TohoSpec 3100 Film Thickness

The TohoSpec 3100 is a low cost film thickness measurement system that utilizes a modern small spot spectroscopic reflectometer built on a simple-to-use tabletop platform. Incorporating core technology acquired from market leader Nanometrics, this system is specifically designed for a wide variety of R&D applications. The reliable solid state linear diode array provides fast, precise measurements of single-layer films such as oxide, nitride and photo-resist, as well as the top layer on film stacks of up to 3 layers in the thickness range of 100Å to 30µm. An outstanding value, complete with up to 15 standard film thickness measurement algorithms, this rugged and accurate system is used in laboratories worldwide to provide precision film thickness measurements in a compact design.

The flexible software platform makes it simple and easy for the user to configure measurement programs and recipes for both simple and advanced measurement applications. With the ability to select film constants, scan ranges and substrate types, the 3100 is the ideal tool for rapid measurement program development.

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Spec Sheet

Standard Features

Comprehensive Measurements

The 3100 provides scanning from 380 to 800 nm and can measure single layer films such as oxide, nitride and photoresist. Measurements can also be made on a wide variety of other substrates including silicon, aluminum and gallium arsenide.

Highly Configurable

The 3100 is highly configurable. Small spot size measurements can be performed with an optional 50x lens. Higher precision measurements are possible with an optional 10x lens. With the 3100T model, film layers as thick as 70 µm are measurable with an installed small-aperture system. Consult the optional features list for a full listing of options available to the TohoSpec 3100.

Dynamic Software

The advanced software platform provides the process engineer with complete freedom and flexibility in creating custom measurement programs to meet the demanding needs of today's new micro-electronic Research and Development, especially during process startups. Data management features, including statistical analysis, histograms, and the ability to import and export data files, are all standard.

Options & Accessories

• Desktop or Laptop PC: The TohoSpec 3100 is compatible with any desktop or laptop PC meeting the following specifications:

Desktop or Laptop, Intel Core i5 or better, 32 bit Windows 7 Pro operating system Interface: RJ45 (plugs into the same port as a standard LAN cable) A PC may also be purchased separately from Toho Technology.

• Optional 10x objective

• Optional 50x objective

• Small spot with 100x objective – 0.75 µm

• Small aperture system for thick film measurement

• High-sensitivity, high resolution head (Model 3100T)

• RS-232 or HSMS

• USB Color video camera with dedicated 17” flat panel display

• Vibration resistant stage (for high resolution lenses)

• CD-RW drive

• Color printer

• Cleanroom operations manual (hard copy)

• NanoStandard film thickness standard wafer (6- or 8-inch) 1 Notes:

1 NanoStandard® wafers are NIST·traceable film thickness standards consisting of six pads of different oxide thicknesses on silicon.

With a worldwide installed base of over 300 systems, the TohoSpec 3100 has been engineered to provide outstanding film thickness measurements. Widely respected as the leader among many copy products, leading specifications and performance place the TohoSpec 3100 at the top of its class. Specifications are listed below.

TohoSpec 3100 Film Thickness Specification                           R&D
Film Stack / Number of Films  Up to 3 layers 
Wavelength Range  380 -800 nm  (standard)
  380 -850 nm  (Thick film)
Film Thickness Range1    
Standard Configuration (5x) 100 Å - 30 µm 
Thick Film Configuration (5x)  100 Å - 70 µm 
Repeatability 2 Å 
Film Type  / n & k values Obtained
Measurement Time  0.1  to 25 seconds/site (3100) 
  0.01  to 2.5 second / site (3100 T) 
Data Management  Statistical data analysis, Data export (ASCII) 
Hardware Configuration   
Wafer Sizes  Stage handles 3, 4, 5, 6, 8 inch wafers 
Head Unit Reflectometer Linear Array
Optics / Spot Sizes 
5x (standard)  50 µm  (15 µm for Thick film)
10 x (optional)  25 µm  (7.5 µm for Thick film)
50x (optional)  5 µm  (1.5 µm for Thick film)
100 x (optional for Thick film)  (0.75 µm for Thick film)
Optical Filters (Manual Cutoff Filters)   
Yellow cutoff filter  480 nm (measured at 50% light transmission) 
Orange cutoff filter  560 nm (measured at 50% light transmission) 
Light Source  Halogen
Computer  Intel Core i3 or better
Monitor  16:9 Full HD (1920x1080)
Facilities Requirements   
Dimensions  753 H x 280 W x 472 D (mm) 
  (optics stand)
 System Weight  22kg / 50 lbs
Electrical  AC100V, 5 A 
  1. Film thickness range assumes oxide on silicon. Ranges for other films may vary.

Theory: Reflectometry

The TohoSpec 3100 employs non-destructive, optical thin film measurement which analyzes the light-interference caused by thin layers. The reflection at the layer surface and layer-substrate interface results in constructive and destructive interference depending on the wavelength of the light.

As light strikes the surface of a film it is either transmitted or reflected at the upper surface. Light that is transmitted reaches the bottom surface and may once again be transmitted or reflected. The Fresnel equations provide a quantitative description of how much of the light will be transmitted or reflected at an interface. The light reflected from the upper and lower surfaces will interfere. The degree of constructive or destructive interference between the two light waves is dependent upon the difference in their phase. This difference is dependent upon the thickness of the film layer, the refractive index of the film, and the angle of incidence of the original wave on the film. Additionally, a phase shift of 180° or 𝜋 shift occurs if the refractive index of the medium the light is travelling through is less than the refractive of the material it is striking. In other words, if n1 > n2 and the light is travelling from material 1 to material 2, then a phase shift will occur upon reflection. The pattern of light that results from this interference can appear either as light and dark bands or as colorful bands depending upon the source of the incident light. This basic theory is applied to the TohoSpec 3100.

As the layer thickness cannot be calculated out of these refection spectra directly, a special best-fit-algorithm is used to determine the layer thickness. In this way not only single layers but also multi-layer stacks with known optical data (n,k) can be measured easily and very quickly.

The TohoSpec 3100 is most effective when these criteria are fully met.

1. A difference in the refractive index of the layers and the substrate must be present to get any reflection at the interface.

2. The layers must be transparent or semi-transparent in the spectral range in order to let the light through.

3. The substrate and the layer surface must be smooth enough (10 ~ 20nm) to obtain enough directly reflected light bounced back.

TohoSpec 3100 is designed to provide accurate film thickness measurements within a vast array of applications.

Layers: Guaranteed 3 layer measurement and in some cases beyond 3 depending on parameters

Substrates: Most smooth or semi-smooth surfaces with some reflectance

Sample Info: Sequence of the film stack, film materials, nominal thickness of each layer

  • LED
  • Solar
  • OLED
  • Photomask
  • Power Device
  • SOI
  • Magnetic head for HDD

TohoSpec 3100 : The Standard Model for most applications / 512 pixels / 100Å ~ 30µ

TohoSpec 3100T : Upgrade Model for Standard and Thick film applications / 1024 pixels / 100Å ~ 70µ