Semiconductor Wafer Mass Fingerprinting for Process Control
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Solution Overview
Problem
Existing semiconductor wafer metrology techniques are limited in measuring certain materials and processes, such as opaque films and etched or recessed structures, and require test wafers that are costly and reduce productivity, while also being unable to detect process errors that affect device properties like stress and refractive index non-destructively.
Innovation Solution
A method that assigns a 'mass fingerprint' to each process step, allowing for the comparison of measured mass change distributions with characteristic distributions to detect process errors and adjust parameters non-destructively, using mass measurements to monitor layer thickness, uniformity, stoichiometry, and stress, and enabling feedback and feed-forward control to prevent unsatisfactory wafer production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If test wafers are used to monitor process quality, then process control capability is improved, but productivity decreases and costs increase
Solution Approach 1:
The patent extracts the monitoring function from separate test wafers and integrates it into the product wafers themselves by creating dedicated measurement regions within the active device areas. This allows process monitoring data to be obtained directly from product wafers without requiring additional test wafers, thereby maintaining productivity while achieving reliable process control.
Solution Approach 2:
The measurement regions within the product wafers serve multiple functions: they act as both active device structures and process monitoring targets. The same wafer that produces the final product also contains regions that provide process control data, eliminating the need for separate test wafers and enabling simultaneous product manufacturing and process monitoring.
2Reliability
If test sites are added to product wafers for process monitoring, then process control is improved, but value space is reduced and productivity decreases
Solution Approach 1:
The wafer is segmented into different functional regions: active device areas that produce valuable products and measurement regions that provide process monitoring data. By spatially separating these functions within the same wafer, the patent enables process monitoring without sacrificing product value space, as the measurement regions are strategically placed in areas that would otherwise be unused or less valuable.
Solution Approach 2:
Different regions of the wafer are assigned different qualities and functions: product regions are optimized for device fabrication while measurement regions are optimized for process monitoring. This local differentiation allows each region to perform its specific function effectively without compromising the other, maintaining both productivity and process control capability.
3Measurement precision
If conventional metrology techniques are used, then measurement capability is limited to certain materials, but device complexity and measurement versatility are reduced
Solution Approach 1:
The patent introduces mass change as an intermediary measurement parameter that can be universally applied to all materials and processes. Instead of using material-specific techniques (ellipsometry for transparent films, resistivity probes for metals), the system measures the mass change caused by material addition or removal, which is applicable to all materials including opaque films, metals, dielectrics, and etched structures, thereby achieving universal measurement capability while maintaining precision.
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 method allows for efficient detection and correction of process errors before they lead to unsatisfactory wafers, reducing waste and maintaining productivity by using mass measurements to monitor and adjust process parameters, even for properties that are difficult to measure directly, such as stress in thin SiN films.
Implementation Method 1
A common feature of many semiconductor device fabrication steps is that material will be added or removed. In WO 02/03449, it was suggested that SPC could be applied to deposition process steps using the accurate mass measurement method.
Data Source
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AI summary
A semiconductor wafer fabrication metrology method in which process steps are characterised by a change in wafer mass, whereby during fabrication mass is used as a measurable parameter to implement statistical process control on the one or more of process steps. In one aspect, the shape of a measured mass distribution is compared with the shape of a predetermined characteristic mass distribution to monitor the process. An determined empirical relationship between a control variable of the process and the characteristic mass change may enable differences between the measured mass distribution and characteristic mass distribution to provide information about the control variable. In another aspect, the relative position of an individual measured wafer mass change in a current distribution provides information about individual wafer problems independently from general process problems.