Electron cyclotron rotation (ECR)-enhanced hollow cathode plasma source (HCPS)

Techniques are disclosed for an electron cyclotron rotation (ECR)-enhanced hollow cathode plasma source (HCPS). A cylindrical magnet is placed around the neck of a hollow cathode under the influence of an RF field. A plasma gas is introduced in the hollow cathode that undergoes phase transition to a plasma containing free electrons and gas ions. The magnetic field of the magnet causes ECR that confines free electrons to a narrow spiraling beam traveling down the body of the hollow cathode. Unlike traditional methods, the present ECR-enhanced design confines the electrons and ions to a narrow path away from the walls of the cathode. The high-density, stable plasma is available at the distal end of the hollow cathode. A multicavity design utilizes multiple cavities with multiple aligned magnets in a single reactor suitable for various processes including, PECVD, PEALD, ALE, etc.

FIELD OF THE INVENTION

This invention relates generally to hollow cathode plasma sources (HCPS), and more specifically to electron cyclotron rotation-enhanced HCPS.

BACKGROUND OF THE INVENTION

For semiconductor manufacturing, numerous techniques exist for creating plasma such as capacitively coupled plasma (CCP) systems, inductively coupled plasma (ICP) systems, slotted plane antenna (SPA) plasma systems, etc. Plasma is formed due to the interaction of process gas(es) with electro-magnetic (EM) field propagation at frequencies in the radio frequency (RF) or microwave spectrum.

Of special interest to this disclosure are hollow cathode plasma sources (HCPS). These sources have shown advantages over other traditional plasma sources for depositing films by processes including plasma enhanced chemical vapor deposition (PECVD) and plasma enhanced atomic layer deposition (PEALD/PAALD). Such a traditional HCPS design of the prior art is depicted inFIG.1.

In the prior art HCPS system10ofFIG.1, a plasma gas12, such as Argon (Ar), is passed through a hollow tube18that acts as a cathode. An RF-power, typically greater than 100 W is applied to hollow cathode18from an RF-power source16. Under the influence of the electromagnetic field resulting on the inside of cathode16due to RF-source16, plasma gas12is ionized. The electrons thus liberated collide with the walls of the cathode tube in a zig-zag manner or what is referred to as a “pendulum effect”. One such electron14is schematically shown inFIG.1.

Through these collisions, these electrons heat tube18sufficiently to liberate more electrons from it via field-enhanced thermionic emission. The resulting electrons and the ionized process gas from this self-sustaining process create a high-density plasma20at the far end of cathode tube18. The plasma may then be utilized for deposition of other gas species on semiconductor wafer via processes such as PECVD or PEALD.

But such a traditional HCPS design exhibits several shortcomings including the following. The pressure of resulting plasma20needs to be too high for certain applications. Specifically, the pressure cannot be lower than 0.1 Torr in the traditional design ofFIG.1. Due to the intense pendulum effect of the electrons, positive gas ions that follow the electrons bombard the walls of tube18. This results in atoms from the wall being removed in a process called sputtering. Excessive sputtering contaminates cathode18that must be periodically cleaned. Furthermore, the electrons are also lost to the walls of tube18thereby reducing the density of plasma20. Plasma20is also not very uniform and stable across the cathode. RF-power source16as a result experiences fluctuating load making it harder for a stable operation.

OBJECTS OF THE INVENTION

In view of the shortcomings of the prior art, it is an object of the invention to provide a hollow cathode plasma source (HCPS) that can generate plasma under extremely low pressures. The present design accomplishes this through its innovative use of electron cyclotron rotation (ECR)-enhanced design of the HCPS.

It is thus also an object of the present ECR-enhanced HCPS design to generate high-density plasma with minimal sputtering.

It is also an object of the present ECR-enhanced HCPS design to minimize loss of free electrons to the walls of the hollow cathode.

It is further an object of the present ECR-enhanced HCPS technology to produce a very stable and uniform high-density plasma.

It is further an object of the present design to allow for a very stable load on the RF power source, thus allowing for smooth and stable operation.

Still other objects and advantages of the invention will become apparent upon reading the detailed description in conjunction with the drawing figures.

SUMMARY

The objects and advantages of the present technology are secured by methods and apparatus or systems for an electron cyclotron rotation (ECR)-enhanced hollow cathode plasma source (HCPS). According to the chief aspects, an axially magnetized cylindrical magnet is placed around the neck of a hollow cathode or cavity.

