John P. O'Connor

Energy and mass analysis of secondary ions sputtered from metallic targets by MeV heavy ions

Abstract The success of heavy ion induced desorption mass spectrometry and the discovery of anomalously high sputtering yields in some dielectric substances underscore the need for a more complete understanding of the interaction of MeV heavy ions with surfaces. Here, we report initial results of a study of the interaction of MeV ions with the surfaces of elemental metallic targets. Secondary ion mass and energy spectra have been measured for Cu, Nb, and Ta targets bombarded by 75 MeV 79 Br 8+ ions. Sputtered metal ions and surface contaminants have been observed. The energies of the emitted ions are, on average, lower than for keV ion bombardment.

An analysis of vacuum effects on ion implanter performance

Abstract The generation of an ion beam and its impact into photoresist-masked wafers will have an adverse effect on the vacuum of an ion implanter. This is particularly significant when doping with boron using BF 3 or BCl 3 as the source feed material. As well as affecting high voltage performance, poor vacuum will allow charge exchange and partial neutralization of the ion beam which could cause energy contamination as well as dosimetry errors. The nature of these effects depends not only on the system design but also on the implanted species and its charge state and energy. This paper discusses these effects on ion implanter performance and shows how a matrix-based general vacuum model may be used to investigate vacuum integrity. A time-dependent vacuum model that simulates the effect of pressure on dosimetry is also described.

Total sputtering yield of Nb bombarded by MeV heavy ions

Abstract The angular distribution and total yield of atoms sputtered from polycrystalline Nb by 70 MeV 79 Br 7+ ions have been measured. For comparison, measurements have also been made using 100 keV 40 Ar + and 100 keV 79 Br + projectiles. Targets were sputtered in ultra-high vacuum and sputtered material was collected on cylindrical AI foils. The areal density of collected material was subsequently determined by Rutherford backscattering using 850 keV 4 He + and 15 MeV 16 O 3+ incident ions. The low energy results were consistent with previous measurements in this energy regime where collision cascades are the dominant sputtering mechanism. For the 70 MeV Br irradiation, we measured a total yield, Y = 0.14, which is also consistent with a collisional description of the sputtering process.

A comparison of secondary ion emission from polycrystalline metals under MeV and keV heavy ion bombardment

Abstract Mass spectra of positive secondary ions emitted from polycrystalline metal targets bombarded by 70 MeV 79Br7+ and 100 keV 40ar+ ions have been measured under similar conditions in order to identify changes which may be attributed to the increased energy of the projectile. Presented here are results obtained from Al, Ti, V, and Ni foils. A significant enhancement of some low-mass target constituents relative to the atomic metal ions is observed with MeV ion bombardment. Most prominent is the increase in abundance of 16O+ secondary ions.

Performance characteristics of the Genus Inc. 1510 high energy ion implantation system

Abstract The Genus IX-1500 ion implantation system has been developed to meet the needs of users requiring low and medium dose implants from 40 to 3000 keV. A review of the performance characteristics of the system with respect to key parameters such as beam current, beam stability, dose uniformity, implant profiles, wafer throughput, particle performance, ease of operation and maintainability are presented from a users point of view.

The beam performance of the Genus G-1500 ion implanter

Abstract The current ion beam performance of the Genus G-1500 MeV ion implanter is described in this paper. Substantial improvements of beam currents have been realized by modification of the hot-cathode PIG source used on the ion implanter. Approximately 250 μA of 11 B − and 1100 μA of 31 P − are routinely achieved at the injector Faraday cup of the G-1500 system. Typical maximum beam currents of boron and phosphorus on target are ~ 110 μA and ~ 350 μA, respectively. Recent results of acceleration of carbon, oxygen and silicon are also described. Finally, the result of unique neutral-hydrogen-molecule injection into the tandem accelerator to obtain H + on the target is given in this paper.

The use of negative ions to enhance beam currents at low energies in an MeV ion implanter

Abstract Since the introduction of the G1500 ion implanter, the use of tandem accelerators in production ion implantation systems has become well established. However, the beam currents which are attainable at present at low energies (

A high current injector for tandem accelerators

Abstract Tandem accelerators have been employed for ion implantation in the semiconductor industry. The advantages of tandem acceleration, such as reliability and simplicity, are well known. The limitations of these systems until the present have been beam current related. Tests of a new negative ion injector system based on charge exchange have shown its applicability in production MeV ion implantation systems. With a Na vapor charge exchange canal, measurements using mA beams of 45 keV 11 B + , 31 P + , and 75 As + projectiles have yielded negative equilibrium charge state fractions of 10, 21, and 15%, respectively. In conjunction with a high current positive ion source, several hundred μA of B − and > 1 mA of P − and As − may be produced. The increase in the angular divergence of the ion beams due to multiple scattering in the Na vapor has been found to be minimal.

A comparison of secondary ion mass spectra from keV and MeV ion bombarded vanadium, niobium and copper☆

Abstract Positive secondary ion mass spectra have been measured from stainless steel, copper, niobium, and vanadium targets bombarded by 70 MeV 79 Br 7+ and 100 keV 40 Ar + ions using a modified quadrupole residual gas analyzer. Additional spectra have also been measured from the vanadium target for a number of 79 Br and 40 Ar projectile energies from 25 keV up to 5 MeV. As has been previously reported [13], under MeV ion bombardment there is an enhancement in the yield of positive ions of electronegative trace constituents relative to the yield of singly charged metal substrate ions. These data suggest that projectiles capable of large inelastic energy deposition may induce secondary ion emission by a mechanism whose contribution to the total ion yield is insignificant or absent when the projectile energy is limited to a few keV. The similarity of these data to recent results in electron- and photon-stimulated desorption is noted.

Secondary ion emission from oxidized vanadium as a function of projectile energy in the range 10–90 MeV

Abstract The intensity of secondary ion emission from oxidized V bombarded by 10–90 MeV 79 Br projectiles has been measured. The intensity of V + ion emission was proportional to the nuclear stopping cross section for Br in V indicating that these ions were produced as a consequence of a collision cascade. However, I (O + ) and I (F + ) were approximately constant across the projectile energy range demonstrating that those ions were produced by a different mechanism. The variation of I (VO + ) with projectile energy was intermediate between that of I (V + ) and I (O + ). Possible mechanisms for the production of the O + and F + secondary ions are discussed.