Type of Document	Thesis
Author	Surpaneni, Yamini
URN	etd-09182003-184527
Title	Laser Induced Desorption Time Of Flight Mass Spectrometer Analysis Of Adsorbed Surface Contaminants On Vacuum Ultraviolet Lithography Optic Materials
Degree	Master of Science
Department	Electrical and Computer Engineering, Department of
Advisory Committee	Advisor Name Title Susan Davis Allen Committee Chair Jim P. Zheng Committee Member Rajendra Arora Committee Member Simon Foo Committee Member
Keywords	Laser Cleaning Process Semiconductor Processing
Date of Defense	2003-08-02
Availability	unrestricted
Abstract The semiconductor industry currently uses optical lithography processes at the 130 nm node (90 nm gate length) for fabricating integrated circuits (ICs). This lithography process uses a 248nm wavelength light source to write features on wafers. The next generation of integrated chips is slated to be fabricated at a 90 nm node using 193 nm wavelength light source. 193 nm lithography tools that have already met International SEMATECH (ISMT) standards are ready for use in mass production of ICs. In the next next generation, 157nm is the candidate optical lithography tool to produce ICs at the 70 nm node. The optical elements that are being used in stepper tools until now are highly absorptive at 157nm. Calcium fluoride (CaF2) is the material of choice for optical elements at 157nm due to its high transmittance in the deep ultraviolet (DUV) and vacuum ultraviolet (VUV) spectral ranges. Adsorbed surface contaminants on optical elements absorb light energy in an optical lithography system and, if left unclean, will result in reduced wafer yield. In order to nondestructively analyze the surface adsorbate of different CaF2 samples, a laser induced desorption - Time of Flight Mass Spectrometer (LID-TOFMS) technique was developed. The main object of this technique is to investigate the surface composition of adsorbed contaminants as a function of position on the sample. An Er:YAG laser at 2.94µm was used as the light source to induce desorption. Electron impact ionization was used to obtain ionization of desorbed molecules. The detection of ionized species was accomplished by TOFMS operated in Angular Reflectron (AREF) mode to obtain better resolution. Super polished, (100) CaF2 and different off-axis (such as 10ï and 15ï off (100))CaF2 samples were investigated in this work. Water, alcohols, ketones and alkali metal ions were found on all the samples. Water ions and hydrocarbon ions (from alcohols and ketones) were seen at most of the sites while alkali metal ions were less frequently observed. A degenerate desorption threshold model was used to quantitatively analyze the desorbed species and to determine desorption threshold energy density at numerous sites on all the samples. Surface maps of water ions and hydrocarbon ions for different samples were plotted and they showed similar distribution patterns of water and hydrocarbon ions on the sample surface. This suggests that water and hydrocarbons are co-adsorbed or incorporated into surface defects during the polishing and cleaning operations. Atomic force microscope (AFM) scans of the samples were performed to identify surface topography. The data reported here can be used in semiconductor industries either to modify conventional processing or to design a new efficient laser cleaning process for optical elements.
Files	Filename       Size       Approximate Download Time (Hours:Minutes:Seconds)     28.8 Modem   56K Modem   ISDN (64 Kb)   ISDN (128 Kb)   Higher-speed Access    1.Title.pdf 3.63 Kb 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01   2.Signature_page.pdf 5.04 Kb 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01   3.Dedicated.pdf 3.19 Kb < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01   4.Acknowledgements.pdf 5.75 Kb 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01   5.Table_of_Contents.pdf 8.30 Kb 00:00:02 00:00:01 00:00:01 < 00:00:01 < 00:00:01   6.List_of_tables.pdf 4.11 Kb 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01   7.List_of_figures.pdf 61.76 Kb 00:00:17 00:00:08 00:00:07 00:00:03 < 00:00:01   8.ABSTRACT.pdf 10.09 Kb 00:00:02 00:00:01 00:00:01 < 00:00:01 < 00:00:01   91.CHAPTER_1.pdf 98.25 Kb 00:00:27 00:00:14 00:00:12 00:00:06 < 00:00:01   92._Chapter2.pdf 380.28 Kb 00:01:45 00:00:54 00:00:47 00:00:23 00:00:02   93.CHAPTER_3.pdf 771.02 Kb 00:03:34 00:01:50 00:01:36 00:00:48 00:00:04   94.CHAPTER_4.pdf 1.87 Mb 00:08:38 00:04:26 00:03:53 00:01:56 00:00:09   95.CHAPTER_5.pdf 17.45 Kb 00:00:04 00:00:02 00:00:02 00:00:01 < 00:00:01   96.Appendix.pdf 80.12 Kb 00:00:22 00:00:11 00:00:10 00:00:05 < 00:00:01   97.References.pdf 26.63 Kb 00:00:07 00:00:03 00:00:03 00:00:01 < 00:00:01   98.BIOGRAPHICAL_SKETCH.pdf 5.17 Kb 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01