Ion implantation is an important process in semiconductor/microelectronic manufacturing. The ion implantation process is used in integrated circuit fabrication to introduce controlled amounts of dopant ions into semiconductor wafers. An ion-source is used to generate a well-defined ion beam for a variety of ion species from a dopant gas. Ionization of the dopant gas generates the ion species which can be subsequently implanted into a given workpiece.
Carbon has emerged as a widely used dopant in the semiconductor industry for a variety of material modification applications such as inhibiting diffusion of co-dopants or enhancing stability of the doped region. In this regard, carbon dioxide (CO2) and carbon monoxide (CO) are two commonly used dopant gas sources for carbon implantation. However, CO2 and CO are prone to accumulation of deposits along surfaces of the ion chamber. Additional deposits can form along surfaces of electrodes of the ion source apparatus. The deposits may form directly from the dopant gas or from interaction of the dopant gas and/or its ionization product with the chamber components.
Such deposit formation is problematic. Deposits along surfaces of the electrodes of an ion implantation system create conditions susceptible to energetic high voltage discharge. Voltage discharge results in momentary drops in the beam current, commonly referred to as “beam glitching”. Deposits on the extraction aperture degrade the beam uniformity and hence the uniformity of dopant levels in the doped region. Beam uniformity and the number of beam glitches (i.e., glitch rate) during the operation of an ion source can be key metrics for the performance of an ion implantation system, such as, for example, a ribbon beam ion implantation system as commonly known in the art.
Based on the process sensitivity, there may be an upper threshold to the glitch rate and/or beam non-uniformity beyond which the implant process cannot operate with acceptable efficiency. In the event the ion source performance degrades beyond the upper threshold, the user must stop the implant operation and perform maintenance or replace the ion source. Such downtime results in productivity loss of the ion implantation system. Hence, it is desirable to maintain proper functioning of the ion source for extended periods of time in order to perform an efficient implant process.
As will be discussed, among other advantages of the present invention, an improved method and system for minimizing deposits and beam glitching during an ion implantation process is desired.