Specific Process Knowledge/Etch/OES
Optical endpoint detection on the dry etch tools at DTU Nanolab
Several dry etch tools at DTU Nanolab are equipped with an endpoint detection system. Out of those systems only one is not of the type optical endpoint detection. The instruments are:
- ICP Metal Etch
- III-V ICP
- Pegasus 1
- Pegasus 4
The section below describes the principle behind the optical endpoint detection system.
Optical Emission Spectroscopy
As an example, let's take the etching of silicon by fluorine in one of the dry etchers. The fluorine is supplied to the system as SF6 gas that is fed to the process chamber using mass flow controllers. Driven by the RF generators (both coil and platen) the plasma will decompose the gas in a series of dissociation and ionisation reactions to form fluorine radicals F*. In the areas on the wafer that are not covered by a mask, the exposed silicon atoms will be attacked aggressively by the fluorine to form volatile SiF that
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| Monitored species | Wavelength (nm) | Monitored species | Wavelength (nm) | |
| Al | 308.2, 309.3, 396.1 | In | 325.6 | |
| AlCl | 261.4 | N | 674.0 | |
| As | 235.0 | N2 | 315.9, 337.1 | |
| C2 | 516.5 | NO | 247.9, 288.5, 289.3, 303.5, 304.3, 319.8, 320.7, 337.7, 338.6 | |
| CF2 | 251.9 | O | 777.2, 844.7 | |
| Cl | 741.4 | OH | 281.1, 306.4, 308.9 | |
| CN | 289.8, 304.2, 387.0 | S | 469.5 | |
| CO | 292.5, 302.8, 313.8, 325.3, 482.5, 483.5, 519.8 | Si | 288.2 | |
| F | 703.7, 712.8 | SiCl | 287.1 | |
| Ga | 417.2 | SiF | 440.1, 777.0 | |
| H | 486.1, 656.5 |