| AVS 57th International Symposium & Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1-WeA |
| Session: | Plasma Surface Interactions (Fundamentals & Applications) II |
| Presenter: | E. Kunnen, IMEC, Belgium |
| Authors: | E. Kunnen, IMEC, Belgium A. Vaglio Pret, IMEC, Belgium O. Luere, CNRS-LTM, France L. Azarnouche, STMicroelectronics, France E. Pargon, CNRS-LTM, France P. Foubert, IMEC, Belgium R. Gronheid, IMEC, Belgium D. Shamiryan, IMEC, Belgium M.R. Baklanov, IMEC, Belgium W. Boullart, IMEC, Belgium |
| Correspondent: | Click to Email |
At today’s date 193 immersion lithography is used in semiconductor industry to print lines of less than 40nm half pitch, continuing the scaling. One of the challenges is to reduce line edge variations, or Line Width Roughness (LWR). It has already been pointed out earlier that LWR can be significantly reduced during the subsequent dry etch step. One of the important components acting on LWR during the dry etch is the VUV light emitted from the plasma, however, the exact mechanism is not yet revealed.
The photoresist pattern profile and its chemical modifications are studied as a function of VUV dose. A 172 nm Xe2* excimer 30mW/cm2 light source is used to expose patterned and blanket (resist & organic BARC) wafers, exposing them from 2 to 256 seconds under nitrogen ambient and controlling the temperature within 2°C. SEM-CD top-down image analysis gives us spatial and information in both spatial and frequency domain through Critical dimension (CD), CD-Uniformity, LWR and Power Spectr al Density (PSD). Three dimensional information is recorded by CD AFM measurements. The thickness, refractive index and extinction coefficient are deduced from spectral ellipsometric (SE) measurements. Mass measurements provide density. Fourier Transformed Infrared Spectroscopy (FTIR) analyses provide information on the molecular bonds. Finally, chemical analysis will be performed by elastic recoil detection (ERD) and Time of flight secondary ion mass spectrometry (TOFSIMS).
Significant changes in CD and LWR are observed up to 12s (360 mJ/cm2) of VUV exposure time corresponding to a dose of about 1 photon per atom. For higher exposures the integrity of the lines deteriorates compromising the accuracy in the SEM-CD analyses. Initially, CD and LWR decreases while the correlation length increases. PSD analysis shows that the reduction is attributed to a decrease in the high frequency roughness region. For longer exposure, a CD increase is observed and finally low frequency roughness increases, the total LWR. The CD evaluation indicates a resist reflow that is driven by surface tension towards a more rounded shape. Mass and thickness measurements over the whole exposure range show a decrease that goes linearly with the logarithm of the exposure time, while density remains about constant. FTIR indicate a correlation of the observed changes with the removal of the lactone bonds at 1800 cm-1.
In conclusion the dose range at which VUV impacts LWR is measured to be around 1 photon/atom. Initially a CD and LWR decrease is observed while for larger doses the trend is the opposite. Change of mass and thickness follows a first order kinetic equation, which is quite typical for simple desorption processes.