Ion source assembly for ion implantation apparatus and a method of generating ions therein
View Patent ↗A hydrogen ion implanter for the exfoliation of silicon from silicon wafers uses a large scan wheel carrying 50+ wafers around its periphery and rotating about an axis. In one embodiment, the axis of rotation of the wheel is fixed and a ribbon beam of hydrogen ions is directed down on a peripheral edge of the wheel. The ribbon beam extends over the full radial width of wafers on the wheel. The beam is generated by an ion source providing an extracted ribbon beam having at least 100 mm major cross-sectional diameter. The ion source may use core-less saddle type coils to provide a uniform field confining the plasma in the ion source. The ribbon beam may be passed through a 90° bending magnet which bends the beam in the plane of the ribbon.
1. An ion source assembly for ion implantation apparatus, comprising:
a vacuum chamber;
an arc chamber in said vacuum chamber, said arc chamber having a linear dimension and walls including a front wall extending along said linear dimension;
a source of gas containing a species to be ionized in the ion source to provide ions required for implantation;
at least one electrode in the arc chamber suitable, when electrically biased, to provide a source of electrons for ionizing said species;
an ion extraction slit in said front wall aligned with said linear dimension, wherein said extraction slit is at least 100 mm in length; and
a magnetic field device to provide a magnetic field along said linear dimension of the arc chamber to constrain electrons to spiral along said field within said chamber, said magnetic field having a flux density which has a non-uniformity less than 5% along said linear dimension over the length of said extraction slit.
2. An ion source assembly as claimed in claim 1 , wherein said flux density has a non-uniformity over the length of the extraction slit which is less than 1%.
3. An ion source assembly as claimed in claim 1 , wherein said flux density of said magnetic field over the length of the extraction slit is equal to or less than 500 Gauss.
4. An ion source assembly as claimed in claim 3 , wherein said flux density is between 200 Gauss and 300 Gauss.
5. An ion source assembly as claimed in claim 1 , wherein said magnetic field device comprises core-less electromagnetic saddle coils.
6. An ion source assembly as claimed in claim 5 , wherein said saddle coils are mounted external to said vacuum chamber.
7. An ion source assembly as claimed in claim 6 , wherein the vacuum chamber comprises a first tubular part made of non-ferromagnetic metal, and a second tubular part which is electrically insulating and connected end to end to said metal first tubular part;
wherein said arc chamber is mounted on an end of said second tubular part remote from said metal first tubular part, so as to be located within and electrically insulated from said metal first tubular part; and
wherein said electromagnetic saddle coils are mounted around said metal first tubular part.
8. An ion source assembly for ion implantation apparatus, as claimed in claim 1 , wherein said source of gas provides a source of hydrogen gas for producing H + ions for implanting.
9. An ion source assembly for ion implantation apparatus, as claimed in claim 1 , wherein there are two said electrodes located facing each other along said linear dimension providing a plasma space between them extending over the full length of said ion extraction slit.
10. A method of generating ions in an arc chamber of an ion source for extraction as a ribbon beam through an extraction slit having a slit length of at least 100 mm, comprising the steps of:
introducing into the arc chamber a gas containing a species to be ionized to provide ions required for implantation;
biasing an electrode in the arc chamber to provide a source of electrons to generate a plasma in the arc chamber containing said ions required; and
applying a magnetic field in the arc chamber, which is aligned with the extraction slit to confine said plasma generated to a region in the arc chamber in front of and extending over the length of said slit, wherein said magnetic field has a flux density with a non-uniformity of less than 5% over the length of the slit.
11. A method as claimed in claim 10 , wherein said flux density has a non-uniformity over the length of the extraction slit which is less than 1%.
12. A method as claimed in claim 10 , wherein said flux density of said magnetic field over the length of the extraction slit is equal to or less than 500 Gauss.
13. A method as claimed in claim 12 , wherein said flux density is between 200 Gauss and 300 Gauss.
14. A method as claimed in claim 10 , wherein said magnetic field is applied using core-less electromagnetic saddle coils.
15. A method as claimed in claim 14 , wherein said saddle coils are mounted external to said vacuum chamber.
16. A method as claimed in claim 10 , wherein the gas introduced into the arc chamber is hydrogen gas to provide H + ions for implanting.