Plasma etching of silicon: Surface chemistry and the plasma environment

The plasma etching of silicon is examined from both the viewpoint of the interaction of particles representative of etching plasmas with the silicon surface and the generation of particles in such plasmas. Silicon chloride etch product formation resulting from the thermal and ion-enhanced etching of a Si(100) single crystal surface with chlorine gas is examined by single-photon ionization time-of-flight mass (SPI-TOFMS.) spectrometry. Neutral atomic and molecular species that emanate from electron cyclotron resonance (ECR) and inductively couple plasma (ICP) sources are measured by modulated beam time-of-flight mass spectrometry to gain an understanding of the production of species that subsequently interact with the silicon surface during plasma etching. The study of particles produced in plasmas and their interaction with a silicon surface further aids the development of a global understanding of the plasma etching process.; Etch products including atomic silicon and silicon chlorides (SiCl, SiCl ₂) are ionized by 118 nm photons without fragmentation or interference from background gases. Thermal etching of a single crystal Si(100) surface with molecular chlorine is examined in the range of surface temperatures between 1023–1373 K. SiCl₂ is the dominant product below 1100 K. As the surface temperature is increased the direct desorption of SiCl precludes the formation of SiCl₂ and becomes the dominant product. Above 1300 K silicon atom desorption become a significant product. SPI-TOFMS is also used to detect etch products resulting from the simultaneous exposure of a Si(100) surface to molecular chlorine and a modulated argon ion beam with energy in the range between 200–1000 keV. SiCl is observed to be the dominant etch product. however, significant amounts of atomic Si and SiCl ₂ are also observed. A kinetic model for the formation of SiCl is suggested from which a sputter yield of ∼4 SiCl molecules per impacting Ar + is determined.; Species produced in plasmas used in materials processing are also examined. Neutral atoms and molecules that emanate from ECR and ICP plasmas of argon, nitrogen and chlorine gas are measured by modulated beam time of flight analysis and range in kinetic energy between 0.1–0.4 eV. The kinetic energy of neutral species increases with decreasing source pressure with the kinetic energy of the atomic species somewhat greater than molecular species. A mechanism involving the production of fast neutral species via resonant charge exchange with plasma ions accelerated by sheath and/or ambipolar fields within the plasma is proposed. The dissociation of gases is much greater for the ECR source as compared to the ICP source, while the latter produces species with slightly higher kinetic energy.