André Weill

Diffusion phenomenon and loss of adhesion in chemically amplified negative resists

Abstract This paper shows that pattern profile abnormalities appear when three component negative resists are deposited onto an aluminium substrate. Because of the amphotere behavior of aluminium, the acid molecules react when they come in contact with the substrate, thus generating a concentration gradient within the resist material. Because of the lack of acid molecules near the interface, crosslinking of the resist cannot be achieved. We propose a thin intermediate layer deposition as a solution and conclude with a mechanism of diffusion of the catalyst from the resist materials towards the interface.

Resist polarity changes during the silylation process

Abstract In this paper we describe our investigations on surface tension characterisation of the Plasmask ’ resist during the HMDS silylation process. Emphasis is put on the decrease of the polar component during the process. Whereas non modified novolacs are not soluble in non polar solvent like xylene, toluene or chlorobenzene, these solvents are found to dissolve the upper part of the exposed areas.

Role of surface tension in silylation processes

The DESIRER process has been proposed as an attractive solution to lithographic problems, combining the performance of multilayer systems to the simplicity of monolayer processes. Despite the large number of studies devoted to this type of process, the various mechanisms involved during the silylation and dry development steps are not yet totally understood. The first part of the paper deals with the changes in solubility of the resist layer before and after silylation and suggests that the polarity of the resist is modified during the process. Surface tension measurements are then reported in order to quantitatively evaluate the changes in polarity of the silylated resist. Finally it is shown that the work of adhesion between silylated and non-silylated material can easily explain both the stability of the silylated islands during the HMDS process and the motion of these silylated areas during the dry development step.

E-bean patterning by a double exposure process

Abstract The Double Exposure (DE) process simply consists in performing an optical blanket exposure of the resist before or after the E-beam exposure. This paper addresses the basic principle of the DE process, the required experimental conditions and the major outcomes (profiles, resolution, throughput and thickness loss). The best results we obtain are chosen as an illustration of the DE process efficiency. They show that the DE process contains major improvements that should make the E-beam patterning technique more efficient.

CVD photoresist performance for 248-nm lithography

Some of the major limitations of top surface imaging schemes are now well documented: critical dimension (CD) control across the wafer can be a serious issue as well as line edge roughness (LER). A primary focus of our work has been to investigate the performance of the 248 nm bi-level negative tone approach of the CVD photoresist process based on the plasma polymerization of methylsilane. In this paper, CD control data within a field and across the wafer are presented. CD control is shown to be very strongly dependent on the uniformity of the development step. The best results are obtained when using straight chlorine for the plasma etch development step.

Latitude of the BAR process compared to the monolayer and TAR processes for 0.35-μm design rules at gate level

The aim of this paper is to investigate experimentally the performances of three photolithographic processes, the monolayer, AQUATARR and BARLiR processes, for 0.35 micrometer patterning using the exposure-defocus (E-D) tree technique. Parameters of practical importance are considered such as exposure latitude and depth of focus for dense and isolated features, and their overlapping latitudes, i.e. the proximity effect. The influence of the resist thickness (minimum and maximum incoupling thicknesses) and the impact of a 50 nm sizing of the mask have also been evaluated. Using the BARLiR process, significant improvements have been demonstrated for proximity and CD swing effects. The results highlight the problems of pushing i-line lithography to the 0.35 micrometer regime and demonstrate that, to achieve acceptable CD control, a BAR process must be used.

Charge effect elimination for automatic CD inspection of 0.4-μm contact holes in resist

This paper deals with a technique recently developed at France Telecom/CNET for increasing the electrical conductance of novolak and polyvinylphenol based photoresist patterns and consequently for avoiding any charge effect occurring during SEM inspection. The process consists in subjecting the photoresist patterns to an argon plasma, which, under specific conditions, creates the graphitization of the surface of the photoresist, leading to a significant decrease in electrical resistivity and total suppression of the charge effect. When the size of the hole becomes sufficiently small, and despite the high resolution capability of the equipment, only the top of the hole is well defined. Due to charge effects, the image at the bottom of the hole is badly resolved and therefore the dimensions cannot be registered. However if the resist layer is previously exposed to an argon plasma, the charge effects totally disappear and the contour of the image can then be very clearly defined, by the sharp transitions of the intensity profile. The process is cost effective, principally nondestructive and has been demonstrated to be a real industrial method. When wafers are treated using the plasma process described above, an automatic, highly reliable, nondestructive inspection of a 7 X 7 matrix can be performed in less than 45 min. The results include top and bottom measurement using standard low energy SEM CD equipment.

Melt flow of the silylated areas during the desire process

The DESIRE@ process has been proposed as an attractive solution to lithographic problems, combining the performance of multilayer systems to the simplicity of monolayer processes. Despite the large number of studies devoted to this type of process, the various mechanisms involved during the silylation and dry development steps are not yet totally understood. The effects of substrate heating, occuring during the dry development process, on the viscous strain of the silylated areas have been recently reported (1). The main results are listed hereafter : * The etch rate selectivity between silylated and non-silylated areas decreases from 15 to15 when the film temperature increases from 20 to 100 “C. * RBS measurements confirm the thermally activated diffusion of silylated chains in the novolac matrix. * Silylation induces a net decrease (from 70 to 5°C) of the glass transition temperature of the novolac polymer. Therefore, the so-called polymer fluid state can be reached during etching, and consequently allows the flow of polymer chains one with respect to each other. Thus, it was shown that the top silylated material can spread and coat the sidewalls of the pattern during the dry development step.

Advanced i-line lithography: processes for positive and negative patterning using the same acid hardening resist

Abstract In this paper, we propose two sub 0.5 μm i-line processes (0.40 NA stepper), for negative and positive patterning, using the same acid hardening resist: the negative patterning is achieved via wet development and the positive patterning via silylation and dry development. We first considere the wet development negative process. Such a negative process is strategic for many lithographic levels, and we here demonstrate its application for sub 0.5 μm gates fabrication [the level of IC fabrication requiring the highest resolution]. The lithographic results obtained over flat and topographic polysilicon wafers are presented and discussed in terms of exposure dose and focus latitudes. The plasma etching behavior of the resist is then studied and discussed as a function of the gas chemistry: the best conditions are finally used for transfering the patterns into a 0.38 μm thick polysilicon layer. In the second part of this paper, we demonstrate a positive dry development process using vapor silylation; different silylation conditions and development modes are evaluated. Such a process could be used where regular wet development processes reach their limits, or where a positive process is better adapted to the geometry of the level in fabrication: only one resist would then be necessary for both polarities.

Advanced i-line lithography: evaluation of a new chemical amplification negative resist

A new chemical amplification negative resist for i-line lithography (XP 2068 F1 from Shipley) is evaluated. First, a process for 0.5 micrometers features is developed and optimized, using a Tagushi matrix: the compatibility of the resist absorption with the polysilicon and aluminum reflectivities is then tested, and the high thermal stability demonstrated. Second, the process latitude is evaluated in terms of dose-focus latitude, CD linearity, and PEB temperature latitude. Finally, the suitability of the resist for gate fabrication is studied: 0.5 micrometers features are transferred into polysilicon using two different plasma chemistries.