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Endpoint detectors (EPD) are an important tool for achieving optimal process results. The use of an EPD ensures processes are carefully controlled and consistent, to ensure reliable repeatable results are achieved wafer-after-wafer, batch-to-batch. Several techniques exist and it is vitally important to understand the strengths of each and how they fit with your process requirements to achieve what you need. Upgrade now and receive multiple benefits.
We supply a wide range of endpoint detector upgrades under these two categories:
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| Options | Ocean Insight USB4000 | AvaSpec - Mini2048CL | Verity SD1024G | Verity SD1024GH | Horiba EV 2.0 |
| Wavelength range | 200 - 850 nm | 200 - 1100 nm | 200 - 800 nm | 200 - 800 nm | 200 - 1050 nm |
| Spectrometer | Real time | Real time | Real time | Real time | Real time |
| Endpoint | Yes | Yes | Advanced algorithms | Advanced algorithms | Advanced algorithms |
| Chamber condition analysis | Yes | Yes | Yes | Yes | Yes |
| Etch process monitor | Yes | Yes | Yes | Yes | Yes |
| Reprocess | No | No | Yes | Yes | Yes |
| Resolution | Good for general single layer process | Good for general single layer process | Excellent for complex multilayer | Superior for complex multilayer | Good for complex multilayer |
| Suitable for | PECVD, RIE, ICP-RIE, CVD and ALD Systems | PECVD, RIE, ICP-RIE, CVD and ALD Systems | RIE and ICP-RIE Systems | RIE and ICP-RIE Systems | RIE and ICP-RIE Systems |
| Example Applications | PECVD chamber clean, SiO2/SiNx etch, PR strip, general purpose etching | PECVD chamber clean, SiO2/SiNx etch, PR strip, general purpose etching | SiO2/SiNx etch, GaAs/ AlGaAs/ GaSb/ AlGaSb, InP/ InGaAs/ InGaAsP/ InAlGaAs, Metals, Plasma analysis | SiO2/SiNx etch, GaAs/ AlGaAs/ GaSb/ AlGaSb, InP/ InGaAs/ InGaAsP/ InAlGaAs, Metals, Plasma analysis, Deep Si, GaAs VCSEL | GaAs/ AlGaAs/ GaSb/ AlGaSb, InP/ InGaAs/ InGaAsP/ InAlGaAs, PR Strip, Plasma analysis |
Optical emission spectroscopy (OES) monitors the light emitted by the plasma. Measuring the intensity of light emitted at a specific wavelength in a spectrum allows a relative measurement of the concentration of a given species.
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 in the plasma, depending also on etch rate and plasma emission intensity.
A popular application of OES is in the plasma cleaning of PECVD chambers. 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 when the chamber walls become clean, providing an endpoint.
Typical endpoint units for PECVD chamber clean endpointing are as follows:
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| Options | Horiba LEM | Intellemetrics LEP500 |
| Movement | XY and tilt adjustment | XY and tilt adjustment |
| Sample image magnification | x50 | x50 |
| Laser wavelength | 670/ 905 nm | 670/ 980 nm |
| Laser spot size | 30 to 60μm | 8 to 24μm |
| Layer structure modelling | No | Yes |
| Suitable for | RIE and ICP-RIE Systems | RIE and ICP-RIE Systems |
| Example Applications | SiO2/ SiNx, Metals, GaAs/ AlGaAs/ GaSb/ AlGaSb, PR strip, Failure Analysis | Metals, GaAs VCSEL, GaAs/ AlGaAs/ GaSb/ AlGaSb, InP/ InGaAs/ InGaAsP/ InAlGaAs, PR strip |
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 also provides a TV image of the wafer surface to allow precise positioning of the laser spot onto the correct region.
The etch rate can be calculated by monitoring ripples in the laser signal due to interference effects within the thin film, 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).
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