1. Field of the Invention
This invention relates to a device for an ion implant machine used in semiconductor manufacturing, and particularly to a fitting in an ion source assembly and more particularly to a fitting between a vaporizer heater and an arc chamber.
2. Description of the Prior Art
Ion implantation is an important process in semiconductor manufacturing and must be performed accurately and reliably. An ion implanter implants impurity ions into a semiconductor substrate to form doped regions, such as sources and drains. The fundamental purpose of an ion implant system is to deliver a beam of ions of a particular type and energy to the surface of a silicon substrate. FIG. 1 shows a schematic view of an ion implanter. An ion source supply 80 and an ion source power supply 82 connect to the ion source assembly 60. Following the ion path 81, on the left-hand side, a gas source 80 supplies a small quantity of source gas such as BF.sub.3 into the ion source assemble 60, where the ions pass through a vaporizer oven 58, a conduit 11, and into an arc chamber 50. In the arc chamber 50, a heated filament causes the molecules to break up into charged fragments. This ion plasma contains the desired ion and many other species from other fragments and contamination. An extraction voltage, about 20 kV, moves the charged ions out of the ion source assembly 60 along the ion path 81 into the analyzer 84. The pressure in the remainder of the machine is kept below 10.sup.-6 Torr to minimize ion scattering by gas molecules. The magnetic field of the analyzer 84 is maintained such that only ion with the desired charge to mass ratio travel through without being blocked by the analyzer walls. Unblocked ions continue to the acceleration tube 86, where they are accelerated to the implantation energy as then move from high voltage to ground. The beam is well collimated by the apertures. The beam is then scanned over the surface of the wafer 90 using electrostatic deflection plates. The wafer 90 is offset slightly from the axis of the acceleration tube 86 so that ions neutralized during their travel will not be deflected on the wafer 26. A wafer handling system 88 loads/unloads wafers into an implanter wafer holder.
It is critical that the ion source assembly 60 is leak proof so that outside air does not enter the assembly or that ions do not leave. If air and contamination enter the assemble, the air and contamination disrupt the ion beam causing the ion implant to degrade which results in yield losses on wafers. In the current ion source assembly 60, the connections between the conduit 11 and the arc chamber 52 leak gas thus causing frequent chip yield losses. The connections are stressed by the constant heating and cooling cycle which cause a separations (e.g., gaps, spaces) between the conduit 11 and arc chamber 50. Moreover, yield losses, maintenance costs and down time make the gas leakage problem costly.
Therefore there is a need to develop an improved ion source assembly that is gas leak proof and that can maintain its integrity over time and many heat cycles.