stokes waferskan™ ellipsometer LSE-WS




300mm stokes waferskan™ ellipsometer
The model LSE-WS Stokes WAFERSKAN Ellipsometer is a high speed film thickness mapping system measuring one site per second including stage travel! It uses advanced StokesMeter™ technology (previous winner of Photonics Spectra and R&D 100 best new products awards) to give tilt-free, focus free, 2D/3D color thickness and index images on any size wafer up to 300mm . The units' elegant design offers unprecedented ease of use and instantaneous measurement at a cost much lower than conventional production control metrology systems. Affordably priced the LSE-WS is a popular choice in a high precision scanning ellipsometer. 


  • Trouble-free, no moving parts advanced StokesMeter™ measurement head.
  • Measures complete state of polarization providing increased accuracy.
  • Accurate, stable measurements using spectrally precise laser ellipsometry.
  • Fastest possible instrument for thin film measurement.
  • Tilt-free, focus free, hands-off operation for similar wafers.
  • Simple, compact tabletop instrument - competitively priced.

high accuracy and performance
The model LSE-WS builds on the production proven Gaertner WAFERSKAN™ line of ellipsometers in widespread use throughout the world. From thin gate oxides only tens of angstroms thick to thick polyimides and photoresists Gaertner has earned a reputation for providing precise, reliable results. The model LSE-WS sets a high performance standard to meet today's more demanding metrology applications.

Single Layer films such as oxides, nitrides and photoresists can be measured to sub-angstrom precision. Two, three and four layer films, with know bottom layers such as poly on oxide and oxide on poly on oxide can be measured for the thickness and refractive index of the top layer or for both thicknesses. Windows™ software enhances ease of use and understanding.

great graphics 
The measurement results are displayed on the computer monitor and can be sent to a printer. Results stored in a text data file are displayed in a 2D contour or 3D Map images. The images can be rotated, tilted, reduced or enlarged for immediate viewing and interpretation.

2D contour image of film thickness


3D contour image of film thickness


Main Screen

easy to use
The LSE-WS Stokes WAFERSKAN™ is simple to operate. The user interacts with a single main program screen so the set up is easy to understand and the measurement can be quickly made. Stored recipes are readily accessed for scanning different films and patterns. Similar wafers are automatically scanned with a single mouse click. The operator can chose 1, 5, 9, or 49 point circular measurement,  X-Y grid, diameter, or Polar Scans with up to 1000 measurement points and set the wafer edge exclusion. 

high precision stages
High quality stepping motor stages provide precise and repeatable positions. The wafer is held on the optically flat table by vacuum. The stages move automatically in rapid yet precise steps under programmed computer control. Measurement time is less that one second per point including stage travel. Step precision is better than 10 microns, with the area of coverage and points within that area easily set for automatic scanning.

speed and stability
The LSE-WS Ellipsometer measures by reflecting a polarized laser beam from the sample surface at a 70° incident angle and determines the change in polarization caused by the sample virtually instantaneously. Since there are no moving parts in the StokesMeter™ measuring head the measurements are accurate and repeatable even after many months of continuous use. Precision of measurement is further enhanced by the use of a stable, spectrally precise, high signal to noise HeNe gas laser light source.

description of stokesmeter™ technology
This advanced device uses no moving parts and no modulators to quickly and accurately determine the complete polarization state of the measuring beam.

The diagram above shows the StokesMeter™ photopolarimeter for the simultaneous measurement of all four Stokes parameters of light. The light beam, the state of polarization of which is to be determined, strikes, at oblique angles of incidence, three photodetector surfaces in succession, each of which is partially spectrally reflecting and each of which generates an electrical signal proportional to the fraction of the radiation it absorbs. A fourth photodetector is substantially totally light absorptive and detects the remainder of the light. The four outputs thus developed form a 4x1 signal vector I which is linearly related, I=AS, to the input Stokes vector S. Consequently, S is obtained by S=A(-1)I. The 4x4 instrument matrix A must be nonsingular, which requires that the planes of incidence for the first three detector surfaces are all different. For a given arrangement of four detectors, A can either be computed or determined by calibration.

technological advantage
The simple, compact StokesMeter™ replaces a typical rotating analyzer assembly consisting of a drum, prism, encoders, switches, motor and detector and their associated electronics. In addition, the waveplate mechanism on the polarizer arm, is eliminated. This results in a fast, precise, stable no moving parts ellipsometer.

