Liquid gas jet sources for table top X(E)UV generation

efficient low debris EUV and XUV source for lithography, spectroscopy, and microscopy

Why Xe plasma sources and EUV?

The semiconductor industry generally follows Moore’s law, stating that the feature size of ICs will be halved every two years. The reason for this is the continuous demand for higher processor speed, higher memory density and lower power consumption, all enabled by smaller feature sizes. However, there are fundamental limits, imposed by nature, on the wavelength of the light used to print small features. In order to continually print smaller features, the wavelength of the light must also decrease. Extreme Ultraviolet Lithography (EUVL) is the next generation lithography technology, enabling sub 50 nm features.

Extreme ultraviolet (EUV) lithography is opening up a new chapter in semiconductor development. It is the leading contender to establish nextgeneration lithography technology that makes possible features as small as 50 nm.
 
Optical lithography is a key element in semiconductor production. It involves passing light through a mask of the chip design and projecting it on to the silicon wafer, where it exposes special photoresist chemicals used to protect unetched circuit details. Until now, visible light sources have sufficed, but new processing technology based on extreme ultraviolet light (EUV) lithography will be required for next generations chips that are expected to be much more complex and powerful than today’s ones. EUV has shorter wavelengths than visible and UV light and can therefore be used to define smaller and more numerous features. However, there are drawbacks to its use. For example, EUV can be absorbed by air and by the types of lenses that have been traditionally used in chip-making technologies. To get around those limitations, the process needs to take place in a vacuum, with highly sophisticated mirror systems to project chip patterns on to the silicon wafers.

In the past, lithography for high-end semiconductor devices used h- or i-line mercury lamps for respectively 436 and 365 nm wavelengths; but 0.25 micron dimensions needed pulsed gas discharge excimer lasers offering wavelengths of 248 nm. Stepping down to 100 and 70 nm details required argon fluoride (ArF) and molecular fluorine (F2) excimer lasers at 193 and 157 nm, respectively.
Next generation lithography (NGL) technology will be required to shrink the structures even further, to 50 nm and below. Industry consensus is that EUV at a wavelength of 13.5 nm will be necessary. But, while EUV appears to be the most promising technology for NGL, none of the known laser and electrical discharge excited sources appears to be reliable or resilient enough to be produced industrially – although each has its own advantages and disadvantages. E-beam and X-ray lithography are still on the list of competitive technologies. However, more and more companies are now concentrating just on EUV and have stopped supporting the alternatives. This makes it more likely that EUV will be established as the future lithography technology.

The principal challenges of EUV lithography involve developing a high power source, illumination and demagnifying optics working at 13.5 nm, and appropriate manufacturing techniques for EUV masks. A high power yet very narrow waveband source is essential as, at the required 13.5 nm wavelength, materials used to make refractive lenses have too strong an absorption and it is necessary to use optics based on carefully designed systems of mirrors which reflect only a single wavelength.

Highly excited plasmas are the answer. The main challenge is to apply the very high energy input to the plasma and to achieve very high energy conversion efficiency at the desired wavelength.

Microliquids GmbH provides laser driven liquid gas (cryogenic)sources in vacuum for table top applications in lithography, spectroscopy, and microscopy.

Microliquids GmbH develops systems that may be included in EUV source systems used by stepper companies that will integrate the source with other critical components and then supply complete stepper units to the semiconductor manufacturers.

Applications of liquid gas jet X(E)UV table top sources beyond lithography

Microscopy

Efficient soft x-ray generation for x-ray microscopy in the water window region is possible, using liquid jet and liquid gas jets (with XUV emission of highly ionized O-, N-, F-, Ar-, and C-atoms) in a table top setup.

The laser plasma is a point source that can be refocussed and imaged which opens up several applications including XUV microscopy.

Spectroscopy

Liquid targets are also appreciated for the generation of ultra short XUV pulses from laser driven plasmas.