Multiple gas plasma forming method and ICP source

This is a continuation of U.S. application Ser. No. 11/694,354, filed Mar. 30, 2007, hereby expressly incorporated by reference.

This invention relates to the inductively coupled sources, and particularly to plasma sources for processes that use multiple gases, and to plasma processing systems and reactors.

A number of plasma processes, including several used in the manufacture of semiconductor wafers, involve the ionizing of more than one kind of gas or vapor. Often the relative degree of ionization and energy levels of different gases in a plasma make a difference in the effectiveness or quality of the plasma process being performed. For example, downstream plasma used for cleaning, surface preparation and modification, plasma used for wafer processing utilizing preferentially reactive radicals and charged species, plasma enhanced CVD, plasma etching, etc., each are most effective when any given gas is in an optimum energy or ionization state.

The optimum parameters for ionizing different gases in a multiple gas plasma typically differ from one gas to another. However, when gases are mixed, the allocation of energies among the different gas species when energizing a plasma are not readily controlled. As a result, optimal energy distribution or ion fraction ratios of different gases in a plasma are not achieved.

Accordingly, active species distribution among different gases in a multiple gas plasma is in need of improved control, particularly in semiconductor manufacture.

An objective of the present invention is to better distribute active species and energy among different gases within a plasma.

Another objective of the present invention is to provide independent multiple gas delivery in a plasma state into a reaction chamber at low cost.

According to principles of the present invention, gas and plasma are separately introduced through multiple inlet zones into a plasma processing chamber where they may undergo mutual interaction within a processing zone. Control of the active species distribution within the processing chamber is provided by energizing the gases in the separate inlet zones before combining them in the processing zone.

In accordance with embodiments of the invention, multiple inlet zones are provided through which separate gases can be introduced into a processing chamber, and an inductively coupled plasma (ICP) source is provided to energize the gas in each zone. RF energy is coupled through one or more antennas to energize the gas in each zone. The active species of each of the gases from each zone are combined in a processing chamber after the plasma is formed in the gases. This allows the gases to be brought together in their active states, rather than being combined and then activated. It also allows the same or different parameters to be applied in each of the inlet zones to optimize the conditions for forming plasma in each of the respective gases.

In certain embodiments of the invention, an antenna or coil winding is configured to couple energy into each of a plurality of the inlet zones. As such, the gases in the plurality of zones each appears as an impedance connected in series in the conductor circuit of the antenna. This stabilizes the plasma generation, which is particularly helpful when the ignition of the plasmas in the different inlet zones is not simultaneous or does not present the same impedance. The stabilization allows better control when using a single RF energy source to energize the plasmas in different zones. To provide initial or starting impedance, an easily ignitable gas can be used in one of the inlet zones.

In some embodiments of the invention, a single RF antenna couples energy to all of the inlet zones. In other embodiments, more than one antenna is used, each coupling energy into each of the inlet zones. Other combinations of plural antennas each coupling energy into different combinations of multiple inlet zones may also have increased utility in some systems.

The multiple inlet zones with simple ICP excitation capability are described in axially symmetrical multiple-zone sources and in linearly arranged multiple-zone sources. Other zone configurations can be used depending on the plasma processing system.

In the illustrated embodiments, multiple tubular zones serve as individual local plasma sources. Multiple quartz or ceramic tubes may enclose the separate zones. Instead of multiple ceramic tubes, a single block of dielectric material having multiple pass-through zones can be used. A single inductive antenna is preferably used to deliver RF power to all of the pass-through zones. As such, multiple plasma zones present serial impedances to the RF antenna circuit current, thus avoiding instability that typically results for parallel connected antennas. Because a single antenna is used as an ICP generation tool, a single match box and RF generator can be used.

