Gilles R. Amblard

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.

Characterization of the development of DNQ/novolac resists by surface energy measurements

The resist processes used for optical lithography are mainly positive tone, based on the use of DNQ/novolac photoresists. It has been demonstrated that enhancing the resist pattern profiles is possible by optimization of the development step. Development techniques, such as two-step or interrupted development, have been introduced to enhance the contrast of DNQ/novolac resists. This paper demonstrates that the resist surface modifications occurring during development can be followed by surface energy measurements. The surface energy changes of four commercial resists (JSR IX 500, Shipley SPRT 510, OCG HPR 504 and Hoechst AZ 5206) during development are investigated. The results are then correlated to the changes in pattern profiles obtained when using the interrupted development technique.

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.

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.

Three dimensional modelling of the e-beam double exposure process

Abstract The Double Exposure (DE) Process has been proposed previously (1,2) together with crude calculations and preliminary experimental results. One-dimensional modelling with qualitative explanations and good resist experimental profiles were exhibited. This paper presents the full three-dimensional modelling of this process including a Monte-Carlo simulation (3) for the E-Beam exposure.

Comparative evaluation of e-beam charge-reducing processes

The intrinsic registration capability of current e-beam lithographic tools has to approach or even go below the 0.10 micrometers value ( + 3(sigma) ). However, the actual level to level overlay measurements are generally found above this limit as resist materials trap the electric charges: the electron beam is deflected by the electrostatic forces, resulting in misalignment and distortion of the delineated patterns. Large pattern displacements can be observed depending on the experimental conditions. This paper aims to compare various charge reducing processes when used under exactly the same conditions (20 keV industrial machine and trilevel resist structure). No system appears as a perfect solution. There are partial solutions, but none is simple and satisfying; this contributes to the picture of electron- beam lithography as a marginal technique for IC manufacturing.

Wet-developed, high-aspect-ratio resist patterns by 20-keV e-beam lithography

In order to enhance the contrast of the e-beam negative resist, Suga has combined DUV and e- beam exposures. This application has been further extended to the high sensitive three component SAL 601 resist. As the absorption phenomenon of UV light by resist layers obeys Lamberts law, the optically deposited energy density in a photolithographic process decreases through the photoresist layer from top to bottom. In contrast, for a 20 KeV imaging process of an electron-sensitive resist, the energy deposition profile corresponds to that of the particles implanted in the resist, i.e., a Gaussian profile centered at 2 to 3 micrometers in depth. Therefore, the deposited energy density throughout a 1 micrometers thick resist layer is an increasing function from the surface to the resist to the substrate. The combination of both exposure modes provides an almost constant density of deposited energy throughout the layer depth, giving rise to better profiles. This paper discussed the experimental characteristics of the DUV flood exposure which are required for the process to work correctly. As DUV flood exposure aims to treat the top part of the resist, making it more sensitive to the electron beam than the bottom part, it is of prime important to adjust the absorption coefficient of the resist, and consequently the wavelength spectrum of the light, so that light is principally absorbed near the surface and does not insolate the bottom of the resist.