High Current Ion Implantation System Research Articles

Tuning for optimal performance in angle control, uniformity, and energy purity

Advances in reducing the sizes of device structures and line widths place increasing demands on the accuracy of dopant placement and the control of dopant motion during activation anneals. Serial process high current ion implantation systems seek to produce beams in which the angles are controlled to high precision avoiding the angles introduced by conical structures used for holding wafers on spinning discs in batch systems. However, ion optical corrections and control of incident beam angle, dose uniformity, high throughput and energy purity often present apparently contradictory requirements in machine design. Data is presented to illustrate that tuning procedures can be used to simultaneously optimize angle purity in both x and y planes as well as control energy purity and dose uniformity.

Performance characteristics of the NV-20A high current ion implantation system

High current ion implantation systems are now widely used in the manufacture of VLSI and ULSI devices. As device designs become more complex and diverse, the demand for tighter process control in the implanter also increases. Sensitivity to subtle contamination levels, particles, charging stress, energy variations, and other undiscovered causes continue to emerge as temporary limitations to device manufacturing technology. Continuous improvement programs are now a way of life for the equipment supplier. The large parameter space requiring evaluation and the limitations of much of today's metrology require that sophisticated statistical techniques be utilized in designing experiments and analyzing the results. This paper summarizes the process and performance measurements taken as part of a continuous improvement program for the Baton NV-20A high current implantation system. The results of designed experiments and the subsequent equipment and process modifications are presented for the following areas: dose control, wafer charging, cross contamination, and equipment reliability.

Pressure compensated dose control in high current ion implantation systems

High power ion implantation into photoresist coated wafers poses special problems for the process engineer. As the incoming ion enters the photoresist layer, molecules and atoms from the photoresist are liberated and become part of the background gas through which the ion beam must travel. Subsequent atomic collisions between the background gas atoms and the beam ions result in some degree of neutral beam flux which cannot be measured by conventional faraday systems. The Baton high current ion implantation systems utilize faradays to measure beam current and ion gauges to measure pressure simultaneously. The beam current and pressure measurements are combined to provide a means of estimating the degree of neutral particle flux and controlling dose rate based on these measurements. This paper describes the pressure compensated dose control concept, presents procedures for optimizing the control, and presents typical performance results.

Control of ion beam current density and profile for high current ion implantation systems

One solution for the problems of the local temperature increase and the charge-up of a wafer during high current ion implantation is to decrease the beam current density while maintaining the total beam current necessary on the wafer. To solve these problems, a method, that maintains the beam spatial profile on a wafer by controlling the normalized perveance and the pole face angle of the analyzing magnet for various beam currents, has been developed experimentally. As a result, under the experimental conditions of 1 to 8 mA of 35 keV As +, the beam uniformity, defined as [average current density]/[maximum current density], became more than 0.2 and the beam profile on the wafer was maintained by using a suitable value of the perveance.

A high-current ion implanter system

The important issues in the design and development of the Eaton NV20A high-current ion implantation system are discussed. The control system is based on a Sun Microsystems workstation connected through an Ethernet to a multiprocessor controller. The software is based on an object-oriented environment with a layered operator interface design. An adaptive robotics-based wafer handling system, and clampless wafer holding allow for high throughput with good particulate performance. The modular design of the beam optics add to system versatility.

Advances in the Extrion 1000 and XP Series high-current ion implantation systems

During the past decade, ion implantation systems have evolved from labor-intense, novel machines in the manufacturing environment to automatic, highly productive manufacturing tools. Performance advances have been made in several areas: wafer charging, high-energy operation, BF 2 + dissociation, reliability and automation of the machine and information transfer to the host computer. The changes and improvements in these areas are discussed for the Varian High Current XP Series and the EXTRION 1000 ion implantation systems.

