Papers by Keyword: HF Last

Abstract: Ultrapure water contains dilute hydrogen peroxide as an impurity. In order to clarify an impact of the dilute hydrogen peroxide on cleaning processes, a SiGe epitaxial layer was deposited on a Si(100) wafer which surface was treated by HF last process with hydrogen peroxide contained UPW or hydrogen peroxide removed UPW. The defect in the SiGe epitaxial layer was reduced when the hydrogen peroxide removed UPW was used.

Abstract: “HF Last” process are widely used as pre epi cleans. They enable a Si-H surface to grow a perfect Si layer by epitaxy. Nonetheless, such hydrophobic wafers are extremely sensitive to watermarks formation during the wafer drying. A design of experiments has been used to determine which parameters impact their formation on a single wafer cleaning tool. Plus, the silicon surface stability has been compared between this tool and an immersion batch cleaning tool.

Abstract: Epitaxial growth requires a clean starting surface for the growth of a high-quality crystalline layer. For epitaxy on Si, an HF-last wet clean followed by an in-situ high-temperature hydrogen bake is the reference pre-epi clean sequence to obtain an oxygen-free surface [1, 2]. The temperature required to remove all residual oxygen also makes the surface atoms mobile, resulting in reflow. The high temperatures used during the H₂-bake can also result in intolerable doping profile changes. A lower temperature pre-epi clean sequence is required to avoid this reflow, especially when moving away from Si. In addition the high temperatures needed during a H₂-bake would result in the relaxation of high mobility channels, e.g. strained Si_1-xGe_x or III-V materials [3]. Several low temperatures pre-epi cleaning solutions have been proposed in the past, e.g. GeH₄-assisted H₂-bake [4] or more recently, a GeH₄-assisted HCl clean [5]. In this study we looked at the interaction between HF-last wet clean and the in-situ GeH₄-assisted HCl clean prior to Si_0.8Ge_0.2-on-Si epitaxy.

Abstract: Amorphous/crystalline silicon heterojunction solar cells are commonly made by low temperature deposition of front and back side thin films on bare H-passivated Si wafers, obtained by HF last processes. This work discusses the impact of HF last step parameters on cell performance, considering textured and cleaned Si (100) wafers. A complete native oxide removal is mandatory and achieved in a short time (< 5 min) by HF concentration higher than 1% (by weight). Above 1%, surface passivation and cells performance slightly increases with the concentration. The best process time is found to be the minimum time to deoxidize textured wafers, as seen by a good dewetting. For [H > 2% this is less than 1 min. Longer process times slightly degrade surface passivation. Post rinse and drying, provided they do not reoxydize the surface, were seen to have no impact. The delay between the HF last and deposition steps is critical and depends on the efficiency of the cleaning before the HF last. With a high performance cleaning, leading to a very good surface passivation (< 10 cm/s surface recombination velocity), 30 min delay has no impact and 90 min leads to about 5% relative degradation of cell performance. Regarding the HF cleanliness, HCl spiking is an efficient way to enhance robustness of surface passivation keeping < 10 cm/s values when the metallic contamination, including Cu, is in the sub 50 ppb range.