Solid State Phenomena Vol. 255

Abstract: For the Ge nanowire formation in a gate-all-around (GAA) integration scheme, a selective etch of Si_0.5Ge_0.5 or Si_0.3Ge_0.7 selective to Ge is considered. Two wet process approaches were evaluated: a boiling TMAH as a commodity chemistry is compared with a formulated chemistry using a multi-stack SiGe/Ge layer as a test vehicle. The boiling TMAH exhibits an anisotropic etch of the SiGe whereas the formulated semi-aqueous chemistry removes the sacrificial SiGe by an isotropic etch which makes the process suitable for a Ge nanowire release process.

Abstract: The silicon surface passivation with diluted HF solutions is hereby explained. Without a very stable, correct Si-H surface passivation, a rough silicon surface can be obtained, leading to poor gate oxide integrity or bad epi film quality. Detailed mechanism are depicted and solutions to obtain best Si-H passivated surface are given

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: Tetramethylammonium hydroxide (TMAH) is a common etchant for Sigma shape formation in IC manufacturing. The impact of oxygen dissolved in TMAH solution on process was studied in this paper. A novel O2 gas injector was developed to improve the process stabilization by control of the oxygen concentration in TMAH solution

Abstract: The impact of rinsing liquid for Germanium surface after wet chemical treatment is described. The different Ge loss after processing with different rinse (UPW and CO₂ water) were determined and the different surface morphologies on the Ge surface after processing with different chemicals (AOM, HF and HCl) were determined by XPS. It was found that the investigation of surface morphology after chemical treatment is necessary to understand the rinse effect and the results showed the CO₂ water rinse can decrease and suppress Ge loss at chemical treatment

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: In Situ gas phase passivation methods can enable new channel materials. Toward this end pure anhydrous HOOH and H2NNH2 membrane gas delivery methods were developed. Implementation led to Si-OH passivation of InGaAs(001) at 350C and Si-N-H passivation of SiGe(110) at 285C. XPS and initial electrical characterization has been carried out. Feasibility for In Situ dry surface preparation and passivation was demonstrated.

Abstract: Tristrimethylsilylgermane, (Me₃Si)₃GeH, was employed as a molecular model compound for hydrogen terminated Ge(111) surfaces. Time and temperature dependent NMR spectroscopy yielded rate constants for the reaction between (Me₃Si)₃GeH and elemental sulfur and allowed for the determination of the activation energy for this molecular model reaction to mimic germanium surface passivation.

Abstract: Over the course of the past few years, the semiconductor industry has continued to invent and innovate profoundly to adhere to Moore’s Law and Dennard scaling. At each of the technology nodes starting with 45nm, new materials and integration techniques, such as high-K & metal gates, double patterning techniques, and now 3D FinFet / Trigate device geometries are being introduced in order to maintain device performance. This places a large burden on unit process development to accommodate and deliver advanced process capability and is growing the need for the ultimate etch solution: etching with atomic layer precision. Atomic layer etching is a promising path to answer the processing demands of thin high mobility channel devices on the angstrom scale. Self-limiting reactions, discrete reaction & activation steps, or extremely low ion energy etch plasmas are some of the pathways being pursued for precise sub-nanometer material removal. In this invited paper, previously published in SPIE, the ability to achieve atomic layer etch precision is reviewed in detail for a variety of material sets and implementation methods. For a cyclic approach most similar to a reverse ALD scheme, the process window to achieve a truly self-limited atomic layer etch process is identified and the limitations as a function of controlling the adsorption step, the irradiation energy, and the reaction process are examined. Alternative approaches, including processes to enable pseudo-ALE precision, are then introduced and results from their application investigated. While these new plasma-enhanced atomic layer etch (PE-ALE) processes show encouraging results, most patterning applications are best realized by optimizations through discharge chemistry and/or plasma parameters. Significant improvements however were obtained when applying PE-ALE approaches to small pitch patterns. In particular the increased selectivity to OPL seems to offer a potential benefit for patterning high aspect ratio features.