Etching silicon with hydrofluoric acid containing halogen - hydrogen halides - halogenoxide acids (HF-HX-HOnX-X2 mit X = Cl, Br)

在半导体和微系统技术以及光伏产业中，硅的湿法化学刻蚀在晶片表面的定向结构中起着重要的作用。根据要获得的形貌，可以使用碱性蚀刻溶液或含有氢氟酸的酸性溶液。碱性介质，主要基于KOH，具有各向异性、晶格相关的刻蚀特性，例如在用于光伏的单晶硅晶片上产生金字塔结构。另一方面，在半导体工业的抛光晶片制造过程中，酸性HF-HNO3混合物是消除SAW损伤的理想选择。硅溶解的机理和形成不同表面结构的原因尚不完全清楚，这适用于这两个系统。在我们团队中，在以前的工作中，我们广泛地研究了硅在新型含氯氢氟酸水溶液中的腐蚀行为。首次发现了具有各向异性腐蚀特性的酸性腐蚀介质。这项工作包括对反应序列的初步研究，尽管刻蚀机理尚未完全阐明。例如，潜在的中间氯氧物种的影响和卤素对硅溶解的影响没有被理解。在本项目中，将研究硅在HF、HCl、HOnCl和Cl2的水溶液中或HF、HBr、HOnBr2和Br2的混合物中的腐蚀行为，包括腐蚀速率和由此产生的表面形貌。为了能够包含尽可能多的参数并仍然将测试数量保持在限制范围内，将使用实验设计(DOE)。此外，还应预先选择酸或其盐类，以确定其稳定性。将对溶液、气相和硅表面进行全面表征。因此，XPS和DR-FT-IR光谱可用于表面分析，FT-IR和拉曼光谱可用于气相和腐蚀混合物的分析。可能作为中间体出现的物种也应使用原位红外光谱进行确定。其目的是为硅在不同组成的HF-HX-HOnX-X2溶液(X=Cl，Br.)中的溶解机理提出一个通用的建议。我们希望得到关于各向同性和各向异性效应的信息，溶解机制和形态(抛光，织构)之间的关系，以及在每种情况下使用的卤素。对于选定的系统，应评估这些工艺对太阳能、微系统技术和/或半导体行业的适用性。

The wet chemical etching of silicon plays an important role in the targeted structuring of wafer surfaces in semiconductor and microsystem technology as well as photovoltaic industries. Depending on the morphology to be achieved, either alkaline etching solutions or acidic solutions containing hydrofluoric acid are used. Alkaline media, mostly based on KOH, have an anisotropic, crystal lattice-dependent etching characteristic, which e.g. generates a pyramidal structure on monocrystalline silicon wafers for photovoltaics. Acidic HF-HNO3 mixtures, on the other hand, are ideal for removing saw damage during the manufacturing of polished wafers for the semiconductor industry. It applies to both systems that the mechanisms of silicon dissolution and the reasons for the formation of different surface structures are not yet fully understood. In our group, the etching behavior of silicon in novel chlorine-containing aqueous hydrofluoric acid solutions was extensively examined in previous work. For the first time an acidic etching medium with an anisotropic etching characteristic was found. The work included preliminary studies on the reaction sequences, although the etching mechanism has not yet been fully clarified. For example, the influence of potential intermediate chlorine oxygen species and the influence of the halogen on the dissolution of the silicon are not understood. In this project, the etching behavior of silicon in aqueous mixtures of HF, HCl, HOnCl and Cl2 or mixtures of HF, HBr, HOnBr and Br2 will be investigated regarding etching rates and the resulting surface morphology. In order to be able to include as many parameters as possible and still keep the number of tests within limits, design of experiments (DOE) will be used. Also, a preselection of acids or their salts regarding their stability is to be made. The solutions, the gas phase and the silicon surfaces will be comprehensively characterized. Therefore, XPS and DR-FT-IR spectroscopy are available for surface analysis, FT-IR and Raman spectroscopy for the analysis of the gas phase and the etching mixtures are investigated via NMR spectroscopy. Species that may occur as intermediates should also be determined using in-situ IR spectroscopy. The aim is to develop a universal proposal for the mechanism of the dissolution of silicon in different variants of compositions of HF-HX-HOnX-X2 solutions (with X = Cl, Br). We hope to get information about isotropic and anisotropic effects, the relationship between the dissolution mechanism and morphology (polishing, texture) and the halogen used in each case. For selected systems, the suitability of the processes for the solar, microsystem technology and / or semiconductor industry should be evaluated.