Medium Current Implanter Research Articles

Beam shape control system by machine learning on the NISSIN BeyEX medium current ion implanter

Beam shape control system by machine learning on the NISSIN BeyEX medium current ion implanter

Charging Phenomena During Medium Current Ion Implantation of Carbonized Photo-Resist Surface Layers

Charging phenomenon caused by ion implantation into the photo-resist has been evaluated with use of a surface potential measurement tool to clarify the mechanism of burst-like discharge of the accumulated charge in medium current implantation machines. The molecular bond of the photo-resist is cleaved by the kinetic energy of the implanted impurity ions selectively at the portion of the smallest bond energy, and cross-linking develops from this point. Bond breaking and cross-linking is accompanied by out-gassing of hydrogen released by collisions with the dopant atom and recoil cascade atoms. Finally, a carbon-rich layer with low resistance is formed on the photo-resist surface. When arsenic ions are implanted, the degraded layer of low resistance including the carbonization is being formed even under low dose (1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> or less) conditions. This is called the medium current charging phenomenon with a current of a few hundred μA. The charges are accumulated on the photo-resist, until the low resistance layer is formed on the surface of the photo-resist. When the induced voltage reaches a critical value, they rush into the open area through the layer. As a result, an explosive local melting of silicon occurs, with the critical value depending on the mask-pattern arrangement.

Charging control on high energy implanters: A process requirement demonstrated by plasma damage monitoring

Charging phenomena is one of the main problems faced in ion implantation. Anti-charging system such as plasma flood gun (PFG) are currently running on high current and medium current implanters to reduce potential charging damage on device structures. However, in a conventional production line, high energy implantation steps are still often used without any charge compensation technique. Faced with micro-arcing defects detected after Well implantation steps on production lots, we have clearly demonstrated that the defectivity issue was eradicated by enabling the PFG system on the VIISta3000 high energy implanter. In addition we have investigated charging as a function of PFG properties by plasma damage monitoring (PDM) and proved that voltages developed on oxidized wafers processed on the VIISta3000 were not insignificant.

Verification and reduction of surface charging during high/medium current implantations by implementing plasma damage monitoring

Dielectric charging damage during IC processing is the result of complex interactions between the wafer environment and the wafer itself. Understanding these interactions and recognizing the relative importance of the different mechanisms capable of causing damage, is essential for successful diagnosis and control of charging damage during wafer manufacturing. Avoiding gate oxide damage due to excessive wafer charging has always been an issue with high current implanters. Whether it is caused by shrinking of device dimensions, or its use as a backup for high current applications, charging level awareness becomes the primary limiting factor for running higher beam currents in medium current implanters. Flooding the wafer with low energy electrons from a plasma flood gun (PFG) which is a self-regulated electron shower, has been the widely accepted means of reducing wafer charging. The effectiveness of the PFG in reducing charging as a function of primary ion current, voltage of electron extraction from the PFG, ion beam positioning and other parameters in a beam path to the wafer have been investigated. This investigation was carried out on medium and high current implanters, VIISta 810HP and VIIStaHC respectively, using the plasma damage monitoring (PDM) technique on metrology tool FAaST350.

Characterization and simulation studies on high tilt ion implantation for precision halo implant applications

Precision dopant placement at high tilt angles for halo applications is required in the fabrication of advanced devices to achieve better transistor characteristics, such as suppression of short channel effects, Vt control and drive current. However, monitoring high tilt implants is not popular in semiconductor fabs, even though most have started monitoring zero-tilt implants in the recent couple of years. In this paper, the authors explore the possibilities of using high tilt angles with higher Miller Index channels. As an example, axial channeling along the 〈112〉 direction is used to evaluate the angle control performance of the VIISta 810EHP medium current ion implanter. Crystal-TRIM (a Monte Carlo simulation code) calculations are compared with experimental SIMS (Secondary Ion Mass Spectrometry) profiles. In addition, the effects of wafer orientation on the platen and wafer mis-cut on the dopant profiles are discussed. Metrology characterization, such as ThermaWaveTM and SIMS, of the 〈112〉 ion channeling is presented.

