Self-centering calibration tool and method of calibrating

Details Self-centering calibration tool and method of calibrating Self-centering calibration tool and method of calibrating

2000-01-13

2002-10-15

Raevis, Robert (Department: 2856)

Measuring and testing

Instrument proving or calibrating

Displacement, motion, distance, or position

Reexamination Certificate

active

06463782

ABSTRACT:

FIELD OF INVENTION
The present invention generally relates to a self-centering calibration tool and a method for calibrating a wafer platform and more particularly, relates to a self-centering calibration tool that is equipped with a centering device having at least three legs extending radially outwardly from a center aperture for engaging a wafer platform to effectuate a self-centering calibration and a method for calibrating a wafer platform.
BACKGROUND OF THE INVENTION
In the fabrication of semiconductor devices, metal contacts and vias are frequently formed in contact holes and via openings on silicon wafers that have been pre-processed with insulating layers on top. Devices are then fabricated by connecting the components with metal contacts and vias to form the integrated circuits. In particular, aluminum, aluminum alloys, tungsten and tungsten alloys are frequently used for depositing into contact holes and via openings on silicon substrates. The deposition process can be carried out either in a physical vapor deposition chamber or in a chemical vapor deposition chamber.
As the dimensions of semiconductor devices continuously to shrink in the miniaturization of modem semiconductor devices to the sub-half-micron range, via openings and contact holes must also shrink. Consequently, the opening and holes to be filled have larger aspect ratios, i.e., the ratios between the depth of the opening or hole and the diameter.
Difficulties have been encountered in depositing conductive metal into via openings and contact holes as they become smaller and deeper, the bottom and sides of an opening or hole receive fewer deposited metal particles than the top surfaces of the device. The end result of such a phenomenon, sometimes called a shadowing effect, is that metal layers formed by the particles hang over the opening forming an overhang. The overhang closes before the opening is completely filled as the deposition process progresses and thus creating a void in the opening or hole.
One techniques used to remedy the shadowing effect of the sputtering process is to use a tungsten chemical vapor deposition (W CVD) technique for filing openings and holes that have large aspect ratios. The W CVD process solves the difficult problem in metalization to ensure enough metal continuity in contact windows and vias. The step coverage of deep openings or holes by the W CVD particles is greatly improved over that possible by any other deposition technique. The basic chemistry is represented by:
WF
6
+3
H
2
→W+6HF  (Equation A)
2WF
6
+3Si→2W+3SiF
4
  (Equation B)
There may also be reactions between WF
6
and SiH
4
and furthermore, WF
6
may be reduced by Ai and Ti through different chemical processes.
During a W CVD deposition process, a wafer is usually held on a vacuum chuck that is heated to a temperature between about 400° C. and about 500° C. A shower head is positioned opposite to the wafer where WF
6
, H
2
or SiH
4
gases are injected. Normally, a two or three-step process is involved where SiH
4
is first introduced without any flow of WF
6
to initiate a deposition of a very thin seed layer amorphous silicon as a prenucleation layer. The nucleation process is then followed by SiH
4
+WF
6
silane reduction nucleation process for depositing a thin W nucleation layer and then the faster-rate H
2
+WF
6
hydrogen reduction process for bulk W deposition. During the nucleation stage, less than 100 nm of tungsten is deposited, while the bulk of the tungsten deposition is by the hydrogen reduction process. The multi-stage deposition process is designed such that during the initial nucleation stage, the silicon from the source/drain area is not consumed in the reaction since WF
6
would react readily with Si. When WF
6
reacts with Si from the source/drain region, a defect known as junction leakage may occur. The introduction of SiH
4
into the reaction avoids the consumption of Si from the substrate. The initial introduction of SiH
4
into the reaction without WF
6
for the deposition of the prenucleation layer of Si is known as a silane soak step.
In the W CVD process, a W CVD is frequently blanket-deposited onto a wafer surface and into the contact holes after a metal nucleation layer is first deposited on the entire wafer. The W deposited on the insulating layer, i.e. a SiO
2
layer, is then etched off in an etchback process by a process of reactive ion etching. After the etchback process, only the thicker W in the contact holes are left. Since the process relies on the removal of all W CVD except in the contact holes, the uniformity of the W deposition and the RIE etchback process is critical for the successful formation of W contact plugs. When the process is not accurately controlled, such as with the pre-deposition of a nucleation layer of Ti/TiN, the W contact plugs may be substantially recessed after the etchback process and thus results in poor step coverage on the device.
In the deposition of contact plugs by the W CVD method, the process chamber utilized must be cleaned on a preventive maintenance schedule. Such preventive maintenance schedule is frequently performed on a monthly basis. After the process chamber and the components inside the chamber are cleaned, the wafer transport system, including a robot arm must be recalibrated according to the position of the wafer platform inside the chamber. The robot transport calibration, or commonly known as the hand-off procedure, must be performed at the tungsten plug deposition temperature, i.e. at about 440° C. Due to the large thermal expansion coefficients of the chamber components including those made of quartz and stainless steel, the robot transport calibration for wafer positioning must be carried out in its work environment, i.e. at the high deposition temperature. Any calibration procedure conducted at room temperature would be inaccurate when the robot transports at high temperatures.
To carry out the calibration process at the 440° C. high temperature after a preventive maintenance procedure, a quartz cover, i.e. a transparent cover, must first be placed on the CVD machine and then the process chamber is evacuated. The temperature of the process chamber is then ramped up to the process temperature of 440° C. which requires between 2~3 hours. The calibration procedure can then be carried out by loading a dummy wafer into the process chamber and placing on top of the wafer platform (or the heater), and its accuracy in positioning is checked and adjusted for the robot arm. The temperature is then ramped down to room temperature such that the quartz cover can be removed after the chamber is vented. The ramp down process also requires 2~3 hours. The total calibration process therefore requires a minimal of 6 hours which is extremely time consuming and wasting of machine process time.
As a result, a hand-off calibration tool is provided by the machine manufacturer for performing calibration at room temperature. This is shown in
FIGS. 1A-1E
. The hand-off calibration tool
10
, shown in
FIG. 1A
is formed by two disks
12
,
14
that are of different diameters. Four calibration apertures
16
are provided for performing a visual calibration of the robot transport system (not shown). The upper disk
12
further includes apertures
18
for lift pins for lifting a wafer positioned thereon, and apertures
20
for guide pins for the positioning of a wafer onto the wafer platform
30
. A total of four apertures
18
are provided for the lift pins, while a total of six apertures
20
are provided for the guide pins. The upper disk
12
is further provided with a slot opening
22
in its top surface
24
. A plane view of the hand-off tool
10
is shown in FIG.
1
B.
A perspective view of a wafer platform, or a heater
30
is shown in FIG.
1
C. The wafer platform
30
is supported by a base portion, a shaft
32
for providing up-and-down motion of the wafer platform
30
. In a top surface
34
of the platform
30
, six apertures
36
are provided for the guide pins (not shown) w

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