Pre-alignment Measurement Device for Lithographic Wafers
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Solution Overview
Problem
Current pre-alignment methods for lithographic wafers face issues such as poor image quality for glass substrates in transmissive systems and interference from chuck grooves in reflective systems, along with insufficient resolution due to unaccounted vertical and horizontal magnifications.
Innovation Solution
A measurement device using a laser, cylindrical lenses, and a CCD detector, which forms images with different horizontal and vertical magnifications to match resolutions, and includes a calibration mark plate with varying reflectivities to accurately determine the position and height of the wafer, overcoming interference from chuck grooves and enabling reliable alignment of bonded wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transmissive pre-alignment system is used, then the alignment precision is improved, but the image quality deteriorates for glass substrates
Solution Approach 1:
The patent introduces a calibration mark plate with specific reflectivity characteristics as an intermediary element. This plate is placed on the wafer stage and serves as a mediator between the light source and the measurement system, providing reliable reference marks for alignment that work effectively with glass substrates in transmissive systems.
2Device complexity
If a reflective pre-alignment system is used, then the alignment process is simplified, but the measurement precision deteriorates due to chuck groove interference
Solution Approach 1:
The patent extracts the reference marking function from the wafer edge itself and places it on a separate calibration mark plate. This separation allows the system to use reflective illumination while avoiding interference from chuck grooves, as the calibration marks are positioned and designed to be distinct from the wafer-edge-chuck interaction region.
Solution Approach 2:
The calibration mark plate utilizes reflectivity differences (analogous to color changes in optical properties) to create high-contrast reference marks. The plate has regions with different reflectivities that produce clearly distinguishable images on the CCD detector, enabling precise measurement despite the reflective illumination method used.
3Device complexity
If uniform magnification is used in both horizontal and vertical directions, then the device structure is simplified, but the measurement precision deteriorates due to mismatched resolutions
Solution Approach 1:
The patent deliberately introduces asymmetric magnification into the optical system by placing cylindrical lenses at specific positions. The first cylindrical lens creates horizontal magnification while the second cylindrical lens creates vertical magnification, allowing independent optimization of horizontal and vertical resolutions to match the anisotropic requirements of the measurement task.
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
This solution ensures precise pre-alignment by matching horizontal and vertical resolutions, eliminating interference from chuck grooves and allowing reliable alignment of bonded wafers, thereby improving the accuracy and reliability of the pre-alignment process.
Implementation Method 1
a light beam is emanated by the laser and is transformed into a line beam after passing through the first cylindrical lens; and the line beam is reflected by the object under measurement and then passes through the second cylindrical lens to form a CCD image
Implementation Method 2
a light beam is emanated by the laser and is transformed into a line beam after passing through the first cylindrical lens; and the line beam is reflected by the object under measurement and then passes through the second cylindrical lens to form a CCD image which has different horizontal and vertical magnifications
Data Source
AI summary
A pre-alignment measurement device includes, disposed in a direction of propagation of light, a laser, a first cylindrical lens, a first imaging lens, an illumination diaphragm, a second imaging lens, a second cylindrical lens and a CCD detector. The laser, an object under measurement and the CCD detector are arranged at respective apexes of a triangle formed by the measurement device for pre-alignment. A light beam is emanated by the laser and is transformed into a line beam. The line beam is reflected by the object under measurement and then passes through the second cylindrical lens to form a CCD image which has different horizontal and vertical magnifications, allowing horizontal and vertical resolutions to be matched with horizontal and vertical measuring ranges, respectively. The CCD image contains information of a position and a height of a step defined by the object under measurement and the wafer stage.