Optical Monitors

Model OM820
In-Situ Spectroscopic Optical Monitor

Full Spectrum, Real-time Analysis and Control of Reflectance and
Transmittance During Thin-Film Deposition


FEATURES

  • Full Spectrum Analysis
  • Multiple Endpoint Techniques
  • Real-time Chamber Characterization
  • Optical Constants (N & K)
  • Full Spectrum Analysis
    Spectrometer monitors from 200-900nm to analyze the true reflection or transmission of the test chips being monitored.
  • Multiple Endpoint Techniques
    The Model OM820 can be configured to endpoint each layer with Pre-Quarter wave, Post-Quarter wave or Simulation Template Match (Template Match requires a simulation program such as Essential Macleod, which is offered as an option).
  • Real-time Chamber Characterization
    Because the Model OM820 monitors the full spectrum during the deposition process, the system can identify shifts in spectrum due to various changes in material composition. The spectrum data can then be used to calculate new N&K values which can update the design of the product being produced.
  • The Model OM820 can also characterize the optical constants of the films during venting and spectral shifts due to temperature and/or O2 flow rates.
  • Plasma Diagnostics/Endpoint
    The Model OM820 software includes the capability for control and analysis of plasma processes.
  • Offline Stage (optional)
    Measurement of transmission, reflection or Color for QC of Filter, Prisms, or Beam Splitters.

FUNCTIONAL DESCRIPTION

The Model OM820 is a multi-wavelength spectrophotometer comprised of a long life (10,000 hrs) , low voltage halogen light source, silicon photodiode array detector, embedded computer and software with sophisticated algorithms integrated into an easy to use instrument. State of the art fiber optic components deliver high signal to noise ratio and long-term stability. The photodiode array allows the entire range of individual wavelengths in the spectrum to be detected simultaneously and is especially suitable for resolving low level signals in a noisy environment. A curve fitting approach to layer termination further assists in detecting and controlling small signals in a environment when dispensing materials like SiO2 on glass substrates.

Transmission Mode
The light is illuminated from the bottom (or Top) of the chamber by the light source probe. The light will transmit through the test chip and into the transmission probe on the top (or bottom) of the chamber. The light is collected in the probe and focused into a fiber where it is transferred to the spectrometer for analysis. See Figure 1 for illustration.

Reflection Mode
The light is illuminated from the bottom of the chamber by the light source probe. The light will reflect from the test chip and back down to the bottom of chamber to the reflection probe. The light is collected in the probe and focused into a fiber where it is transferred to the spectrometer for analysis. See Figure 1 for illustration.

Endpoint Techniques
The optical monitor is capable of using several techniques for controlling the thickness of each layer.. The techniques are described below.

Quarter Wave
The quarter wave technique is the most common technique used in the deposition industry. It consists of monitoring a single wavelength vs time during the coating process. During this time, the single wavelength intensity signal will change due to the constructive and destructive wavelength interference, based on the refractive index of the film being deposited. From the wavelength and refractive index of the material, the film thickness can be calculated.

Wavelength /(Refractive Index)
An illustration of multiple quarter wave reflectivity is shown in Figure 3.

Template Match
In the Template Match technique the raw collected spectrum is compared to a predicted simulation from a simulation software like Essential Macleod. The algorithm uses a variation of a Root Means Squared comparison to identify the match. A single file of templates are used to control all layers. See figure 4 for illustration.


Figure 2 shows the full spectrum of
five-quarter waves of TIO2.
The spectrum can be used to recalculate N&K (Refractive Index) of deposited material or actual film thickness

Figure 3 shows multiple quarter waves during the deposition of TIO2.
Pre-Quarter wave or Post-Quarter waves are used for layer termination.


Figure 4 shows the template matching technique. The screen on the left displays the raw collected value (black line) and the template used for matching (blue line). The screen on the right shows the "Root Means Square" algorithm fit of the data vs. time. When the two spectral displays (on the right) match within a user defined threshold, the system will terminate the layer deposition. A simulation package, such as Essential Macleod must be used to generate the templates for matching.



Model OM820 Specifications


  • Photosensitive area: 50 micron pixel pitch x 2.5 mm pixel height
  • Quantum efficiency: 75% @ 600 nm
  • Sensitivity: 2200 photons/count @ 600 nm
  • Response: 4.5 x 10-4 coulombs/joule/cm2
  • Dark Current: 2 pico-amps
  • Saturation Charge: 22 pico-coulombs
  • Precision/Stability: Less then or equal to 0.2% of full scale/hour
  • Min. Signal Acquisition Time: 50 msec
  • Size (Width x Height x Depth): 19" x 8.75" x 10" (483 mm x 223 mm x 254)
  • Weight: 40 pounds (18.25 kg)
  • Computer Processor: Pentium II 266 MHz
  • Computer Memory: 128 RAM
  • Computer Hard Drive: 20 GB IDE
  • Computer Operating System: Windows 98, Windows 2000
  • Computer Communications Ports: 2 Serial Ports, 1 parallel port, 2 TTL inputs, 2 TTL outputs
  • Computer Display: 15" Flat Panel, active-matrix LCD
 

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