Investigations into the wear of a WL10 ion source

WL10 is an alloy of tungsten and 1% La2O3. It combines the advantages of pure tungsten, such as chemical resistance and the high melting point, with a significantly improved machinability. Unlike molybdenum, tungsten and lanthanum show no mass interferences for BF2 implants.In this paper, the wear of a WL10 ion source during operation with BF3 and argon in a Varian 350 D medium current implanter is studied and compared to the wear of a molybdenum and a graphite ion source, respectively.Considering the weight loss and the broadening of the extraction slit, the WL10 ion source showed a slightly better wear behavior than the molybdenum ion source. The wear of the graphite ion source was only slightly higher than that of the WL10 and the molybdenum ion source. However, since graphite showed the strongest reactions during BF3 operation, it is difficult to compare the results.

90 nm device validation of the use of a single-wafer, high-current implanter for high tilt halo implants

As CMOS device dimensions shrink, the depths of the halo regions are shrinking and the implant doses used to form these regions are increasing to minimize short-channel effects. Shallow implant depths require lower implant energies, so the beam currents and wafer throughputs on the traditionally used medium-current implanters are starting to drop and become a concern for device manufacturers. In addition, halo implants are typically performed with a high tilt angle of 20–30° and require tight angle control. All of these requirements are leading to increased interest in use of single-wafer, high-current implanters for halo implants. This paper reports the results of a study where 90nm CMOS transistors had halo implants performed on the Applied Materials’ Quantum® X implanter. A comparison with device wafers whose halos were implanted on a medium-current implanter was also conducted. In addition, the sensitivity of the device parameters to the implant dose and angle was evaluated.

Cathodoluminescence and electron field emission of boron-doped a-C:N films

The optical and electrical properties of so-called carbon nitride films (a-C:N) and boron doped so-called carbon nitride films (a-C:N:B) are studied with cathodoluminescence (CL) spectroscopy and electron field emission measurement. The a-C:N films were first deposited on Si by a filtered cathodic arc plasma system, and then boron ions (∼1 × 10 16 cm −2) were implanted into the a-C:N films to form a-C:N:B films by a medium current implanter. The structural and morphological properties of a-C:N and a-C:N:B films were then analyzed using secondary ion mass spectrometer, X-ray photoelectron spectroscopy, FT-IR spectra, Raman spectroscopy and atomic force microscopy. The a-C:N film exhibits luminescence of blue light (∼2.67 eV) and red light (∼1.91 eV), and the a-C:N:B film displays luminescence of blue light (∼2.67 eV) in CL spectra measured at 300 K. Furthermore, the incorporated boron atoms change the electron field emission property, which shows a higher turn on field for the a-C:N:B film (3.6 V/μm) than that for the a-C:N film (2.8 V/μm).

Metals contamination in high and medium current implanters

As +, 80 keV implants at specification beam currents were conducted on both the Varian E1000 and E220/E500 implanters to study metals contamination. The E1000 was configured with a silicon coated disc and spill-over cup and a newly designed low particulate acceleration column, with a graphite entrance collimator and a graphite exit electrode. The E220/E500 was configured with a metals reduction kit and, in one implant, with an experimental silicon coated acceleration tube. TXRF and SIMS measurements were performed on the implanted wafers. A TRIM based approximation was developed to analyze the aluminum contamination of 132 ppm, all of which was non-energetic. On the E220.2500 with the metals reduction kit the value was 91 ppm, with some energetic contribution. When the experimental silicon coated electrode acceleration tube was studied the energetic contribution was eliminated. TXRF measurements for Ti, Cr, Fe, Ni, Cu, and Zn indicated little or no added contribution from these metals for both implanter types as compared to an unimplanted reference wafer.

