Wafer Surface Position Detection Using Phase Difference
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Solution Overview
Problem
Conventional autofocus sensors in semiconductor device manufacturing face challenges in accurately detecting the surface position of a wafer surface coated with a resist, as measurement light is affected by light reflected from the circuit pattern, leading to measurement errors due to shared optical paths.
Innovation Solution
A surface position detecting apparatus that imparts a phase difference between light traveling via the resist surface and other surfaces, using aperture stops in the optical path to reduce the intensity of interfering light, allowing for high-accuracy detection of the surface position by minimizing the impact of light from underlying surfaces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If measurement light is applied onto the resist surface, then surface position information can be obtained, but light entering the interior of the resist and reflected on the circuit pattern causes measurement errors
Solution Approach 1:
The patent converts the harmful interference light from the circuit pattern into a beneficial signal by detecting its phase difference relative to the reflection from the resist surface. The phase difference information, which initially represents measurement error, is transformed into useful data for determining both the surface position and the presence of underlying patterns.
Solution Approach 2:
The patent introduces an intermediary analysis method that separates the measurement into two components: light reflected from the resist surface and light that entered the resist and reflected from the circuit pattern. By analyzing the phase difference between these two components, the system can extract accurate surface position information while accounting for the interference from underlying structures.
2Measurement precision
If conventional AF sensor measures light reflected from wafer surface, then surface position can be detected, but light from multiple surfaces (resist and substrate) cannot be distinguished
Solution Approach 1:
The patent applies the principle of color changes by utilizing phase difference as a distinguishing characteristic between light from different surfaces. Just as color changes can identify different objects, the phase difference acts as a signature that allows the system to distinguish between light reflected from the resist surface and light reflected from the underlying circuit pattern, enabling selective measurement.
3Manufacturing precision
If high resolving power exposure is performed, then pattern fineness increases, but depth of focus range decreases requiring precise focus control
Solution Approach 1:
The patent replaces conventional mechanical focus adjustment methods with an optical measurement system that uses phase difference detection. Instead of relying solely on mechanical precision to maintain focus, the system optically measures the exact position of the resist surface and provides feedback for focus control, achieving the precision required for high-resolution patterning.
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 precise detection of the wafer surface position, even when other surfaces are present near the target surface, thereby improving the accuracy of focus control during lithography processes, ensuring high-resolution pattern transfer in semiconductor device manufacturing.
Implementation Method 1
receive light reflected from the wafer surface
Implementation Method 2
form an image of the slit by focusing the light
Implementation Method 3
impart a phase difference between different portions from each other in the light
Implementation Method 4
project the image of the slit from an oblique direction onto the wafer surface
Data Source
Figure 1A~1D
Figure 2
Figure 3A~3D
AI summary
A surface position detecting apparatus which detects position information of a predetermined surface in an object, comprising a first optical system (51E) which projects light from an oblique direction to the predetermined surface (14a); a second optical system (52E) which receive the light from the object; a detecting system (13) which receives the light from the second optical system and which detects the position information of the predetermined surface in a direction intersecting the predetermined surface based on the light; and a phase difference imparting system which is arranged in an optical path of at least one of the first and second optical systems (51E, 52E) and which imparts a phase difference between different portions from each other of light traveling via a surface other than the predetermined surface (14a) in the object, in the light from the second optical system (52E).