Workpiece processing chamber having a rotary microwave plasma source

In a processing reactor having a microwave plasma source, the microwave radiator is mounted on a rotary microwave waveguide coupling for continuous rotation, to form the reactor for processing a workpiece.

BACKGROUND

Technical Field

The disclosure concerns a chamber or reactor for processing a workpiece such as a semiconductor wafer using microwave power.

Description of Related Art

Processing of a workpiece such as a semiconductor wafer can be carried out using a form of electromagnetic energy, such as RF power or microwave power, for example. The power may be employed, for example, to generate a plasma, for carrying out a plasma-based process such as plasma enhanced chemical vapor deposition (PECVD) or plasma enhanced reactive ion etching (PERIE). Some processes need extremely high plasma ion densities with extremely low plasma ion energies. This is true for processes such as deposition of diamond-like carbon (DLC) films, where the time required to deposit some type of DLC films can be on the order of hours, depending upon the desired thickness and upon the plasma ion density. A higher plasma density requires higher source power and generally translates to a shorter deposition time.

A microwave source typically produces a very high plasma ion density while producing a plasma ion energy that is less than that of other sources (e.g., an inductively coupled RF plasma source or a capacitively coupled RF plasma source). For this reason, a microwave source would be ideal. However, a microwave source cannot meet the stringent uniformity required for distribution across the workpiece of deposition rate or etch rate. The minimum uniformity may correspond to a process rate variation across a 300 mm diameter workpiece of less than 1%. The microwave power is delivered into the chamber through a microwave antenna such as a waveguide having slots facing a dielectric window of the chamber. Microwaves propagate into the chamber through the slots. The antenna has a periodic power deposition pattern reflecting the wave pattern of the microwave emission and the slot layout, rendering the process rate distribution non-uniform. This prevents attainment of the desired process rate uniformity across the workpiece.

A limitation on processing rate is the amount of microwave power that can be delivered to a process chamber without damaging or overheating the microwave window of the chamber. Currently, a microwave window, such as a quartz plate, can withstand only low microwave power levels at which DLC deposition processes can require hours to reach a desired DLC film thickness. The microwave window provides a vacuum boundary of the chamber and is consequently subject to significant mechanical stress, rendering it vulnerable to damage from overheating.

SUMMARY

A reactor for processing a workpiece comprises a chamber comprising a microwave transmissive window, a gas distribution plate, a microwave radiator overlying the microwave transmissive window and comprising a microwave input port, a rotary waveguide coupling comprising (a) a stationary member comprising a microwave power receiving port, and (b) a rotatable member coupled to the microwave input port of the microwave radiator, and a rotation actuator coupled to the rotatable member.

In one embodiment, the rotation actuator comprises a motor and a rotatable drive gear coupled to the motor, and the rotatable member comprises a driven gear fastened to the rotatable member and engaged with the rotatable drive gear. In a related embodiment, the rotatable drive gear is at a stationary location and is rotatable about a radial axis, and the driven gear is at a location fixed relative to the rotatable member.

A related embodiment further comprises an axial waveguide connected between the microwave input port of the microwave radiator and the rotatable member. The axial waveguide may be coaxial with the axis of symmetry.

A related embodiment further comprises a microwave generator and a flexible waveguide conduit connected between the microwave generator and the microwave power receiving port of the stationary member.

In a further embodiment, a reactor for processing a workpiece comprises (a) a chamber and a workpiece support in the chamber, the chamber comprising a ceiling and a side wall, the ceiling comprising a microwave transmissive window, (b) a first gas distribution plate overlying the workpiece support and comprising plural gas injection orifices, a process gas plenum overlying the first gas distribution plate and a process gas supply conduit coupled to the process gas plenum, (c) a microwave radiator overlying the microwave transmissive window and comprising a cylindrical hollow conductive housing having a top, a side wall and a bottom floor, an array of openings in the bottom floor, and a microwave input port, (d) a rotary waveguide coupling comprising a stationary member fixed with respect to the chamber and having a microwave power receiving port, and a rotatable member coupled to the microwave input port of the microwave radiator and having an axis of rotation coincident with an axis of symmetry of the cylindrical hollow conductive housing, and, a rotation actuator coupled to the rotatable member, whereby the microwave radiator is rotatable by the rotation actuator about the axis of symmetry.

In an embodiment, the rotation actuator comprises a motor and a rotatable drive gear coupled to the motor, and the rotatable member comprises a driven gear fastened to the rotatable member and engaged with the rotatable drive gear.

In an embodiment, the rotatable drive gear is at a stationary location and is rotatable about a radial axis, and the driven gear is at a location fixed relative to the rotatable member.

In one embodiment, the reactor further comprising an axial waveguide connected between the microwave input port of the microwave radiator and the rotatable member. In an embodiment, the axial waveguide is coaxial with the axis of symmetry.

One embodiment further comprises a microwave generator and a flexible waveguide conduit connected between the microwave generator and the microwave power receiving port of the stationary member.