The hollow cathode or cavity is under the influence of a radio frequency electromagnetic field, or simply an RF field.

A gas, referred to as the plasma gas, is flown through the neck of the cavity and into the cavity. Under the influence of the RF field the plasma gas undergoes a state transition to a plasma state or simply plasma. The plasma consists of a free electrons and gas ions. As a key innovative aspect of the present design utilizing the cylindrical magnet, the free electrons thus generated remain confined to a narrow spiraling beam as they travel downward through the body of the hollow cathode/cavity.

This is due to the magnetic field of the cylindrical magnet placed around the neck or the top portion of the cavity where the plasma is stuck. More specifically, it is due to the familiar phenomenon of electron cyclotron rotation (ECR). In other words, as a result of the ECR caused by the magnetic field of the magnet, the electrons spiral down the hollow cathode, instead of undergoing a wild, zig-zag motion or the “pendulum effect” of the techniques of the prior art. Subsequently, the high-density and uniform plasma is produced or outputted or is available at the bottom or far or distal end of the hollow cathode or cavity.

The preferred embodiment utilizes multiple arrangements of the above hollow cathode/cavities in a multicavity design or reactor or chamber. Cylindrical, axial magnets around the tops/necks of the cavities are all oriented in the same direction or are aligned in such an embodiment. The high-density and uniform and stable plasma produced by the multiple cavities is transmitted through mating interfaces via output holes of a showerhead, and into a process volume. The reactant gas(es) are also passed via a trap volume and then through pinholes of the showerhead into the same process volume. It is the process volume where the reactant gas(es) and the plasma first interact.

The above design allows for high-density and stable/uniform plasma to be generated at low pressures. Variety of embodiments of the design utilize varying substrate temperatures and operating pressures. Variations further utilize varying ion energies by controlling RF-bias of the platen holding the substrate. Consequently, embodiments of the present multicavity ECR-enhanced HCPS based design may be used to perform a variety of vacuum deposition processes/operations, including plasma enhanced chemical vapor deposition (PECVD), plasma enhanced/assisted atomic layer deposition (PEALD/PAALD), atomic layer etching (ALE), etc.

Preferably, the frequency of the RF field is substantially 13.56 Megahertz to be compatible with commercial technologies. Preferably, the power of the RF field is greater than 100 Watts. Preferably, the shape of each hollow cathode is like a bottle with a neck, a shoulder and a body. In other words, preferably the hollow cathode is bottle-shaped, although that is not a requirement. Preferably, the magnets are cooled using an innovative arrangement of a thermally conductive ceramic plate, a cooling plate and an inflow/outflow of cooling water.

Clearly, the system and methods of the invention find many advantageous embodiments. The details of the invention, including its preferred embodiments, are presented in the below detailed description with reference to the appended drawing figures.

DETAILED DESCRIPTION

Electron Cyclotron Rotation (ECR)-Enhanced Hollow Cathode Plasma Source (HCPS)

The present invention will be best understood by first reviewing the schematic diagram of the ECR-enhanced HCPS design based on present principles as illustrated inFIG.2.FIG.2shows an instant ECR-enhanced HCPS50that is an improvement over the prior art design10ofFIG.1discussed earlier in the Background section. A key innovation of the instant design of ECR-enhanced HCPS50ofFIG.2over traditional HCPS10ofFIG.1is the use of a cylindrical magnet52around the neck of a hollow cavity or cathode58. While the embodiment ofFIG.1shows one such cavity/cathode58with one magnet52, there may be multiple such arrangements as will be taught later.

As shown, cathode58is bottle-shaped with a body58C, a shoulder58B, and a neck58A indicated by the dotted-and-dashed line. Note, that neck58A is narrower than body58C with an intervening shoulder58B. However, that is not a requirement. In other words, in certain embodiments, cavity58may not have a distinct narrower neck. In other words, neck58A may have the same diameter as body58C. Still differently put, cavity58may be cylindrical. Alternatively, there may be a narrower neck58A but without shoulder58B. In still other embodiments, the neck may be wider than the body, etc.

