FLOW ENTRY · PROCESS START · Step 1
Wafer In
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The 40nm BSI CMOS Image Sensor (CIS) process flow covers the complete fabrication of a backside-illuminated image sensor, from incoming wafer through color filter array and microlens formation.
Unlike front-side illuminated (FSI) sensors, the BSI architecture places the photodiode beneath the metal interconnect stack and receives light from the thinned wafer backside, achieving higher quantum efficiency and better low-light performance.
Key process modules include Shallow Trench Isolation (STI), photodiode formation, frontside Deep Trench Isolation (F-DTI) for pixel-to-pixel optical and electrical isolation, multi-level copper dual-damascene interconnects (MET0–MET6), Direct Bond Interconnect (DBI) for wafer-to-carrier bonding, backside thinning and passivation, Light Shield Grid for stray-light suppression, Color Filter Array (CFA) in a Bayer pattern, and microlens fabrication.
The flow spans 417 process steps across 42 specialized modules, providing detailed rationale and risk analysis for each step — grounded in academic papers, patents, and authoritative textbooks. This flow is completely free to access without login.
This is a backside-illuminated CMOS image sensor, and its integration is organized around getting light to the photodiode. The wafer is thinned and flipped so that light enters from the back, striking the photodiode directly instead of passing through the metal wiring that would otherwise block and scatter it. Deep trench isolation walls the pixels off from one another so that charge generated under one pixel does not leak into its neighbor and blur the image. The back surface is anti-reflection coated so that incoming photons enter the silicon rather than reflect away, and separately passivated so that the defects left by thinning the wafer do not trap photo-generated carriers or inject the dark current that would otherwise show up as noise. The cross-sections below show how the photodiode, isolation, and backside optical stack are constructed layer by layer.