The Extrion 1000: A new high current ion implantation system for automated fabrication environments and intelligent process control

The next generation of ion implantation systems will require new techniques for intelligent process control while satisfying the increasing need for high reliability and serviceability. The Extrion 1000, a new Varian batch process ion implantation system designed to address these needs, is described. The new implanter features extensive real time process monitoring capability, failure prediction technology, wide dynamic range, and rapid changeover between processes requiring different implant angles or wafer sizes. Adaptive control techniques are used within the framework of an automated fabrication environment to assure high yield and throughput.

Ion beam system for the new high current ion implantation system Extrion-1000

To meet the challenging performance requirements of next generation high current ion implanters, several new technologies have been developed for the ion beam system of the new Varian high current ion implanter, Extrion-1000. A novel strong focussing accel/decel scheme with a new ion source guarantees high beam output even down to very low energies. Its multiple crucible vaporizer is based on a new concept and allows easy maintenance, longer lifetime, improved time response and rapid species change. Great care was taken in the design of the vacuum system to provide appropriately low pressures at critical points ensuring high beam purity and high dosimetry accuracy.

New method of solid state wafer cooling in the Extrion 1000 high current ion implantation system

A new method of wafer cooling during implantation has been developed which meets the process needs of the 1990s. Cooling levels four times better than existing gas cooling techniques are achieved in a clampless, low stress system designed for high beam power. A new antistick technology is described which reduces particle contaminations and wafer breakage.

The NV-10SD high-current ion implantation system

NV-10SD is a high-current ion implantation system newly developed to satisfy recent VLSI process requirements. The particulate increase during processing is less than 20 particles per 6 in. wafer (larger than 0.28 μm). The guaranteed throughput of the system is more than 220 6 in. wafers/hour for a 1 × 10 15 ions/cm 2 dose, and 80 6 in. wafers/hour for a 1 × 10 16 ions/cm 2 dose. The maximum wafer temperature during a 160 keV, 15 mA (2400 W), 1 × 10 16 ions/cm 2 dose implantation is less than 100 ° C. The guaranteed beam current above 40 keV is more than 15 mA for phosphorus and arsenic and 1.8 mA for 10 keV boron. The system incorporates a new cylindrical target electron shower gun system. The shower reduces the voltage built up on the wafers to a level with very few charging-induced pattern failures. The system also has a machine automation controller which is capable of auto beam setup and tuning, process monitoring, host communication and remote control. Thus, the NV-10SD is fully compatible with no-operator process lines.

XP series high current ion implantation systems for up to 200 mm wafer processing

VLSI and ULSI integrated circuit designs and 200 mm wafers are reaching pilot production and production applications. The resulting process compatibility and production cost-effectiveness issues have led Varian/Extrion to develop a new family of high current, batch process ion implantation systems. The “XP” extra performance series of 80, 120 and 160 kV systems meet these market needs. Equipment has been designed and process evaluations are reported in this publication. The issues of gentle wafer handling, automation, wafer charge control, dopant uniformity, particulate contamination, process flexibility, ion source advances, and equipment reliability are reviewed.

Improvements in dose uniformity on high current ion implantation systems

A summary of the work done to improve the uniformity and repeatability of the model 160-10 ion implanter to a point where results routinely show ≤ 0.75% is given. The customization of the ion beam scan speed, as it traverses the disc containing product, has been shown to yield repeatable uniformity for all wafer sizes up to 200 mm. The use of customized scan maps not only applies to subtle machine to machine differences, but also applies to process changes such as species, wide beam current, energy and dose ranges and spot size changes due to wafer outgassing effects.

A new computer designed faraday system for high current ion implantation systems

This paper will describe a new Faraday/flood gun system which has been designed for use on Varian duel end station batch process ion implanters. This system provides improved beam profile control through reduction in the extent of the deneutralized region, increases the pumping conductance at the wafer surface and permits the incorporation of a number of improvements addressing system reliability and particulate generation. A new biasing arrangement and improved flood gun optics provide increased levels of lower energy flooding electrons for enhanced compatibility with the thinner gate oxides used in VLSI device structures.

