Spin-On-Dielectrics: Characteristics and Modeling …

1 Spin-On-Dielectrics: Characteristics and Modeling John A. Smythe A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Materials Science and Engineering University of Washington 2004 Program Authorized to Offer Degree: Materials Science and Engineering University of Washington Graduate School This is to certify that I have examined this copy of a master s thesis by John A. Smythe and have found that it is complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Committee Members: _____ Scott Dunham _____ Guozhong Cao _____ Fumio Ohuchi Date:_____ In presenting this thesis in partial fulfillment of the requirements for a master s degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection.

2 I further agree that extensive copying of this thesis is allowable only for scholarly purposes, consistent with fair use as prescribed in the Copyright Law. Any other reproduction for any purposes or by any means shall not be allowed without my written permission. Signature _____ Date _____ i TABLE OF CONTENTS Page List of Figures .. ii List of iv 1 A Brief History of Spin-On- dielectric 1 Background and 1 A Historical 2 Highlights of Existing Spin-Coating Models .. 27 Initial Work Plan Concepts .. 30 Section 1 31 2 Planarity and Density Model Approach .. 35 Introduction .. 35 Discussion of Available Modeling Approaches for 36 Modeling Spin-Coating Planarization .. 40 Proposed Work for Global 45 Proposed Work for Small Feature Effect.

3 49 Materials and 53 Analytical Methods .. 54 Next Steps .. 54 Section 2 55 3 Experimental Plan and 58 Introduction .. 58 Experimental .. 58 Test Pattern Layout .. 59 Experimental 62 Optical Results .. 62 Surface Profile Results .. 70 4 Conclusions and Model Development .. 84 Conclusions .. 84 Model Development 84 Section 4 86 iiList of Figures Page Figure 1-1: General Schematic of Planarity 4 Figure 1-2: SOG on CVD Oxide Schematic 6 Figure 1-3: MSQ Cross-Linking Reaction24 21 Figure 2-3: Global Planarity for Large Features 46 Figure 2-4: Global Planarity for Large Features - Zoomed View 46 Figure 2-5: Optical Image of Large Feature Sample 47 Figure 2-6: Calculated Omega2 for expected condition 48 Figure 2-7: Calculated Omega2 in sub-micron range 48 Figure 2-8: Small Feature Image without Etch 50 Figure 2-9.

4 Small Feature Image with Etch 50 Figure 2-10: Small Feature Effect 51 Figure 2-11: Wide Feature Density 51 Figure 2-12: Thickness Effect of Densification Reaction 52 Figure 2-13: Thickness Effect of Densification Reaction 53 Figure 3-1: Test Pattern Schematic - Quadrant Position 60 Figure 3-2: Test Pattern Schematic - Quadrant Spacing Dimensions 60 Figure 3-3: Test Pattern Schematic - Quadrant Detail 61 Figure 3-4: Test Pattern Schematic - Minimum Feature Detail 61 Figure 3-5: Optical microscope example of measurement points 62 Figure 3-6: Optical measurements 7114_08 quadrant I to quadrant II (same pattern) 63 Figure 3-7: Optical measurements for 7114_08 quadrant II to quadrant I (next pattern) 64 Figure 3-8: Measurement sites for GOF measurements 64 Figure 3-9: Step planarity by optical measurement 65 Figure 3-10: Large spot GOF by position 65 Figure 3-11: Optical measurements for 7114_09 quadrant II to quadrant I (next pattern)66 Figure 3-12: Optical measurements for 7114 08 vs.

5 09 quadrant II to quadrant I (next pattern) 66 Figure 3-13: Percent Fill 7114 08 vs. 09 67 Figure 3-14: Percent of Test Wafer for 7114 08 and 09 68 Figure 3-15: Fill Efficiency for 20 m gap 7500 and 11000 nominal 68 Figure 3-16: 7114 08 within quadrant uniformity 69 Figure 3-17: 7114 08 global uniformity right side of quadrant 70 Figure 3-18: 7114_03 scan 1 complete 71 Figure 3-19: 7114 03 scan 1 segment 300 to 600 71 Figure 3-20: 7114_03 Scan 1 segment 350 to 600 72 Figure 3-21: 7114_03 Scan 2 complete 72 Figure 3-22: 7114_03 Scan 2 segment 700 to 950 73 Figure 3-23: 7114_03 Scan 3 complete 73 Figure 3-24: 7114_03 Scan 3 segment 700 to 950 74 Figure 3-25: 7114 08 scan 1 complete 75 Figure 3-26: 7114_08 Scan 2 Complete 75 iiiFigure 3-27.