Examples of antennas that are useful include those that surround the plural zones or are surrounded by an arrangement of plural zones. To compensate for or avoid a standing wave pattern at an antenna, specifically when higher frequencies are used, several independently powered antennas can be used with terminal ends distributed inlets along zone arrangement. For example, a combined serpentine antenna shape can be used. Various geometrical arrangements of the inlet zones can be used, with symmetrical arrangements sometimes preferred, such as annular, rectangular or linear arrangements, and even more complex shapes.

In particular embodiments, common or separate gas inlets can be connected to each local plasma source zones. One or more gases can be used. An advantage of pre-igniting different gases before introduction into a process chamber is that each gas is excited into a plasma state without mixing with another gas, or at-least mixing at significantly reduced concentration of another gas. The pre-ignited gases subsequently interact in the main reaction chamber. With the invention, plasma downstream of the plasma source can be controlled for uniformity. For example, gas flow, RF coupling and other parameters can be controlled among the inlet zones.

The inlet zones can all have the same or similar geometries and dimensions. Alternatively, at least one or more of the inlet zones can have a different geometry or dimensions that differ from those of the other zones. For example, a gas flow cross section or diameter of individual zones can differ, or different perimeter lengths of individual zones that are exposed to the RF can differ. Such differences can be determined based on the individual plasma conditions desired and the ways the gases are to be combined in the chamber.

These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description, in which:

FIG. 1 is a perspective diagram of one embodiment of a plasma processor having a multiflow integrated ICP source according to principles of the invention.

FIG. 2 is a perspective diagram of an alternative embodiment of the multiflow integrated ICP source FIG. 1 according to principles of the invention.

FIG. 3 is a perspective diagram, similar to FIGS. 1 and 2 , of further embodiment of a multiflow integrated ICP source according to principles of the invention.

FIG. 4A is a power density distribution graph of the embodiment of FIG. 3 .

FIG. 4B is a power density distribution graph, similar to FIG. 4A , illustrating the embodiment of FIG. 3 with only the large outer inductive antenna energized.

FIG. 5 is a perspective diagram, similar to FIGS. 1 , 2 and 3 of still another embodiment of a multiflow integrated ICP source according to principles of the invention.

FIG. 6 is a perspective diagram, similar to FIGS. 1-3 and 5 of yet another embodiment of a multiflow integrated ICP source according to principles of the invention.

FIG. 7 is a perspective diagram, similar to FIGS. 1-3 , 5 and 6 of an linear embodiment of a multiflow integrated ICP source according to principles of the invention.

A plasma processor 10 , as illustrated in FIG. 1 , includes a plasma source 20 that have multiple pass-through zones 21 a through 21 g , each having a gas flow passage 22 a - 22 g therethrough that communicates with an opening in a top plate 14 of a vacuum processing chamber 12 . In the embodiment of FIG. 1 , the zones 21 a - 21 g are formed of individual quartz tubes 23 that are bundled together. In the embodiment of FIG. 2 , a plasma source 20 a is illustrated having zones 21 a - 21 g that are formed of a single block of dielectric material 24 . An inductive antenna 30 surrounds the tubes 23 in FIG. 1 and is coupled to an appropriate source (not shown) of RF power. The use of generally circular shapes in FIGS. 1 and 2 provides some desirable symmetry, but other shapes can be used, and the cross-sectional shapes of the zones 21 a - 21 g which can be selected to as most suitable for the given substrate geometry, size and uniformity requirements, and gas ratios Annular, rectangular, linear, or more complex shapes of geometrical cross sections may be suitable for particular applications. The material for the tubes 23 or block 24 can be any number of dielectric or insulating materials of choice, such are quartz, alumina, AlN, silicon carbide, or other appropriate materials. For example, single block design can be easily made from bulk TEFLON material.

In FIG. 1 , the antenna 30 is a single inductive outer conductor, which delivers RF power to all seven of the pass-through zones 21 a - 21 g of this embodiment. As such, the multiple plasma zones 21 a - 21 g present serial impedances to the RF current, which helps avoid the instability that is typical of parallel connected impedances. Because the single antenna 30 is used for ICP generation, a single match box 51 and RF generator 50 can be used to supply power to all of the zones 21 .

