Etch product identification during CH4-H-2 RIE of InP using mass spectrometry

The composition of the plasma phase during InP RIE in CH4-H-2 is investigated in detail by quadrupole mass spectrometry for the identification of the in and P etching reaction products. The plasma phase species are analysed in detail by means of neutral and positive ion detection during the InP CH4-H-2 RIE process. The complexity of the gas phase reactions in the CH4-H-2 discharge is shown by the formation of various CnHm molecules and CnHm+ positive ions. In the presence of InP on the RF driven electrode, PH3 and H2PCH3 are evidenced as the neutral products of P present in the plasma phase. But H2PCH3 contributes to about 5% of the total neutral P plasma species, clearly demonstrating phosphine as the major etch product of P. No organoindium compounds of general formulation In(CH3)(x) with x = 0-3 can be detected as neutrals. However organoindium compounds are still regarded as the etch product of indium since In+ and In(CH3)(2)(+) positive ions are evidenced by mass spectrometric sampling of ionic species during the CH4-H-2 RIE process of InP. A semi-quantitative analysis effectively shows that these In positive ions probably originate from the direct ionization of the indium etch product, probably an organoindium compound. In contrast, it is shown that the phosphine positive ions mostly result from secondary ion-molecule reactions in the plasma phase between PH3, the major P neutral product, and the positive ions of the discharge. As a results these ions cannot be confidently used to determine the P etch products and to monitor the P etching process.