Development Rate Monitoring (DRM)

Transcription

1 MCEE 505 Lithography Materials ad Processes Page 1 of 5 Developmet Rate Moitorig (DRM) Microelectroic Egieerig 1. OBJECTIVE The objective of this experimet is to uderstad ad characterize the developmet ad dissolutio properties of photoresist materials. 2. INTRODUCTION Developmet of covetioal resist materials is based o image-wise dissolutio discriatio. To uderstad ad optimize photoresist developmet, it is ecessary to characterize exposure depedet dissolutio properties. The extractio of developmet rate ad exposure relatioships allows for tremedous isight ito the imagig capabilities of a resist process. A family of ormalized thickess verses developmet time curves for a resist material exposed at various dose levels ca be geerated. Such curves ca be obtaied usig laser iterferometry techiques ad separate substrate exposure 1, 2 or a sigle substrate ad multiple exposures 3. A developmet rate vs. exposure curve ca be produced from a family of these dissolutio curves. To fully characterize the dissolutio properties of a resist throughout its etire thickess, a rate curve may ot suffice sice developmet rate is a fuctio of resist thickess. Surface ihibitio reduces the developmet rate sigificatly at the top surface of the resist. Developmet rate vs. resist thickess curves show how developmet rate icreases from the top surface of the resist toward the bottom. Whe developmet rate ad exposure are plotted i a log-log fashio, a liear regio exists that ca be described i terms of a developmet rate log-slope (DLS): l( dev. rate) DLS l( dose) Dissolutio rate cotrast ca be expressed as: R Cotrast R where R ad R are the maximum ad the imum developmet rate respectively. Together, DLS ad dissolutio rate cotrast are effective measuremets of the dissolutio properties of a resist material. High levels of both metrics are desirable. Furthermore, developmet rate ca be related to exposure usig models such as those developed by Mack 4 : where: a 11 m a1 m max R m Rmax R

2 MCEE 505 Lithography Materials ad Processes Page 2 of 5 a 1 1 M th 1 ad m is the relative cocetratio of the photoactive compoud (PAC), is the selectivity, ad Mth is the threshold PAC cocetratio. Equatio 14 ad figure 7 i F. H. Dill s paper Characterizatio of Positive Photoresist ca be used to either calculate or approximate the ihibitor cocetratio. Cotrol of the resist ad developmet properties ca be used to some extet to ifluece performace. A moderate cotrast value ear 10,000 is geerally sufficiet. As developer ormality is chaged, the RMAX ad RMIN will both be affected (as log as base cocetratio does ot fall below a critical level, ph ~12.5) but their ratio ad the shape of the curve will remai fairly costat 5. RMAX is primarily a fuctio of the polymer itself. Major resist, sesitizer, ad solvet factors that will ifluece developmet rate iclude: Polymeric structure PAC/PAG/ihibitor structure PAC/PAG/ihibitor cocetratios (DNQ loadig > 20%) Protectio ratio (PHS protectio ratio > 25%) Solvet cocetratio Polymeric molecular weight (>1.3 x104 g/mol) Polydispersity (< 3) Developer compositio (metal io vs. TMAH) Developer catio size ad cocetratio Resist surfactat Resist dissolutio ihibitio/acceleratio state Developer surfactat Hydroxyl group positios o PHS polymer will also impact dissolutio rate, a fuctio of hydroge bodig ad steric hidrace with the polymer backboe 6. Copolymers of 2- ad 4- hydroxystyree have bee demostrated to allow cotrol of PHS dissolutio properties. 3. PROCEDURE This lab will ivolve the measuremet of photoresist developmet rate. 3.1 Maual DRM procedure 1. Obtai several bare silico wafer substrates (150mm). 2. Either coat the wafers with photoresist by either had or use the appropriate track (SVG or SSI). a. To had coat, dehydrate bake the substrates at 100 C for 60 secods ad prime with P-20 primer (80% PGMEA-20%HMDS) at appropriate RPM, followed by a bake at 100 C for 60 secods. b. Coat photoresist at appropriate RPM, ad soft-bake at appropriate temperature for 60 secods.

