As semiconductor processing requirements evolve to meet the demands of decreasing geometries, new approached in plasma metrology will be needed to monitor the performances of the equipment and its processes. This performance has traditionally been monitored via Statistical Process Control (SPC) on output parameters such as etch rate and uniformity. These measurements are typically taken on single film wafers which may not be an accurate representation of product. With emerging, nonintrusive, RF sensor technology, equipment and process engineers have access to signals which provide better resolution in determining the health of the equipment. This paper will discuss the relationships between machine settings, real-time RF sensor measurements and the etch rate and uniformity metrics typically used in machine/process qualifications. Run to run control algorithms using the RF sensor measurements will also be presented. Finally, the implications of using RF sensor measurements to provide real-time closed loop control of machine settings will be discussed.
The business climate of the integrated circuit industry in the 1990's is very different from that of the 1970's. Today's industry demands that manufacturers produce newer more complex designs with shrinking design time windows and higher return on investment for fabrication facilities. This tighter business climate inposes stricter controls on the day to day operation of the fabrication process. Now, not only must new equipment make significant improvements in process capability but every effort must be made to insure that older (already depreciated) equipment is used to its fullest. To this end extensive work has been undertaken to establish "sensor based manufacturing" (SBM) schemes with the goal of improving wafer to wafer as well as within a wafer repeatability and extending equipment useful lifetime. This improvement in repeatability translates into reduced need for expensive, time consuming, in-line metrology. The end result is improved cycle time and reduced overall facility costs.
Early work on this topic centered around the generation of a parametrical view of the plasma process module. By viewing the module as the convolution of a plasma based chemical factory and the hardware necessary to establish and sustain it, a scheme for improved control becomes clear. Present control schemes are based only on hardware or machine parameters, yet the wafer results are defined by the plasma parameters. Therefore, shifting the focus of module control from the traditional machine parameters to the less conventional plasma parameters would place the focus of control closer to the wafer and improve process performance. This paper deals with the application of SBM concepts to establish the real time monitoring of fundamental machine and plasma parameters known to have direct correlation to wafer results such as etch rate and uniformity. Proper usage of SBM generated information includes improved end point capabilities, real time SPC and "go-no-go" decision analysis.
Polysilicon etching in a single-wafer, parallel-plate, magnetically- enhanced RIE tool has been examined using two different approaches to the non-physical modeling of the system characteristics. The behavior of both process responses (polysilicon and oxide etch rates) and plasma parameters (voltage and current metrics) have been examined as a function of five variables (rf power, pressure, magnetic field, gas flow rate, and He backside cooling). The variable-response mapping was examined using both neural network and response surface approaches. The greater fitting power of the former method is demonstrated in a side-by-side, internally consistent comparison of the same data set using these two approaches.
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