecular alkane elimination reaction . The high carbon contamination levels reported for InSb samples grown by OMVPE using these precursors at 300 and 325 degrees C are postulat ed to be caused by the formation of (C3H7)Sb(CH3)(2) during the co-pyr olysis of DIPSbH and TMIn, but not during the pyrolysis of each precur sor alone.