Negative-ion implantation technique

Negative-ion implantation is a promising technique for charging-free implantation for the forthcoming ULSI fabrication, in which the water charging by positive-ion implantation will become a troublesome problem even with an electron shower. The negative-ion implantation technique remarkably ameliorates such a charging problem since the incoming negative charge of implanted negative ions is easily balanced by the outgoing negative charge of a part of secondary electrons. Thus, the surface charging voltage is maintained to within about ± 10 V for isolated conducting materials and insulators, and is free from space and time fluctuations. A high-current negative-ion source and a medium current negative-ion implanter developed for this technique are described with the design concepts. In addition, the fundamental measurements of interactions between the negative-ion beam and the gas/solid are also described.

Using a wedge oxide to monitor low energy beam purity by means of therma-wave measurements in the Eaton NV-8200P ion implanter

A technique using a Therma-Wave Therma-Probe has been developed which allows the possibility of the detection of parts per million levels of high energy contaminants in low energy beams [C. Jaussaud et al., Nucl. Instr. and Meth. B 74 (1993) 571]. This technique relies on the differential hold up of the desired (low energy) and contaminant (high energy) ions in a screen oxide. In this study we have extended this technique by using a wedge oxide, varying from 0 to 1700 Å as the hold-up oxide. This approach, instead of using a single oxide thickness across the wafer, makes possible the empirical determination of the exact oxide thickness required to completely trap the desired energy ions while at the same time allowing the maximum number of contaminant ions to pass through the oxide and produce a Therma-Wave signal in the underlying silicon. Using an Eaton NV-8200P medium current implanter, we implanted a 2 × 10 15 ions/cm 2 dose of boron at 3 and 10 keV and BF 2 at 13.36 and 44.55 keV. We then compared these Therma-Wave values to the Therma-Wave values produced by reference “contaminant” boron implants, on other wafers, at 15 and 40 keV. These measurements indicate that the wedge oxide allows for the determination of the energetic purity of the beam at less than or equal to the 5–10 ppm level.

Negative-Ion Implantation

AbstractNegative-ion implantation is a promising technique for forthcoming ULSI (more than 256 M bits) fabrication and TFT (for color LCD) fabrication, since the surface charging voltage of insulated electrodes or insulators implanted by negative ions is found to saturate within so few as several volts, no breakdown of insulators would be expected without a charge neutralizer in these fabrication processes. Scatter-less negative-ion implantation into powders is also possible. For this purpose an rf-plasma-sputter type heavy negative-ion source was developed, which can deliver several milliamperes of various kinds of negative ion currents such as boron, phosphor, silicon, carbon, copper, oxygen, etc. A medium current negative-ion implanter with a small version of this type of ion source has been developed.

Redistributed of Fe, Cr and Mo in buried oxide silicon-on-insulator structures during high-temperature furnace annealing

Traces of transition metals (Fe, Cr and Mo) were inadvertently introduced into buried oxide silicon-on-insulator structures during oxygen implantation in a medium current implanter. The redistribution of these metal impurities during post-implantation annealing between 900 and 1300 degrees C was studied by secondary-ion mass spectroscopy. The microstructure of the as-implanted and annealed specimens was characterized by transmission electron microscopy (cross-sectional and plan view). Auger electron spectroscopy was used to investigate the oxygen depth profiles. A correlation is shown between the density and depth distribution of Fe, Cr and Mo and the microstructural changes that occur upon annealing. The redistribution of Fe and Cr was found to be strongly influenced by damage recovery whereas Mo remained immobile during heat-treatment. These results are discussed on the basis of diffusion mechanisms, radiation-enhanced diffusion, supersaturation of silicon interstitials, surface segregation, metal impurity precipitation and dislocation trapping.

