Développement de procédés de gravure plasma innovants pour les technologies sub-14 nm par couplage de la lithographie conventionnelle avec l'approche auto-alignée par copolymère à blocs

摘要

Shrinking transistor’s dimensions below 14 nm is so expensive that lower-cost complementary techniquessuch as Directed Self-Assembly (DSA) combined with 193 nm-lithography are currently beingdeveloped. Either organized as trenches for the FinFET’s fin or vertical cylinders for contact holes(which is our case study), Polystyrene-b-polymethylmetacrylate (PS-b-PMMA) is a well-studied blockcopolymer but introduces challenging etching issues due to the chemical similarities between the PS andPMMA blocks. The aim of this thesis is to overcome those etching challenges.In our case where PS is the dominant phase, the principle of DSA is to obtain through self-assemblya pattern of vertical cylinders of PMMA inside a mask constituted of PS. PMMA is then removed eitherby solvent or plasma, revealing the patterns in the PS mask, which will be used as an etching mask forpattern transfer. In order to allow self-assembly, a thin brush layer of random copolymers PS-r-PMMAis used to neutralize the affinity of each phase with the substrate.One of the main issues with DSA is the control of the dimensions (CD control): usually, PMMAis dissolved in acetic acid bath and the brush layer is etched by an Ar/O2 plasma which increasesdramatically the pore’s diameter (CD) by laterally etching the PS. Short duration of thermal annealingsuitable for the Industry induces some “mushroom” shape at the top of the mask which consequentlyincreases the measured CD dispersion (~ 4-5 nm).Our work shows that CD uniformity can be corrected by faceting the top of the patterns throughplasma etching. As a first step, a dry-etch process for PMMA based on H2N2 chemistry has beendeveloped in order to free ourselves from acetic-acid’s and O2-based plasma’s issues. As far as we know,the discovered kind of defects has never been reported in the literature: few nanometer-thick films madeof PS can randomly be found in the PMMA’s domain, thus delaying the etching of random cylinders. Inorder to etch those defects without loosing the CD control, an other process constituted of an acetic acidbath followed by a synchronously-pulsed H2N2 plasma at low duty cycle and high bias power has beendeveloped. This process removes PMMA, facets the top of the PS features (decreasing CD dispersionbelow 2 nm), etches both the defects mentionned above and the brush layer without increasing thepores’ diameters by more than one nanometer. One last etching challenge comes from the aggressivedimensions and the high aspect ratio of the contact holes. In order to limit the lateral etching and themask consumption overall, passivation’s layer are usually deposed on the sidewall of the features duringthe etching process, but at dimensions below 15 nm, those layers are too thick and cause a CD control lossthough they are only few-nanometer thick. The polymerization’s capacity of plasmas has to be loweredat this scale and oxidized layer’s formation by adding O2 to the plasma chemistry has to be avoided.Last but not least, the techniques based on SEM images to determine the pore’s dimensions are notrobust enough at those scales. In order to gain in robustness, image reconstruction and anti-aliasingalgorithm have been implemented.