There is an RF-power source16providing an RF electromagnetic field in the radio frequency (RF) spectrum, referred to herein as RF field, to cathode58as shown. Preferably, the electrical power provided to the RF field, referred to herein as the RF-power, is greater than 100 Watts (W). Now, a gas12, such as Argon (Ar), is flown through hollow cathode or cavity58as shown by the arrow. Under the influence of the RF field from RF-power source/supply16, the gas is ionized inside of cathode or cavity58, undergoing a phase transition to a plasma state or simply plasma containing free electrons and gas ions. Since gas12is used to produce plasma, it may be referred to as the plasma gas with the knowledge that plasma is generated/struck from gas12only after it undergoes the phase transition to plasma state inside cavity58.

Now, because of the instant innovative design of using cylindrical magnet52around the neck of cavity58where plasma is struck, the resulting electrons are confined to a narrow beam. This is a significant innovation over the prior art design ofFIG.1where electrons undergo a zig-zag motion striking the walls of the cathode. Consequently, inFIG.1, the heavy positive gas ions attracted to the electrons (as the plasma tries to maintain neutrality), also bombard the walls of the cathode. As a result, in the prior art design ofFIG.1, sputtering occurs from the walls of the tube/cathode as well as loss of electrons to the walls, thereby reducing the plasma density.

In the contrasting design of present hollow cathode58, electrons resulting from plasma generation, along with the gas ions of the plasma, are confined to a narrower beam inside the cathode tube. This significantly minimizes sputtering and the loss of electrons to the walls of the cathode, as compared to the traditional techniques.

The electrons are confined in the instant design as depicted inFIG.2due to the magnetic field of cylindrical magnet52per above. More specifically, the electrons are confined due to the magnetic field lines54of magnet52. Cylindrical magnet52is axially magnetized as shown by its North (N) and South (S) poles. Preferably, it is a Neodymium magnet. Preferably, the maximum strength Bmaxof magnetic field54is 13,200 Gauss. Preferably, the outside and inside diameters of cylindrical magnet52are 0.75 inches and 0.25 inches respectively. Magnetic field54is present circumferentially around the part of cathode58where plasma is struck/generated, ensuring that electrons are confined to a more narrowly focused path down cathode58as compared to the techniques of the prior art.

This innovation of the present design is due to the phenomenon referred to as electron cyclotron rotation (ECR). More specifically, ECR occurs when the frequency of incident radiation coincides with the natural frequency of rotation of electrons in a magnetic field, such as magnetic field54of magnet52. As a result of ECR, free electrons in static and uniform magnetic field54move in a circle due to the Lorentz force. As a result, the electrons spiral down, or travel in a narrow/confined spiraling beam, down instant cathode cavity58and specifically its body58C shown inFIG.2. Subsequently, a very stable and high-density plasma60is produced or outputted or is available at the far or distal end of cathode58as shown.

High-density plasma60of the instant ECR-enhanced HCPS design ofFIG.2has several advantages over plasma20generated by traditional HCPS designs as will be taught further below. But first, let us understand a highly preferred embodiment of the present ECR-enhanced HCPS design employing multiple hollow cathodes and cylindrical magnets. For this purpose, let us take advantage ofFIG.3.

FIG.3shows a chamber assembly or simply a chamber100utilizing an ECR-enhanced HCPS based on the instant principles. As provided in this disclosure, an ECR-enhanced HCPS based chamber, such as chamber100, supports both PECVD, PEALD and other forms of deposition/etching processes. However, special attention in the immediate teachings will be given to PECVD process requiring high-density and uniform plasma generated by the instant ECR-enhanced HCPS design.

FIG.3shows a perspective view of chamber100. In the preferred embodiment, chamber100of the instant design comprises an upper or top section or portion102and a lower or bottom section or portion120. There is a substrate/wafer surface or a substrate/wafer sample or simply a substrate or a wafer or a sample140in lower portion120on which deposition or coating by PECVD is performed. Typically, the substrate is a silicon substrate. Sometimes the immediate volume inside chamber100surrounding the substrate is also referred to as the process volume. Of course, the process volume exists once top and bottom sections102and120respectively of chamber100are closed. Substrate140is placed on top of a rotating and heated platen (not shown). The platen is located on the inside of the process volume below the showerhead as will be explained further below.

