Why Your Optical Profiler Readings Drift and How to Fix Them

Quick answer

Most optical profiler drift is environmental or setup-related, not a failed instrument. Start by checking vibration, temperature, and sample stability before touching calibration. If readings still drift after those are controlled, recalibrate with a certified step standard and verify stage motion.

Symptom check: Is it drift or a one-time offset?

Drift means readings change over time without a deliberate change in the sample or setup. A one-time offset stays constant across repeated measurements. Before adjusting anything, measure the same stable sample three times over 10 minutes. If the values wander, you have drift. If they are consistently off by the same amount, you have an offset that calibration can address.

Likely cause 1: Vibration and acoustic noise

Optical profilers are interferometric instruments. Floor vibration, nearby pumps, or even loud HVAC can shift fringes and make height readings drift. This is one of the most common profiler vibration issues. Move the system to a quieter location or add an isolation table. If you already have isolation, check that it is leveled and that the isolators are inflated correctly.

Likely cause 2: Thermal changes in the room or sample

A 1°C room change can move metal parts enough to register as drift on a high-resolution profiler. Let the instrument and sample stabilize for at least an hour after any temperature change. Avoid placing the profiler near windows, doorways, or equipment that cycles on and off. For critical measurements, record room temperature alongside your data.

Likely cause 3: Stage motion or loose fixturing

If drift appears only when you move the stage, the problem is mechanical. Check that the sample is firmly clamped and that the stage is not binding. On systems with motorized axes, a worn or misaligned stage can cause repeatable drift in one direction. The NewView 1 axis motion kit provides motorized Z with manual XYRP adjustment, so if your setup uses manual XY, verify those locks are tight before blaming the electronics.

Corrective action: Recalibrate with a certified standard

When environment and fixturing are ruled out, recalibrate using a certified step standard. The 88nm Step Standard with ZYGO Certification is supplied as SKU 6300-0917-01 and is associated with an ISO 17025 certified laboratory, which means its reported value is traceable. Follow your system's calibration procedure and compare the measured step height to the certified value. If the error is within your process tolerance, you are done.

When to stop and call service

Stop adjusting and contact Zygo service if drift continues after you have controlled vibration, temperature, and fixturing, and after a successful calibration with a certified standard. Also stop if you see sudden jumps larger than your calibration uncertainty, or if the instrument reports hardware errors. Repeatedly recalibrating a drifting system can mask a failing component and waste time.

Drift diagnosis flow

• Symptom: Readings wander over minutes: Check for vibration and thermal changes first. Measure the same sample three times over 10 minutes to confirm drift. If stable, the issue is an offset, not drift.
• Symptom: Drift only when moving the stage: Inspect sample clamping and stage locks. On NewView 8000/9000 systems, verify the motion kit's Z and XYRP adjustments are not slipping. If the stage is tight, the problem is likely environmental.
• Symptom: Drift persists after environment and fixturing are controlled: Recalibrate with a certified step standard such as the 88nm Step Standard with ZYGO Certification. Compare measured vs. certified value. If drift continues after a valid calibration, stop and contact Zygo service.

Product facts that matter for drift diagnosis

• 88nm Step Standard with ZYGO Certification: 88nm Step Standard with ZYGO Certification is supplied as SKU 6300-0917-01 in the Standard configuration and is associated with an ISO 17025 certified laboratory. A traceable step standard lets you separate true drift from a calibration offset and gives you a defensible reference when troubleshooting.
• NewView 1 axis motion kit: The NewView 1 axis motion kit is a ZYGO accessory for the NewView 8000/9000 platform. It provides one axis of motion with motorized Z and manual XYRP adjustment. If drift appears only during stage moves, this kit's motorized Z and manual XYRP adjustment help you isolate whether the issue is in the motion system or the optics.