Coating apparatus – Interfacing control of plural operations
Reexamination Certificate
2000-11-22
2004-02-10
Hassanzadeh, P. (Department: 1763)
Coating apparatus
Interfacing control of plural operations
C118S698000, C118S7230IR, C118S7230ER, C118S7230MW
Reexamination Certificate
active
06689220
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an apparatus for processing of semiconductor wafers, and more particularly to a system and method for deposition of thin films.
BACKGROUND OF THE INVENTION
A fundamental process in IC fabrication is chemical vapor deposition (CVD), which uses vapor precursors to deposit thin films on a semiconductor substrate. The reactor used for CVD processes includes a precursor delivery system, a substrate and an energy source to decompose the precursor vapor to reactive species to allow a thin film to form on the substrate (CVD process). Effective power sources are heat and plasma energy such as radio frequency (RF) power, microwave energy (MW), low frequency (10 KHz-1 MHz) power, and optical energy (e.g. a laser or ultraviolet light) which decompose the introduced precursors. Plasma energy power is below 6000 W. The amount of power required in each process is determined by the process reaction and a typical power level is between 500-1000 W. Also, the substrate could be biased or heated (to 100° C.-1200° C.) to promote the reaction of the decomposed atoms or molecules and to control the physical properties of the formed films.
Traditionally, precursors used in semiconductor CVD processes are gaseous. An example of a CVD process to deposit silicon dioxide (SiO
2
) is to use gaseous precursors such as silane gas (SiH
4
) and oxygen gas (O
2
):
SiH
4
(gas)+O
2
(gas)−(heat)→SiO
2
(solid)+2H
2
(gas)
The basic requirements of a precursor are that the desired product (in this example, SiO
2
) is solid, and all other products are gases (in this example, H
2
) to be exhausted away. The energy required for the reaction to take place is the thermal energy, about 400-800° C.
To broaden the processes, more and more liquid and solid precursors have been used, especially in the area of metal-organic chemical vapor deposition (MOCVD). To perform this task, a liquid precursor is typically turned into vapor, and the vapor is then decomposed and reacts on the substrate. A solid precursor must often be dissolved into a solvent to form a liquid precursor. The liquid precursor then needs to be converted into vapor phase before being introduced into the deposition zone. An example of CVD process to deposit copper (Cu) is to use liquid precursor vapor copper HexaFluoroACetylacetone TriMethylVinylSilane (hfac-copper-tmvs, C
5
HO
2
F
6
—Cu—C
5
H
12
Si):
2Cu-hfac-tmvs(vapor)−(heat)→Cu(solid)+hfac-Cu-hfac(gas)+2tmvs(gas)
Another deposition technique is the atomic layer epitaxy (ALE) process. In ALE, the precursors are pulsed sequentially into the ALE process chamber with each precursor taking turn to generate a chemical surface reaction at the substrate surface to grow about one atomic layer of the material on the surface. The growth of one atomic layer in ALE is controlled by a saturating surface reaction between the substrate and each of the precursors. Sometimes a reduction sequence activated with extra energy such as heat or photon can be used to re-establish the surface for a new atomic layer. The fundamental of ALE is having a minimum of two different chemical reactions at the surface with each reaction carefully controlled to generate only one atomic layer. An example of ALE is the growth of ZnS at ~470° C. using sequential flow of elemental zinc and sulfur as precursors as disclosed by Suntola et al., U.S. Pat. No. 4,058,430. Another example of ALE is the growth of germanium (Ge) on silicon substrate at ~260-270° C. using a first step pulsing of GeH
4
vapor flow to generate an atomic layer coverage of GeH
4
and a second step pulsing of an Xe lamp exposure to decompose the surface GeH
4
as disclosed by Sakuraba et al, J. Cryst. Growth, 115(1-4) (1991) page 79.
ALE process is a special case of atomic layer deposition (ALD) process. The focus of ALE is the deposition of epitaxial layers, meaning perfect crystal structure. In contrast, ALD process seeks to deposit one layer at a time with the focus on film uniformity, not single crystal structure.
The major drawbacks of CVD and ALD processes are the high temperature needed for the chemical reactions and the limited number of available precursors. Each CVD or ALD process always starts with an extensive evaluation of various precursors and their chemical reactions to see if there is any suitable process reaction.
To lower the temperature needed for the chemical reaction, and to further promote possible reaction, plasma energy is being used to excite the precursors before the reaction takes place in CVD processes. Such processes are called plasma enhanced CVD (PECVD) processes. An energy source using radio frequency (RF) power or microwave (MV) power can be used to generate a plasma, which is a mixture of excited gaseous species, to supply energy to the precursors thus promoting the chemical reactions.
However, there is no plasma enhanced ALD process or equipment. The main advantages of a plasma enhanced ALD are the low temperature needed for the reaction to occur, and the addition of plasma energy to excite the precursors, leading to more selections of precursors. Furthermore, a plasma treatment could modify the surface condition, leading also to a wider range of precursor selection.
It would be advantageous if there is a plasma enhanced ALD system.
It would be advantageous if a plasma treatment could be incorporated in an ALD process.
SUMMARY OF THE INVENTION
Accordingly, a plasma enhanced atomic layer deposition (PEALD) apparatus is provided to offer atomic layer deposition capability using plasma source to excite the precursor. In addition to the prior art surface reactions using non plasma-excited precursor, the present invention also offer surface reactions using plasma-excited precursor. With plasma-excited precursor, the surface reaction could be either deposition reaction, or material modification by plasma bombardment.
The basic component of the present invention apparatus is a pulsing plasma source capable of either exciting or not-exciting a first precursor. The pulsing plasma source includes an energy source to generate a plasma, and a plasma adjusting system to cause the plasma to either excite or not-excite a precursor. The precursor could flow continuously (an aspect totally new to ALD), or intermittently (or pulsing, standard ALD operation process).
The plasma power source is preferably an inductive coupled plasma (ICP) source, but any plasma source such as capacitance plasma source, microwave guide plasma source, electron cyclotron resonance plasma source, magnetron plasma source, DC power plasma source, etc. works equally well.
In the simplest design, the plasma adjusting system is a power switch, causing the plasma to either ON or OFF. When the plasma is OFF, the precursor is not excited by the plasma (because there is no plasma). When the plasma is ON, the precursor is excited by the plasma. Typical plasma power when ON is between 15 to 6000 W. The low power is used for sensitive precursors such as those containing organic components. The timing for this design is long, in the order of many seconds because of the needed time for the plasma to stabilize.
To shorten the plasma stabilizing time, the plasma adjusting system comprises a two-level plasma power switch: a low power first level and a high power second level. The first level plasma power generates a plasma, but not enough to excite the precursor, either by low enough power or the precursor is far away from the plasma. The second level plasma power generates a large enough plasma to excite the precursor. By using a first level plasma, the stabilizing time is much shorter because the plasma is already present, and powering up from the first level to the second level power takes shorter time. The first power level is typically from 15 to 300 W and the second power level, from 100 to 6000 W.
Another way to block the plasma is to apply an electric field. The plasma adjusting system then comprises an electrode having a potential. By varying the potential, the plasma could either pas
Hassanzadeh P.
Nguyen Tue
Simplus Systems Corporation
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