FIG.3is the chamber assembly taught in detail in incorporated by reference herein, U.S. application Ser. No. 16/738,240 filed on Jan. 9, 2020 to Birol, except with some very important differences. The first difference is that instead of a planar inductively coupled plasma (ICP) source, it is an instant ECR-enhanced hollow cathode plasma source (HCPS)104A contained in the top portion102of chamber assembly100. The second difference is that there is no grounding metal plate of the ICP-based design of the above-mentioned reference. This is because such a ground plate would unacceptably extinguish the high-density plasma generated by instant HCPS104A. The third difference is that there is no RF port that provides RF power to the above grounding metal plate. That is because instead of the metal plate acting as an RF source for PECVD, it is HCPS104A that is utilized for as the plasma source for PECVD in the present design.

Now, HCPS104A ofFIG.3has a ducting or tubing or line106A to carry process gas(es) to the showerhead of the below teachings at two laterally opposite gas feedthrough points106B and106C as shown. There is also a plasma gas input107to feed plasma gas to HCPS104A. There is also an RF power feed-through or input104B providing RF-power to HCPS104A, and specifically its RF cathode per below teachings. The RF-power source is not explicitly shown inFIG.3to avoid distraction from the main principles being taught.

The preferred embodiment ofFIG.3also shows a chamber lift108and a base plate190on which chamber or chamber assembly100is mounted. Further shown are ducting/lines126A required to carry the process gas(es) to chamber100. It should be noted that inFIG.3, top portion102and bottom portion120of chamber100are shown ajar to delineate their components on the inside. Of course, the deposition process is carried out once the two portions/sections are closed together with a snug and airtight fit to seal chamber100. This is accomplished by utilizing O-rings per the teachings already provided in the above-mentioned reference, and which are not repeated here for brevity. We may refer to the sealed state of chamber100as a substantially sealed state in order to represent the range of vacuum conditions required to carry out the operation of the system. The vacuum conditions are preferably obtained by a combination of backing and turbomolecular pumps.

The gases flowing via lines126A from lower portion120to upper portion102may include reactant gases, plasma gasses, purge gases, or other types of gases as required for a given application or process recipe. The gases flow through stainless steel gas lines126A around which O-rings are provided where upper portion102and lower portion120close together. The above mechanism allows top and bottom portions102,120respectively to separate from each other without requiring flexible tubing to bring gasses to top portion102. As a result, top chamber102can be pneumatically lifted (manually or otherwise) using chamber lift108while still allowing gases to flow from bottom portion120to top portion102when the two portions are in a closed position. As will be appreciated by those skilled in the art, that the use of stainless-steel lines of the above design provides for a higher reliability than flexible tubing, and the pneumatic lift design provides for a user-friendly system operation.

FIG.3also explicitly shows a process computer112that runs the control software for managing/controlling the processes or recipes executed in chamber100. Further shown are two water inlet/outlet ports109A and109B that are used to flow cooling water. The water cools a cooling plate (not shown inFIG.3) that in turn is used to cool the cylindrical magnets that get hot due to the plasma during the operation of the system per below teachings. Conveniently, a plasma viewport146is also provided in the system as shown to visually monitor the plasma during system operation as needed.

After having learned the overall design of the multi-cavity chamber utilizing the instant ECR-enhanced HCPS in conjunction with the teachings already available in the above-referenced U.S. application Ser. No. 16/738,240 filed on Jan. 9, 2020 to Birol, let us now pay special attention to the design of the ECR-enhanced HCPS itself. For this purpose, let us take advantage ofFIG.4.FIG.4shows a detailed cross-sectional view of upper portion102of chamber assembly100ofFIG.3containing our ECR-enhanced HCPS104C. As already mentioned, RF-power feed104B provides RF-power to HCPS104A.

Explained further, RF-power feed104B is used to carry and establish RF field around hollow cathode cavities104D shown inFIG.4. For simplicity, we may sometimes refer to RF-feed104B as RF-power, with the knowledge that it is the RF-power source/supply (not shown) that actually generates the RF field carried by feed104B. The frequency of the RF field is preferably kept at or near 13.56 Megahertz to be compatible with commercial equipment. As shown, cavities104D have a bottle shape, with a body, a shoulder and a neck narrower than the body as in the embodiment ofFIG.2. However, similar to the embodiment ofFIG.2, that is not a requirement. The necks, shoulders and bodies of cavities104D are not marked explicitly in order to avoid clutter inFIG.2.

