Research on High Quality Single Wafer Wet Processing for Semiconductor Surfaces
218 , 2015-03-24 , 法政大学
Despite accounting for nearly 40% of the number of steps in semiconductor-manufacturing processing, wet-treatment technologies for treating semiconductor surfaces have heretofore been considered unattractive for developing new technology. However, the high functionality of these technologies is rapidly pushing us into this area. To obtain uniform surfaces from etching and cleaning, we focus herein on single-wafer-spinning wet-processing (SWSWP), which delivers superior performance compared with dry techniques for a large range of materials. In other words, technology has been rapidly transitioning in recent years from the dipping wet-processing technologies, which we have grown accustomed to, to SWSWP technology.However, despite the high performance of SWSWP, further research is required to optimize it. Moreover, the recent development of high-performance, high-functionality semiconductor devices and the adoption of new materials require the urgent development of the corresponding SWSWP techniques.This thesis presents research that we have conducted on new techniques of SWSWP that can be applied to various materials. In Chapter 1, we provide the background of this study and describe the challenges that we strive to overcome with this research. We also present the latest trends in wet-processing technology.In Chapter 2, we describe the principle and configuration details of the SWSWP equipment used in this study. Chapter 3 presents the results obtained with the etching techniques of SWSWP.In Section 1, we explain that, by removing defect layers introduced by the back-grinding process of SWSWP, the minority-carrier lifetime can be greatly improved, which significantly impacts the electrical characteristics of the resulting semiconductor.In Section 2, we propose a new SWSWP technology whereby film planarization is improved by chemical-mechanical polishing. We clarify that planarization by chemical-mechanical polishing yields a more uniform thickness after film deposition, independent of the deposition distribution of the film resulting from SWSWP.In Chapter 4, we describe the development and theoretical considerations for surface cleaning by SWSWP. In the first section, we discuss the results of high-performance removal of fine particles and metal contamination. The first paragraph of this section, discusses research into the mechanism of removal and reattachment of fine nitride particles by cleaning with an ammonia peroxide mixture and clarifies the importance of control and reattachment of fine particles. Furthermore, we clarify that reattachment of fine particles can be suppressed by controlling the medium-boundary-layer thickness.5The second paragraph describes the development of a new ultrasonic cleaning technology that avoids pattern collapse. We consider the material changes caused by the acoustic energy of ultrasonic cleaning. By optimizing the material parameters, we suppress pattern collapse. The distance between the ultrasonic plate and the wafer and the effect of added oxygen in the cleaning liquid is found to be important. Finally, we show that fine (65 nm) nitride particles can be efficiency removed without the collapse of fine patterns using a newly developed ultrasonic cleaning technique.In the third paragraph, we consider the use of a chemical solution to remove particles and propose a new electrochemical cleaning method based on this mechanism. This method combines low ultrasonic cleaning, a diluted ammonia peroxide mixture, and strong alkaline ionized water at pH 12. The result is free of film loss and pattern collapse.Previously, removing particles without etching or by physical force has been difficult. However, in the fourth paragraph, we propose a cleaning method that uses only deionized water and is environmentally friendly and economic.The fifth paragraph describes a novel cleaning method that efficiently removes any Pt that has contaminated the wafer backside and bevel. The method uses hydrochloric and nitric acid to generate aqua regia directly on the wafer. By inhibiting the formation of the highly corrosive gases of nitrosyl chloride and chlorine, we reduce the rate at which the production equipment deteriorates. Additionally, we clarify how to efficiently remove metals, such as Pt, with low ionization energy.In Chapter 4, Section 2, we describe how pretreatment with SWSWP of a copper-film-deposition process affects the copper damascene interconnect technology.The first paragraph of this section explains how the initial nucleus of the copper film can be generated by pretreating the surface by SWSWP before depositing the seed copper film by electroplating. With this approach, we reduce the resistivity of the resulting thin copper film that forms the high-aspect-ratio contact.The second paragraph of this section describes how ideal shape control with high adherence and low contact resistance can be realized by pretreating the copper surface by SWSWP before deposition of CoWP as a cap layer, which is deposited by electroless plating. Furthermore, we propose a cleaning technology that is highly selective against the interlayer dielectric layer.In Chapter 4, Section 3, we propose a new drying technology that dispenses with water marks by using isopropyl alcohol. This approach proves to be a better drying technology for hydrophobic surfaces. No water mark is generated because isopropyl alcohol has a very low surface tension and is highly volatile.6Finally, in Chapter 5 we propose a new single-wafer spin technology that combines dry and wet processing. We clarify the photoresist into which a high dose of ions are implanted at high energy. This photoresist is quite difficult to remove by SWSWP with a sulfuric ozone mixture or a sulfuric peroxide mixture (SPM); however, it can be quickly removed by a continuous process that combines an atmospheric inductively coupled plasma and SWSWP with a sulfuric peroxide mixture.To conclude, we summarize all these studies.