Thierry Mourier

New dry-development process of trilayer resist systems for advanced lithography

A parametric study of the pattern transfer step in a trilevel resist system using oxygen-based plasmas has been made using a distributed electron cyclotron resonance reactor with independent rf biasing. In pure oxygen plasmas, critical dimension loss is always present in the O2 pressure and ion bombardment energy ranges investigated. The mechanisms most likely to be responsible for these defects during the pattern transfer process are presented and discussed. Perfect anisotropy can only be obtained at substrate temperatures below -60 degree(s)C. A novel plasma etching process based on sidewall passivation by sulfur is proposed using SO2/O2 mixtures. Perfect anisotropy without critical dimension loss is obtained at room temperature by using an 80% SO2/20% O2 mixture and a moderate ion bombardment energy. The ultimate resolution using this new plasma process in conjunction with deep UV exposure and a phase-shift mask is presented.

Undercut elimination in DUV negative systems: application to lithography and etching of metal levels

When a negative tone DUV chemically amplified resist is used on TiN, an undercut at the resist/TiN interface can be observed. This effect leads to a limitation of the performance and optimal use of these resists. In our study of the Shipley SNR 200 resist, a typical representative of these formulations, this undercut has been quantified versus soft bake (SB) and post exposure bake (PEB) temperatures, and for different types and times of development. The results obtained show that for high SB temperatures (greater than 120 degrees Celsius), undercut is minimized, whereas for SB lower than 120 degrees Celsius, undercut occurs. Whatever the SB conditions, undercut significantly increases for PEB temperatures above 120 degrees Celsius. The influence of the development parameters is negligible. By using both DSC thermal analysis and the wafer curvature measurement (WCM) technique, the glass transition of the SNR 200 resist has been determined at 115 degrees Celsius. This result clearly correlates the diffusion mechanisms involved in the undercut phenomenon with the viscoelastic properties of the resist. For these optimized lithographic conditions as well as for the metal etch conditions, a 100% electrical yield for isolation patterns was obtained down to 0.35 micrometer spaces.

Characterization of dry developed processes using silylation application to the PRIME process

A new positive working system for deep UV lithography, called PRIME (Positive Resist IMage by dry Etching) using silylation and dry development was proposed1. This system is derived from photolithographic DESIRE process. In order to better understand mechanisms involved in the PRIME process, different characterization experiments were carried out. For this purpose an experimental silylation module was built. This module includes an in-situ silylation detection based on resist reflectivity variations during wafers treatment. Reflectivity variations are due to index variation and swelling of the silylated resist. This feature ensures not only a better reproductibiity but also the measurement of kinetics and thermodynamics parameters. In a second part, results obtained with PRIME in deep UV lithography will be discussed. At 248 nm with a mask aligner, 0.2 jun L/S patterns were resolved in 0.7 j.un thick resist. Moreover these patterns were transfered in 0.6 im thick silicon dioxide and 0.3 pm polysilicon. A resolution of 0.25 im lines and spaces in 1.1 jim thick resist was achieved with ASM PAS 5000-70 deep UV stepper *.

Comparative study of deep-UV resist processes for 0.35-um technology

Deep UV lithography at 248 nm has shown resolution down to 0.3 micrometers on flat substrates by using wet developable resists. However, due to higher reflectivity at this wavelength, interference effects are enhanced and CD variations have been observed on topography. Different approaches can be used to decrease these effects. In this paper we propose to study two processes related to this problem: (1) a dyed monolayer wet developable resist, and (2) a bilayer system, including a dry developable organic antireflective coating. Several dyed versions of XP 89131 resist from Shipley were studied first, on flat substrates and then on wafers with topography. On flat substrates, the influence of different parameters, such as resist absorption, solubility, bake temperatures, and development time for a given exposure dose on CD, slope, and process latitude have been quantified for 0.3 and 0.35 micrometers . The resist profile modification on reflective topography is discussed. In the case of a bilayer system, a deep UV transparent layer can be used as the top layer (XP 89131). The bottom antireflective (ARC) layer is the resist XP 91218 from Shipley. Dry anisotropic etching of this ARC has been studied by screening of plasma parameters (gas pressure, ion energy, gas type) in various etching equipments (DECR and RIE).

ANR photoresist process optimization at 248 nm

The purpose of this article is to propose a residue-free process using ANR resists specifically designed for deep UV lithography. The influence of development steps, process conditions and resist formulation on residues were studied. An optimized process point with a new resist formulation is proposed. Using this residue-free process point, very high resolution was achieved for deep UV and e-beam lithography. Moreover, the temporal effects on the coated wafers were investigated.

EDMES: an expert system for process optimization in microlithography

We have developed an expert system based on statistical knowledge and photolithographic knowledge. The philosophy of our system is to minimize the number and the cost of the experiments to reach a final objective or to show that the process will never achieve it. The system suggests intermediate objectives to test stability of the resist sensitivity before testing the final objective i.e., an optimized process point for the photolithography of a specific level. When a partial objective is completed the system proposes a goal involving more expensive experiments, and so on, until the final objective is reached. In this paper we demonstrate the capability of our system on the more advanced photolithographic processes. The first example is the study of delay time effect on positive deep UV resists. The second example is the optimization of a deep UV negative process for the gate level. As a conclusion, a comparison between the necessary steps required for this study and a standard approach is done.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Evaluation results for the positive deep UV resist AZ DX 46

This contribution emphasizes resist application site by communicating lithographic results for AZ DX 46, obtained using the GCA XLS 7800/31 stepper, NA equals 0.53, equipped with krypton fluoride excimer laser ((lambda) equals 248 nm), model 4500 D, as exposure source, delivered by Cymer Laser Technologies. As far as delay time experiments are concerned ASM-L PAS 5500/70 stepper, NA equals 0.42, was used in combination with Lambda Physik excimer laser, model 248 L.