[Photolithography Par4] CD Measurement & Control

Welcome back to our comprehensive series on optical photolithography for silicon wafers in semiconductor fabrication. In this fourth episode, we dive into the precision world of Critical Dimension (CD) measurement and control within optical lithography. Photolithography isn't just about creating patterns—it's about achieving those patterns with exactitude down to the nanometer. This session zeroes in on the sophisticated tools and techniques, such as the In-line CD-SEM, that play pivotal roles in ensuring each dimension is precisely controlled for consistency across the lithography process. We'll cover the operational nuances of these tools and their critical importance in maintaining the exactness of semiconductor patterning. Below, you'll find the key sections of this episode. Click on any timestamp to directly access specific parts of the discussion.

1.Introduction to CD Control
[00:00] Introduction: Overview of the series and what to expect in this episode.

2. CD Measurement
[01:25] The Role of CD-SEM: "You can't control what you can't measure."
[05:00] CD Terminology: ADI, APEI, ASEI, AEI, ACI.
[07:20] Basic Principles of SEM Instruments: Electron Gun, Condenser/Objective Lens, SE/BSE Detector.
[11:40] Electron-Specimen Interaction: Comparing Secondary Electron (SE) vs Back Scattered Electron (BSE).
[15:45] In-line CD-SEM: Its evolution as a key method in 300mm wafer fab.
[21:25] Hitachi’s Flagship In-Line CD-SEM Models: CG6300, CV6300 for 300mm wafer measurements.
[26:40] Image Resolution Improvement History in Hitachi CD-SEM: From 15nm to 1.3nm resolution.
[31:00] Edge Slope Effect: Measuring CD using edge detection algorithms.
[36:05] Electron Charging Effect & Asymmetry Issue: Solutions involving faster vector scans.
[40:30] CD Slimming Issue in ArF Photoresist: ArF mode solutions.
[43:25] In-line CD-SEM: Automated measurement processes with Design Gauge tool.
[47:45] High-Voltage SEM (HVSEM): Application to overlay measurement and assessing damage risk.

3. CD Control
[51:00] Dose & Exposure Latitude (EL): Controlling CD with dose amount.
[53:35] Depth of Focus (DoF): Definition and principles.
[56:00] Focus-Expose Matrix (FEM) & Bossung Curve (SMILE Curve): Describing the optimum dose & focus to meet the target CD.
[59:35] E-D Tool vs Bossung Curve: Comparing tools to describe the optimum process window.
[1:02:55] Solutions for In-Wafer & In-Field CD Uniformity: Correction Per Exposure (CPE), Dose Mapper (Unicom & Dosicom).
[1:06:05] Local CD Uniformity (LCDU): Importance in smaller features, Line Edge Roughness (LER), Line Width Roughness (LWR), Chemical Enhancement Ratio (CER), Nonlinear Imaging Scaling (NILS).
[1:10:00] LER Improvement Technologies: Sidewall Image Transfer (SiT), Atomic Layer Etching (ALE), Inpria MOR, Lam's Dry Resist.
[1:12:25] Strategic CD Measurement and Statistical Process Control (SPC) in 300mm wafer fab.

4. Wrap Up
[1:15:50] Review of Content: Including a mind map with keywords.