Infrared Reflectometer Wafer Depth Measurement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for measuring the depth of high aspect ratio etched features on wafers, such as Through Silicon Vias (TSVs), are either destructive, costly, and time-consuming, or limited by optical techniques that struggle with aspect ratios greater than 2:1, failing to provide accurate and non-destructive measurements.
Innovation Solution
A system utilizing an infrared reflectometer positioned to illuminate and measure from the non-etched surface of the wafer, allowing for direct and non-destructive measurement of high aspect ratio etched features by analyzing the interference patterns in reflected light, which distinguishes between different layers and provides accurate depth measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If optical non-contact measurement techniques are used to measure etched features, then measurement speed and non-destructiveness are improved, but measurement precision deteriorates for high aspect ratio features (aspect ratio > 2:1)
Solution Approach 1:
The patent inverts the conventional measurement approach by measuring from the back surface of the wafer rather than from the front surface where the etched features are located. This allows optical techniques to accurately measure high aspect ratio features by viewing the etch depth from the opposite side, avoiding the geometric limitations that prevent accurate measurement from the front surface.
2Measurement precision
If the illuminating spot size is reduced to illuminate the bottom of narrow etched features, then measurement precision is improved, but the angular spectrum contains light rays too steep to effectively illuminate the bottom
Solution Approach 1:
The patent reverses the measurement direction by illuminating and measuring from the back surface of the wafer. This eliminates the problem of steep angles and insufficient illumination at the bottom of narrow etched features, as light now travels through the wafer thickness rather than attempting to illuminate the bottom of deep, narrow features from the front surface.
3Measurement precision
If scanning electron microscope is used for measurement, then measurement precision is improved, but cost and time consumption increase
Solution Approach 1:
The patent replaces the mechanical scanning electron microscope system with an optical measurement system. By measuring from the back surface of the wafer, the invention achieves accurate etch depth measurements using non-contact optical techniques, eliminating the need for expensive and time-consuming electron microscopy while maintaining measurement precision.
4Ease of operation
If wafer is thinned to expose TSVs, then measurement accessibility is improved, but structural integrity may be compromised
Solution Approach 1:
The patent measures from the back surface of the wafer without requiring the wafer to be thinned. This approach maintains the wafer's structural integrity while still enabling accurate measurement of TSV and etched feature depths, as the measurement is performed through the full wafer thickness rather than requiring exposure of the features.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate, non-destructive, and cost-effective measurement of high aspect ratio etched features with high spatial resolution, improving the precision and efficiency of wafer manufacturing processes, particularly for SOI wafers and TSVs, by avoiding the limitations of traditional optical methods.
Implementation Method 1
analyzing the interference patterns in reflected light
Implementation Method 2
infrared reflectometer positioned to illuminate and measure from the non-etched surface
Data Source
AI summary
A system (10) for directly measuring the depth of a high aspect ratio etched feature on a wafer (80) that includes an etched surface (82) and a non-etched surface (84). The system (10) utilizes an infrared reflectometer (12) that in a preferred embodiment includes a swept laser (14), a fiber circulator (16), a photodetector (22) and a combination collimator (18) and an objective lens (20). From the objective lens (20) a focused incident light (23) is produced that is applied to the non-etched surface (84) of the wafer (80). From the wafer (80) is produced a reflected light (25) that is processed through the reflectometer (12) and applied to an ADC (24) where a corresponding digital data signal (29) is produced. The digital data signal (29) is applied to a computer (30) that, in combination with software (32), measures the depth of the etched feature that is then viewed on a display (34).