Progress report on Aramis, the 2 MV tandem at Orsay

Aramis is a home built multipurpose 2 MV electrostatic tandem accelerator. A large variety of ions are available for high energy implantation. Characterization possibilities are also quite large in the Van de Graaff mode owing to the Penning positive ion source in the terminal. A second beam line is now available that sends the beam into the target chamber of the 200 kV medium current implanter. We will provide a progress report on the machine and present some results regarding in situ studies of multilayer mixing and implanted silicide layers

Annealing behaviors of residual defects in high-dose BF +2-implanted (001)Si under different implantation conditions

The annealing behavior of residual defects in high-dose BF + 2-implanted (001)Si under different implantation conditions has been studied by cross-sectional transmission electron microscopy and four-point probe sheet resistance measurements. Three kinds of samples were prepared with different implanters. M, MC and H samples were implanted with 80 keV, 4×10 15/cm 2 BF + 2 in a medium-current implanter without deliberate end-station cooling, a medium-current implanter with a freon-cooled end station, and a high-current implanter with a water-cooled end station, respectively. The BF + 2 ion dissociation effects were revealed by the comparison of M or MC and H samples. Rod-like and equi-axial dislocation loops beneath the original a/c interface were observed in the M and MC samples. The dopant activation of the annealed samples was found to correlate well with microstructural changes.

A survey of implant particulate process control and yield effects

This paper is a review of current work to improve particulate control in ion implantation equipment. The first section includes current published research work which will be outlined and summarized. The second section focusses on work performed at National Semiconductor Corporation on testing and implementing an in situ particle monitoring system. The first equipment test consisted of a single monitor mounted in a medium current implanter. This test indicated that the particle signal correlated to surface scan monitor tests and that operating characteristics of the ion implanters which produce particles were observable. Our followup effort was an implementation of the in situ counters on all the implanters as a single particle counting system for the fab. The result of this work was a pareto-like analysis of machine and process issues which result in particle events. A correlation of lot-specific particle counts to yield was also developed. The advances in machine particulate control are contrasted with the needs and trends in process development. Although the advances in particulate control have been excellent, the predicted future requirements are even more stringent. The implications of these needs on both particulate performance and measurement are discussed.

Mechanically scanned ion implanters with two-axis disk tilt capability

New techniques for high-density circuit integration require parallel scanning in combination with the ability to reposition the circuit devices during implantation. A new family of high- and medium-current implanters utilizing a common end-station concept has been developed in a cooperative effort of design groups in Japan, Massachusetts and Texas. The new family utilizes rotating-disk, mechanically scanned batch processing with vacuum-lock wafer loading and unloading. A small, high-speed robot performs the in-air handling associated with loading the vacuum lock. The disk has a gimbal mount which permits two-axis tilting of the disk during implantation. Construction details and process capabilities of this implanter family are described and discussed.

Benefits of real-time, in situ particle monitoring in production medium current implantation : Peter G. Borden and Lawrence A. Larson. IEEE Trans. Semiconductor Mfg2(4), 141 (1989)

Benefits of real-time, in situ particle monitoring in production medium current implantation : Peter G. Borden and Lawrence A. Larson. IEEE Trans. Semiconductor Mfg2(4), 141 (1989)

A comparison of batch and single wafer high dose arsenic ion implantation techniques

High dose, low energy (4×10 15 cm −2 at 15 keV) arsenic ion implantation into silicon was performed in batch and single wafer mode using medium and high current ion implanters. An investigation of implanted and annealed samples by Rutherford backscattering (RBS), transmission electron microscopy (TEM), thermal wave technique, and sheet resistance mapping showed little to no difference of arsenic profiles and residual damage between batch and single wafer implantation conditions when the sample temperature during implantation was kept below 120° C.

Production implanter Nissin NH-20SR

A new medium current ion implanter, Nissin NH-20SR, has been developed. The NH-20SR provides novel mechanisms such as a spinning platen and variable tilt angle mechanism (VTAM). The spinning platen's maximum rotation speed is 2 rps and it provides both smooth and stepwise motion. VTAM's angle span is from 0° to 60° and changing its tilt angle stepwise during implantation is possible with a minimum step angle of 1°. These mechanisms have made it possible to implant into trench sidewalls, to suppress channeling effects, and to improve dose uniformity as well as asymmetrical electric characteristics of MOS transistors.