Sputter magnetron having two rotation diameters

Details Sputter magnetron having two rotation diameters Sputter magnetron having two rotation diameters

1999-10-22

2001-05-08

Diamond, Alan (Department: 1753)

Chemistry: electrical and wave energy

Apparatus

Coating, forming or etching by sputtering

C204S298190, C204S298210, C204S298220, C204S298270, C204S298280, C204S298090, C204S298370, C204S192120, C204S192320, C134S001100, C134S001200, C315S039510, C315S039630, C315S039570

Reexamination Certificate

active

06228236

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to the deposition of materials by sputtering. In particular, the invention relates to a magnetron creating a magnetic field to enhance sputtering.
BACKGROUND ART
The fabrication of modern semiconductor integrated circuits requires the deposition and patterning of multiple levels of metallization interconnecting together the active semiconductor devices in the silicon or other semiconductor substrate and also connecting the devices to external electrical lines. Typically, a layer of dielectric, such as a silica-based material, is deposited. Photolithography is then used to pattern into the dielectric a series of vertically extending contact or via holes and possibly other interconnecting structures. Hereafter, only via holes will be referred to although most of the discussion is equally applicable to contact holes and other metallization structures formed in the dielectric. An interconnect metal, such as aluminum, is then filled into the holes and over the top of the dielectric layer. In the past, the horizontal interconnects have been typically etched by a metal etching process. However, more recently, a damascene process has been developed. Prior to the metal deposition, the horizontal interconnect pattern is etched into the dielectric in the form of trenches. The metal is then deposited into the vias, the trenches, and over the top of the dielectric. Chemical mechanical polishing removes any metal above the top of the trenches. Also, more recently, low-k dielectrics have been developed to replace the silicon dioxide or silicate glass dielectric, and process have been developed to replace aluminum with copper as the metallization.
Sputtering, also called physical vapor deposition (PVD), has been the favored technique for depositing metals. Sputtering is relatively fast, sputtering equipment and materials are relatively inexpensive, and the equipment is more reliable compared to that for chemical vapor deposition (CVD). Techniques have been recently developed to electroplate copper into deep via holes. However, electroplated copper like most other metallizations deposited over silicate-based dielectrics requires one or more thin layers to be first deposited on the sides and bottom of the via hole as an adhesion layer, a seed layer for subsequent deposition, and as a barrier layer preventing atomic migration between the metal and the dielectric. These barrier and other layers are typically composed of Ti/TiN for aluminum metallization and of Ta/TaN for copper metallization, but other materials are possible. Sputtering is still preferred for at least some of these initial layers deposited over the dielectric.
Advanced semiconductor integrated circuits structures are densely packed, and vias have an increasingly large aspect ratio, which is the ratio of the depth to the minimum width of the hole being coated or filled. Aspect ratios of above four are being required. Conventional sputtering, however, is poorly suited for conformal deposition into holes having such high aspect ratios because conventional sputtering produces an angularly wide distribution of sputtered particles which therefore have a low probability of reaching the bottom of a deep and narrow via hole.
Nonetheless, sputtering equipment and techniques have been developed that better provide for filling high aspect-ratio vias. In one approach, referred to as ionized metal plasma (IMP) sputtering, an RF coil couples additional energy into the sputtering plasma to create a high-density plasma (HDP). This approach, however, suffers from high equipment cost.
Another approach, often referred to as self-ionized plasma (SIP) sputtering, uses modified DC magnetron sputtering apparatus to achieve many of the effects of IMP sputtering and in some situations has been observed to deposit better films. The equipment developed for SIP sputtering is also usable for sustained self-sputtering (SSS) of copper, in which no argon working gas is required, as will be explained later.
A conventional PVD reactor
10
, with a few modifications for SSS or SIP sputtering, is illustrated schematically in cross section in FIG.
1
. The illustration is based upon the Endura PVD Reactor available from Applied Materials, Inc. of Santa Clara, Calif. The reactor
10
includes a vacuum chamber
12
sealed through a ceramic isolator
14
to a PVD target
16
composed of the material, usually a metal, to be sputter deposited on a wafer
18
held on a heater pedestal electrode
20
by a wafer clamp
22
. Alternatively to the wafer clamp
22
, an electrostatic chuck may be incorporated into the pedestal
20
or the wafer may be placed on the pedestal
20
without being held in place. The target material may be aluminum, copper, aluminum, titanium, tantalum, alloys of these metals containing a few percentages of an alloying element, or other metals amenable to DC sputtering. A shield
24
held within the chamber protects the chamber wall
12
from the sputtered material and provides the anode grounding plane. A selectable and controllable DC power supply
26
negatively biases the target
14
to about −600V DC with respect to the shield
24
. Conventionally, the pedestal
20
and hence the wafer
18
are left electrically floating, but for some types of SSS and SIP sputtering, an RF power supply
28
is coupled to the pedestal
18
through an AC coupling capacitor
30
or more complex matching and isolation circuitry to allow the pedestal electrode
20
to develop a DC self-bias voltage, which attracts deep into a high aspect-ratio holes positively charged sputter ions created in a high-density plasma. Even when the pedestal
20
is left electrically floating, it develops some DC self-bias.
A first gas source
34
supplies a sputtering working gas, typically argon, to the chamber
12
through a mass flow controller
36
. In reactive metallic nitride sputtering, for example, of titanium nitride or tantalum nitride, nitrogen is supplied from another gas source
38
through its own mass flow controller
40
. Oxygen can also be supplied to produce oxides such as Al
2
O
3
. The gases can be admitted from various positions within the chamber
12
including from near the bottom, as illustrated, with one or more inlet pipes supplying gas at the back of the shield
24
. The gas penetrates through an aperture at the bottom of the shield
24
or through a gap
42
formed between the wafer clamp
22
and the shield
24
and the pedestal
20
. A vacuum system
44
connected to the chamber
12
through a wide pumping port
46
maintains the interior of the chamber
12
at a low pressure. Although the base pressure can be held to about 10
−7
Torr or even lower, the conventional pressure of the argon working gas is typically maintained at between about 1 and 1000 mTorr. However, for semi-ionized sputtering, the pressure may be somewhat lower, for example, down to 0.1 mTorr. For SSS sputtering, once the plasma has been ignited, the supply of argon may be stopped, and the chamber pressure may be made very low. A computer-based controller
48
controls the reactor including the DC power supply
26
and the mass flow controllers
36
,
40
.
When the argon is admitted into the chamber, the DC voltage between the target
16
and the shield
24
ignites the argon into a plasma, and the positively charged argon ions are attracted to the negatively biased target
16
. The ions strike the target
16
at a substantial energy and cause target atoms or atomic clusters to be sputtered from the target
16
. Some of the target particles strike the wafer
18
and are thereby deposited on it, thereby forming a film of the target material. In reactive sputtering of a metallic nitride, nitrogen is additionally admitted into the chamber
12
, and it reacts with the sputtered metallic atoms to form a metallic nitride on the wafer
18
.
To provide efficient sputtering, a magnetron
50
is positioned in back of the target
16
. It has opposed magnets
52
,
54
coupled by a magnetic yoke
56
producing a magnetic field within th

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