3 MCEE 505 Lithography Materials ad Processes Page 3 of 5 3. Measure thickess o the Naospec at 5 radial locatios o the wafer. 4. Expose the sample usig either the GCA 6700 stepper or the ASML i-lie stepper. a. See sectio 3.2 for the stepper procedures. 5. Post-exposure bake the substrates at appropriate temperature for 60 secods. 6. Pour approximately 250mL of MF CD-26 developer ito a 9 x9 Pyrex dish. Moitor the temperature of the developer util it reaches room temperature. Usig the 11-step time icremet series [5, 5, 5, 10, 10, 20, 20, 30, 30, 30, 60, 60sec] isert the wafer ito the developer for the time icremet idicated the remove, rise ad measure (usig the Naospec) the photoresist thickess i the 16 die i the array for each step. A overall develop of 255 secods will be used. 7. Plot: a. Photoresist thickess versus developmet rate for each exposure dose. b. From that plot geerate a developmet rate versus exposure dose curve at 50% thickess c. Ad a l(developmet rate) versus l(exposure dose curve) at 50% thickess. 8. Calculate RMIN, RMAX, DLS, ad Cotrast. 3.2 Stepper procedures GCA 6700 procedure 1. Make sure that the switch below the keyboard is i the Time Mode positio. 2. Load the ETM reticle ad first wafer. 3. EXPO MCEE PASS: 1 5. STARTING ROW: 2 6. ENDING ROW: 9 (ca be adjusted to lower umber if ecessary) 7. STARTING COLUMN: 2 8. ENDING COLUMN: 9 (ca be adjusted to lower umber if ecessary) 9. OVER: E 10. Iput the desired startig exposure time 11. Iput the desired icremet value 12. FOCUS: Use the most up-to-date focus settig (it should be writte ear the scree) 13. Do ot ru a ope frame test 14. RETICLE BAR CODE: NONE (just hit ENTER ) 15. FLOOR #: eter the appropriate value. 16. ALIGNMENT MARK PHASE (P/N/X): N 17. Follow istructios i GCA user maual for wafer size beig used.

4 MCEE 505 Lithography Materials ad Processes Page 4 of ASML i-lie procedure Follow istructios i ASML user maual for Dose to Clear Test (Exposure Matrix). 4. Data Aalysis Plot the followig from the data collected. The first few data poits my eed to be excluded if they were collected before the wafer was fully iserted (for the automated procedure). If stadig waves are observed i the secod plot, calculatig a accurate slope may require averagig alog a rage. 1. A characteristic exposure curve (ormalized thickess [t/t0] versus log(exposure dose [mj/cm 2 ])) for 30 secods developmet time. 2. Normalized photoresist thickess versus developmet time [sec] for each exposure dose. 3. Developmet rate [m/sec] versus relative exposure dose. Calculate developmet rate values at 50% ormalized thickess, ad ormalize exposure dose to the dose-to-clear. This figure ca be used to fid RMIN. 4. Developmet rate versus ormalized photoresist thickess, for each exposure dose. Is surface ihibitio observed? What causes this? 5. l(developmet rate) versus l(exposure dose). Calculate developmet rate values at 50% ormalized thickess. Idetify the liear regio ad calculate RMIN, RMAX, DLS, ad Cotrast. Usig the Mack model, fit Mth ad parameters to the data. Explai ay differeces betwee the data collected from wafers that received a PEB ad the data collected from wafers that did ot. REFERENCES 1. K. L. Koerth, F.H. Dill, IEEE Tras. Electro, Devices, ED-22, 453 (1975). 2. S. D. Chowdhury, D. Alexader, M. Goldma, A. Kukas, N. Farrar, C. Takemoto, B.W. Smith, Proc. SPIE 2438, 659 (1995). 3. For istace the Perki Elmer Developmet Rate Moitor (DRM). 4. C. A. Mack, A Comprehesive Optical Lithography Model, SPIE 538, (1985) 5. R. A. Arcus, Proc. SPIE 631, 124 (1986). 6. R. R. Dammel et al, Proc. SPIE 2195, 542 (1994). ).

5 MCEE 505 Lithography Materials ad Processes Page 5 of 5 Maual DRM Data Sheet (Use appropriate uits) Develop Time 5sec Exposure Dose Remaiig Resist Thickess (Å) 0 mj/cm 2