Wire Saw Resumption Method for Wafer Surface Topography Control
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Solution Overview
Problem
The interruption of the wire sawing process due to unplanned events like wire breakages leads to uneven wear of the sawing wire, resulting in deep incisions and impaired surface topography of semiconductor wafers upon resumption, as the method for resuming the process does not account for the changed wire wear.
Innovation Solution
The method involves resuming the wire sawing process by initially adjusting the forward and backward wire lengths and speeds to match the pre-interruption settings, gradually increasing the forward wire length to minimize wire wear and prevent deep incisions, with the sawing wire moving at reduced speeds in the presence of a liquid cutting medium to maintain surface quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the wire sawing process is resumed after unplanned interruption using conventional methods, then the sawing process can continue, but deep incisions and impaired surface topography occur on the wafer surfaces
Solution Approach 1:
The wire forward length and wire backward length are dynamically adjusted during the resumption phase. The control unit increases the wire forward length in defined increments over multiple oscillation cycles until reaching the original pre-interruption length, while simultaneously adjusting the wire backward length to maintain appropriate tension. This dynamic adaptation prevents deep incisions while restoring normal sawing operation.
Solution Approach 2:
The oscillation parameters (wire forward length L1, wire backward length L2, oscillation amplitude) are changed during the resumption process. The control unit modifies these parameters in a controlled sequence: initially using reduced wire forward length to minimize incision depth, then gradually increasing to original dimensions. This parameter evolution resolves the contradiction between maintaining productivity and preserving surface quality.
2Speed
If the wire forward length is immediately restored to pre-interruption settings after resumption, then normal sawing speed is achieved, but deep incisions are created on the wafer surfaces
Solution Approach 1:
Before restoring normal sawing speed and wire forward length, the control unit first initiates a gradual adaptation phase. During this preliminary action phase, reduced wire forward length is used to re-enter the workpiece and establish stable cutting conditions without creating deep incisions. Only after this preliminary stabilization does the system progressively increase to full operating parameters.
Solution Approach 2:
The wire oscillation operates in distinct periodic phases: an initial resumption phase with reduced wire forward length (L3 < L1) to prevent deep incisions, followed by intermediate phases with incremental increases, and finally the normal oscillation phase with original parameters. This periodic structuring of the sawing process resolves the speed-precision contradiction.
3Device complexity
If the wire wear is not accounted for after interruption, then the resumption process is simple, but uneven wire wear causes impaired surface topography
Solution Approach 1:
The control unit implements a feedback mechanism that monitors the sawing process state and automatically adjusts wire forward length and oscillation parameters during resumption. Based on detected conditions (interruption status, current wire wear state), the system dynamically modifies operating parameters to maintain surface quality. This automated feedback resolves the contradiction between system complexity and manufacturing precision.
Solution Approach 2:
The control system automatically detects the interruption event and initiates the adapted oscillation sequence without external intervention. The system self-adjusts wire forward length, oscillation amplitude, and timing based on its internal state monitoring, eliminating the need for manual parameter setting while ensuring surface quality. This self-service capability justifies the increased device complexity.
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 minimizes the depth of saw incisions on the wafer surfaces, ensuring consistent minimum sawing thickness and maintaining the nanotopography of semiconductor wafers, thus making the wafers suitable for further processing.
Implementation Method 1
the wire web penetrates by forward movement with a first speed v1 of the sawing wire into the existing sawing kerfs of the workpiece with the addition of a liquid sawing medium
Implementation Method 2
a sawing wire which spans a wire web including a plurality of wire sections arranged in parallel
Data Source
AI summary
A method resumes an interrupted process for sawing a workpiece into wafers using a wire saw that includes advancing a wire web into existing sawing kerfs of the workpiece with a forward movement of the sawing wire with a first speed in the presence of a liquid sawing medium until the wire web or workpiece has reached a position corresponding to the interruption of the wire sawing process. The sawing wire is moved in defined time intervals by a forward movement of a particular length with a second speed and a backward movement of another length with a third speed, where the backward length is less than the forward length and the forward and backward movement correspond to a cycle. The wire length that is unwound during the forward movements is increased until the length during the forward movement corresponds to the length of the forward movement before the interruption.