Planarizing machines and control systems for mechanical...

Details Planarizing machines and control systems for mechanical... Planarizing machines and control systems for mechanical...

2000-08-30

2003-08-26

Nguyen, Dung Van (Department: 3723)

Abrading

Precision device or process - or with condition responsive...

Computer controlled

C451S006000, C451S287000

Reexamination Certificate

active

06609947

ABSTRACT:

TECHNICAL FIELD
The present invention is directed toward mechanical and/or chemical-mechanical planarization of microelectronic substrates. More specifically, the invention is related to planarizing machines and to control systems for monitoring and controlling the status of a microelectronic substrate during a planarizing cycle.
BACKGROUND
Mechanical and chemical-mechanical planarizing processes (collectively “CMP”) remove material from the surface of semiconductor wafers, field emission displays or other microelectronic substrates in the production of microelectronic devices and other products.
FIG. 1
schematically illustrates a rotary CMP machine
10
with a platen
20
, a carrier assembly
30
, and a planarizing pad
40
. The CMP machine
10
may also have an under-pad
25
attached to an upper surface
22
of the platen
20
and the lower surface of the planarizing pad
40
. A drive assembly
26
rotates the platen
20
(indicated by arrow F), or it reciprocates the platen
20
back and forth (indicated by arrow G). Since the planarizing pad
40
is attached to the under-pad
25
, the planarizing pad
40
moves with the platen
20
during planarization.
The carrier assembly
30
has a head
32
to which a substrate
12
may be attached, or the substrate
12
may be attached to a resilient pad
34
positioned between the substrate
12
and the head
32
. The head
32
may be a free-floating wafer carrier, or the head
32
may be coupled to an actuator assembly
36
that imparts axial and/or rotational motion to the substrate
12
(indicated by arrows H and I, respectively).
The planarizing pad
40
and the planarizing solution
44
define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate
12
. The planarizing pad
40
can be a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is typically a non-abrasive “clean solution” without abrasive particles. In other applications, the planarizing pad
40
can be a non-abrasive pad composed of a polymeric material (e.g., polyurethane), resin, felt or other suitable non-abrasive materials. The planarizing solutions
44
used with the non-abrasive planarizing pads are typically abrasive slurries that have abrasive particles suspended in a liquid.
To planarize the substrate
12
with the CMP machine
10
, the carrier assembly
30
presses the substrate
12
face-downward against the polishing medium. More specifically, the carrier assembly
30
generally presses the substrate
12
against the planarizing liquid
44
on the planarizing surface
42
of the planarizing pad
40
, and the platen
20
and/or the carrier assembly
30
move to rub the substrate
12
against the planarizing surface
42
. As the substrate
12
rubs against the planarizing surface
42
, material is removed from the face of the substrate
12
.
CMP processes should consistently and accurately produce a uniformly planar surface on the substrate to enable precise fabrication of circuits and photo-patterns. During the construction of transistors, contacts, interconnects and other features, many substrates develop large “step heights” that create highly topographic surfaces. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo patterns to within tolerances approaching 0.1 micron on topographic surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical surface into a highly uniform, planar surface at various stages of manufacturing microelectronic devices on a substrate.
In the highly competitive semiconductor industry, it is also desirable to maximize the throughput of CMP processing by producing a planar surface on a substrate as quickly as possible. The throughput of CMP processing is a function, at least in part, of the ability to accurately stop CMP processing at a desired endpoint. In a typical CMP process, the desired endpoint is reached when the surface of the substrate is planar and/or when enough material has been removed from the substrate to form discrete components on the substrate (e.g., shallow trench isolation areas, contacts and damascene lines). Accurately stopping CMP processing at a desired endpoint is important for maintaining a high throughput because the substrate assembly may need to be re-polished if it is “under-planarized,” or components on the substrate may be destroyed if it is “over-polished.” Thus, it is highly desirable to stop CMP processing at the desired endpoint.
In one conventional method for determining the endpoint of CMP processing, the planarizing period of a particular substrate is determined using an estimated polishing rate based upon the polishing rate of identical substrates that were planarized under the same conditions. The estimated planarizing period for a particular substrate, however, may not be accurate because the polishing rate or other variables may change from one substrate to another. Thus, this method may not produce accurate results.
In another method for determining the endpoint of CMP processing, the substrate is removed from the pad and then a measuring device measures a change in thickness of the substrate. Removing the substrate from the pad, however, interrupts the planarizing process and may damage the substrate. Thus, this method generally reduces the throughput of CMP processing.
U.S. Pat. No. 5,433,651 issued to Lustig et al. (“Lustig”) discloses an in-situ chemical-mechanical polishing machine for monitoring the polishing process during a planarizing cycle. The polishing machine has a rotatable polishing table including a window embedded in the table. A polishing pad is attached to the table, and the pad has an aperture aligned with the window embedded in the table. The window is positioned at a location over which the workpiece can pass for in-situ viewing of a polishing surface of the workpiece from beneath the polishing table. The planarizing machine also includes a light source and a device for measuring a reflectance signal representative of an in-situ reflectance of the polishing surface of the workpiece. Lustig discloses terminating a planarizing cycle at the interface between two layers based on the different reflectances of the materials. In many CMP applications, however, the desired endpoint is not at an interface between layers of materials. Thus, the system disclosed in Lustig may not provide accurate results in certain CMP applications.
Another optical endpointing system is a component of the Mirra® planarizing machine manufactured by Applied Materials Corporation of California. The Mirra® machine has a rotary platen with an optical emitter/sensor and a planarizing pad with a window over the optical emitter/sensor. The Mirra® machine has a light source that emits a single wavelength band of light.
U.S. Pat. No. 5,865,665 issued to Yueh (“Yueh”) discloses yet another optical endpointing system that determines the endpoint in a CMP process by predicting the removal rate using a Kalman filtering algorithm based on input from a plurality of Line Variable Displacement Transducers (“LVDT”) attached to the carrier head. The process in Yueh uses measurements of the downforce to update and refine the prediction of the removal rate calculated by the Kalman filter. This downforce, however, varies across the substrate because the pressure exerted against the substrate is a combination of the force applied by the carrier head and the topography of both the pad surface and the substrate. Moreover, many CMP applications intentionally vary the downforce during the planarizing cycle across the entire substrate, or only in discrete areas of the substrate. The method disclosed in Yueh, therefore, may be difficult to apply in some CMP application bec

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