Also, not all the cavities are marked by reference numerals for reasons of clarity. In the instant design, the compartment marked by reference numeral104E may be referred to as the RF cathode of the present multi-cavity ECR-enhanced HCPS embodiment. It is where electromagnetic radiation/energy of the RF field is imparted to intervening cavities104D under the influence of RF-power104B. Preferably, bottle-shaped cavities104D are made out of aluminum because of its high thermal and electrical conductivity.

FIG.4also shows cylindrical magnets105of the above teachings around the top portions or necks of each instant hollow cathode/cavity104D as shown. Cylindrical magnets105are axially magnetized per above teachings ofFIG.2and are all oriented in the same direction. We refer to magnets105being oriented in the same direction as being aligned in the present disclosure. In other words, by aligned we mean that the north pole (N) or conversely the south pole (S) of all the magnets is either facing up or down. Of course, for the embodiment ofFIG.2, single magnet52will be considered aligned whether its north pole (N) or conversely south pole (S) is facing up or down.

Note that due to the cross-sectional view of magnets105around cavities104D shown inFIG.4, each cylindrical magnet105appears as two dark bars or portions around the neck of cavities104D. It is understood that, each pair of left and right dark portions around the neck of each cavity104D represents a cylindrical magnet105that wraps around circumferentially around the cavity neck. Note, the left and right portions of only one such magnet are shown marked inFIG.4by reference numerals105in order to avoid clutter.

Referring toFIG.3, once chamber100is sealed, a plasma gas such as argon (Ar), ammonia (NH3), oxygen (O2), nitrogen (N2) or a mixture of one or more thereof, etc., is flown through gas feed107. The plasma gas flows into volume104G via gas feed107. From there, it seeps into cavities104D via respective pinholes104H. Pinholes104H connect volume104G to cavities104D passing through housing104F and ceramic plate115further discussed below. Note, only four such pinholes104H are shown inFIG.4connecting into respective cavities104D and only two such pinholes are explicitly marked by reference numerals104H in order to avoid clutter.

Plasma is struck in each of hollow cathode cavities104D under the influence of the RF field due to RF-power104B. Now, due to the instant innovative design of using cylindrical and aligned magnets105around each hollow cathode cavity104D, the electrons generated due the plasma are confined to a narrow beam due to the phenomenon of ECR per above teachings. As a result, the high-density plasma produced/generated or is available at the far or distal or bottom ends of cavities104D is a lot more stable, at a lot more desirably low pressures and with minimal sputtering on the walls of the cavities than the techniques of the prior art.

Other advantages of the instant plasma generated by the above ECR-enhanced HCPS design will be enumerated further below. Note that while it is understood that the plasma gas undergoes phase transition to the plasma state inside cavities104D, we refer to the generation or production or the outputting of plasma only once it arrives at the bottom or distal ends of cavities104.

FIG.4further shows a water inlet port109A and a water outlet port109B (or vice versa). Also shown is a cooling plate111. Cooling plate111is a cylindrical plate that wraps around the axis of chamber102in a circumferential manner. When cooling water is circulated on top of cooling plate111via ports109A/109B, it draws heat away from magnets105. Otherwise, magnets105may get too hot from plasma generated in cavities104D, causing risk to the integrity of the system.

Also shown inFIG.4is a circular ceramic ring or spacer113with a reverse hatched pattern that is meant to electrically isolate RF cathode104E with its numerous hollow cathode cavities104D from the housing or body104F of instant ECR-enhanced HCPS104C. Housing/body104F is electrically grounded. Further shown is a circular ceramic plate115that is meant to provide RF isolation to housing104F from RF cathode104E which is under the influenced of the RF field due to RF-power104B per above. Ceramic plate115must also be thermally conducting/conductive in order to transmit heat away from RF cathode104E and its magnets105to cooling plate111from where it is transported away by cooling water via ports109A-B per above.

Before proceeding further, let us take a look at another view of top portion102shown inFIG.4of chamber100ofFIG.3based on the instant design. Such a left perspective view from below is shown inFIG.5. Not all the reference numerals fromFIG.4are shown inFIG.5and not all the details are shown in order to avoid clutter. For example, only one pinhole104H is shown marked inFIG.5and only two such pinholes are shown. There is a trap volume104J shown inFIG.4andFIG.5. Referring toFIG.5now, trap volume104J is created by affixing a bottom component or “showerhead”104L to the rest of housing/body104F of our ECR-enhanced HCPS104C. This affixing is preferably done via screws or bolts104I shown inFIG.4-5. Note, that not all such screws/bolts are shown or marked inFIG.4-5for clarity.