An outstanding feature is the Stokes Ellipsometer's compensation for small changes in angular beam deviation caused by sample out-of-flatness. This compensation permits fast, uninterrupted scanning over the entire wafer surface without the need to pause to correct for focus and tilt. When scanning similar wafers, tilt-free, focus-free, hands-off operation at high speed is the obvious benefit.

Optional LMS Microspot system shown above

optional Microspot System LMS    
for measuring small areas on your wafer with a 15 micron measuring laser beam diameter.  10 micron stage positioning and  CCD camera  viewing of the measurement area on your PC permits areas as small as 15 X 45 micron to be viewed and measured using advanced StokesMeter™ technology .

optional Small Spot optic LSS   
Reduces standard 1 mm laser beam to 0.25 x 0.75 mm on sample

Rough scattering samples common in the solar cell industry are difficult to measure accurately with most ellipsometers because of the loss of signal strength and depolarization of the measurement beam. Although there are ways to boost the signal strength and capture more scattered light, dealing with depolarization is much more difficult and ideally requires the determination of the complete state of polarization namely the measurement of the 4 stokes parameters s0, s1, s2, s3. Gaertner Stokes Ellipsometers do this naturally as our StokesMeterä polarimeter is used as the ellipsometer analyzer. This gives Stokes Ellipsometers the unique ability to instantly separate the polarized from the unpolarized components of the measuring beam thereby delivering a highly accurate measurement of film thickness and index based only on the totally polarized component of light. The L-SCAT scatter option includes a hardware modification to capture more of the scattered light from rough, textured surfaces and a program display of the degree of polarization P.  Keep in mind however that some samples may be simply too rough and scatter too much light to be measured ellipsometrically.

optional Stokes Calibration Kit L118-KIT 
Recalibrate any Stokes Ellipsometer using 4 Gaertner traceable wafers plus glass (L118G-KIT) or
4 NIST traceable wafers plus glass (L118N-KIT).  Most users will not require ellipsometer recalibration.  Intended for the most exacting semiconductor manufacturers with extremely tight tolerances and regulatory compliant users.

stokes waferskan™ ellipsometer LSE-WS specifications

Alignment: Tilt and table height via computer alignment screen.  Proprietary tilt and table height system corrects for ordinary sample tilt and out-of-flatness with no need for sample readjustment or complicated, costly and slow autofocusing systems.
Incidence Angle: 70°
Method of Measurement: Advanced StokesMeter reads the complete beam polarization using no moving parts and no modulators, only 4 stationary silicon detectors so measurements are exact and stable.
Measurement Time: One second per point including stage travel.
Measurement Laser: Spectrally precise, stable, long lasting HeNe 6328A Laser with 1 mm beam diameter (1x3 mm on wafer at 70 Typical lifetime is over 3 years. Similar light source used by NIST to produce calibration standards.
Optional Microspot has a 15 x 45 micron spot with CCD camera viewing.
Alignment Laser: 670 nm Laser Diode
Software: 2D/3D color graphics runs under Windows™ included 
Sample (Wafer) Size: Up to 300mm diameter standard. Vacuum held (requires 5 inch Hg.).
Stages: Precision Stepping Motors under user programmed computer control with manual pushbutton override. 150mm linear and 360° rotary motion covers any point on the sample. Tiltable table permits correction for sample out-of-flatness up to 1° in both X and Y planes. Map any size wafer up to 300mm at 1 second per point.
Stage Precision: Within 10 microns
Data Output: 2D/3D color images of film thickness, refractive index and location to monitor, file or printer. Text data file is easily exported to other programs.
Computer: Windows™ 10 Laptop PC  included 
Film Thickness Range: 0 - 60,000 Angstroms on substrate or on 1, 2 or 3 known sublayers
Precision & Repeatability: Sub-Angstrom over most of the measurement range.
Refractive Index: ± .0005 over most of the measurement range.
Power: 115V, 100V, 220V, 240V (50/60 Hz)
Dimensions(LSE-WS): Height:  18 inches   Width: 28 inches   Depth: 20 inches
Net Weight: 85 lbs.  Shipping Weight: 200 lbs.
CE Compliance: S series Ellipsometers comply with European safety directives and carry the CE mark.
CDRH Compliance: All laser ellipsometers supplied by Gaertner comply with CDRH requirements 21CFR 1040 for a Class II laser product emitting less than 1 mW  or Class IIIb less than 5 mW of low power radiation. As with any bright source such as the sun or arc lamp, the operator should not stare directly into the laser beam or into its reflection from highly reflecting surfaces.
Warranty: 1 year warranty covers all parts and labor exclusive of shipping costs

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