{"title":"Effect of process parameters on the growth of AlN coatings on Al-based alloy","authors":"","doi":"10.1016/j.ijrmhm.2024.106944","DOIUrl":null,"url":null,"abstract":"<div><div>Semiconductor fabrication equipment extensively uses Al alloys which form an AlF layer when exposed to fluorine gas used in semiconductor processing. The AlF layer can flake off, rendering the chamber components unfit for semiconductor manufacturing. With the goal of resisting fluorine attack, the growth of protective AlN coatings on Al-6061 substrates was investigated, and this paper reports on the effects of process parameters on coating quality. It was found that Mg powders in a powder bed placed before the sample along the gas flow path can supply a rapid burst of magnesium vapor to the sample during exothermal nitridation (combustion) of Mg powders. This burst of supersaturated magnesium vapor can convert the native protective Al<sub>2</sub>O<sub>3</sub> to non-protective MgO on the sample surface if the extent of magnesium supersaturation, the temperature of the sample, and the residence time of the vapor around the sample are high enough. At the same time, the magnesium supersaturation should not be so high as to get significant gas phase nucleation of Mg<sub>3</sub>N<sub>2</sub> particulates that can stick to the front edge of the sample causing a ‘front edge anomaly’. This balance is achieved by using a bimodal distribution of magnesium powders. Conversion of Al<sub>2</sub>O<sub>3</sub> to MgO is accompanied by the formation of a Mg<sub>3</sub>N<sub>2</sub> layer above the MgO layer, with incomplete surface coverage. Microstructural analysis suggests that AlN nucleation is preferred on this Mg<sub>3</sub>N<sub>2</sub> layer, with uncovered areas being regions of outward Al diffusion from the alloy. The coating grows outward with the AlN dendrites growing outwards and laterally leading to a dense coating with a dendritic network of AlN in an Al matrix. Even a small concentration of oxygen or water vapor in the reaction chamber leads to excessive MgO formation on the AlN coating surface, particularly during the sample cooldown. Excessive MgO formation on the coating surface, termed as ‘MgO poisoning’, inhibits further coating growth. The residual Mg and Mg<sub>3</sub>N<sub>2</sub> in the powder bed getter the oxygen and moisture, respectively, thereby keeping the oxygen content sufficiently low to avoid MgO poisoning provided the chamber has good hermetic integrity.</div></div>","PeriodicalId":14216,"journal":{"name":"International Journal of Refractory Metals & Hard Materials","volume":null,"pages":null},"PeriodicalIF":4.2000,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"International Journal of Refractory Metals & Hard Materials","FirstCategoryId":"88","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0263436824003925","RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"MATERIALS SCIENCE, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Semiconductor fabrication equipment extensively uses Al alloys which form an AlF layer when exposed to fluorine gas used in semiconductor processing. The AlF layer can flake off, rendering the chamber components unfit for semiconductor manufacturing. With the goal of resisting fluorine attack, the growth of protective AlN coatings on Al-6061 substrates was investigated, and this paper reports on the effects of process parameters on coating quality. It was found that Mg powders in a powder bed placed before the sample along the gas flow path can supply a rapid burst of magnesium vapor to the sample during exothermal nitridation (combustion) of Mg powders. This burst of supersaturated magnesium vapor can convert the native protective Al2O3 to non-protective MgO on the sample surface if the extent of magnesium supersaturation, the temperature of the sample, and the residence time of the vapor around the sample are high enough. At the same time, the magnesium supersaturation should not be so high as to get significant gas phase nucleation of Mg3N2 particulates that can stick to the front edge of the sample causing a ‘front edge anomaly’. This balance is achieved by using a bimodal distribution of magnesium powders. Conversion of Al2O3 to MgO is accompanied by the formation of a Mg3N2 layer above the MgO layer, with incomplete surface coverage. Microstructural analysis suggests that AlN nucleation is preferred on this Mg3N2 layer, with uncovered areas being regions of outward Al diffusion from the alloy. The coating grows outward with the AlN dendrites growing outwards and laterally leading to a dense coating with a dendritic network of AlN in an Al matrix. Even a small concentration of oxygen or water vapor in the reaction chamber leads to excessive MgO formation on the AlN coating surface, particularly during the sample cooldown. Excessive MgO formation on the coating surface, termed as ‘MgO poisoning’, inhibits further coating growth. The residual Mg and Mg3N2 in the powder bed getter the oxygen and moisture, respectively, thereby keeping the oxygen content sufficiently low to avoid MgO poisoning provided the chamber has good hermetic integrity.
期刊介绍:
The International Journal of Refractory Metals and Hard Materials (IJRMHM) publishes original research articles concerned with all aspects of refractory metals and hard materials. Refractory metals are defined as metals with melting points higher than 1800 °C. These are tungsten, molybdenum, chromium, tantalum, niobium, hafnium, and rhenium, as well as many compounds and alloys based thereupon. Hard materials that are included in the scope of this journal are defined as materials with hardness values higher than 1000 kg/mm2, primarily intended for applications as manufacturing tools or wear resistant components in mechanical systems. Thus they encompass carbides, nitrides and borides of metals, and related compounds. A special focus of this journal is put on the family of hardmetals, which is also known as cemented tungsten carbide, and cermets which are based on titanium carbide and carbonitrides with or without a metal binder. Ceramics and superhard materials including diamond and cubic boron nitride may also be accepted provided the subject material is presented as hard materials as defined above.