Mécanismes d'anisotropie dans la gravure du silicium en plasma SF6. Modèle de gravure

Abstract

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. Abstract -The mechanisms responsible for etching of silicon in low pressure SF6 plasma under low energy ion impact are studied using Microwave Multipolar Plasmas. Experimental results using both mass spectrometric and etch profile analysis show the evolution of anisotropy and etch rate as a function of pressure. In particular, a transition to perfect anisotropy is observed below a threshold pressure. To account for these experimental results, a new interpretation is proposed for the surface processes observed in plasma etching. To make the current models consistent, it is necessary to add three following assumptions : i) large lateral repulsive interactions between chemisorbed fluorine atoms in nearest neighbour positions ; ii) chemisorbed fluorine atom diffusion on the silicon surface ; iii) multilayer adsorption for the Si/F system. The analytical treatment of the model points out that the etch rate is limited by the partial pressure of atomic fluorine, and that the anisotropy is controlled by the ion current density.

Surface diffusion model accounting for the temperature dependence of tungsten etching characteristics in a SF6 magnetoplasma

“…26,42,45,46 This is expressed, under steady-state conditions, by the one-dimensional equation for surface diffusion: where o is the density of adsorption sites for F atoms within the monolayer, D is the diffusion coefficient, and x is the curviline abscissa along the surface. 26,42,45,46 This is expressed, under steady-state conditions, by the one-dimensional equation for surface diffusion: where o is the density of adsorption sites for F atoms within the monolayer, D is the diffusion coefficient, and x is the curviline abscissa along the surface.…”

SF 6 Plasma Etching of Silicon: Evidence of Sequential Multilayer Fluorine Adsorption

“…However, in this case, the situation is complicated by the possibility of finding more than one adsorption site per Si surface atom. In particular, for Si(lOO), each silicon atom may exhibit two dangling bonds, so that a four-step adsorption schema [2] can be devised as shown in fig. 1, the formation of a full SiF layer preceding that of the SiFz layer.…”

Parametric study of the etching of SiO2 in SF6 plasmas: Modeling of the etching kinetics and validation

“…However, this Si-like overlayer on SiO 2 where silicon is linked to oxygen ͑Si-O back bonds͒ is different from a Si layer on bulk silicon ͑Si-Si back bonds͒; ͑d͒ there is no surface diffusion of oxygen adatoms: the activation barrier for oxygen diffusion is much greater than thermal energy at room temperature; ͑e͒ as a consequence of ͑d͒, there are no adsorption sites on surfaces free of ion bombardment ͑lateral walls͒; ͑f͒ as a consequence of ͑d͒ and ͑e͒, at room temperature, empty adsorption sites are available for fluorine adsorption only on surfaces submitted to ion bombardment; ͑g͒ as a consequence of ͑d͒ to ͑f͒, lateral etching of SiO 2 cannot occur at or below room temperature; ͑h͒ with fluorine, the etching mechanisms of the fraction of the Si-like monolayer on SiO 2 are similar to those of bulk Si; ͑i͒ as a consequence of ͑h͒, the etch rate of the Si overlayer can include two components, i.e., the ion bombardment induced etching and spontaneous etching; ͑j͒ as for bulk Si, the spontaneous etching of the Si overlayer by fluorine can only occur above a fluorine threshold coverage t ( F Ͼ t ): 23,24,26-28 ͑k͒ the value of the threshold coverage is t ϭ3/4 23,24,[26][27][28] if the saturation density 0 of adsorption sites for fluorine corresponds to a complete SiF 2 monolayer ͑or t ϭ1/2 if 0 corresponds to a complete SiF 3 monolayer͒. However, this Si-like overlayer on SiO 2 where silicon is linked to oxygen ͑Si-O back bonds͒ is different from a Si layer on bulk silicon ͑Si-Si back bonds͒; ͑d͒ there is no surface diffusion of oxygen adatoms: the activation barrier for oxygen diffusion is much greater than thermal energy at room temperature; ͑e͒ as a consequence of ͑d͒, there are no adsorption sites on surfaces free of ion bombardment ͑lateral walls͒; ͑f͒ as a consequence of ͑d͒ and ͑e͒, at room temperature, empty adsorption sites are available for fluorine adsorption only on surfaces submitted to ion bombardment; ͑g͒ as a consequence of ͑d͒ to ͑f͒, lateral etching of SiO 2 cannot occur at or below room temperature; ͑h͒ with fluorine, the etching mechanisms of the fraction of the Si-like monolayer on SiO 2 are similar to those of bulk Si; ͑i͒ as a consequence of ͑h͒, the etch rate of the Si overlayer can include two components, i.e., the ion bombardment induced etching and spontaneous etching; ͑j͒ as for bulk Si, the spontaneous etching of the Si overlayer by fluorine can only occur above a fluorine threshold coverage t ( F Ͼ t ): 23,24,26-28 ͑k͒ the value of the threshold coverage is t ϭ3/4 23,24,[26][27][28] if the saturation density 0 of adsorption sites for fluorine corresponds to a complete SiF 2 monolayer ͑or t ϭ1/2 if 0 corresponds to a complete SiF 3 monolayer͒.…”

“…͑14͒ and ͑15͒ is the addition of a spontaneous etching component 23,24,[26][27][28] to the ion induced component, when Ͼ t . ͑14͒ and ͑15͒ is the addition of a spontaneous etching component 23,24,[26][27][28] to the ion induced component, when Ͼ t .…”

“…The second term of the right hand side of this equation corresponds to the spontaneous etching component, 23,24,[26][27][28] where is the adsorption lifetime of fluorine adatoms before their spontaneous desorption as part of the reaction product SiF 4 . 23,29,30 If R is the activation energy for the associative desorption of SiF 4 , the adsorption lifetime of fluorine adatoms, which is proportional to the inverse of their reaction probability, can be simply expressed as 23,29,30 …”