Method and apparatus for generating high-density uniform plasma

Details Method and apparatus for generating high-density uniform plasma Method and apparatus for generating high-density uniform plasma

2000-04-10

2002-09-17

Mills, Gregory (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With radio frequency antenna or inductive coil gas...

C156S345330, C118S7230IR

Reexamination Certificate

active

06451161

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a plasma reactor and particularly to such a reactor consisting of a unique configuration of plural induction coils atop an adjustable dielectric ceiling for producing a dense uniform plasma and a high etch rate over a large substrate.
BACKGROUND ART
Plasma-enhanced semiconductor processes for etching, deposition, resist stripped, passivation, or the like are well known. Generally, plasma may be produced from a low-pressure process gas by inducing an electron flow which ionizes individual gas molecules through the transfer of kinetic energy through individual electron-gas molecule collisions. Most commonly, the electrons are accelerated in an electric field, such as a radiofrequency (RF) electric field. Various structures have been developed to supply RF fields from devices outside of a vacuum chamber of a plasma reactor to excite a gas therein to a plasma state. Inductively coupled plasma (ICP) caused by coil is one kind of such devices. One conventional apparatus is described by Jacob et al. in U.S. Pat. No. 3,705,091, in which the plasma is generated inside a low pressure cylindrical vessel within the helical coil which is energized by 13 MHz RF radiation. This apparatus has serious contamination due to sputtering of the dielectric vessel walls caused by capacitive coupling created by the RF potentials on the coil with the vessel walls.
In U.S. Pat. No. 4,948,458, Ogle et al. describe a plasma generated at a low pressure such as 0.1 milliTorr to 5 Torr by using a spiral coil positioned on or adjacent to a planar dielectric called a window. The coil is responsive to an RF source having a frequency in the range of 1 to 100 MHz (typically 13.56 MHz), and is coupled to the RF source with an impedance matching network. According to the disclosure in U.S. Pat. No. 5,619,103, the extra dielectric acts as a means to reduce the effects of capacitive coupling between the coil and the plasma.
ICP offers many processing advantages including high densities of reactive species, high process rates, as well as low and controllable sheath voltage. To produce an RF inductively coupled plasma, the coil inductor is adjacent to the chamber. However, plasma generated by such induction plasma sources, no matter what the shape (spiral or helical) of the coil is, may have significant plasma density distribution nonuniformity. One of the causes of non-uniform plasma ion distribution is the coil geometry and location. Another cause is the shape of the plasma itself, which is mainly determined by the shape of the reactor chamber.
In U.S. Pat. No. 5,614,055, Fairbairn et al. disclose a dome-shaped plasma reactor to improve the plasma generation uniformity of a oxygen gas by increasing the height of the coil antenna above the wafer treated. U.S. Pat. No. 5,556,521 discloses a sputter etching apparatus having a dome-shaped dielectric extending into the processing chamber toward a substrate, in which a contoured inductive coil is disposed on the dielectric so as to generate dense uniform plasma for a uniform etch rate at low pressure about 1 milliTorr.
Hanawa et al. in U.S. Pat. No. 5,753,044 describe a dome-shaped reactor like that taught by Fairbairn et al.. This reactor includes specially designed dual coils to produce uniform plasma. The coil antenna is consisted of two portions winding adjacent to the chamber. One cylindrically surrounds the side wall of the reactor chamber, and the other having a shape of a flat disc is disposed upon the dome-shaped ceiling of the reactor chamber. The plasma generated can be adjusted to an optimal uniformity by changing the location and the shape of these two coil portions.
Recently, ICP processing has approached to a large substrate surface area such as 300 mm of wafer, flat panel display wafer or substrate (including glass substrate), and liquid crystal display substrate, etc. However, as a plasma processing chamber gets larger, a nonuniformity in plasma will unavoidable occur and a more dense plasma is also required. For a single coil system, the coil size, diameter, and the number of turns may be increased to achieve these goals. A major obstacle in achieving these goals is the increased-impedance resulting from a larger size coil, which must match the resonance frequency thereof. The inductance of a coil is proportional to the square of its diameter and the number of turns. The resonance condition of a coil is &ohgr;
2
=1LC, where &ohgr;: resonance frequency, L: inductance, C: capacitance. To satisfy the resonance condition at a certain frequency, when the inductance, L, increases by a factor, the capacitance, C, has to be decreased by the same factor accordingly. Taking a helical coil having 8″ 4-turn diameter being upgraded to 12″ 6-turn diameter as an example, the inductance would be increased by the factor of (12/8)
2
×(6/4)
2
=5.0625. The capacitance will have to be decreased by the same factor. Unfortunately, there is no variable capacitor available that can be operated in a low capacitance region for a typical high-density plasma condition in standard ISM (Industry, Scientific, Medical) frequency bands, such as 13.56 MHz. A solution for current manufacturers is to avoid using standard ISM bands; instead a nonstandard band, e.g., 2 MHz is selected. However, two negative consequences become obvious. First, radio communication interference and disturbance can become a disastrous issue. Second, plasma efficiency decreases as frequency decreases, which is not desirable. This challenge can be overcome by using a plural RF inductors system.
In U.S. Pat. No. 5,669,975 Ashtiani et al. disclose an apparatus for processing a surface of an article with a substantially planar induction coil. The induction coil has two spiral portions which are symmetrically formed a continuous S-shape. The shape of the induction coil helps minimizing the capacitive coupling between the induction coil and the plasma, and further improves plasma uniformity across the surface of wafer, and, in particular, semiconductor substrates having large surface areas.
In U.S. Pat. No. 5,907,221 Sato et al. disclose an inductively coupled plasma reactor having, plural inductive coil loops for processing a substrate. These coil loops are electrically separated from one another and independently connected to separately controllable plasma source RF supplies. The RF power level in each independent coil loop is separately programmed and instantly changeable, thus providing a perfectly uniform plasma ion density distribution across the entire large substrate surface.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a new and improved RF field excited plasma reactor comprising a tailor-made inductance by configuring multiple inductors in series, or in parallel, or the combination of both that could perfectly match and produce a uniform high-density plasma at low pressure over semiconductor substrates having large surface areas.
It is another object of the present invention to provide an improved uniformity in a high-density plasma across a material having a large area in such reactor.
It is still another object of the present invention to provide a unique induction coil configuration which will reduce capacitive coupling between plasma and such induction coil in order to minimize the amount of damaged devices which may occur during plasma processing.
It is a further object of the present invention that the reaction space between the coil configuration and wafer in the reactor chamber is changeable according to the shape of the dielectric window of the reactor chamber, thus providing optimal plasma ion distribution and plasma power.
Accordingly, for accomplishing these objects of the present invention, a unique induction coil configuration atop a dielectric window for exciting gases in a RF vacuum plasma reactor is disclosed.
In accordance with another aspect of the present invention, an inductively coupled plasma reactor comprises a dielectric window having a planar base and an integral

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