Purity of III/V semiconductor precursors: trimethylgallium,triethylgallium, ethyldimethylindium,arsine, trimethylarsine and phosphine

The purities of the metallorganic chemical vapor deposition (MOCVD) reagents trimethylgallium Ga(CH₃)₃], triethylgallium Ga(C₂H₅)₃], ethyldimethylindium In(CH₃)₂C₂H₅], arsine (AsH₃), phosphine (PH₃) and trimethylarsine As(CH₃)₃] were evaluated by Fourier transform ion cyclotron resonance mass spectrometry (FTICR). Both conventional 70-eV electron impact ionization and low-pressure chemical ionization were used to evaluate sample purities. The trimethylgallium sample is 79% pure with significant amounts of dimethylgallium chloride and fluoride (19%), tetramethylsilane (0.11%) and various hydrocarbons. The triethylgallium sample is 53% pure with large amounts of hydrocarbons (46%) and also ethyl chloride (0.7%) and hydrogen sulfide (0.08%). The ethyldimethylindium sample is 73% pure with trimethylindium (10%) and methyldiethylindium (18%) also present. One arsine sample is 99.999% pure whereas the other contains significant amounts of methylarsine (38 ppm), dimethylarsine (36 ppm) and hydroxyarsine (36 ppm). The phosphine sample is 99.4% pure with 0.57% N₂, 400 ppm NH₃ and 100 ppm PH₂CH₃. Four trimethylarsine samples show purities of 99.3–99.8% in the liquid. Impurities observed are N₂, O₂ H₂S, PH₃, HCl, S(CH₃), Si(CH₃)₄, AsH₃, Ge(CH₃)₄ and Ar. Overall, the samples are typically less pure than stated, except for one arsine sample. The impurities detected are volatile and possible difficult to detect by conventional methods. Improvements in MOCVD reagent purities and their analysis will be required.