In one embodiment, the array of openings in the bottom floor of the microwave radiator has a periodic spacing corresponding to a function of a microwave wavelength.

An embodiment further comprises a second gas distribution plate underlying the first gas distribution plate and comprising second plural gas injection orifices, an underlying process gas plenum between the first and second gas distribution plates, and a second process gas supply conduit coupled to the underlying process gas plenum.

In a related embodiment, the first process gas supply conduit is coupled to receive a non-reactive process gas and the second process gas supply conduit is coupled to receive a reactive process gas.

One embodiment further comprises an inductively coupled RF power applicator adjacent to the microwave transmissive window and an RF power generator coupled to the inductively coupled RF power applicator. In one embodiment, the inductively coupled RF power applicator couples RF power through the microwave transmissive window. A related embodiment further comprises a controller governing an output power level of the RF power generator.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

DETAILED DESCRIPTION

The problem of process non-uniformity attributable to the periodic power deposition pattern of the microwave antenna is solved in one embodiment by continuously rotating the microwave antenna relative to the workpiece. The rotation is performed during or contemporaneously with application of microwave power. The rotation may be about an axis of symmetry. This axis of symmetry may be the axis of symmetry of the process chamber, the workpiece and/or the antenna.

The problem of having to limit microwave power to avoid damaging the microwave window is solved by providing a channel through the window and flowing a coolant through the channel. In one embodiment, the coolant is a liquid that does not absorb microwave power (or absorbs very little). In one embodiment, the microwave window is provided as a pair of window layers separated by the channel.

An advantage of the microwave plasma source is that it efficiently generates plasma in a wide range of chamber pressures, generally from above atmospheric pressure down to 10−6Torr or below. This enables its use across a very wide range of processing applications. In contrast, other plasma sources, such as inductively coupled plasma sources or capacitively coupled plasma sources, can only be used in much more narrow ranges of chamber pressures, and are therefore useful in correspondingly limited sets of processing applications.

Referring now toFIG. 1, a workpiece processing reactor includes a chamber100containing a workpiece support102. The chamber100is enclosed by a side wall104and a ceiling106formed of a microwave transparent material such as a dielectric material. The ceiling106may be implemented as a pair of dielectric windows108and110formed in the shape of parallel plates. A microwave antenna114overlies the pair of dielectric windows108,110. The microwave antenna114is enclosed by a conductive shield122consisting of a cylindrical side wall124and a disk-shaped cap126. In one embodiment depicted inFIG. 2, the microwave antenna114is disk-shaped.

As shown inFIG. 1, the microwave antenna114is fed by an axial waveguide116. The axial waveguide116is coupled through an overlying rotary microwave coupling118to a microwave feed120. The rotary coupling118includes a stationary member118-1and a rotatable member118-2. The stationary member118-1is stationary relative to the chamber100and is connected to the microwave feed120. The rotatable member118-2is connected to the axial waveguide116and has an axis of rotation coinciding with the axis of symmetry114aof the microwave antenna114. The rotary microwave coupling118permits microwave energy to flow from the stationary member118-1to the rotatable member118-2with negligible loss or leakage. As one possible example, a slip-ring RF seal (not shown) may be placed at the interface between the stationary and rotatable members118-1and118-2.

A rotation actuator140is stationary relative to the chamber100and includes a rotation motor140-1and a rotating drive gear140-2driven by the rotation motor140-1. A driven gear118-3bonded or fastened to the rotatable member118-2is engaged with the drive gear140-2, so that the motor140-1causes rotation of the rotatable member118-2about the axis of symmetry114a. The driven gear118-3may be implemented, for example, as a circular array of teeth on the bottom surface of the rotatable member118-2.

In the embodiment ofFIGS. 1 and 2, the microwave antenna114is a hollow conductive waveguide including a disk-shaped floor130, a disk-shaped ceiling132and a cylindrical side wall134. The floor130faces the ceiling106and has an array of slots136, best seen inFIG. 2A, affecting the antenna radiation pattern. The ceiling132includes a central opening132ainto which the axial waveguide116extends. The spacing between slots may be selected as a function of the wavelength of the microwave power fed to the microwave antenna114, and the slot pattern and shape may not necessarily conform with the pattern depicted inFIG. 2A.

In one embodiment depicted inFIGS. 1 and 3, a gas distribution plate (GDP)144is disposed beneath the ceiling106, and has an array of gas injection orifices145extending through it to provide a gas flow path to the interior of the chamber100. A gas supply plenum146overlies the GDP144and receives process gas from a process gas supply147. In a further embodiment depicted inFIG. 4, the GDP144consists of an upper GDP144-1and a lower GDP144-2fed with respective process gases by respective upper and lower gas supply plenums146-1and146-2that receive process gases from respective upper and lower gas supplies147-1and147-2. For example, the upper gas supply147-1may furnish a non-reactive or inert gas, while the lower gas supply147-2may furnish a reactive process gas (such as a fluorine-containing gas).

