Coating apparatus – Program – cyclic – or time control
Reexamination Certificate
2002-07-08
2004-11-23
Edwards, Laura (Department: 1734)
Coating apparatus
Program, cyclic, or time control
C118S715000, C156S345330, C156S345340, C700S121000
Reexamination Certificate
active
06821347
ABSTRACT:
TECHNICAL FIELD
The present invention is related to the field of thin film deposition in the manufacturing of micro-devices.
BACKGROUND
Thin film deposition techniques are widely used in the manufacturing of microelectronic devices to form a coating on a workpiece that closely conforms to the surface topography. The size of the individual components in the devices is constantly decreasing, and the number of layers in the devices is increasing. As a result, the density of components and the aspect ratios of depressions (e.g., the ratio of the depth to the size of the opening) is increasing. The size of workpieces is also increasing to provide more real estate for forming more dies (i.e., chips) on a single workpiece. Many fabricators, for example, are transitioning from 200 mm to 300 mm workpieces, and even larger workpieces will likely be used in the future. Thin film deposition techniques accordingly strive to produce highly uniform conformal layers that cover the sidewalls, bottoms and corners in deep depressions that have very small openings.
One widely used thin film deposition technique is Chemical Vapor Deposition (CVD). In a CVD system, one or more precursors that are capable of reacting to form a solid thin film are mixed in a gas or vapor state, and then the precursor mixture is presented to the surface of the workpiece. The surface of the workpiece catalyzes the reaction between the precursors to form a thin solid film at the workpiece surface. The most common way to catalyze the reaction at the surface of the workpiece is to heat the workpiece to a temperature that causes the reaction.
Although CVD techniques are useful in many applications, they also have several drawbacks. For example, if the precursors are not highly reactive, then a high workpiece temperature is needed to achieve a reasonable deposition rate. Such high temperatures are not typically desirable because heating the workpiece can be detrimental to the structures and other materials that are already formed on the workpiece. Implanted or doped materials, for example, migrate in the silicon substrate when a workpiece is heated. On the other hand, if more reactive precursors are used so that the workpiece temperature can be lower, then reactions may occur prematurely in the gas phase before reaching the substrate. This is not desirable because the film quality and uniformity may suffer, and also because it limits the types of precursors that can be used. Thus, CVD techniques may not be appropriate for many thin film applications.
Atomic Layer Deposition (ALD) is another thin film deposition technique that addresses several of the drawbacks associated with CVD techniques.
FIGS. 1A and 1B
schematically illustrate the basic operation of ALD processes. Referring to
FIG. 1A
, a layer of gas molecules A
x
coats the surface of a workpiece W. The layer of A
x
molecules is formed by exposing the workpiece W to a precursor gas containing A
x
molecules, and then purging the chamber with a purge gas to remove excess A
x
molecules. This process can form a monolayer of A
x
molecules on the surface of the workpiece W because the A
x
molecules at the surface are held in place during the purge cycle by physical adsorption forces at moderate temperatures or chemisorption forces at higher temperatures. The layer of A
x
molecules is then exposed to another precursor gas containing B
y
molecules. The A
x
molecules react with the B
y
molecules to form an extremely thin solid layer of material on the workpiece W. The chamber is then purged again with a purge gas to remove excess B
y
molecules.
FIG. 2
illustrates the stages of one cycle for forming a thin solid layer using ALD techniques. A typical cycle includes (a) exposing the workpiece to the first precursor A
x
, (b) purging excess A
x
molecules, (c) exposing the workpiece to the second precursor B
y
, and then (d) purging excess B
y
molecules. In actual processing several cycles are repeated to build a thin film on a workpiece having the desired thickness. For example, each cycle may form a layer having a thickness of approximately 0.5-1.0 Å, and thus it takes approximately 60-120 cycles to form a solid layer having a thickness of approximately 60 Å.
FIG. 3
schematically illustrates an ALD reactor
10
having a chamber
20
coupled to a gas supply
30
and a vacuum
40
. The reactor
10
also includes a heater
50
that supports the workpiece W and a gas dispenser
60
in the chamber
20
. The gas dispenser
60
includes a plenum
62
operatively coupled to the gas supply
30
and a distributor plate
70
having a plurality of holes
72
. In operation, the heater
50
heats the workpiece W to a desired temperature, and the gas supply
30
selectively injects the first precursor A
x
, the purge gas, and the second precursor B
y
as shown above in FIG.
2
. The vacuum
40
maintains a negative pressure in the chamber to draw the gases from the gas dispenser
60
across the workpiece W and then through an outlet of the chamber
20
.
One drawback of ALD processing is that it is difficult to avoid mixing between the first and second precursors in the chamber apart from the surface of the workpiece. For example, a precursor may remain on surfaces of the gas dispenser or on other surfaces of the chamber even after a purge cycle. This results in the unwanted deposition of the solid material on components of the reaction chamber. The first and second precursors may also mix together in a supply line or other area of a reaction chamber to prematurely form solid particles before reaching the surface of the workpiece. Thus, the components of the ALD reactor and the timing of the A
x
/purge/B
y
/purge pulses of a cycle should not entrap or otherwise cause mixing of the precursors in a manner that produces unwanted deposits or premature reactions.
Another drawback of ALD processing is that the film thickness may be different at the center of the workpiece than at the periphery. To overcome this problem, the center of some distributor plates do not have any holes
72
. In practice, however, this may cause the film at the center of the workpiece to be thinner than the film at the periphery. Moreover, the center portion of such plates may become coated with the solid material because it is difficult to purge all of the precursors from this portion of the gas dispenser
60
during normal purge cycles. Therefore, there is a need to resolve the problem of having a different film thickness at the center of the workpiece than at the periphery.
SUMMARY
The present invention is directed toward reactors for deposition of materials onto a micro-device workpiece, systems that include such reactors, and methods for depositing materials onto micro-device workpieces. In one embodiment, a reactor for depositing a material comprises a reaction chamber and a gas distributor that directs gas flows to a workpiece. The reaction chamber can include an inlet and an outlet, and the gas distributor is positioned in the reaction chamber. The gas distributor has a compartment coupled to the inlet to receive a gas flow and a distributor plate including a first surface facing the compartment, a second surface facing the reaction chamber, and a plurality of passageways. The passageways extend through the distributor plate from the first surface to the second surface. Additionally, at least one of the passageways has at least a partially occluded flow path through the plate. For example, the occluded passageway can be canted at an oblique angle relative to the first surface of the distributor plate so that gas flowing through the canted passageway changes direction as it passes through the distributor plate.
The compartment of the gas distributor can be defined by a sidewall, and the distributor plate can extend transverse relative to the sidewall. In one embodiment, the distributor plate has an inner region, an outer region, and a peripheral edge spaced laterally inward from the sidewall to define a gap between the peripheral edge and the sidewall. In other embodiments, the peripheral
Carpenter Craig M.
Dando Ross S.
Derderian Garo J.
Mardian Allen P.
Tschepen Kimberly R.
Edwards Laura
Micro)n Technology, Inc.
Perkins Coie LLP
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