Threshold ionization mass spectroscopy of radicals in RF silane discharge Progress report 11/19/2003 Contributors: Alan Gallagher Peter Horvath Karoly Rozsa : Design of apparatus Damir Kujundzic : Forevacuum assembly and RF Power Supply Wengang Zheng : Design of QMS for threshold ionization

Schematics of TIMS apparatus

Diagram of the vacuum system Current status: The system is built Vacuum in the chamber can reach 3x10 -7 Torr Argon and silane lines are built Pyrolizer is tested at 900 O C with silane flow Gauges and leak valves are calibrated for 0-10 sccm air, argon and silane flow Hydrogen line is to be built

Schematics of the vacuum chamber assembly Current status: All parts are manufactured Discharge chamber is assembled (windows are needed) Discharge was operated in argon flow Ionizer and mass spectrometer are to be assembled

Flow test for the differential pumping Flows are obtained by previous calibration of foreline pressures The ionizer & mass spec. chambers are not separated yet.

Electronics Current status: New RF Power Supply for the discharge is under construction Fully computer controllable (power supply works, minor components are needed) Data acquisition computer boards are acquired (installation is needed) QMS electronics will be identical to Wengang Zheng’s TIMS apparatus for Hot Wire Silicon Deposition experiment The commercial Ametek QMS needed to be modified (will be discussed later) The modified apparatus works satisfactory in the HWSD experiment An other unit need to be modified for the discharge experiment Software is written for HWSD experiment (Labview) Software need to be adapted for discharge experiment

Rectifier (unknown) Comp Reference RF Amplifier Programmable Oscillator Commercial Ametek QMS Internal microcomputer Problems: No coupling capacitor for rods Programmable frequency (internally controlled) RF amplitude is controlled by internal microcomputer Unable to lock on given mass RF amplitude is tested against 4 values to get the mass peak int. Cannot be controlled from our own computer (& unit is broken  ) ± ½ AMU

Rectifier (our) Comp Reference from our own computer RF Amplifier Crystal Oscillator Modified QMS Modifications: tuning capacitor fixed frequency oscillator our own rectifier our own feedback loop external DC voltages TIMS-related modifications: Own ionizer, variable energy Our own ion optics Electron Multiplier Advantages: Full control over RF and DC voltages Full control of ionizer energy High stability quartz oscillator Amplitude stability by feedback Tunable capacitor

Results of modification Mass scan in HWSD experiment Original unit With broken frequency control 1 and without feedback for RF amplitude 2 Modified unit With stable frequency and own feedback for RF amplitude 1 by accident, IC cannot be replaced 2 removed to gain control over RF amplitude

Neutral ParentsSi + SiH + SiH 2 + SiH 3 + Si8.2 SiH SiH SiH SiH Priciples of Threshold Ionization Mass Spectrometry Threshold energies (eV) for SiH n ions from neutrals

Operation of TIMS Sample threshold (energy) scan in HWSD experiment In silane w/o radicals (cold filament) W/ radicals (hot filament)

To do in the near future… Assemble and wire the ionizer and mass spectrometer Finish computer controlled RF Power Supply Modify commercial QMS unit Build our own step-up transformer and rectifier for QMS Build computer control of MS, ionizer and ion optics Optimize ion optics Calibrate MS Measurements…