Characteristics of ion beams from a Penning source for focused ion beam applications

Abstract

Focused ion beam characteristics, measured by using PMMA resist exposures, show significant improvement of the previously reported results for hydrogen ion beams. A beam current density of >50 mA cm−2 at 6–7 keV has been obtained over a spot size of 2.3 μm, estimated from the full width at half maximum of the intensity distribution. A single Einzel lens with magnification of about 0.1 was used. A target current density of >1 A/cm2 can be achieved with this beam for a lens system with overall magnification of ∼0.01. In experiments with Ar, both the discharge current and extracted beam current increased by more than a factor of 2 when the discharge cell length was increased by about 25% with respect to the nominal cell length for operation with H. Ar ion beams were extracted with an angular beam intensity of >5 mA sr−1, brightness (90% beam) of ∼103 A sr−1 cm−2 at 10 keV, and energy spread of ∼4.5 eV. Greatly improved beam characteristics, with brightness >104 A sr−1 cm−2, are expected by optimization of the source for Ar beams.

Quest for high brightness, monochromatic noble gas ion sources

“…8͑b͔͒ depends upon many parameters, such as the gas pressure, the magnetic field, the depth of the cell ͑L͒, the spacing between the anode A and cathode K, and the dimensions of the emission aperture. 67 Guharay et al 66 have operated Penning plasma ion source in pulsed mode and have obtained negative ion beams with a reduced brightness of 10 5 A/m 2 Sr V with an energy spread of ϳ3 eV. This brightness is about three to four orders of magnitude higher than typical values for dc beams from duoplasmatron sources.…”

“…The two types of plasma ion sources known as the Penning type [66][67][68][69][70][71][72][73][74][75] and the multicusp type [76][77][78][79][80][81][82][83][84][85][86][87] have been widely studied for focused beam applications. We will discuss these plasma ion sources and compare them with the LMIS.…”

Performance of multicusp plasma ion source for focused ion beam applications

“…The main issue with these sources is that of low source brightness. Recent work by Guharay et al on the use of a Penning type ion source 4 have indeed revealed an image-side brightness of 10 3 A/cm 2 sr ͑for the whole beam, at 10 keV͒ and 1 eV energy spread. This is due to the large virtual source size.…”

A high brightness source for nano-probe secondary ion mass spectrometry

“…With argon a maximum reduced brightness of 10 3 A m À2 sr À1 V À1 with DE = 4.5 eV has been achieved [18], while with H À a pulsed (1% duty factor) brightness of 7 Â 10 4 A m À2 sr À1 V À1 and an energy spread of 3 eV were possible, however, the time averaged reduced brightness is still only 700 A m À2 sr À1 V À1 . For O À , Guharay reports a factor of 4 reduction in brightness over H À [19], resulting in a time averaged brightness of only 175 A m À2 sr À1 V À1 .…”