Structural devices
Structural devices

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Structural devices

8.4.1 Open-loop control

Open-loop is the crudest way of controlling etch depth. It relies on ensuring that every aspect of the process that can affect the rate of progress of the etch is kept under tight control. This can add up to a sizeable list. Table 5 shows just some parameters that affect both wet and dry etching.

Whether it involves wet or dry etching, once all these variables have been fixed, the etch system must then be calibrated for etch rate. A sample wafer is etched for a known amount of time after which the etch depth is accurately measured, either with a surface profiler or by looking at a cross section under an SEM.

Pure open-loop control of etch depth is the last resort. With so many parameters needing control, there are many ways in which the process can go wrong. It is rarely possible to guarantee the etch depth to better than a few per cent and in many cases this is simply not good enough. What is really needed is some way of keeping track of the etching while it is going on, and this leads us to the next approach to the problem.

T356_1

Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has over 40 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus