Magnetron sputtering source for low pressure operation

• US 5,593,551 A
• Filed: 02/28/1995
• Issued: 01/14/1997
• Est. Priority Date: 05/05/1993
• Status: Expired due to Term

• Current Assignee: Novellus Systems Incorporated (Lam Research Corporation)
• Original Assignee: Varian Associates, Inc.
• Inventors: Lai, Kwok F.
• Primary Examiner(s): NGUYEN, NAM X
• Application Number:
  US08/396,366
• Time in Patent Office: 686 Days
• Field of Search: 204/192.12, 204/298.16, 204/298.18, 204/298.19, 204/298.2
• US Class Current: 204/192.12
• CPC Class Codes: C23C 14/35 by application of a magnetic field, e.g. magnetron sputtering C23C14/3457 takes precedence
• CPC Class Codes: H01J 37/3408 Planar magnetron sputtering
• CPC Class Codes: H01J 37/3452 Magnet distribution
• CPC Class Codes: H01J 37/3494 Adaptation to extreme pressure conditions

Abstract

A magnetron sputtering source which is capable of very low pressure operation is disclosed. The source comprises a dish-shaped sputter target behind which is mounted a primary magnet for confining a plasma discharge adjacent to the front surface of the sputter target. A bucking magnet, positioned adjacent to the perimeter of the sputter target and, preferably, at the same level as the target, is used to prevent the magnetic field created by the primary magnet from spreading out at near the edge of the sputter target. This enables the source to operate at very low pressure and reduces the impedance of the discharge.

Claims

1. A magnetron sputtering system for depositing a selected material onto a substrate, said system comprising:

a chuck for holding a generally flat wafer-type substrate disposed generally in a first plane, said substrate having a first surface on which the selected material is to be deposited facing outwardly from said chuck;

a single, generally dish-shaped sputter target having a front surface disposed generally in a second plane and comprising a selected material to be sputtered and a back surface, said dish-shaped target having a perimeter, said second plane being substantially parallel to said first plane and separated therefrom by a fixed distance while said system is in operation;

a first closed-loop magnet means positioned proximate said sputter target back surface for creating a closed-loop magnetic tunnel adjacent to said sputter target front surface, said first closed-loop magnet means having inner and outer edges relative to a central axis of said dish-shaped sputter target and having opposite magnetic polarities at said inner and outer edges, said first closed-loop magnet means comprising a plurality of magnets each having a first magnetic pole and a second magnetic pole of opposite magnetic polarity to said first pole, each of said magnets having a magnetic polar axis passing through both said first pole and said second pole, each said polar axis disposed generally in a third plane generally parallel to said second plane;

a second closed-loop magnet means positioned proximate said sputter target perimeter, said second closed-loop magnet means having inner and outer edges relative to said central axis and having opposite magnetic polarities at said inner and outer edges, said second closed-loop magnet means comprising a plurality of bucking magnets each having a first magnetic pole and a second magnetic pole of opposite magnetic polarity to said first pole, each of said bucking magnets having a magnetic polar axis passing through both said first pole and said second pole, each said polar axis disposed generally in a fourth plane generally parallel to said third plane, the magnetic polarity at the inner edge of said second closed-loop magnet means being the same as the magnetic polarity of said outer edge of said first closed-loop magnet means such that the magnetic field generated by said second closed-loop magnet means prevents said closed-loop magnetic tunnel from intersecting said sputter target perimeter, and the magnetic field intensity generated by each of said bucking magnets being fixed during operation of the system.

2. The sputtering system of claim 1 wherein said first closed-loop magnet means is rotatable about an axis which passes through said sputter target.

3. The sputtering system of claim 2 wherein said first closed-loop magnet means is generally heart-shaped.

4. The sputtering system of claim 3 wherein said first closed-loop magnet means has a cross section which is substantially constant over substantially the entire loop.

5. The sputtering system of claim 2 wherein said magnetic tunnel has a narrow cross section.

6. The sputtering system of claim 1 wherein said sputter target is planar.

7. The sputtering system of claim 1 wherein said sputter target is concave.

8. The sputtering system of claim 1 wherein said sputter target perimeter is substantially circular.

9. The sputtering system of claim 8 wherein said second closed-loop magnet means is substantially circular and has a diameter which is greater than the diameter of said sputter target.

10. A magnetron sputtering system for depositing a selected material onto a generally flat semiconductor substrate, said system comprising:

a chuck for holding the generally flat semiconductor substrate disposed generally in a first plane, said substrate having a first surface on which the selected material is to be deposited facing outwardly from said chuck;

a single, generally dish-shaped sputter target having a front surface comprising a material to be sputtered and a back surface, said front surface having a generally circular peripheral edge generally defining a second plane, said second plane being substantially parallel to said first plane and separated therefrom by a fixed distance while said system is in operation;

a first closed-loop magnet assembly rotatable about an axis which passes through said second plane, said first closed-loop magnet assembly having an upper surface generally defining a third plane that is generally coplanar with said second plane and an outer edge relative to said axis of rotation, said outer edge of said first closed-loop magnet having a single magnetic polarity while said sputtering system is in operation, said first closed-loop magnet assembly comprising a plurality of magnets each having a first magnetic pole and a second magnetic pole of opposite magnetic polarity to said first pole, each of said magnets having a magnetic polar axis passing through both said first pole and said second pole thereof, each said polar axes disposed generally in a fourth plane generally parallel to said third plane; and

a second stationary, fixed intensity, generally annular closed-loop magnet assembly having a diameter greater than the diameter of said sputter target, said second closed-loop magnet assembly having an upper surface defining a fifth plane that is generally coplanar with said second plane, and an inner edge which is generally adjacent to said peripheral edge of said sputter target, said inner edge of said second closed-loop magnet assembly having the same magnetic polarity as the outer edge of said first closed-loop magnet assembly while said sputtering system is in operation, said second closed-loop magnet assembly comprising a plurality of bucking magnets each having a first magnetic pole and a second magnetic pole of opposite magnetic polarity to said first pole, each of said bucking magnets having a magnetic polar axis passing through both said first pole and said second pole, each said polar axis disposed generally in a sixth plane generally parallel to said fifth plane;

wherein said first and second closed-loop magnet assemblies cooperate to confine the plasma discharge within said sputtering system to the region adjacent to said front surface of said sputter target, such that there is no substantial contact between said plasma and said semiconductor substrate.

11. The sputtering system of claim 10 wherein the plane defined by said second closed-loop magnet upper surface is closer to said substrate than the plane defined by said first closed-loop magnet.

12. A method of sputtering a selected material onto a generally flat substrate in a conventional magnetron sputtering system, said method comprising:

positioning a generally flat semiconductor substrate within a vacuum chamber in a generally opposing relationship to a sputter target having a dish-shaped front surface;

creating a plasma within said vacuum chamber proximate to said front surface;

rotating a first magnet assembly positioned behind said front surface to confine said plasma to a region adjacent to said front surface;

positioning a second magnet assembly of generally annular shape and having a constant magnetic field intensity and polarity adjacent to an outer edge of said front surface to prevent said plasma from spreading out beyond the edge of said front surface when said vacuum chamber is operated at low pressure;

sputtering the selected material within said vacuum chamber at a low pressure in a range of about 0.1 millitorr to about 4.0 millitorr;

whereby said first and second magnets cooperate to prevent said plasma from contacting said substrate.