Reduction of charge exchange effects on the VIISta810

The VIISta810 medium current implanter can be used in a wide range of applications due to its good process performance, high productivity and low cost of ownership. However, tests have shown that at the elevated pressures characteristic of high energy, high dose applications, charge exchange effects can result in dose and uniformity issues. These pressures can be avoided by use of the end station pressure interlock, which, however, leads to a reduction in throughput. In moving from the VIISta810 to the VIISta810HP, additional cryo pumps were installed, one on the process chamber and one on the corrector magnet chamber, to improve the vacuum performance. Furthermore, the position of the closed-loop Faraday was moved upstream and an adjustable, conductance limiting aperture was installed. To test the repeatability and uniformity dependence on process parameters and photo resist coverage, 200 and 300 mm cross hair wafers were implanted with the VIISta810 and VIISta810HP vacuum configurations. Maximum energy and 80% of the maximum beam current for single and double charged ions of various species were applied. Sheet resistance measurements were performed and vacuum pressures and beam current variations were recorded. Test results have shown that the improvements lead to a distinct reduction of the charge exchange effects and their influence on dose. The upgraded vacuum configuration, provided good dose repeatability and uniformity on photoresist wafers, even in the high energy and high dose range, without reduction in throughput relative to bare wafers.