Removing Aluminum Cap in 90 nm Copper Technology Emanuele Capitanio Matteo Nobile Didier Renard ST Microelectronics Agrate (Italy) ST Microelectronics Agrate (Italy) Credence
Content What Alucap is Needs for FIB edits Involving problems Problem solving Results Conclusion
What Alucap is Aluminium structures at the top metal layer electrically floating Alucaps avoid fractures-scrapes on the oxide during passivation deposition process Alucaps keep constant the metal vs. Dielectric density all over the wafer
Needs for FIB edits Remove the intrinsic topography from the top surface to deprocess the successive metal layers Expose uniformly the first underneath metal layer even on the edge of an alucap 8.50 µm 2.50 µm Vision 3D
Problems Spread over the whole surface Alucap is Floating metal Alucap is not planar
Problems Spread over the whole surface Alucap is Floating metal Alucap is not planar
Problems ~1.0µm 2.5µm Spread over the whole surface Alucap is Floating metal Alucap is not planar
Etching Rate Yield FIB Milling Rate Overetching at the edges Slow 90 Fast Incident angle 0º ~80º 0º Copper line exposed 0º 80º
Problem solving
Problem solving Alucap is Floating metal Calibrate the milling time for a given process on a FIB grounded Alu cap
Calibrated values: Passivation Aluminum L shaped Box = 8.5 µm x 8.5 µm x 2.5 µm Passivation Removal Dielectric Etch Ip = 250 pa Time measured = 6 minutes Aluminum Removal Metal Etch = 250 pa Time measured = 7 minutes
~1.0µm 2.5µm Problem solving Spread over the entire surface Alucap is Floating metal Alucap is not planar Etch inside and leave the edges
Alucap Removal First step
Explanation Passivation Removal L shape Box = 8.5 x 8.5 x 2.5 µm3 Dielectric Etch Ip = 250 pa Time Removal = 6 minutes based on calibrated time Aluminum Removal L shape Box = 8.5 x 8.5 x 2.5 µm3 Metal Etch Ip = 250 pa Time Removal = 7 minutes based on calibrated time L shape L shape during the process
Top Oxide & Aluminum Removing Top Passivation removed Aluminum etching Aluminum removed
The Alucap deprocessing can stop if Top view Editable area in the Alucap Alucap removed Alucap not removed
Results from the first step 2.5 um 6.0 um 8.5 um Probe point or cuts are possible below the Alucap Box Size = 2.4um x 3.0um
Alucap Removal Second step
Next step depends on edits Any edit touching or close to the edges requires to get rid of these walls
FIB Milling Rate How to remove the remaining topography? Slow Fast Cu Cu Direct way Way to planarization
Removing «walls» Refill the structure with deposited oxide L shaped Box = 9 x 9µm2 & 3µm width Insulator Deposition Ip = 250 pa Time Deposition = 7 minutes Dielectric Refill Broad area deposition of insulator Box Size = 18 µm x 18 µm Insulator Deposition Ip = 1nA Time Deposition ~30 minutes Broad area deposition
Removing «walls» Broad Insulator deposited The purpose is to planarize the surface by building up a thicker structure on top of the target area Insulator Deposition Removing Box Size = 18 µm by 18 µm Dielectric etch Ip = 1nA Time = 4 minutes Alu cap removed
Alucap Results First Technique: FIB editing area quite small Easy FIB Editing (2 layers under the Alucap) Time to remove the single dummy: about 30 minutes.
Alucap Results First Technique: FIB editing area quite small Easy FIB Editing (2 layers under the Alucap) Time to remove the single dummy: about 30 minutes. Second Technique: Bigger FIB editing area Complex Fib Editing (4-5 layers under the Alucap) Time to remove dummy Alucap: about 50 minutes.
Alucap Results First Technique: FIB editing area quite small Easy FIB Editing (2 layers under the Alucap) Time to remove the single dummy: about 30 minutes. Second Technique: Bigger FIB editing area Conclusion: Complex Fib Editing (4-5 layers under the Alucap) Time to remove dummy Alucap: about 50 minutes. Possible to reach buried metal layers maintaining a planar edit even with high topography on the top