As shown inFIG. 5, a remote microwave generator150is coupled to the rotary coupling118by the microwave feed120. In the embodiment ofFIG. 5, the microwave feed120is in the form of a long flexible waveguide. The microwave feed120may be of sufficient length to accommodate a separation between the remote microwave generator150and the chamber100of several meters or more, for example. Such a separation between the chamber100and the microwave generator150permits the microwave generator150to be of a large size for high power without affecting the size or footprint of the chamber100. The flexible waveguide120may be of a commercially available type formed of corrugated metal which enables it to be bent while maintaining its cross-sectional shape and waveguide characteristics.

Referring again toFIG. 1, the ceiling106may consist of a pair of dielectric windows108,110generally parallel to one another and enclosing a void or channel112between them. The channel112lies along a radial plane orthogonal to an axis of symmetry114aof the microwave transmission antenna. A coolant circulation source160pumps a heat exchange medium, such as a liquid or gas coolant, through the channel112between the dielectric windows108and110. The coolant circulation source may be a heat exchanger for cooling the heat exchange medium. In one embodiment, the heat exchange medium is a liquid that does not absorb microwave energy. Such a fluid is disclosed in U.S. Pat. No. 5,235,251. In this manner, the microwave windows108and110are cooled so as to withstand very high microwave power levels. This in turn removes a limitation on microwave power, enabling the use of high microwave power levels to provide high processing rates. For example, in the PECVD formation of DLC films, a very high deposition rate may be realized that shortens the process time to a fraction of currently required process times, using microwave power in the kiloWatt range for continuous wave mode or in the megaWatt range for pulsed mode.

Referring toFIG. 6, in one embodiment a half-circular array of radial inlets112ato the channel112are fed by an inlet plenum113a. The radial inlets112aare formed through an inner annular barrier125a. Further, a half-circular array of outlets112bfrom the channel112are drained by an outlet plenum113b. The inlet and outlet plenums113a,113bare coupled to an output and a return port, respectively, of the coolant circulation source160through respective ports115a,115b. The respective ports115aand115bare formed in an outer annular barrier125b.

As depicted in dashed line inFIG. 7, in one embodiment a cooling source162injects a heat exchange medium such as a cooled gas (cooled air or nitrogen, for example) through the axial waveguide116into the interior of the microwave antenna114. This gas exits the microwave antenna114through the waveguide slots136(FIGS. 2 and 2A) toward the dielectric window108. For this purpose, the cooling source162is coupled to the interior of the axial waveguide116through the rotary coupling118, for example. A gas return conduit164may be coupled to a return port of the cooling source162through the shield122so as to return the gas to the cooling source for cooling and recirculation. The cooling source162may include a refrigeration unit to re-cool the gas received from the gas return conduit.

Microwave Source with Controllable Ion Energy for Lattice Defect Repair During Film Deposition:

During deposition of a film in a PECVD process, the layer being deposited may have some empty atomic lattice sites. As additional layers are deposited, the additional layers cover the empty lattice sites, thus forming voids in the crystalline structure of the deposited material. Such voids are lattice defects and impair the quality of the deposited material. A microwave source such as that employed in the embodiment ofFIG. 1generates a plasma with very low ion energy, so that it does not disturb the lattice structure of the deposited material, including the lattice defects. Such a microwave source may have a frequency of 2.45 GHz, which generates a plasma having a negligible ion energy level. In one embodiment, the problem of lattice defects is solved by supplementing the microwave source with an inductively coupled plasma (ICP) source. Such a combination is depicted inFIG. 7in which the ICP source is an overhead coil antenna170. Power is applied from an RF generator172through an RF impedance match174to the coil antenna170during the time that the microwave source generates a plasma performing a PECVD process. The level of RF power from the RF generator172is selected to be at a minimum level required to remove (sputter) small amounts of atoms deposited during the PECVD process. The level of RF power from the RF generator172may be set slightly above this minimum level. A fraction of such sputtered atoms tend to redeposit in the voids referred to above during the PECVD process. As a result, the formation of lattice defects or voids in the deposited material is prevented. For this purpose, a controller176is provided that enables the user (or a process management system) to select an ideal power level of the RF generator172.

In the embodiment ofFIG. 7, each of dielectric windows108and110has a recessed annulus at its edge to form an annular pocket600into which the coil antenna170is received below the plane of the microwave antenna114. For this purpose, the dielectric window108has a disk-shaped major portion108a, an annular recessed edge portion108band an axial cylindrical portion108cjoining the major portion108aand the recessed edge portion108b. Similarly, the dielectric window110has a disk-shaped major portion110a, an annular recessed edge portion110band an axial cylindrical portion110cjoining the major portion110aand the recessed edge portion110b. The annular pocket600is defined between the axial cylindrical portion108cand the side wall124of the shield122. The annular pocket600is sufficiently deep to hold the entire coil antenna170below the plane of the microwave antenna114.