Electricity: measuring and testing – Magnetic – Combined
Reexamination Certificate
2001-08-02
2003-04-08
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Combined
C324S202000, C324S260000, C324S263000, C156S345490, C204S298320, C216S059000, C438S005000, C438S014000
Reexamination Certificate
active
06545468
ABSTRACT:
TECHNICAL FIELD
The present invention is generally related to magnetically enhanced reactive ion etching equipment, and more particularly to the calibration of the magnetic field of such equipment.
BACKGROUND OF THE INVENTION
Reactive ion etchers are used extensively by the microelectronics industry in the manufacturing of semiconductor and silicon based devices. Such devices include, for example, integrated circuits and micro-machined devices. Reactive ion etching is a dry etching process by which undesirable portions of a layer or film of one particular material are removed from a substrate wafer or layer of another material by chemical and/or physical interaction with a plasma etchant. For example, reactive ion etching may be used in conjunction with a mask layer to remove material in one or more layers beneath the mask layer in accordance with a pattern defined by the mask layer. In other words, certain etchants react with and remove the material in the layer or layers beneath the mask layer which are exposed to the etchant. The mask layer is substantially immune to the etchant's effects and remains in place. Additionally, reactive ion etchers are used to remove mask layers while leaving substantially undisturbed the layers below the mask including those portions that may be exposed to the etchant by virtue of the pattern established in the mask layer. Of course, the selection of the etchant, among other factors, will determine the chemical and/or physical reactivity or neutrality of the reactant's effect upon the various layers and mask utilized in any particular process.
Magnetically enhanced reactive ion etchers expose a wafer to a reactive plasma contained within a chamber which is additionally subjected to a controlled magnetic field conventionally provided by electromagnets. As used herein, magnetically enhanced reactive ion etchers include any of a variety of plasma based etchers wherein a controlled magnetic field, also referred to as a B-field, is impressed upon the plasma to control various plasma characteristics such as temperature, plasma uniformity and ion-bombardment energy. Process optimization therefore requires a repeatable, controllable B-field.
In
FIG. 1
a typical reactive ion etching apparatus 100 is illustrated. Such an apparatus includes central plasma chamber
2
and a plurality of magnetic drive coils
10
a
,
10
b
,
12
a
and
12
b
symmetrically surrounding the chamber
2
. Each coil is oriented orthogonally with respect to the two immediately adjacent coils such that the magnetic field passing through the center of each coil is substantially orthogonal to the magnetic field passing through the center of each immediately adjacent coil. Opposing coil pairs are established by the two sets of non-adjacent coils
10
a
,
10
b
and
12
a
,
12
b
. Wafers are passed into the chamber through the center of coil
12
b
and valve slit
6
.
Turning to
FIG. 2
, an exemplary sectional view taken through opposing coil pair
11
a
,
11
b
is illustrated. The magnetically enhanced reactive ion etching apparatus
200
in this figure is illustrated without a chamber lid in place, which would be conventional when service maintenance such as wet cleaning, kit changes or magnetic calibration is being performed. Illustration of a conventional lid assembly
60
is shown in FIG.
3
. In the present illustration, access to chamber liner
31
through the lid opening
32
at the top of the apparatus
200
is required for magnetic probe tool
50
conventionally utilized in taking magnetic field measurements during chamber calibration.
Chamber walls
30
which are manufactured from a non-magnetic material such as aluminum generally define the plasma chamber liner
31
. Within the chamber is cathode
20
, which during process operation is subjected to an RF signal by generator
41
. Electrostatic chuck
22
is attached to cathode
20
and is employed for holding a semiconductor wafer in a reaction plasma chamber with a high level of accuracy during semiconductor processing.
Calibration tool
40
comprises a base portion
44
defining a locating feature
46
for accepting magnetic probe tool
50
including element
52
. Element
52
may for example be a Hall device. Calibration tool
40
also includes standoff legs
42
which locate the tool to electrostatic chuck
22
at the desired height and orientation. With tool
40
properly located, a controlled location for probe tool
50
is established and the measurements of the magnetic fields generated by the coils will be repeatable.
Calibration of the apparatus
200
requires accurate measurements by the magnetic probe
50
of the magnetic field generated by each coil. Calibration of the coils may be required for example upon process changes requiring kit swapping or for such reasons as replacement of a coil driver or loss of data due to controller hard disk failures. In the former scenario, it is generally conventional practice to open the chamber and perform a variety of maintenance operations prior to releasing the apparatus for production use in the manufacturing environment. This includes venting of the chamber, removal of the chamber lid, gas distribution plate and all process kits. A wet cleaning of the chamber, lid and gas distribution plate as well as other ancillary maintenance operations are performed. This maintenance can take significant time and manpower resources. Eight to twelve hours of apparatus down time is common. In the latter scenarios, the same maintenance operations must be performed in conjunction with the conventional invasive calibration method. It is, however, generally desirable to avoid such otherwise unnecessary process steps.
As mentioned, calibration of the chamber magnetic field requires measurement of the magnetic field. This is accomplished by providing each coil in turn with a known DC drive voltage or current and taking a measurement of the magnetic field by the probe
50
via line
53
. The known voltage or current can be applied to the coils manually by way of controlled voltage or current sources or automatically through coil drivers
70
,
71
which control the voltage or current to coils
11
a
and
11
b
, respectively. Each coil driver
70
,
71
respond to external input signals
72
,
73
, respectively, such as a commanded voltage or current level from a process controller (not shown). The process controller may take many forms, for example a dedicated microprocessor based process controller with operator interface allowing voltage and current level selections during a calibration routine, or a general purpose PC based process controller with conventional keyboard/mouse operator interfaces also providing for voltage and current level selections during a calibration routine. Data corresponding to the generated magnetic field vector is collected for each coil. If a manual process is followed, data may be read by an operator from a data acquisition display of a device interfaced with the probe
50
. The manually read data is input to the process controller such as may be requested during a calibration routine executed by the controller. The process controller may also be adapted to automate the calibration process through data acquisition circuitry for monitoring and processing the signal from probe
50
element
52
during the calibration process via line
53
.
It may be desirable to take readings of the magnetic field of each coil for both phases of coil excitation. That is to say one reading at a positive DC voltage and current and one reading at a negative DC voltage and current. An average of the absolute value of the two readings or an aggregate of the absolute value of the two readings may then be used in the further steps of the calibration process. Also, multiple readings for each coil taken at different voltage or current magnitudes may be taken depending upon the granularity of the calibration method employed by the process controller. In summary, magnetic field measurements would be taken in accordance with the methodology set forth by the process equipment man
Cheng Strellson
Kuo Hui Ming
Strecker Gerard R.
Taiwan Semiconductor Manufacturing Co. Ltd
Tung & Associates
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