Meng Guo, Donald Pfettscher, Kimberly Pollard, Richard Peters, Travis Acra Dynaloy LLC, a subsidiary of Eastman Chemical Company Thierry Lazerand, Kenneth D. Mackenzie, Marco Notarianni Plasma-Therm LLC

 Also known as “Bosch Process”  Provides a highly anisotropic etch in wafer substrates  Can create features that are hundreds of micrometers thick and have aspect ratios of ~20:1  Industry Uses ◦ Power Devices, Capacitors, Cantilevers, through-silicon vias for 2.5D and 3D advanced packaging, and plasma dicing to singulate chips 1 1 “Wafer Dicing using Dry Etching on Standard Tapes and Frames,” Proceedings from IMAPS, San Diego CA, October 13-16, 2014.

 Uses Bosch Process to singulate chips from semiconductor wafers ◦ Wafers are adhered to a dicing frame with dicing tape for handling post process  Damage free process with high throughput  Decreases the requirement for street sizes ◦ More silicon area for additional devices

 Bosch process uses two Plasma source gases ◦ SF 6 for Etching Step ◦ C 4 F 8 for Passivation Step  The passivation step creates a fluorinated polymer liner on trench sidewall  The etching step leaves the liner material behind as a residue. Silicon Photoresist SF 6 Plasma Silicon C 4 F 8 Plasma Silicon SF 6 Plasma

 Post-Bosch process cleaning is needed to remove: ◦ Highly fluorinated polymeric residue from etching through passivation layer located primarily on the sidewalls  Residue is inert, hydrophobic, difficult to remove, and harder to dissolve  Fluorine contamination can cause upstream integration issues 1 ◦ Photoresist used as mask during Bosch process  Two common cleaning processes ◦ O 2 plasma treatment ◦ Wet chemical stripping – focus of this presentation 1 Surface and Interface Analysis, “Fluorine-induced Corrosion of Aluminium Microchip Bond Pads: an XPS and AES Analysis”, V.21, pp , 1994.

 Wet Cleaning may provide advantages over O 2 plasma cleaning ◦ Increased throughput, lower maintenance cost, reduced utilization of valuable plasma tool time ◦ Tailoring of the wet cleaning chemistry can allow for specific needs of specific processes to be met  Wet cleaning has previously been shown to remove Post-Bosch etch residue and damaged photoresist in TSV creating process 1,2 1.“TSV resist and etch residue removal for 3DIC,” Proceedings from IWLPC, San Jose, CA, November 2013; “Efficient TSV Resist and Residue Removal in 3DIC,” IMAPS Device Packaging Conference, Phoenix, AZ, March “Formulation Development for Bosch Etch Residue Removal: Effect of Solvent on Removal Efficiency,” Proceedings from IMAPS, Advanced Packaging & the Internet of Things: The Future of Our Industry, Orlando, FL, October 2015.

 Definition of Clean: Complete removal of polymer based residue, including all fluorine, and compatibility with the underlying silicon surface.  Techniques for Determining Cleaning ◦ Optical Microscope ◦ Scanning Electron Microscope (SEM) ◦ Energy Dispersive X-ray (EDX) ◦ Auger Electron Spectroscopy (AES)

 Optical Microscopy ◦ Due to feature size and shape this technique is not suitable  SEM ◦ Can be used to determine if morphology differences are present but can’t easily distinguish between silicon defects and residue  EDX ◦ Useful in determining difference between Silicon defect and residue. Analyzing for Fluorine is used to determine cleanliness. Detection limits too high for TSVs due to aspect ratio and geometry effects.  AES ◦ Very surface sensitive technique for determining cleanliness of surface. Analyzing for Fluorine is used to determine cleanliness. Lower detection limits compared to EDX when analyzing TSVs.

 Chemistry Characteristics ◦ TMAH-free ◦ Water and IPA rinse able ◦ High flash point  Beaker test were used to determine effectiveness ◦ All test were performed at 70°C with varying times Flash point (°C) Specific Gravity (g/mL) 25°C, (cP) 38°C, (cP) Surface tension (mN/m)

TSV Cleans

Pre-process SEM - EDX Inspection Fluorine Top Middle Bottom Vias Diameter = 5µm Pitch = 10µm

Post-process SEM - EDX Inspection Top Middle Bottom Vias Diameter = 5µm Pitch = 10µm No Fluorine Detected No Fluorine Detected No Fluorine Detected Beaker Process Conditions 5 60 °C Low agitation

Post-process AES Inspection Vias Diameter = 5µm Pitch = 10µm Beaker Process Conditions 5 60 °C Low agitation No Fluorine Detected at top, middle, bottom of via by AES

Plasma Dicing Cleans

 4 x 200 mm full thickness wafers with 15µm unified streets and 1mm 2 square die used as test vehicles o All wafers had a 6µm photoresist (PR) mask o All wafers were partially etched to a depth of ~300µm o Some wafers had post-etch, in situ O 2 plasma treatment o All wafers were processed by Bosch etch but the polymer passivation step time was varied.

 Coupons were cleaved along the etched trench for SEM and EDX inspection  EDX spectra were collected at the top, middle, and bottom of trench sidewalls before and after cleaning

Wafer Etch Process ConditionsBeaker Process Conditions Standard processing conditions; PR mask left intact on wafer °C Low agitation TopMiddleBottom Pre - Clean Post - Clean Fluorine Wt% = 40 Fluorine Wt% = 34 Fluorine Wt% = 21

Wafer Etch Process ConditionsBeaker Process Conditions Enhanced passivation step; PR mask left intact on wafer °C Low agitation TopMiddleBottom Pre - Clean Post - Clean Fluorine Wt% = 39 Fluorine Wt% = 42 Fluorine Wt% = 37

Wafer Etch Process Conditions Beaker Process Conditions Standard processing conditions; PR mask stripped by in situ O 2 plasma treatment °C Low agitation TopMiddleBottom Pre - Clean Post - Clean Fluorine Wt% = 6 Fluorine Wt% = 3 Fluorine Wt% = 2

Wafer Etch Process Conditions Beaker Process Conditions Enhanced passivation step; PR mask stripped by in situ O 2 plasma treatment °C Low agitation TopMiddleBottom Pre - Clean Post - Clean Fluorine Wt% = 22 Fluorine Wt% = 10 Fluorine Wt% = 3

Test Sample Process Temp (°C)/Time (min) Sidewall Condition, Pre-Clean (F wt.%, measured using EDX) Sidewall Condition, Post-Clean (F wt.%, measured using EDX) Result TopMiddleBottomTopMiddleBottom #170/ ND Clean #270/ ND Clean #370/10632ND Clean #470/ ND Clean ND = not detected

 The Bosch-process is being implemented in many areas of semiconductor manufacturing  One of the exciting new areas is Plasma Dicing to singulate Chips  A proposed chemistry for post Bosch-process wet cleaning was able to completely remove fluorinated polymer passivation residue from 4 types of wafers with varying degrees of residue  The wet cleaning process has the potential to replace a two step process with a one step solution