Projection Lens Focus Correction via Reticle Marks
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Solution Overview
Problem
In semiconductor device manufacturing, the existing methods for automatic focus correction in projection exposure apparatuses are inadequate, leading to defocusing issues due to temperature-induced deformation and refractivity changes in projection lenses, which result in dimensional errors and pattern formation failures.
Innovation Solution
The method involves a reticle with automatic focus correction marks both in the actual device region and the peripheral region, allowing for focus correction using marks in the center and edge portions of the projection lens, thereby preventing defocusing and ensuring accurate pattern formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If automatic focus correction marks are provided only in the peripheral region (recto) of the reticle, then the occupation ratio of the chip region is increased, but the focus correction accuracy for the center portion of the projection lens deteriorates
Solution Approach 1:
The reticle is divided into two functional regions: the peripheral recto region containing focus correction marks for edge portion correction, and the center actual device region containing focus correction marks for center portion correction. This segmentation allows independent optimization of each region's function, enabling both high chip occupation ratio and accurate focus correction across the entire projection lens.
Solution Approach 2:
Different regions of the reticle are assigned different qualities/functions: the peripheral region contains marks optimized for correcting focus in the edge portion of the projection lens, while the center region contains marks optimized for correcting focus in the center portion of the projection lens. This local differentiation resolves the contradiction by providing region-specific focus correction capabilities.
2Productivity
If exposure light is repeatedly applied to the projection lens, then productivity is improved, but temperature-induced deformation and refractivity changes cause defocusing
Solution Approach 1:
The system employs feedback mechanisms where focus correction marks are used to continuously monitor and detect focus deviations caused by temperature changes during repeated exposure. The detected focus state is fed back to adjust the wafer stage position, compensating for thermal deformation and maintaining reliable focus throughout high-volume production.
Solution Approach 2:
Focus correction marks are provided in advance in both the peripheral and center regions, allowing the system to pre-determine and store focus correction values for different regions. During actual exposure, these pre-prepared correction values are applied to quickly compensate for thermal effects without interrupting the exposure flow, thus maintaining both productivity and reliability.
3Area of stationary object
If focus correction is performed using only peripheral marks, then device region occupation is maximized, but dimensional accuracy in the center region deteriorates
Solution Approach 1:
The focus correction system is segmented into peripheral focus correction for edge portion exposure and center focus correction for center portion exposure. This segmentation ensures that each region's pattern formation uses the most appropriate focus reference, maximizing both device region occupation and manufacturing precision across the entire wafer.
Solution Approach 2:
Different focus correction marks with locally optimized characteristics are used: peripheral marks for edge region focus correction and center marks for center region focus correction. This local quality differentiation ensures that each region receives focus correction tailored to its specific thermal and optical conditions, maintaining high dimensional accuracy throughout.
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 approach effectively prevents defocusing and dimensional errors by correcting focus across the entire projection lens, improving the reliability and accuracy of semiconductor device manufacturing.
Implementation Method 1
a part of exposure light is blocked by passing through the reticle, and the exposure light transmitted by the reticle is reduced in size by passing through a projection lens to irradiate a surface of a semiconductor substrate
Implementation Method 2
a photosensitive element (detector) under the reference mark detects the exposure light to determine an optimal focus position
Data Source
AI summary
A focus through a projection lens is corrected to prevent the occurrence of a dimensional error in a pattern due to defocusing. At least one automatic focus correction mark is formed over each of chip patterns formed in a reticle used for exposure. Using one of the automatic focus correction marks located in the center portion of an actual device region, automatic correction of the focus of exposure light is performed. In this manner, a variation in the focus of the exposure light through the center portion of the projection lens, which is more likely to reach a high temperature than an end portion of the projection lens, is detected and corrected.