PXS256SE — 65,536-point pressure mapping for CMP polishing heads

A polishing head presses the wafer onto the pad through a compliant backing film, and the pressure it applies is not uniform: the retaining ring carries its own load, the zone behind the wafer does not deliver what the regulator asks for, and the high point moves as the pad wears. A 4,096-point sheet on a 7.6 mm pitch averages all of that into a soft blob. This build exists because the features that matter on a polishing head are 2–5 mm wide.

Sixty-five thousand points, and what that buys

The sensing layer carries 65,536 points on a 360 × 360 mm area — 256 along each axis, 1.4 mm apart, each point 1.2 mm square with a 0.2 mm gap between neighbours. That is about 50 points per square centimetre. A 3 mm retaining-ring land falls across two points and reads as a step rather than a slope; the same land on a 7.6 mm grid is one sample, and one sample cannot tell you whether the ring is loaded evenly. The comparison is set out in what a point pitch can and cannot resolve.

The sheet is square, 366 × 366 mm overall, so it spans the head footprint with the retaining ring included rather than only the wafer. Builds that have to sit inside the head with the ring in place use an annular format instead; both are described on the CMP application page.

What the 100 kPa range rules out

One hundred kilopascals is one bar. Polishing-head contact pressures sit in the tens of kilopascals, so the range suits the application with headroom. It is also why this sheet is not interchangeable with the large-area film: saddles, clamps and bolted joints run from 0.4 to 6 MPa on the standard build, two orders of magnitude above this one. If a programme needs both, it needs two sensors — a wide-range sheet cannot be made dense, and a dense sheet cannot be made wide-range, at the same price.

Reading the numbers honestly

The collector digitises at 10 bit, which over a 100 kPa span is about 0.1 kPa per count. The system accuracy, however, is ≤ ±5 % of full scale — ±5 kPa, or roughly fifty counts. Resolution is therefore not what limits this measurement; the sensing layer, its calibration and the flatness of the interface are. Quoting the 0.1 kPa figure as an accuracy would be a misreading of the arithmetic, and it is worth knowing which number a supplier is quoting before comparing two of them.

Flatness matters more than thickness here

The sheet is under 0.4 mm thick with a flatness error of ±5–10 µm over 360 mm. Both figures matter for the same reason: this sensor is pressed between two hard, flat bodies, and any waviness in the sheet becomes a pressure artefact that looks like a real feature on the polishing head. The thickness also opens the interface by its own value, which is the subject of what a film does to the interface it measures — at these pressures the effect is small, but it is not zero.

What ships, and what is committed

The system is delivered as a complete chain: the 366 × 366 mm sensing sheet, the PXS256SE collector, the acquisition and analysis software on a USB key, a carry case, the printed manual, and a one-year warranty on the whole system, excluding damage from misuse. Software installs on any PC with no licence count and updates are free for the life of the product. A third-party test report and a device accuracy test report travel with the instrument, both of which are named in the delivery conditions.

Lead time is 30 working days from order for build, assembly and calibration. On-site training is included: operators, maintenance and equipment-management staff, covering safety, installation, operation, the main hardware modules and the software. Installation and commissioning take place within seven days of a request. Support response is within 24 hours on working days, and calibration plus technical service remain available after the warranty period.

Where these figures come from

Every value in the table is taken from the product specification sheet (V1.00) that ships with each system. Two entries are derived and labelled as such: point density (65,536 ÷ 36 × 36 cm) and resolution per count (100 kPa ÷ 1024). Nothing in the table is an estimate, and where the specification is silent — weight, ingress protection, cable length — this page is silent too.