Yttrium oxide (Y2O3): thickness measurement

83 Pine Hill Rd. Southborough, MA 01772 Phone +1.617.388.6832 Fax. +1.508.858.5473

email: [email protected] http://www.semiconsoft.com

Thin Film Measurement solution Software, sensors, custom development and integration

Measurement of Yttrium oxide (Y2O3) coating.

Yttrium oxide coating received considerable attention in dry etching, ashing and PECVD equipment manufacturing. Yttrium oxide has a very low etching rate (1/10th of the sapphire and 1/100th of quartz) and has superior resistivity to a highly corrosive halogen gas. Y2O3 coating reduce corrosion and associated particles generation, it also increase the lifetime of components like focus rings, etc.

The thickness of the Y2O3 coating needs to be checked during the manufacturing process and during subsequent maintenance cleaning. Accurate measurement of yttrium oxide coating has several challenges: coating is, frequently, non-uniform (has multiple sublayers) and can have surface roughness, measurement has be done directly on the product.

MProbe HC is perfectly suited for this measurement: manual fiberoptics probe enables easy access to a measurement area, wide wavelength range (400-1000nm) allows measurement of smooth and rough surfaces and 15nm -20µm measurable thickness range covers typical Y2O3 thicknesses (4µm -20µm).

Measurement examples

Sample 1: Coating for PECVD chamber (5.5 µm nominal thickness) as manufactured

Fig. 1 Reflectance spectrum of the Y2O3 coating (sample 1). Coating is

relatively uniform and smooth – no noticeable surface roughness. (see result Fig. 2)



Fig. 2. Measurement results. Y2O3 thickness- 6105nm.

Fig. 3 SEM cross-section of the sample 1.



Sample 2. Y2O3 coating for etch chamber as manufactured (nominal 10 µm)

Fig. 4 Measured reflectance spectrum of sample 2.

Fig. 5 Measurement results sample 2. Total thickness: 9911 nm. Multiple peaks in the spectrum indicate the presence of the sublayers.



Fig. 6 Sample 2- SEM cross-section.

Fig. 7 Sample 3 - Y2O3 coated part from an etch chamber: yellow area was exposed to etching (contaminated area), white ring area was protected and has as deposited Y2O3 coating.



Fig. 8. Measured reflectance spectrum in 2 spots on sample 3. Blue Spectrum (top) showing measurement in un contaminated area (Point 12). Red spectrum shows measurement in contaminated area (Point 2)

Fig. 9 Sample #3 (Point 12 – uncontaminated area). Measurement results: Y2O3 thickness 11.9µm



Fig. 10 Sample #3 (Point 2 – contaminated area). Measurement results: Y2O3 thickness 9.5µm The difference between uncontaminated and contaminated area is very clear: 1. Contaminated area has lower reflectance (~ 4-5% lower) 2. Interference fringes in contaminated area are barely visible (Fig. 8) as a result the peak in FFT spectrum (Fig. 10) is low as compared with the peak in uncontaminated area (Fig. 9) 3. Y2O3 thickness in contaminated area is significantly lower ( by 3 μm ) as compared with uncontaminated/unexposed area. Some of the areas maybe heavy contaminated and special care need to be taken to measure them successfully. There are two parameters that need to be set/adjusted: the FFT noise level and thickness range constraint. FFT noise level is used to prevent false positives and at the same time not miss the correct measurement (false negative). One of the ways to set FFT noise level is to use the measurement of the uncoated substrate (when available). Thickness constraint limits the acceptable range, if the result is outside of the range – it is rejected and thickness is set to 0. For example, one can set a low thickness limit of 2μm.



Fig. 11. Comparison of the reflectance spectra of uncoated substrate (red) and heavy contaminated area (blue).

Fig. 12. FFT decomposition of the reflectance data from bare substrate. It shows that the noise level is ~ 0.1



If now we set FFT noise level > 0.15 and minimum thickness 2μm - we can achieve 0 thickness result for bare substrate and correct result for contaminated Y2O3 measurement area. MProbe HC measurement helps track the progress of cleaning of contaminated area and also determine if part can be reused (enough Y2O3 left) or need to be replaced.

Yttrium oxide (Y2O3): thickness measurement

Technology

Transcript of Yttrium oxide (Y2O3): thickness measurement