The Veeco 4840 automated implant system

Veeco has developed a new, 150 keV, computer automated, high current ion implantation system. This paper describes the system in overview, with emphasis on the technology behind its special features: a solid boron source, a charge neutralizer, automatic beam control, and extended energy range.

Intelligent performance optimization for a fully automatic high current ion implantation system

A major concern in the ion implantation industry today is the automation of ion implantation systems. Most importantly, automation provides improved day-to-day process repeatability and uniformity and product yield by eliminating the human error factor from machine setup, beam optimization and system operation during implant setup. This paper describes the methods used for the Varian/Extrion Model 160XP High Current Ion Implanter to automate functions previously requiring human intervention. These functions include machine startup, machine shutdown, implant setup procedures involving changes in accel mode, beam energy, and species, and intelligent, real-time optimization of the ion beam.

A high-energy, high-current ion implantation system

High current (Pre-Dep TM) ion implanters, operating at 80 keV, have met a need in the semiconductor industry. For certain processes, higher energies are required, either to penetrate a surface layer or to place the dopant ion at a greater depth. The Eaton/Nova Model NV10-160 Pre-Dep TM Ion Implanter has been developed to meet those special needs. Beam currents as high as 10.0 mA are available at energies up to 160 keV for routine production applications. The system has also been qualified for low current, low dose operation (10 11 ions cm −2) and this unique versatility provides the Process and Equipment Engineers with a powerful new tool. The Model NV10-160 also utilizes the Nova-designed, double disk interchange processing system to minimize inactive beam time so that wafer throughputs, up to 300 wafers/h, are achievable on a routine basis. Datalock TM, a computer driven implant monitoring system and AT-4, the Nova cassette-to-cassette wafer loader, are available as standard options. As a production machine, the Model NV10-160 with its high throughput capability, will reduce the implant cost per wafer significantly for doses above 10 × 10 15 ions/cm 2. Performance patterns are now emerging as some twenty-five systems have now been shipped. This paper summarizes the more important characteristics and reviews the major design features of the NV10-160.

Control techniques for a high current ion implantation system

The techniques used to remotely set up the source and steer the beam of a high current ion implantation system are presented.

Low cost molecular ion implantation equipment

A low cost, high current ion implantation system is described which includes fast annealing by laser induced surface melting. The implant machine is very simple, 20 cm in length and consists of an ion source with glow discharge in a gas atmosphere containing the dopant. No mass separation is used and the high density beam (1 mA/cm 2) consists of both atomic and molecular ions. Applications of this system are in the field of large area silicon solar cells.

Applications of Magnetic Scanning to High Current Implantation

High current ion implantation systems employing beams of 75As+ at 10 mA or more at energies of the order of 100 keV depend upon electron space charge neutralization to preserve the ion optical quality of the beam during transport from the source to the wafer implant location. Time varying magnetic fields have been used to deflect these beams over lateral dimensions up to 300 mm at frequencies of the order of 0.1 Hz, without affecting low energy electrons trapped in the potential well of the beam, and without significant modification of the ion beam shape. Hybrid magnetic-mechanical scanning of high current ion beams has been shown to be capable of averaging the implanted dose with uniformities as good as 2? < 1% across 100 mm diameter silicon wafers mounted on an 0.8 meter disc rotating in vacuum at 1000 r.p.m. The physical basis of angle corrected hybrid magnetic-mechanical scanning is analyzed leading to a calculated relationship for the deflection (X) dependent on the scanner magnetic field (Bs). This functional dependence X = f(Bs) has also been measured using the disc as a rotating beam profile monitor. From the measured dependence, implant dose uniformity across a long scan can be obtained as shown by sheet resistance maps of ion implanted wafers. The dependence of dose uniformity on the number of scans has also been evaluated, and data is presented illustrating uniformity 2? < 2% can be achieved using a single scan across the wafer.

A new method to monitor the beam profile in high-current ion implantation systems

By the use of silicon on sapphire (SOS) wafers described the disadvantages of methods used previously (Faraday cups of hydrocarbon foils) can be avoided. If properly annealed, the SOS wafers can be used repeatedly.