Silicon Tetrafluoride dopant gas for silicon ion implantation

Abstract

Silicon Tetrafluoride (SiF₄) is a dopant gas of choice for different silicon ion implantation processes used in semiconductor device engineering. It is a primary source of atomic dopants like Si and F, and a potential source of molecular dopants (e.g. Si₂, SiF_x, x=1-3). A significant challenge associated with the use of SiF₄ is that it can compromise ion source performance, resulting in poor beam stability and source life. This is primarily the result of the formation of a halogen cycle that takes place due to the presence of fluorine from the SiF₄ molecule along with tungsten materials that are present in the ion source (e.g. liners, walls). A second challenge associated with SiF₄ can be limited beam current. In order to improve implant tool performance when using SiF₄, the following investigations have been performed: (1) Characterization of SiF₄ / H₂ mixtures: The addition of hydrogen co-gas can effectively mitigate the halogen cycle and improve source performance. Using the magnitude of the resulting WF_x peaks as an indicator, the degree to which the halogen cycle is mitigated is shown as a function of H₂ flow rate. Also, in that single packages may impart various advantages, SiF₄ / H₂ co-mixture stability data are provided. (2) Characterization of enriched (en) ²⁸SiF₄: The additional enrichment can enable higher beam currents of ²⁸Si⁺. The effect of En-²⁸SiF₄ flow rate on beam current is presented, along with the resulting WF_x spectra. (3) Initial observations of SiF₃⁺ beams are provided, along with the potential benefits that may be obtained in selecting this molecular ion.