6 7114_08 Scan 2 segment 750 to 1000 76 Figure 3-28: 7114_08 Scan 3 Complete 76 Figure 3-29: 7114_08 Scan 3 segment 750 to 1000 77 Figure 3-30: 7114 03 scan 3 segment 886 to 926 linear fit 78 Figure 3-31: 7114_08 AFM Analysis Locations 79 Figure 3-32: 7114_08 AFM scan line vertical step at edge of feature 80 Figure 3-33: 7114_08 AFM scan line vertical results at center of feature 81 Figure 3-34: 7114_08 AFM scan of 21 micron gap 83 Figure 3-35: 7114_08 P-20h scan for AFM comparison 83 iv List of Tables Page Table 1-1: SOG Plasma Etch 5 Table 1-2: SOG Plasma and 20:1 HF Etch 5 Table 1-3: FTIR 10 Table 1-4: Percent Planarity Ranges by Yen and 12 Table 1-5: Poly-Siloxane Thickness and 12 Table 1-6: Table III17 For Viscosity from to mPa-s.

7 15 Table 1-7: Table IV17 for viscosity of solvents from to mPa-s .. 15 Table 1-8: FTIR 19 Table 1-9: FTIR Peaks for MSQ 22 Table 2-1: Table III7 For Viscosity from to mPa-s .. 38 Table 2-2: Table IV7 for viscosity of solvents from to mPa-s .. 38 Table 2-4: Typical Values for Planarity 43 Table 3-1: Sample Treatment .. 59 Table 3-2: 7114 03 fit equation summary .. 74 Table 3-3: 7114 08 fit equation summary .. 77 Table 3-4: 7114_08 Planarity as function of feature position .. 82 vAcknowledgements I would like to acknowledge Joe Wiggins of Micron Technology, Inc. for the AFM sample work and Leigh Soutter for continued assistance in the understanding of FEMLAB software package in preparation for model development. Finally, none of the work would be possible without the continued support of Micron Technology, Inc.

8 Disclaimer The views expressed in this work are strictly those of the author and do not represent those of Micron Technology, Inc. vi Dedication To RaDawn. This work could not have been completed without your continuous support. Thank-you for believing. 1 1 A Brief History of Spin-On- dielectric Materials Background and Introduction The idea of replacing chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), and sputter oxide materials, among others, with a spin-on approach has been of interest in the Semiconductor industry for the last two decades. The basic technique draws from the planarizing nature of a liquid when applied to surface topography.

9 The method was initially known as Spin-On-Glass (SOG) and has more recently taken on the more general acronym of Spin-On- dielectric (SOD). The focus over the years has been to make the material as close to oxide (SiO2) as possible after a cure step or series of cure steps in various ambient gases, temperatures and pressures. The work includes doped oxides such as phosphor-silicate-glass (PSG) because of important mobile cation gettering Characteristics . The many works have addressed issues including, but not limited to, crack resistance, etch rate in both wet and dry etch chemistries, resistance to photo resist stripping conditions, film stress control, and particulate control. The ideal result, in many present day applications, would be to find a material that would match the materials character of densified or as-deposited high-density-plasma (HDP) oxide.

10 There are still applications where matching the materials character of densified (often called reflow or flow ) boro-phospho-silicate-glass (BPSG) or phosphor-silicate-glass (PSG) would be beneficial. The one characteristic that has not been addressed with rigor is the interaction between underlying topography and degree of local and global planarization. The general concepts are widely known in the industry but little has been done to provide models that guide the 2D-layout rules of semiconductor circuit design. Some relevant work has been done outside the industry. The process technology known as Chemical-Mechanical-Polishing (CMP) has conversely received focus in this area with many papers and Doctoral Theses, particularly at MIT, on the subject of Modeling such interactions.