What gets handed over at a chip fab's shift change, and why write it down?

At a chip fab's shift change, what gets handed over is the work that isn't finished yet: which tool is down and how far the repair has got; which lots have been stopped, why, and who decides what happens to them; which numbers need watching; and what was promised to whom. The outgoing shift writes this on a handover sheet, then talks it through with the incoming shift. That is a handover, also called a shift handoff or shift turnover. It has to be written down because the outgoing shift goes home to sleep, and the next shift only has the lines on the sheet.

Why does a fab need handovers?

Because the tools keep running and the people change. A fab runs 24 hours a day, all year (why, see "Why do chip fabs run 24 hours a day?"), and the people looking after the line change shifts at least twice a day (how shifts are set up, see "Is working in a semiconductor fab hard?").

But work doesn't end just before the shift does. A tool that stops in the middle of the night may wait for the morning's engineer and for parts, and only be fixed in the afternoon. A lot that has been stopped waits for the person who decides. A single wafer takes weeks to months to make. One job often spans several shifts and passes through several people's hands.

Think of a relay race. Everyone runs fast, but if the baton is dropped in the exchange zone, the whole team stops anyway. The handover is that exchange zone.

What goes on the handover sheet?

Not a list of everything this shift did, but what the next shift has to keep an eye on:

• Work that isn't finished: how far it has got, what the next step is, and who is doing it now.
• Lots on hold: which lot, why it was stopped, and who decides what happens to it (what a hold is, see "What is a lot hold?"). Without the reason, the next shift just sees a lot sitting there and doesn't know who to ask.
• Tools that are down, and how far the repair has got: why the tool is down, what was replaced, what is still left, and who it is waiting for. If people change halfway through a repair, the locks and tags on it (lockout/tagout) have to be handed over too, so it is never left unlocked in between.
• Numbers to watch: a measurement that is still within the acceptable range but keeps drifting the same way; lots close to their Q-time (how Manufacturing keeps track of them, see "What does the manufacturing department do in a chip fab?"); a reading on some tool that is higher than usual. Add how far it can go before someone should call, and who to call.
• Promises made to others: who you told you'd have an answer for, and by when; who might call; what is due in the morning.

One more thing often gets left out: why a decision was made. Write only "leave it alone", and when things change, the next shift doesn't know whether that still applies. Write "leave it alone, because we don't know yet which wafer has the problem", and they can judge for themselves. For ordinary problems, a fab usually already has an OCAP that says what to do first (see "What does OCAP mean in a chip fab?"). What the handover most needs to spell out is what the OCAP doesn't cover, the things only this shift knows.

How do you hand over without missing anything? Step by step

Step 1: Write it down first

What: Before you leave, go through the kinds of things above and write one line per item: where it stands, what comes next, and who owns it.

Why: People get tired and forget. What is written down can be read again and again, and passed to someone who isn't there yet, like an engineer who comes in later in the morning. The longer the shift, the more you rely on those written lines.

If you don't: A few hours later someone asks "why is that lot sitting there?", and the person who said it has gone home while the person who heard it can't quite remember.

Step 2: Talk it through face to face

What: The two of you meet and go through the sheet together, ideally looking at the same screen or standing at the same tool. As you go, say which lines need someone to follow up today and which are just so they know.

Why: Paper doesn't show what matters most. Face to face, the most important item gets a couple of extra sentences.

If you don't: Five lines all look equally important, and the one that really matters gets treated as routine.

Step 3: The person taking over asks questions and checks for themselves

What: The person taking over says it back in their own words: "So that tool isn't fixed yet, and someone is coming to look at it in the morning, right?" Then they check at the tool and in the system: what color the light is, and whether that lot really is on hold in the system.

Why: The handover sheet shows what the last shift thought was going on. The tool shows what is really going on. Saying it back brings misunderstandings out on the spot.

If you don't: You get the misunderstanding below.

Step 4: Leave enough time

What: Make the handover part of the shift, not something squeezed in on the way out, and don't take other work during those few minutes.

Why: Handovers often fall in the last few minutes of a shift, when people are most tired, and someone rushing to leave only wants to say a sentence or two.

If you don't: Important things shrink to "it's all fine", and the person taking over feels awkward asking more.

A common misunderstanding: "I've looked at it" heard as "it's fixed"

"I've looked at that tool" may mean "I went and looked, and I don't know the cause yet". The person listening may hear "it's been dealt with". Others like it:

• "The tool's been handed back": equipment handing back a repaired tool only means it runs. Whether it makes good wafers still needs a qual run (see "A tool has been fixed. Why does it still need a qual run?").
• "That lot is on hold": on hold in the system, or just a sticker on the box?
• "Someone will deal with it in the morning": who?

The fix is simple: don't sum it up in one word like "done" or "OK". Say three things instead: what is finished, what is still left, and who does the next step. Public handover guidance from workplace safety, hospitals and aircraft maintenance, fields where a missed handover can be costly, says much the same: face to face, both ways, both written and spoken, with time for the person taking over to ask questions, and ideally with what they heard said back to check it.

In fab24hr

In fab24hr, the last thing in quite a few roles' shifts is writing the handover sheet or writing to the next shift. Tap "Clock in", choose "A day in the fab", then on the "Your role today" card tap "Production fab" and swipe to Manufacturing. On the late-night shift you write the handover sheet at 06:40: every extra line takes two more minutes, and the shift changes at 07:30. On the night ETCH-03 goes down, whether to fill in the hold reason is up to you. On the morning shift, Hao from the night shift may have already left, with only a note stuck to the dispatch desk that doesn't say where the first 6 wafers are: you can call him and ask, or go by the note and start lining up lots. The evening shift is called "A Handover One Line Short": the five lines the day shift wrote in the standard format are all right, but one lot is missing. It was on the whiteboard, with 30 minutes of Q-time left.

Swipe to the Facilities engineer and tap "Gases & chemicals" under the name. On the late-night shift, just before dawn, you check the handover sheet line by line before passing it on. On the morning shift at 07:30, Zheng, in his twentieth year on nights, goes through the night-watch colleague's sheet with you line by line: tap a line and he tells you in plain words what it means. Tap "HVAC" or "Water" instead, and the evening shift also ends with handing over to Zheng as he comes on for the night. As the etch process engineer, on the evening shift you may find last year's handover sheet on the floor by the printer. All it says is "ETCH-03 OK."

The company, people, tools, lot numbers and times in the game are fictional. What a handover covers and how it is done follow public, general guidance from fields such as workplace safety, healthcare and aircraft maintenance; the real forms and practice differ from factory to factory. For other jargon, see Chip fab jargon in plain English.