Trap volume104J is a thin space created preferably via a spacer ring (not explicitly shown), between showerhead104L and the rest of housing104E when the two are screwed/bolted together. Of course, there are also one or more O-rings (not shown) outside of such a spacer ring in order to provide a pneumatic seal around trap volume104J when showerhead104L is screwed/bolted to body104F. Connected to trap volume104J are the egresses of process gas inputs106A-B of above explanation. As reactant gases are flowed through gas inputs106A-B, they arrive in trap volume104J from where they seep/inject into the process volume via these egresses or pinholes104K. Recall while briefly referring toFIG.3and prior explanation, the process volume is formed below the showerhead once top portion102of chamber assembly is connected and sealed with bottom portion120. Wafer140resides atop a heated and rotating platen in the process volume per above explanation.

Now, referring again toFIG.4-5, plasma is also transmitted or passed from hollow cathode cavities104D down to the process volume via output holes104M located on the bottom of showerhead104L. Explained further, in trap volume104J there are mating interfaces to the exits of hollow cathodes/cavities104D as shown, that allow the plasma to pass or transmit through to output holes104M without seeping into trap volume104J itself.

Explained even further, pinholes104K are drilled into a trench or groove for the reactant gases, and gases move in the trench where their conductance is higher as compared to the mating interfaces of the plasma which are clamped and provide higher resistance to the gases to come close to the plasma. In this manner, the reactant gases in trap volume104J do not come in contact with the plasma until both they and the plasma have reached the process volume via pinholes104K and output holes104M respectively. Note that not all holes104K and104M are shown marked by reference numerals in order to avoid clutter.

FIG.6shows a frontal view of our showerhead104L ofFIG.5. It shows our bolts/screws104I, output holes104M and pinholes104K. Also shown explicitly are exit holes104N of hollow cathode cavities104D ofFIG.4-5as visible through output holes104M. Again, not all of holes104K,104M and104N are marked explicitly to avoid clutter. Also shown explicitly inFIG.6is O-ring104O that is used to obtain the vacuum seal between top portion102and bottom portion120of chamber assembly100, once the two are closed per above explanation.

