RF-grounded sub-Debye neutralizer grid

Details RF-grounded sub-Debye neutralizer grid RF-grounded sub-Debye neutralizer grid

1999-05-20

2001-12-18

Berman, Jack (Department: 2878)

Radiant energy

Electrically neutral molecular or atomic beam devices and...

C315S111810

Reexamination Certificate

active

06331701

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a “source” (the hardware) that generates the Hyperthermal Neutral Beam. A hyperthermal neutral beam is a beam of translationally energetic neutrals. They can be controlled generally in the energy range of 20 eV<E
K
<400 eV while their thermal spread is in the range of 0.1 eV to 2 eV. The “Hyperthermal Neutral Beam Source” comprises several critical and innovated components. A specific example of this source is the Hyperthermal O-beam Source which generates a beam of hyperthermal atomic oxygen. The Hyperthermal O-beam has many important applications in advanced wafer fabrication processes. In the Lithography area, a Directional Hyperthermal O-beam can be used for anisotropic dry development (bi-layer resist scheme as well as Top Surface Imaging in the DUV and EUV exposure range). In the Interconnect area, a Directional Hyperthermal O-beam can be used for anisotropic etching of polymeric low-&kgr; inter-level dielectric. In the Ion-Implant and Interconnect areas, a Divergent Hyperthermal O-beam can be used for stripping heavily cross-linked polymer. Therefore, the Hyperthermal O-beam Source will be used as an example to elaborate this invention.
High Density Plasma RIE (Reactive Ion Etching)
The present invention comprises an anisotropic polymer etching method for both Dry Development (Lithography) and low-&kgr; polymeric dielectric etching (Interconnect). The O
2
-based high density plasma RIE is basically an ion-assisted plasma etching. This anisotropic etching method has the following undesired issues:
1. Wafer cooling to low temperature, sometimes as low as −100° C., is needed for anisotropy.
2. Gas mixture such as SO
2
+O
2
is needed for side-wall passivation in order to achieve anisotropy; SO
2
also has many undesired effects in wafer processing.
3. Its etching mechanism requires initial chemisorption of thermalized O and O
2
* and followed by directional ion bombardment. The requirement of initial chemisorption makes the etching process strongly dependent on the type of polymer (type of photoresist, polymer film, low-&kgr; polymer) being etched.
4. The etching process parameter window when existed, is very small and unstable.
5. Strong chemical loading effect (“macro-loading” or, pattern-factor loading).
6. Strong “micro-loading” effect (feature-dependent loading or, aspect ratio dependent loading). Under the feature-dependent loading effect, isolated features etch differently than dense features both in terms of etch rate and anisotropy. From the same loading mechanism, high aspect ratio features etch differently than low aspect ratio features both in terms of etch rate and anisotropy.
7. Charging effects on the features. In order to avoid the charging effects, strict restrictions are generally inflicted on the process parameters.
Down-Stream Plasma Etching/Ashing
The present invention also comprises an O
2
based (sometimes with gas mixture) down-stream plasma method for stripping resist after plasma etching steps and after ion implant steps. It is sometimes used for cleaning of organic contaminants. This isotropic etching/ashing method utilizes primarily thermalized O and O*. As a result, the wafer would have to be at high temperature (as high as 250° C.) in order for the Arrhenius reaction to take place. Aside from some stringent organic contaminant cleaning steps, this high temperature environment is fine for wafers with ordinary polymer layers. However, some etching and ion implant steps heavily cross-link the polymer. Heavily cross-linked polymer cannot be etched by this method, not even at high temperature. The removal of such heavily cross-linked resist falls on the undesired liquid acid bath.
Hyperthermal O-beam
A Hyperthermal O-beam is a beam of translationally energetic O and its energy is generally controllable in the range of 20 eV<E
K
<400 eV with thermal spread in the range of 0.1 eV to no more than 2 eV. The Hyperthermal O-beam polymer etching mechanism resembles a chemical sputtering one. It is depicted by FIG.
13
. The translationally hot O impinges the polymer surface penetrating the very top atomic layer and thermalizing with the polymer through bond-breaking collisions until a volatile product such as CO or H
2
O is formed. Then, the etching is done. This chemical sputtering like etching mechanism does not distinguish the polymer type since the up-taking of the O by the polymer is pre-determined by the polymer bond-breaking collisions and it does not depend on the chemisorption of the thermal O by the polymer. Also, this etching mechanism is unlike that of down-stream plasma etching nor that of biased high density plasma etching which both require initial chemisorption of O onto the polymer surface followed by the etch product bond-forming excitation to proceed etching. The requirement of chemisorption of O by the polymer (as in the plasma cases) depends strongly on the polymer type and making the etching polymer type dependent. In
FIG. 13
, a Directional Hyperthermal O-beam (e.g., small divergent angle, &thgr;
0
~6° to 3°) has more than sufficient normal energy to make down to the bottom of a high aspect ratio feature through surface forward scattering off the feature's vertical surface, while still retaining a vast majority of its initial E
K
(kinetic energy). Therefore, a large open area etches the same as a region of dense features; i.e., there is no feature-dependent (sometimes called aspect ratio dependent) loading effect.
Also shown in
FIG. 13
, the incident Hyperthermal O penetrates the top layer and thermalizes with the bulk through bond-breaking collisions with the polymer. The gradient of the equal-E
K
lines indicates the thermalization. In the microscopically-rough sub-surface, when the scattering Hyperthermal O is sufficiently thermalized, the etch product bond can then be formed (e.g., H
2
O, CO, SO
2
, etc.) and etching is done. In ion-assisted plasma etching of polymer, the chemisorption of thermal O from the plasma is a necessary step. The thermal O dosage to the polymer surface in Hyperthermal O-beam etching is many orders of magnitude less than that in the plasma cases. Unlike plasma-based etching, the up-taking of the O in the Hyperthermal O-beam etching is predetermined by the bond-breaking collisions. Roughly, one incident Hyperthermal O is responsible in removing one surface atom, in the form of the etch product. Therefore, Hyperthermal O-beam etching does not distinguish the type of polymer nor the wafer surface temperature and the etching does not exhibit any chemical loading (sometimes called pattern-factor loading) effect.
This invention is the only known method to generate a beam (directional or divergent) of high flux and translationally energetic atomic oxygen with the beam diameter from less than 1″ to greater than 10″. For the 1″ Directional Hyperthermal O-beam Source, the Hyperthermal O flux as high as 15 mAcm
−2
(current-equivalent) and polymer etch rate as high as 1 &mgr;m/min have been obtained.
FIG. 14
shows its polymer etch rate vs. Hyperthermal O energy. The increase in etch rate corresponds to an increase in the Hyperthermal O flux due to the increasing beam energy. For the case of 10″ diameter Directional Hyperthermal O-beam, the first generation prototype can reach a Hyperthermal O flux as high as 6 mAcm
−2
(current-equivalent) and polymer etch rate as high as 4500 Å/min.
FIG. 15
shows its polymer etch rate and etch uniformity vs. total input RF power to the 10″ source. Minor alteration to the accelerator and the neutralizer grid of the 10″ prototype source can double the etch rate and half the etch non-uniformity, as will be described in the body of the invention.
FIG. 16
shows the SEM cross section of the etched dense lines. FIG.
16
(
a
) is SiO
2
masked polymer features and FIG.
16
(
b
) is the etched bi-layer features.
FIG. 17
shows the SEM cross section of the dense lines FIG.
17
(
a
) and the adjacent isolated line FIG

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