Ion implantation system

An ion implantation system of the kind including an ion source, an electrode plate, an extraction voltage supply, and a substrate holder is described. The electrode plate initially has an opening of about 6.35 mm which is enlarged to about 8.38 mm. The aperture is also tapered outwardly on a side thereof opposing the ion source. It has been found that such an electrode plate creates substantially lower suppression currents.

BACKGROUND OF THE INVENTION

1). Field of the Invention

This invention relates to an ion implantation system, its manufacture and its method of use.

2). Discussion of Related Art

Ion implantation systems are frequently used in the manufacture of integrated circuits on wafer substrates. An ion source generates ions and an extraction voltage supply is connected between an electrode plate and the ion source such that the ions are attracted to the electrode plate. An aperture is formed in the electrode plate through which the ions pass. The ions then pass through other components that accelerate the ions and deflect them before they are implanted into a wafer substrate held by a substrate holder.

One such a system is described in U.S. Pat. No. 4,283,631. It has been found that extremely high suppression currents result due to ions that collide with an electrode plate of the ion implantation system of the '631 patent.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 of the accompanying drawings illustrates an electrode plate 10 which is modified according to the invention. The electrode plate 10 has first and second opposed sides 12 and 14 respectively. Before being modified, the electrode plate 10 has a circular aperture 16 extending from the first side 12 to the second side 14 therethrough. The aperture 16 has diameter D 1 of 6.35 mm.

The aperture 16 is modified in a lathe to an aperture 18 which is larger than the aperture 16 . The aperture 18 has a first section 20 extending from the first side 12 into the electrode plate 10 , and a second section 22 extending from the first section 20 to the second side 14 .

The first section 20 has a wall that extends at right angles relative to the first side 12 and has a diameter D 2 of 8.38 mm. It is generally preferred that the diameter D 2 be at least 7 mm more preferably at least 8 mm. The first section 20 extends for a length L 1 of 3.17 mm. It is generally preferred that the length L 1 be less than 4 mm.

The second section 22 extends from the first section 20 and has a wall at an angle other than at right angles relative to the second side 14 . As such, the second section 22 has a diameter D 3 at the second side 14 of 11.55 mm. It is generally preferred that the diameter D 3 be at least 2 mm larger than the diameter D 2 .

FIG. 2 illustrates an ion implantation system 30 according to an embodiment of the invention. The system 30 includes a mass analyzer 32 , an accelerator tube 34 , a quadrupole triplet 36 , deflection plates 38 , and a substrate holder 40 .

The mass analyzer 32 includes a high-voltage chamber 42 . One end of the accelerator tube 34 is attached to the high-voltage chamber 42 . An opposing end of the accelerator tube 34 is connected to ground. A high-voltage power supply 44 is connected between the end of the accelerator tube 34 connected to ground and the high-voltage chamber 42 . The high-voltage chamber 42 is held at a first voltage by the high-voltage power supply 44 .

The mass analyzer 32 further includes an ion source 50 and the electrode plate 10 located within the high-voltage chamber 42 . A vernier adjuster 51 is connected between the electrode plate 10 and the high-voltage chamber 42 . The vernier adjuster 51 maintains the electrode plate 10 at a second voltage which is lower than the first voltage of the high-voltage chamber 42 . The electrode plate 10 is located adjacent the ion source 50 with the first side (reference numeral 12 in FIG. 1 ) facing towards the ion source 50 .

The mass analyzers 32 further includes a holding chamber 52 located within the high-voltage chamber 42 for holding components that are connected to the ion source 50 . An extraction voltage supply 54 is connected between the high-voltage chamber 42 and the holding chamber 52 . The extraction voltage supply 54 maintains the holding chamber 52 at a third voltage which is different from the first voltage of the high-voltage chamber 42 and different from the second voltage of the electrode plate 10 .

The components of the mass analyzer 32 located within the holding chamber 52 include a source magnet power supply 58 , an arc power supply 60 , and a source gas 62 . The source gas 62 is connected to the ion source 50 to provide flow of a gas into the ion source 50 . The arc power supply 60 is connected between the holding chamber 52 and an ionizing filament of the ion source 50 . The arc power supply 60 maintains the ionizing filament of the ion source 50 at a fourth voltage which is different from the first, second, and third voltages. The source magnet power supply 58 is connected between the holding chamber 52 and the ion source 50 so as to create an axial magnetic field across a discharge region of the ion source 50 . The axial magnetic field is at a voltage potential which is different to a voltage potential of the electrode plate 10 .

In use, a gas flowing from the source gas 62 into the ion source 50 is ionized by the arc power supply 60 . The power supply 60 sustains an ion discharge by the filament of the ion source 50 . Ions generated by such ionization are attracted to the electrode plate 10 because of a voltage difference between the discharge region of the ion source 50 and the electrode plate 10 , and therefore because of a voltage difference between the ions and the electrode plate 10 . The ions move towards the electrode plate 10 and then pass through an aperture in the electrode plate 10 . An analyzer magnet 68 of the mass analyzer 32 deflects the ions towards an exit slit 70 . The ions then pass through the exit slit 70 and then experience a voltage drop as they pass through and are accelerated through the accelerator tube 34 .

The ions then pass through the quadrupole triplet 36 which is controlled by a quadrupole control 72 . The ions then pass through the deflection plates 38 which are controlled by a scanning system 74 . The scanning system 74 can apply a variable voltage to selected ones of the deflection plates 38 so that the ions are deflected onto a desired region of a substrate 76 which is held by the substrate holder 40 . By varying the voltages of the scanning system 74 , implantation locations of ions into the substrate 76 can be scanned across the substrate 76 .

Further details of the system 30 are described in U.S. Pat. No. 4,283,631, incorporated herein by reference.

The electrode plate 10 is initially unmodified and therefore has an aperture such as the aperture 16 in FIG. 1 . The electrode plate 10 is then removed from its location adjacent the ion source 50 and from the system 30 . The electrode plate 10 is then modified as discussed with reference to FIG. 1 , i.e. so as to have the aperture 18 . The electrode plate 10 is then located back into its position adjacent the ion source 50 with the first side 12 facing toward the ion source 50 , and connected to the vernier adjuster 51 .

It has been found that the electrode plate 10 before being modified creates extremely high suppression currents through the arc power supply 60 . By modifying the electrode plate 10 as described with reference to FIG. 1 , the suppression currents through the arc power supply 60 are dramatically reduced.