Beam Utilization

A general working definition of beam utilization is the ratio of beam time on the wafer to total beam time  

The effective areas must of course accurately represent the times in (15.1). The beam utilization is critically dependent on the particulars of the implanter, such as beam type (spot or ribbon), endstation type (single or multiwafer) and scan mechanism (mechanical, electric, magnetic, or hybrid). Expressions are developed below for three different types of endstations and scanning mechanisms in use today. 

Multiwafer Endstation Dual Mechanism Scan (Rotary Disk), with Unscanned Spot Beam 

Single-Wafer Endstation Linear Mechanical Scan with Scanned Spot Beam 

A processing chamber in which only one wafer is implanted at a time is typically employed for medium current implanters. The endstation consists of a single scanning arm capable of linear motion of up to 140-200 mm s 1. over a range of up to 400 mm. The wafer is typically held on an electrostatic chuck which may be gas-cooled to maintain adequate wafer temperature. 

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Capacity (Kg/h) = 360 x power Fractional beam utilization efficiency... 

What is the purpose of the high-energy electron beam utilized in a mass spectrometer ... 

Concentrating solar collector systems that utilize the direct beam radiation would be more likely deployed in areas with relatively low aerosol optical depth, to maximize direct beam utilization.13... 

In multiwafer configurations, which are common for high current tools, the wafers typically are mounted onto a rotating disk, which is then linearly translated across the ion beam. The rotation of the disk ensures that each wafer passes completely out of the beam in the direction of rotation. The linear translation must be at least as long as the wafer diameter plus the nominal beam diameter in that direction. Some high current configurations have the linear translation direction across the dispersive plane of the beam, while others have it across the nondispersive plane. Beam utilization efficiency (see Sect. 15.4) is directly coupled to the demands placed on this translation length. 

Increasing beam currents through improvements in beam transport is only part of the solution for improving productivity. The other part is to minimize the time the beam spends off the water, characterized as beam utilization. We present here a treatment of utilization, developed by Brown et al. (2004). We then include a categorization of implanters commercialized over the last 35 years, in terms of beam type and scanning mechanism and the implication of each implanter s architecture on beam utilization. 

Fig. 15.12. Beam utilization versus beam diameter for different implanter architectures...

Brown, D., Tsukihara, M., Ray, A., Splinter, P. Productivity Comparisons of Various Wafer Scanning Schemes in Ion Implanters, Using Beam Utilization as the Figure of Merit, Proceedings of the Fourteenth International Conference on Ion Implantation Technology (2004)... 

Table 1. Scheme of various beams utilized in the source facilities for exposure to the ionizing radiation of the photosynthetic material under different light conditions...

Two other categories of ion implanter deserve mention. First, the hybrid ribbon beam system is unique since the broad, unscanned ion beam does not scan off the wafer in the x-direction. Overscan does occur in the slow mechanically scanned direction, however. While offering an advantage for beam utilization, the ribbon beam must sacrifice uniformity and angle control to some degree. Second, Varian s broad beam approach utilizing nonmass-analyzed plasma doping. 

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