variable angle stokes ellipsometer L116S





variable angle stokes ellipsometer L116S300 description
The model L116S300 for up to 300mm wafers builds on the production proven Gaertner 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 L116S300 model sets a new and even higher 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 LGEMP and optional LMOD modeling software permits multiparameter measurements utilizing the manually selectable angles of incidence.

The Ellipsometer measures by reflecting a polarized laser beam from the sample surface at one of eight available incident angles 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 laser light source.

high speed film thickness measuring system measures in less than a second!

The L116S300, based on advanced StokesMeter™ technology, offers instantaneous measurement at a low cost and is upgradeable to the Imaging Waferskan, Two or Three Wavelength ellipsometers.


  • Tilt-free, focus free, hands-off operation for similar wafers.
  • Fastest possible instrument for thin film measurement.
  • Variable angle useful for difficult to measure films.
  • Trouble-free, no moving parts advanced StokesMeter™ measurement head.
  • Measures complete state of polarization useful for rough,scattering samples.
  • Accurate, stable measurements using spectrally precise laser ellipsometry.
  • Simple, compact tabletop instrument - competitively priced.

An outstanding feature is the Stokes Ellipsometer's compensation for small changes in angular beam deviation caused by sample thickness changes. This permits fast, uninterrupted measurement over the entire wafer surface without the need to pause to correct for focus and tilt. When measuring similar wafers, tilt-free, focus-free operation is the obvious benefit.

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.

The clean, 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.

optional accessories

 Linear Rotary Stage L116LRS (see photo above)
This linear rotary stage is moved by hand in a linear and 360º rotary motion so that different areas on the sample can be conveniently measured. The 8" sample table can accept up to 300mm wafers and has 150 mm left to right cross travel and can be scale read to 1 mm. The L116LRS accepts sample thickness up to 1/2 inch and has provision for vacuum and tilt up to 1 degree. 

 XY Linear Rotary Stage  L116LRSY
This stage is same as the L116LRS except ± 1" micrometer front to back travel in Y is added. The added Y coordinate motion facilities measurement of a XY rectangular pattern.  

Stage Modification L116LRS10 
Same as L116LRS but with stage modification for samples with Philips style hub. 

 Microspot Optics L116MS
Consist of both a projector optic that reduces the normal 1mm laser beam diameter down to 15 microns and a receiver optic. At 70 degrees incidence, 15 X 52 micron sample areas can be measured. At 50 degrees incidence the measured area is 15 X 35 microns. Microspot Optics are factory installed and non-removeable. 

Video Monitor L115VM 
Permits monitoring a wafer pattern on your PC screen. 

Polarizer Drum LPD (see photo above)
Polarizer drum divided 0 to 360º, settable to 0.1º, containing a Glan Thompson prism added to the polarizer arm of the ellipsometer.  Used to change the azimute of the linear polarization for certain in-line transmission measurements of transparent materials.  

Stokes Calibration Kit L118-KIT                                                        
Permits recalibrating any Stokes Ellipsometer using calibration software and 4 NIST traceable samples.  

L116S300 can be equipped with the following laser options:


LS405    Substitutes 405 nm  Blue laser diode in place of 633 nm HeNe Gas Laser 
LS544    Substitutes 544 nm Green HeNe Gas laser in place of 633 nm HeNe Laser  
LS830    Substitutes 830 nm laser diode in place of 633 nm HeNe Gas Laser 


L2W405    Adds 405 nm Blue Laser Diode to 633 nm ellipsometer 
L2W544    Adds 544 nm Green HeNe Gas Laser to 633 nm ellipsometer 
L2W830    Adds 830 nm laser diode to 633 nm ellipsometer  


L3W405.544   Adds 405 Laser Diode and 544 Green Gas Laser to 633 nm ellipsometer 
L3W405.830   Adds 405 Laser Diode and 830nm laser diode to 633 nm ellipsometer 
L3W544.830   Adds 544 Green Gas Laser and 830nm laser diode to 633 nm ellipsometer 


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 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. In addition, 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 are simply too rough and scatter too much light to be measured ellipsometrically.

variable angle stokes ellipsometer  L116S300 specifications

Alignment: Built-in axis of rotation of incident arms is in the sample plane. Angles are easily selectable with no need for alignment prisms or sample readjustment.
Incidence Angle: 30º, 45º, 50º, 55º, 60º, 65º, 70º, 75º, 80º, 90º
Method of Measurement: Advanced StokesMeter measurement head
Measurement Time: Practically instantaneous
Light Source: HeNe 6328 Angstrom Laser gives less than 1 mW output on sample
Beam Diameter: 1mm diameter (1 x 3mm on wafer @ 70º)
Microspot (Optional): 15 micron diameter (15 x 52 micron on wafer @ 70º)
Detectors: All Solid State with no moving parts
Sample Monitor: Combination 39 power microscope (for surface viewing)/tilt monitor (for checking sample out of flatness)
Sample (Wafer) Size: Up to 300mm diameter standard 
Stages standard: Pedestal 8 inch table with provision for vacuum is freely positioned by hand. 1/2 inch height adjustment together with tilt corrects for sample out of flatness of up to 1º in both X and Y planes. Docking pedestal can be separated to accommodate 2 inch thick samples or special fixturing.  
Software: Windows 10/8/7/ VISTA/XP LGEMP measures on up to 4 absorbing layers.
Computer(not included): Windows 10/8/7/VISTA/XP PC with available USB port .
Film Thickness Range: 0-60,000 Angstroms
Precision & Repeatability: Sub-Angstrom over most of the measurement range
Refractive Index: ± .0005 over most of the measurement range.
Power: 115V, 100V, 220V, 230V, 240V
Dimensions: Height: 18 inches
Width: 33 inches
Depth: 15 inches
Net Weight: 65 lbs.
Shipping Weight: 95 lbs.
Interface: USB cable connects Windows PC to ellipsometer  
CDRH Compliance: All laser Ellipsometers supplied by Gaertner comply with CDRH requirements 21CFR 1040 for a Class II laser product emitting less than 1 milliwatt 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.
CE Compliance: All Stokes Ellipsometers comply with European electrical directives and carry the CE mark.

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