Optical end point detectors

Upgrades

Endpoint detectors are an important tool for achieving optimal process results.

Increased tool availability & productivity
Reduced cost of ownership
Extended life of chamber components due to less over-cleaning
Real-time chamber clean endpoint detection
Reduced particulate generation by preventing over-cleaning, leading to improved process yield

Optical emission spectroscopy monitors the light emitted by the plasma.
Measurement of the amount of light emitted at a specific wavelength therefore allows a relative measurement of the concentration of a given species. Measurement of the fluorine emission intensity is used to determine the endpoint of chamber plasma cleaning.
During cleaning the fluorine concentration will be low as it is being consumed by the etching process, but it will rise sharply at endpoint when the chamber walls become clean.
Typical endpoint units for PECVD chamber clean endpointing are as follows:

CCD1 spectrometer kit (200-850nm spectrometer). The full spectrum capability additionally allows chamber and process monitoring, e.g. by comparison of current spectra with a reference to aid with process troubleshooting.
Fixed wavelength PM140 kit (704nm), dedicated to chamber clean endpoint detection.

These end point detectors are available for PlasmaPro® systems: 80Plus, NGP80, 100, 800 System133, NGP1000 and Plasmalab System 100

Endpoint detectors are an important tool for achieving optimal process results.

Optical emission spectroscopy monitors the light emitted by the plasma.
Etch by-products and gas species have characteristic emission wavelengths, so process endpoints can be detected by looking for changes in these emissions as the etch reaches a new layer.
OES endpointing typically requires an etched area of several cm2 to provide a detectable concentration of etched species to the plasma, depending also on etch rate and plasma emission intensity. See table overleaf for typical OES options.

Endpoint detectors are an important tool for achieving optimal process results.

Enables etch depth monitoring and endpointing
Allows ‘etch-to-depth’ within a layer
Precise etch depth control within multi-layer structures
Allows endpointing on small samples or those that do not provide a strong OES endpoint

A laser interferometer measures the change in reflectance of the wafer surface during etching (or deposition), by focussing a laser spot onto the wafer and measuring the intensity of the reflected laser light.
The laser interferometer camera provides the reflectance signal to the Oxford Instruments system PC along with an image of the wafer surface - to allow precise positioning of the laser spot onto the correct region.
The etch (or deposition) rate can be calculated by the monitoring the rate of arrival of the interference ripples of the reflected signal (since each interference cycle = λ/2n), allowing the etch to be stopped at a certain depth within the layer. Interfaces between layers can also be detected, as this typically results in an abrupt change in reflectance.
Laser interferometry typically requires user intervention to position the spot before each run (unless a specific region of the wafer is dedicated for laser endpointing), so is commonly used in a research environment.