Wafer Warp Prediction via Pre-Deposition Shape Analysis
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Solution Overview
Problem
Post-epitaxial warp in semiconductor wafers occurs due to lattice mismatch between doped substrates and epitaxial layers, leading to topology degradation and yield losses, as existing grinding processes cannot effectively control these changes.
Innovation Solution
A method involving a processor that predicts post-epitaxial warp by analyzing measured resistivity and shape changes after grinding or etching processes, and adjusts the grinder to optimize wafer shape before epitaxial layer deposition, using algorithms to determine shift and tilt parameters for the grinding wheels to minimize warp.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If simultaneous double side grinding is used to improve wafer flatness and parallelism, then surface planarity is improved, but post-epitaxial warp control deteriorates due to inability to predict or adjust for epitaxial layer induced shape changes
Solution Approach 1:
The system performs preliminary measurement of wafer shape after grinding and before epitaxial deposition, then uses predictive algorithms to calculate the expected post-epitaxial warp. This preliminary action enables adjustment of grinding parameters in advance to compensate for anticipated warp, rather than discovering warp issues after epitaxial processing.
Solution Approach 2:
The system implements a feedback loop where post-epitaxial warp measurements from previous wafers are fed back into the predictive algorithm to refine predictions for subsequent wafers. This continuous feedback enables progressive improvement of warp control by learning from actual outcomes and adjusting grinding parameters accordingly.
2Ease of manufacture
If lattice mismatch between heavily doped substrate and lightly doped epitaxial layer occurs, then epitaxial layer deposition is achieved, but wafer topology degradation worsens due to substantial bow and warp changes
Solution Approach 1:
The system applies preliminary anti-action by intentionally inducing opposite warp during grinding to counterbalance the expected warp from epitaxial deposition. The predictive algorithm calculates the anticipated epitaxial-induced warp and adjusts grinding parameters to create compensating reverse curvature, so that the net post-epitaxial warp is minimized.
3Measurement precision
If wafer shape measurement and predictive algorithms are implemented, then post-epitaxial warp prediction capability is improved, but device complexity increases due to additional measurement and computational requirements
Solution Approach 1:
The system creates a digital copy or model of the wafer's physical shape through non-contact optical measurement. This digital replica is then processed through predictive algorithms to forecast post-epitaxial warp without requiring physical manipulation or additional hardware during the prediction phase, reducing overall system complexity.
4Manufacturing precision
If grinding parameters are adjusted based on predicted warp, then post-epitaxial warp control is improved, but manufacturing process complexity increases due to dynamic parameter adjustment
Solution Approach 1:
The system changes grinding parameters such as wheel tilt angles, wheel shift positions, or feed rates based on predicted warp values. These parameter adjustments are calculated by the predictive algorithm and automatically applied to the grinding machine, enabling precise control of post-epitaxial warp through systematic modification of processing conditions rather than complex mechanical adjustments.
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 improves wafer quality and yield by predicting and controlling post-epitaxial warp, reducing topology degradation and enhancing the flatness and parallelism of semiconductor wafers.
Implementation Method 1
The pads and wheels are oriented in opposed relation to hold the wafer therebetween in a vertical orientation. The hydrostatic pads beneficially produce a fluid barrier between the respective pad and wafer surface for holding the wafer without the rigid pads physically contacting the wafer during grinding.
Implementation Method 2
The hydrostatic pads beneficially produce a fluid barrier between the respective pad and wafer surface for holding the wafer without the rigid pads physically contacting the wafer during grinding. This reduces damage to the wafer that may be caused by physical clamping and allows the wafer to move (rotate) tangentially relative to the pad surfaces with less friction.
Implementation Method 3
These grinders use a wafer clamping device to hold the semiconductor wafer during grinding. The pads and wheels are oriented in opposed relation to hold the wafer therebetween in a vertical orientation.
Data Source
AI summary
In one aspect, a method of predicting warp in a plurality of wafers after an epitaxial layer deposition process is provided. The method includes receiving, by a processor, a measured resistivity of a first wafer of the plurality of wafers, receiving, by the processor, a measured shape of the first wafer after at least one of a grinding process and an etching process, and calculating, using the processor, a change in wafer shape during the epitaxial layer deposition process. The method further includes superposing, using the processor, the calculated shape change onto the measured shape of the first wafer to determine a post-epitaxial wafer shape and calculating, using the processor, a post-epitaxial warp value based on the determined post-epitaxial wafer shape.