The present design of ECR-enhanced HCPS with cylindrical and aligned magnets around each hollow cathode104D, allows the plasma coming out of output holes104M to be high-density, very stable/uniform, reproducible, and be possible under extremely low pressures. It also allows for minimal sputtering off the walls of cavities104D. Let us now enumerate the various advantages of the present ECR-enhanced HCPS design over traditional art in further detail. These advantages are provided below:1. Uniform, stable and reproducible plasma: The present multi-cavity ECR-enhanced HCPS embodiments taught in reference toFIG.3-6allow ionization of plasma gas and uniform generation of plasma in all cavities104D per above teachings. The design thus allows for a very stable and reliable generation of plasma with a predictable and reproducible quality, as compared to the techniques of prior art.2. Low pressures: In the present design, if Ar is used as the plasma gas, it is experimentally shown that once plasma is struck, it remains sustained down to 0.3 milli Torr at 200 W of RF-power in the embodiments taught in reference toFIG.3-6. In contrast, traditional HCPS designs do not allow the plasma pressure to go below 0.1 Torr.Further, the present technology is compatible with low base pressure chambers where the pressure is of the order of <10−7Torr. Moreover, the pressure in the process volume based on the above design can be made to vary widely, i.e. from 0.3 millitorr to 2 Torr, based on the requirements of an application/recipe.3. Reduced sputtering and loss of electrons: The present design significantly reduces material sputtering from the walls of hollow cathode cavity/cavities58/104D ofFIG.2/FIG.3-5and thus reduces contamination. This is because electrons are confined to a narrow spiraling beam which draws ions away from the walls of the cavity/cavities per above teachings and thus reduced sputtering from the walls. It thus also reduces the loss of electrons to the walls of the cavity/cavities.4. Stable load on RF-power: The present design also produces a well-defined load for the RF-power source preferably working in conjunction with an RF auto-tuner. Preferably, the RF-power source generates RF power of at least 100 W at a frequency of substantially or approximately 13.5 MHz. Since the plasma stays stable, the present design makes it easy for the RF auto-tuner to adapt to changing pressure in the cavity/cavities and to any power changes.5. Scalable: The design can be easily scaled laterally by increasing the surface area of RF cathode104E ofFIG.3-6by introducing more cavities104D. The surface can also be curved as needed. The power of the RF-power source can also be increased further since there is less heat dissipation in the present design. The less heat dissipation is due to reduced collisions of electrons and ions on the cavity walls and due to the cooling of the system with water per above innovative design. Recall from above teachings in reference toFIG.4, that cylindrical, aligned magnets105are cooled as a result of thermally conducting/conductive ceramic plate115, cooling plate111and water inlet/outlet ports109A/109B.6. Separation of plasma generation and process gas injection: Referring to the embodiments ofFIG.4-5, the present design enables separation of plasma generation in cavities104D from the injection of process gas(es) from trap volume104J through pinholes104K into the process volume below showerhead104L. Recall from above, that the plasma enters into the process volume via output holes104M, and it is the process volume where the process gas(es) and the plasma first meet. If the process gas(es) are exposed to plasma generation prematurely, as in some prior art designs, process gas(es), such as silane (SiH4), can easily disassociate before reaching the process volume.In this manner, activation of one species of gas can be decoupled from the other. For example, nitrogen (N2) or ammonia (NH3) or an N2+Ar mixture or an NH3+Ar mixture, can be introduced via plasma gas feed107, while the more delicate SiH4 can be introduced via gas inputs106A-B. The two would subsequently be injected into the process volume via holes104M and104K respectively per above.Furthermore, while allowing a uniform injection of process gas(es) downstream of plasma generation, the above design thus enables an even/uniform gas distribution from showerhead104L into the process volume per above.7. Plasma enhanced/assisted atomic layer deposition (PEALD/PAALD): While the design of the embodiments in reference toFIG.3-6were discussed with special emphasis to PECVD, it must be noted that the same design is also suitable for PEALD or PA LD per the teachings of the above-referenced U.S. application Ser. No. 16/738,240 filed on Jan. 9, 2020 to Birol, and which are not repeated here to avoid repetition. The only difference is the use of the type of the plasma source being used. While the above-mentioned reference uses a planar inductively coupled plasma (ICP) source, the instant design ofFIG.3-6uses our ECR-enhanced HCPS.In this manner, the present embodiments ofFIG.3-6can be used for continuous-flow PEALD or for non-continuous flow PEALD, while utilizing the instant ECR-enhanced HCPS104C. As a result, deposition in the process volume can be accomplished one atomic layer at a time using the self-limiting ALD reactions of the reactants with the substrate or wafer, accruing all the benefits of such a PEALD technology as taught in the above-referenced patent application.8. Atomic layer etching: Related to PEALD above, the design of the embodiments presented above is also suitable for atomic layer etching (ALE). In the case of ALE, a sequence of alternating steps of self-limiting chemical modification and etching of chemically-modified areas is performed. These steps affect only the top atomic layers of the wafer and allow the removal of individual atomic layers one at a time. ALE is a better-controlled process than reactive ion etching (RIE). A typical example is the etching of silicon by alternating reactions with Chlorine for modification and Argon ions for etching.The above ALE process can be achieved by the instant design ofFIG.3-6utilizing our ECR-enhanced HCPS104C, if Chorine is introduced via gas feeds106A-B for attaching to impurities and exemplarily Argon is used as the plasma gas. The plasma gas is introduced sequentially from gas input107programmatically via process computer112. Chlorine with the attached contaminants is then removed from the process volume via one or more purge cycles. The present design thus allows for etching to take place gently at very low temperatures.In other words, the design does not require the platen heater to heat the substrate at high temperatures to facilitate reaction, but instead to only low temperatures where etching is finely controlled. Furthermore, the ion energies can be dialed down as desired. This is easily accomplished by reducing the power of the RF-power source, so that the high-density plasma is generated at low energy levels. Exemplarily, the high-density plasma has a density of (1011-1012ions/cc) with low electron temperatures of 1-2 eV in the process volume. As a result, the ion flux to the platen/plate holding the substrate also has low energy, since ions are accelerated in a potential difference of plasma potential minus plate potential (<100V).In the prevailing art, the widespread use of ALE has been hampered because of low throughput due to the requirement of sophisticated gas handling. This is chiefly due to the requirement of moving the substrate after cleaning to another chamber, thereby reducing the throughput and increasing the overall cost of the operation. Furthermore, the traditional techniques thus subject the wafer to recontamination.The present design solves the above problem by efficiently switching between various gases for ALE and ALD modes of operation without requiring slow and expensive mechanical interventions. As an example, purely by computer-generated signals, one is able to seamlessly switch from Chlorine to Argon in the process volume. This is done programmatically by opening/closing of the various gas feedthroughs of the equipment explained above, allowing for ALE gases to reach the volume for modification/etching, on any requisite carrier gases.9. Biasing for controlling ion energies: As per the teachings of the above-referenced U.S. application Ser. No. 16/738,240 filed on Jan. 9, 2020 to Birol, the platen holding the substrate/wafer in the process volume can be RF-biased for better controlling ion energies. The RF-bias may be provided from a separate RF port from below the chamber assembly.Recall from the teachings of the above reference that the RF-bias on the platen is beneficial for the heavier ions of PECVD layers by inducing ion beam annealing. This allows a practitioner to have a very fine-grained control over the PECVD layers being deposited and thus better manage its density and stress. As a result, the practitioner is able to avoid cracking, compression, stretching, etc. of the PECVD layers.Per above, by controlling the RF-bias to the platen, the present design thus allows for keeping plasma temperature low, while allowing ion energies to be dialed higher or lower depending on the needs of an application/recipe.