In FIG. 2 , both an outer antenna 30 a and an inner antenna 30 b are provided, either one or both of which may be used. For antenna dimensions in range from 10 to 40 cm, the inductance of several loops of antennae is several microHenries (mH). For instance, antenna 30 in FIG. 1 has a 3.6 mH inductance, while the inductance of the outer antenna 30 a in FIG. 2 is about 9.3 mH and of the inner antenna 30 b is about 3.7 mH.

In FIG. 2 , both an outer antenna 30 a and an inner antenna 30 b are provided, either one or both of which may be used. For antenna dimensions in range from 10 to 40 cm, the inductance of several loops of antennae is several microHenries (mH).

A common frequency for the antenna 30 is 13.56 MHz. At much higher frequencies, a standing wave pattern may be generated along the antenna, and generates much higher voltages at the antenna ends. To compensate for such a standing wave pattern on the antenna, several independently powered antennas can be used with distributed inlets along the plasma shape.

FIG. 3 shows a plasma source 20 b , which, as with the source 20 a of FIG. 2 , has multiple zones 21 in a chamber top plate 14 , and two antennas, an outer antenna 30 c and an inner antenna 30 d , utilized to form plasma in the multiple-flow ICP source 20 b . FIG. 4A shows the power distribution in the source 20 b with both antennas 30 c and 30 d energized, where the lighter regions depict power concentrations around both the outer and inner edges of the zones. FIG. 4B illustrates the RF power distribution 61 in the individual zones 21 due to the outer antenna 30 d only, with the lighter regions showing power concentrations highest near the outer surfaces of the zones. More complex antenna shapes are possible to use due to the structured source design. For example, in FIG. 5 , an annular antenna 30 e with a serpentine, sinuous, or alternating “S” conductor used to deliver power into all zones 21 .

FIG. 6 illustrates a source 20 d shown in a disassembled perspective view. The zones 21 are formed in a single annular quartz block 44 that is fixed to a chamber top plate 14 . Common or separate gas inlets can be connected to each local plasma source zones 21 . Two antennas are provided, including an annular inner antenna 30 f around the inner opening of the block 44 , as is an annular outer antenna 30 g , that surrounds the outside of the block 44 . Flow rates can be individually controlled in each of the zones 21 by using conventional gas control components. One or more gases can be fed to each individual zone, and different gases that are to be used for processing in the chamber 12 can be supplied to different ones of the zones, thereby allowing each gas to be excited into a plasma state without or before mixing with the other gases, or at least while at a significantly lower concentration of the other gases, than will ultimately be reached in the chamber 12 . The plasma gases, after plasma creation, are introduced into the chamber 12 where they interact in the main reaction chamber 12 . An example of the gas manifold 40 for three different gases sources 41 , 42 and 43 is illustrated in FIG. 6 .

In the embodiment of FIG. 7 , the zones 21 are defined within separate quartz tubes 22 , all of which are surrounded by each of three single antennas 30 h , 30 i and 30 j . Each of the antennas 30 h , 30 i and 30 j has an inductance of about 1.1 mH. When using three such antennas in parallel, 370 nanoHenries (nH) only will be experienced. Such values of the inductance are easily implementable for RF excitation at frequencies in the range of 100 s of kHz up to 10 s of MHz. The three antennas 30 h , 30 i and 30 j are connected in parallel with respect to one another. With the antennas 30 h , 30 i and 30 j , standing wave dispersion can be provided by staggering the antenna ends 50 h , 50 i and 50 j , as illustrated in FIG. 7 , or by phasing the RF power on the different antennas 30 h , 30 i and 30 j to allow the antenna ends 50 to align.

In each of the embodiments described above, each of the antennas 30 couples power into each of the zones 21 , so that each antenna circuit includes series impedances from each of the zones. This enhances the stability of the plasma excitation system.

Although only certain exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.