Patrick Jean Paniez

Development of Polymers in O2 Plasmas: Temperature Effects and Transition to Imperfect Anisotropy

A parametric study of the etching of a photoresist is performed in an O2 microwave multipolar plasma using a trilevel resist system. The etch rate and the anisotropy evolutions are reported as a function of ion energy, oxygen pressure and substrate temperature, which are important parameters likely to affect anisotropy. A transition from isotropic to imperfect anisotropic etching occurs when the ion energy is increased. However, residual lateral etching always subsists at room temperature, even at the lowest oxygen concentrations. Above room temperature, in contrast with ion-induced etching, the spontaneous lateral etch rate increases with temperature, suggesting a thermally activated reaction process. The phenomena are interpreted in terms of oxygen coverage on the polymer surface, with a threshold coverage being required for purely spontaneous chemical etching to occur, and on the assumption of a photon-induced desorption of volatile products proportional to the oxygen coverage.

The novolak calibration method applied to the GPC analysis of the UV photoresists

Abstract This paper first summarizes the influence of the molecular weight of the novolak-based photoresists on the different microlithographic steps: film deposition, soft bake, exposure, and hard bake. The second part deals with the use of gel permeation chromatography (GPC) for characterizing the photoresists. In order to convert elution curves into molecular weight distribution information, a calibration method is needed. The usual calibration techniques are poorly adapted to the analysis of photoresists. The proposed calibration method uses the first observable low molecular weight oligomers on the chromatogram as a standard. It is shown that experimental results are not dependent on the column set.

Free volume and relaxation effects in polymer layers: application to the spin coating and bake processes

Abstract The variations in free volume of polymer layers can be observed using simple plasma etching techniques along with laser interferometry monitoring. During oxygen plasma etching, the polymer layers are heated and may undergo volume relaxation. Thus, polymers can be classified according to their relative relaxation response. This technique appears to be a simple way of monitoring the baking conditions of lithographic layers.

Robust and environmentally stable deep UV positive resist: optimization of SUCCESS ST2

By optimization of SUCCESS ST2 an environmentally stable and robust deep UV positive resist has been derived where the generally encountered problems related to chemical amplification resists, the formation of T-tops and linewidth changes during delay have been solved. The previously reported chemistry, protected poly-p-hydroxystyrene and SUCCESS type sulfonium salts, has been proven to be insensitive to airborne contaminations. In this paper the optimization of processing conditions, based on thermal analysis is reported. With the derived conditions linewidth changes during delays could be minimized and excellent performance obtained. At the IBM lithography test center in Boblingen an integrated photosector, consisting of equipment, materials, process and control philosophy, was balanced and 0.25 micrometers pattern can routinely be resolved using an ASM-L DUV stepper (NA 0.5).

Acidity of lithographic materials: Characterization by colorimetric titration

Abstract The acidic character of various lithographic materials, namely novolaks, Polyhydroxystyrene and Diazonaphtoquinone photoactive compounds, is investigated using colorimetric titration. The acidity of polymers is studied as a function of the isomer structure, chain length and synthesis conditions. The comparison of the acidic properties of these materials provides useful information on the role of chemical mechanisms in both wet and dry development processes.

Silylation and dry development of three component resists for half-micron lithography

The study of the SAL 601 shows that E-Beam exposure induces selectivity in the diffusion of silylating agents. Two different mechanisms are responsible for silicon incorporation. The HMDS diffusion and reaction in the novolak matrix have been studied as a function of the thermal properties of the polymer. Two main silylation processes have been found by the modification of silicon incorporation mechanisms versus the silylation temperature. Different silylation tools and etchers have been tested in order to achieve correct patterns. Mask formation and grass phenomena have been studied and a model with aggregates formation has been developed. Silicon incorporation into the three different component resists has been studied versus the main silylation parameters. Submicron patterns have been achieved for different processes. This paper demonstrates that three component resists can be silylated by the use of different silylation processes and are good candidates for half-micron lithography.

Free volume and viscosity effects in polymer layers: application to lithographic processes

Due to the numerous hydroxyl groups present in Novolaks and PHS, large amounts of free volume are created during the spin coating process. The free volume variations can be observed using plasma etching techniques along with laser interferometry. The concept of free volume allows a clearer description of the bake process. The detection of free volume implies a better understanding of its role in the various steps of the lithographic process. Several applications of this technique are presented.

Thermal flow properties of novolak polymers

Abstract Planarizing properties of novolak polymers synthesized from pure isomers are investigated as a function of their chemical structure, molecular weight and thermal treatments. Differential Scanning Calorimetry (DSC) has been used to characterize the samples. A simpler characterization technique is also proposed as a substitute for the expensive thermal analysis. A good fit between the two methods is established. This correlation confirms certain assumptions on thermal flow mechanisms and makes the selection of novolaks easy for all customers.

Dry development of silylated resist: influence of substrate temperature

During the last few years, silylation processes have been extensively studied. In particular, the mechanisms of silicon incorporation in the resist have been discussed. However, the importance of the dry etching step, which allows the image transfer in the resist, has often been neglected. In this paper it is shown that under standard dry etching conditions, the slight increase in the substrate temperature leads to the liquefaction of the silylated area which then flows down onto the sidewalls of the patterns.

The role of self diffusion in the dry development and plasma durability of polymers

Abstract The degradation of polymer layers during plasma etching is studied as a function of their viscoelastic properties. Above Tg, the mobility of polymer chains allows the extension of surface degradation to the entire thickness in a self diffusion mechanism. This effect is particularly important in the case of low molecular weight polymers such as novalaks. The same effect can affect silicon transport during silylation processes.