For completeness,FIG.7shows a photograph from viewport146explained in reference toFIG.3. Specifically, the photograph displays output holes104M showing that all instant hollow cathodes/cavities104D discussed in reference toFIG.4-6are lit up by plasma uniformly. Note that only two output holes104M are shown marked by reference numerals to avoid clutter. The uniform brightness of the cavities is a testament to the uniform and stable quality of high-density plasma possible by the present ECR-enhanced HCPS design.

ECR-Enhanced HCPS Parameters and Calculations Based on Instant Principles

Now let us consider the operating parameters of some preferred embodiments of our ECH-enhanced HCPS design and perform downstream calculations.

If rcis the radius of the rotation of free electrons under electron cyclotron rotation (ECR) in cavities58and104D ofFIG.2andFIG.4-5respectively, v is the velocity of electrons and co is their angular frequency, then:
rc=v/ωEq. 1

In Eq. (1) above, ω=2π2.8B and v=3.9 103T1/2m/sec, given B is in Gauss and T is in ° K, and rcis generally referred to as the cyclotron radius by those skilled in the art.

If we set T˜11500° K, for a typical 1 ev or 1.15×104Kelvin electrons in a 13,200 Gauss magnetic field, such as magnetic field54of magnet52ofFIG.2or the magnetic fields of magnets105ofFIG.4-5, from Eq. (1) above we get: rc=1.8 micron. Therefore, the cyclotron radius/radii rcof free electrons in cavity58and cavities104D<<Inner radius/radii of cavity/cavities58/104D ofFIG.2andFIG.4-5respectively. In other words, the instant arrangement keeps newly created free electrons confined to a narrow spiraling beam, and thus prevents their loss to the walls of the cavity/cavities at lower pressures. Furthermore, magnetic field enhances ionization or production of plasma in all hollow cathode cavities and confines the ions away from walls to maintain neutrality, thereby minimizing sputtering.

Referring toFIG.4-6, preferably, pinholes104H are 0.03 inches in diameter. Preferably, the neck of hollow cathode cavities104D is 0.3 inches in length. Preferably, the length of the bodies of cavities104D is 1 inch. Preferably, magnets105(as well as magnet52ofFIG.2) are Neodymium magnets. Preferably still, magnets105are RC48 Neodymium magnets. Preferably, the diameter of pinholes104K is 0.02 inches. Preferably, the number of such pinholes104K is 44. Preferably, the least distance between any two such pinholes104K is 1 inch. Preferably, the diameter of output holes104M is 0.5 inches. Preferably, the number of such output holes104M is 48.

In view of the above teaching, a person skilled in the art will recognize that the apparatus and methods of invention can be embodied in many different ways in addition to those described without departing from the principles of the invention. Therefore, the scope of the invention should be judged in view of the appended claims and their legal equivalents.