What do chip fab engineer interviews ask, and how do you prepare?

In one sentence: an interview for a chip fab engineer mostly wants to find out four things: whether you understand the basics, how you think when something goes wrong, whether you can get work done together with other people, and whether you can live with shifts and the cleanroom. Every company and every interviewer asks in their own way. This article does not describe any company's interviews; it only follows what the job involves every day and lists the directions questions may take.

Why would an interview ask about these things? Start with what the job is

A process engineer looks after a few process steps in one area: reading measurements and control charts, deciding whether a lot can move on, and running experiments to make the results steadier (Is a PE a process engineer or a product engineer?). An equipment engineer looks after whether the tools run: scheduled maintenance, repairs and calls in the middle of the night (What does an equipment engineer do in a chip fab?). For the other jobs, see What jobs are there in the semiconductor industry?; for degrees, see Which degrees work in a chip fab?

So most questions come down to "can you do these things?" University career centers often explain it like this: how you handled things in the past is the best sign of how you will handle them later. That is why many questions ask you to tell about something you actually did.

What directions might the questions take?

These are not questions you will "definitely" get. They are worked back from what the job involves every day.

Introduce yourself, and why this field?

• What may be asked: tell me about yourself; why a fab, and why this role?
• Why: to see whether you know what the job involves day to day.
• How to prepare: cover three parts in a few sentences (an order university career centers often teach): what you are doing now, what you have done before that relates to this job, and why you want this role. Tie your reasons to something you really did.

Your school project or lab work: how did you find the problem?

• What may be asked: what is your project about? Did you ever get stuck? How did you find the cause?
• Why: much of an engineer's work is seeing a number that is wrong and tracing back where things went wrong. How you find problems in a lab is the closest thing to how you will find them in a fab.
• How to prepare: practise explaining your project in words someone who never studied it can follow. Then prepare one time the result was not what you expected: what you suspected first, how you ruled things out one by one, and what you found.

The basics: the PN junction, the transistor, the main process steps

• What may be asked: what is a PN junction? How does a transistor work as a switch? What are the main steps a wafer goes through? What does the area you are applying for (for example etch or litho) do?
• Why: to decide whether a lot is usable or to find a cause, you first have to understand what that step does. The interview wants to see whether you understand the principles and can explain them clearly, not how many terms you have memorized.
• How to prepare: explain each one in your own words. These articles on this site are a good start: What is doping? (where n-type and p-type silicon meet is the PN junction), What is a transistor?, How are computer chips made? and What do the seven process areas of a chip fab do? When you are asked something you don't know, say so, then say how you would think it through and where you would look. University guides to technical interviews often warn against making things up.

Scenario questions: a number out of limits, a tool down, should the lot stop?

• What may be asked: "A measurement is outside the control limits. What do you do?" "A tool goes down in the middle of the night with wafers inside. What do you do first?" "A lot looks wrong and people downstream are waiting for it. Do you stop it?"
• Why: process and equipment engineers commonly run into these. There is often no single right answer; the interview wants to hear the order in which you think.
• How to prepare: first get a few words straight. Control limits ask "is this the same as usual?", spec limits ask "is this acceptable?", so an OOC point does not mean the product is bad (What is an SPC control chart?). When something goes wrong, people follow a plan written in advance, the OCAP (What does OCAP mean in a chip fab?). A lot you are not sure about goes on hold so it stops moving, and then someone decides whether to release, rework or scrap it (What is a lot hold?). Afterwards, the real cause still has to be found (What is root cause analysis?).

When you answer, say your order out loud. For example: stop that lot first, check whether the number was measured wrong and whether it is outside the control limits or the spec, follow the OCAP, tell the people who need to know, and only then decide what happens to the lot. If someone could get hurt, for example in a gas leak, people get out first and the lots come later.

Shifts, cleanroom suits, teamwork

• What may be asked: can you work shifts or be on call? Are you fine working in the cleanroom in a cleanroom suit? What do you do when you disagree with someone?
• Why: a fab runs 24 hours a day. The production line works shifts, and engineers usually take turns being on call, which means a phone call at night when something happens (Why do chip fabs run 24 hours a day?, Is working in a semiconductor fab hard?). Going into the cleanroom means covering yourself from head to toe (What is a bunny suit?). When a tool stops, process, equipment and Manufacturing often have to deal with it together (What departments does a chip fab have?).
• How to prepare: read those articles, decide honestly whether you can live with it, and say so plainly. For teamwork, prepare one real story: a group project where people disagreed, what you did and how it turned out.

How to prepare: tell one thing you did, clearly

Many questions end up as "give me an example." University career centers often teach an order called STAR (Situation, Task, Action, Result). In the table below, the first two share one column, "The situation", and the last column, "What you learned", is a step some guides add (the example is made up):

The situation	What you did	The result	What you learned
The measurements in your project were unsteady: the same sample gave different numbers	You wrote down the conditions every time, changed only one at a time, and found that how long a sample sat before it was measured was different every time	You measured right after making each sample, and the numbers settled	Change one condition at a time, and keep clear records

A few more tips, also from career-center guides:

• Say what "I" did, not only what "we" did.
• A result that went badly is fine to tell; add what you learned.
• Prepare a few stories in advance, for example one time you found a problem, one disagreement and one mistake you fixed.

When it's your turn to ask, what can you ask?

At the end there is often a "Do you have any questions for us?" Career centers suggest preparing a few, and you can build them around what the job involves every day:

• What does someone new in this role usually learn in the first few months?
• Where does most of the day go: reading data, at the tools, or in meetings?
• How are shifts or on-call duty arranged?
• When a tool has a problem, who does this role usually work with?

Asking is also a way to judge for yourself whether a day in this job is the day you want.

In fab24hr

As the etch process engineer, at 10:40 on the morning shift Ya-Ting calls: an OOC lot, its line width a little above the control limit, still inside spec, still on hold. Release it and you write a note; keep it back and the lot waits longer. In Manufacturing, on the late-night shift, ETCH-03 shows a red light. The OCAP says to notify the engineer first, but the engineer is asleep and the lots are waiting: follow the OCAP and call the on-call engineer, or try one reset? Then several lots are queued at wet clean, and each has to start before its Q-time runs out.

You can treat it as practice for "what would I do here?" Tap "Clock in", choose "A day in the fab" (you work the shift for the time it is now), then on the "Your role today" card tap "Production fab", swipe to the process engineer and tap "Etch" under the name, or swipe to Manufacturing. The company, people, lots and tools in the game are fictional. It is not any company's interview, and a real interview may not ask about any of this. The preparation advice follows public, general guides from university career centers.