Semiconductor Manufacturing Process

Before producing an integrated circuit, a semiconductor wafer goes through a wide range of processes steps. The key steps are Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD), photolithography, Rapid Thermal Processing (RTP), Plasma Etch, and Chemical-Mechanical Planarization (CMP). For many years the standard practice to perform these steps was to do so in batches on many wafers at a time so that a large number of identical chips can be produced at the same time. When the demand for smaller critical dimensions (CD) of the devices on the chip is increased and to make the production process flexible, the makers went for integrated circuits. Wafer fabrication comes under Wafer front end.

OVERVIEW OF TYPICAL WAFER PROCESSING EQUIPMENT

The wafer processing equipment is not produced in a single step, there are many process steps which are necessary to produce a ULSI the circuit on a wafer. The physical processes are organized into groups that correspond to the type of equipment that is beneficial to perform the specific process.

The control engineer who is responsible for controlling the processing equipment, the main issues can be summarized with the following five questions:

• What are the processes involved (physics)?
• What are the actuators (inputs)?
• What sensors are available (outputs)? 4. What are the performance metrics?
• What are the uncertainties and disturbances?

CONTROL OF SEMICONDUCTOR PROCESSES

There are three components of the controller; the planner, the regulator, and the estimator. The feedback controller has a regulator and the estimator. The task of the planner is to translate the desired product characteristics into nominal or an ideal set of process inputs and reference signals. According to the type of the process, the inputs can be constant or can follow a complex time history.

If the model and the planner are perfect and there are no process disturbances, the planner is all that is required. But in the real world, this is not possible, there are problems which arise out of the blue. Thus, the regulator comes in handy. The regulator performs the important task of minimizing the differences between uses the difference between the product characteristics and the ideal product requirement. The feedback controller computes the corrections to the nominal process inputs computed by the planner. Together, the planner and the regulator make the model-based control portion of the solution. The complications don’t stop here, in many cases it is not possible to evaluate the relevant product characteristics in-situ either because the sensor is not invented or because the whole process is way too expensive. Thus, a model of the process conditions is used by the estimator. The estimator infers the critical variables from the sensed variables.

Conclusion

The semiconductor manufacturing process is a complex task, there are many issues which are inevitable. These issues can be minimized with the help of expert minds of men and machines. In semiconductor equipment, precision stage repair is required so that tasks don’t halt and there is no loss of productivity.