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. The gas 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 mechanisms to form fluorine radicals F^* that will aggressively react with the silicon atoms at the part of the surface of the wafer that is not masked.

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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