stokes waferskan™ ellipsometer L115S300




Imaging 300mm stokes waferskan™ ellipsometer
The L115S300 Stokes WAFERSKAN Ellipsometer's high speed film thickness mapping system, based on advanced StokesMeter™ technology, measures 49 sites in 49 seconds! It is a fast instrument for thin film measurements giving tilt-free, focus-free, automatic  2D/3D color thickness and index images of the sample surface. The easy to use model L115S300 maps wafers up to 300mm in diameter and offers precise measurements at a cost much lower then conventional production control metrology systems.  


  • Tilt-free, focus free, hands-off operation for similar wafers.

  • 15 Micron measuring spot standard

  • Combination tilt/viewing scope standard

  • Variable angle 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 source.

  • Simple, compact tabletop instrument - competitively priced.


high accuracy and flexibility of application
The model L115S300 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 L115S300 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. New modeling software permits multiparameter measurements utilizing the manually selectable angles of incidence.

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 Image Map. The image can be rotated, tilted, reduced or enlarged for immediate viewing and interpretation.

2D contour image map of film thickness


3D contour image map of film thickness


Main Screen

easy to use
The L115S300 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. 

precision for device wafers
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. The Stokes WAFERSKAN™ comes equipped with a 15 micron measuring beam together with a combination viewing/tilt scope standard.

speed and stability
The L115S300 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.

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 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.

An outstanding feature is the Stokes Ellipsometer's compensation for small changes in angular beam deviation caused by sample out-of-flatness. This 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 tremendous speed is the obvious benefit.

optional accessories


L115S300 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. 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 many samples are simply too rough and scatter too much light to be measured ellipsometrically.

stokes waferskan™ ellipsometer L115S300 specifications

Alignment: Built-in axis of rotation of incident arms in the sample plane means that incidence angles are easily set with no need for alignment prisms. Measurement site remains the same at any angle of incidence with no need for sample readjustment.
Incidence Angle: 30°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 90° Manually selectable
Method of Measurement: Advanced StokesMeter determines the complete beam polarization using no moving parts and no modulators, only 4 stationary silicon detectors so measurements are exact and stable.
Measurement Time: Practically instantaneous. One second per point including stage travel.
Light Source: Spectrally precise, stable, long lasting HeNe 6328A Laser. Typical lifetime is greater than 3 years. Similar light source used by NIST to produce calibration standards.
Beam Diameter: 15 micron diameter (15 x 52 micron on wafer @70°) is standard
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. Vacuum held (requires 5 inch Hg.).
Stages: Precision Stepping Motors driven 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. Maps a 12" wafer at 49 measurement sites in 49 seconds or one second per point.
Stage Precision: Within 10 microns
Data Output: 2D/3D color image maps of film thickness, refractive index and location to monitor, printer or disc file
Computer: Windows PC (included)
Film Thickness Range: 0 - 60,000 Angstroms on substrate or on 1, 2 or 3 known sub layers
Precision & Repeatability: Sub-Angstrom over most of the measurement range.
Refractive Index: ± .001 over most of the measurement range.
Power: 115V, 100V, 220V, 240V (50/60 Hz)
Dimensions: Height:  18 inches   Width: 33 inches   Depth: 16 inches
Net Weight: 145 lbs.  Shipping Weight: 300 lbs.
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: S series Ellipsometers comply with European safety directives and carry the CE mark.

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