Ion beam scanning control methods and systems for ion implantation uniformity

Abstract

Methods are provided for calibrating an ion beam scanner in an ion implantation system, comprising measuring a plurality of initial current density values at a plurality of locations along a scan direction, where the values individually correspond to one of a plurality of initial voltage scan intervals and one of a corresponding plurality of initial scan time values, creating a system of linear equations based on the measured initial current density values and the initial voltage scan intervals, and determining a set of scan time values that correspond to a solution to the system of linear equations that reduces current density profile deviations. A calibration system is provided for calibrating an ion beam scanner in an ion implantation system, comprising a dosimetry system and a control system.

Description

FIELD OF THE INVENTION [0001] The present invention relates generally to ion implantation systems, and more specifically to improved systems and methods for uniformly scanning ion beams across a workpiece. BACKGROUND OF THE INVENTION [0002] In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n-type extrinsic material wafers, and implanting materials such as boron, gallium or indium creates p-type extrinsic material portions in a semiconductor wafer. [0003]FIG. 1A...

AI Technical Summary

Benefits of technology

[0017] The present invention relates to systems and methods for calibrating an ion beam scanner in an ion implantation system, in which the current density contributions of multiple scanner voltage intervals are individually measured for multiple profile points along a beam scan direction to generate a system of linear equations, and a set of scan time values are computed for the voltage scan intervals corresponding to a solution that reduces current density profile deviations. Unlike conventional point-to-point calibration techniques, the invention provides compensation for implant contributions produced by the beam some distance from the beam center, and is thus particularly suitable for use in low energy ion implanters having relatively wide beams and / or in situations where the lateral beam width varies along the scan direction to provide uniform implantation across a workpiece surface. In addition, the invention may be employed to reduce excess overscan, thereby improving system scan efficiency without sacrificing implant uniformity.

[0019] Another aspect of the invention provides a calibration system for calibrating an ion beam scanner in an ion implantation system. The calibration system comprises a dosimetry system and a control system operably coupled with the dosimetry system and a power supply associated with a beam scanner, where the dosimetry system measures a plurality of initial current density values at a plurality of locations along a scan direction in a workpiece location of an ion implantation system. The control system causes the scanner to scan an ion beam across the workpiece location of the ion implantation system in the scan direction according to an initial set of voltage scan intervals and corresponding scan time values so that the dosimetry system can measure a plurality of initial current density values at the plurality of locations along the scan direction in a workpiece location of an ion implantation system, where the initial current density values individually correspond to one of the plurality of initial voltage scan intervals and to one of the corresponding plurality of initial scan time values. The control system is further operable to create a system of linear equations based on the measured initial current density values and the initial scan time values, and to determine a set of scan time values for the voltage scan intervals corresponding to a solution to the system of linear equations that reduces current density profile deviations.

Problems solved by technology

Conversely, high current, low energy ion beams 24 are typically employed for high dose, shallow depth ion implantation, in which case the lower energy of the ions commonly causes difficulties in maintaining convergence of the ion beam 24.

Although the conventional point-to-point scanner calibration techniques may be adequate where the width of the ion beam 24 is narrow and the beam width is relatively constant across the target area, these techniques are less suitable in the case of wider beams 24 and / or in situations where the beam width varies along the scan direction, as in the example of FIGS. 1F-1J.

In particular, if the beam 24 is wide and / or variable across the target area, the point-to-point technique fails to account for the workpiece dose produced by the beam some distance from the beam center.

This situation is particularly problematic with low energy ion beams 24 that experience space charge expansion (e.g., lateral divergence in the scan or X direction).

However, the time that the scanned beam 24 spends outside the target area is essentially wasted, and detracts from the system scan efficiency, defined as the time spent on the target workpiece 30 divided by the total scan time.

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