Patent Description:
Plasma discharges can be used to excite gases to produce activated gases containing ions, free radicals, atoms and molecules. Activated gases are used for numerous industrial and scientific applications, including processing solid materials such as semiconductor wafers, powders, and other gases. The parameters of the plasma and the conditions of the exposure of the plasma to the material being processed vary widely depending on the application.

For example, some applications require the use of ions with low kinetic energy (i.e., a few electron volts) because the material being processed is sensitive to damage. Other applications, such as anisotropic etching or planarized dielectric deposition, require the use of ions with high kinetic energy. Still other applications, such as reactive ion beam etching, require precise control of the ion energy.

Some applications require direct exposure of the material being processed to a high density plasma. One such application is generating ion-activated chemical reactions. Other applications include etching of and depositing material into high aspect ratio structures. Other applications require shielding the material being processed from the plasma because the material is sensitive to damage caused by ions or because the process has high selectivity requirements.

Plasmas can be generated in various ways including direct current (DC) discharge, radio frequency (RF) discharge, and microwave discharge. DC discharges are achieved by applying a potential between two electrodes in a gas. RF discharges are achieved either by capacitively or inductively coupling energy from a power supply into a plasma. Microwave discharges can be produced by coupling a microwave energy source to a discharge chamber containing a gas.

Plasma discharges can be generated in a manner such that both the charged species constituting the plasma and the neutral species, which can be activated by the plasma, are in intimate contact with the material being processed. Alternatively, the plasma discharge can be generated remotely from the material being processed, so that relatively few of the charged species come into contact with the material being processed, while the neutral species can still contact it. Such a plasma discharge is commonly termed a remote or downstream plasma discharge. Depending on its construction, positioning relative to the material being processed, and operating conditions (e.g., gas species, pressure, flow rate, and power coupled into the plasma), a plasma source can have characteristics of either or both of these two general types.

Existing remote plasma sources generally utilize RF or microwave power to generate the plasma. Although present sources support many applications successfully, several technical limitations remain in the practical use of those sources. For example, microwave-based remote plasma sources are generally more expensive than RF sources because microwave power is generally more expensive to produce, deliver and match to a load. Microwave sources and a power delivery system are also generally more bulky than RF sources and require periodic replacement of a tube which generates the microwave power.

RF remote plasma sources that have some degree of capacitive as well as inductive coupling may be less expensive and smaller than the corresponding microwave sources. The capacitive coupling, however, which assists in the plasma ignition process, may lead to degradation of the exposed walls of the plasma chamber due to bombardment of those walls by energetic ions produced in the plasma. RF remote plasma sources that utilize inductive RF coupling, but which minimize associated capacitive coupling, may show less ion-induced degradation of the plasma vessel surfaces. The reduction or elimination of the capacitive coupling, however, can make plasma ignition more difficult to obtain, especially over a wide range of process conditions.

A second difficulty with existing remote plasma sources is removal of the heat generated in the plasma and deposited onto the walls of the plasma chamber. This is especially the case when the plasma chamber has a complex shape and/or when it is composed of a dielectric material for which direct cooling with large quantities of fluid in contact with the dielectric plasma chamber is either undesirable or impractical. This has the effect of limiting the power that can be reliably coupled into the plasma.

Some of the existing plasma chambers, such as the ones described in <CIT>, are manufactured using a quartz material by a combination of high-temperature forming and welding to produce a desired shape (e.g., a torus shape). One main disadvantage of a quartz plasma chamber is that it is incompatible with hydrogen and/or halogen plasma chemistries, such as hydrogen (H*), Fluoride (F*), and/or chlorine (Cl*), due to a high rate of chemical and physical erosion of quartz when exposed to these chemistries.

In addition, some existing plasma chambers, such as the ones described in <CIT>, are manufactured by machining several plasma blocks from aluminum, where the plasma blocks are connected to form a plasma channel of a desired shape (e.g., a torus shape). The internal surface of the plasma channel can be coated using either a deposition process (e.g., chemical vapor deposition, physical vapor deposition or plasma spray) or a conversion process (e.g., hard anodization) to form a dielectric barrier between the base metal and the plasma. One disadvantage of a plasma chamber made from aluminum plasma blocks with dielectric coating is that the coating is typically thin, on the order of a few to tens of micrometers, and therefore cannot withstand high plasma ignition voltages required for igniting in-process gas due to electrical breakdown of the dielectric coating. An inert gas such as argon may be used as ignition gas to lower the ignition voltages, but the transition from ignition gas to process gas leads to a time delay that reduces throughput in pulsed plasma applications. Another disadvantage with thin coatings is that they are unable to adequately protect the plasma chamber body if a defect in the coatings exposes the underlying aluminum to reactive gases in the plasma chamber. Moreover, in the case of conversion coatings, such as using hard anodization, the purity of the coating that is directly exposed to plasma depends on the purity of the base aluminum alloy. For instance, <NUM> aluminum has an aluminum content of <NUM>-<NUM>%, with the balance being other metallic alloying elements. These other metallic impurities can become potential sources of contamination in semiconductor processing. Also, many machined plasma channel geometries have deep holes with an aspect ratio (ratio of length to diameter) in the range of <NUM>:<NUM> to <NUM>:<NUM>. Such high aspect ratio holes are impractical to coat using physical vapor deposition (PVD) or plasma spray methods, as these coatings are applied from an open end and can result in much smaller than necessary coating thickness in hard to reach areas. High aspect ratio holes can be conformally coated using other deposition processes, such as chemical vapor deposition (CVD) or atomic layer deposition (ALD), for example. However, deposition rates for CVD and ALD are much lower than those for spray coating, making these deposition processes slow and prohibitively expensive.

Further, some existing plasma chambers, such as the ones described in <CIT>, are formed by connecting multiple generally linear dielectric tubes to achieve a desired shape (e.g., a torus shape). Although the use of generally linear tubes as building blocks of a plasma chamber widens the range of available materials available, the main disadvantage is that it increases the manufacturing complexity and cost. <CIT> describes a toroidal low-field reactive gas and plasma source having a dielectric vacuum vessel. <CIT> describes a toroidal low-field reactive gas source. <CIT> describes a plasma generation apparatus. <CIT> describes an inductively coupled plasma reactor.

There is a need for plasma chambers having improved resistance to certain plasma chemistries, such as hydrogen and/or halogen plasma chemistries while minimizing metallic contamination in semiconductor processing. There is also a need for plasma chambers that can be manufactured with less complexity and cost.

The present invention provides thick-walled plasma chambers capable of igniting in-process gases, where the plasma chambers can be manufactured from high purity dielectric materials that are compatible with (e.g., having a low erosion rate in) plasma chemistries, such as hydrogen and/or halogen plasma chemistries. The high purity dielectric materials can also minimize metallic contamination in semiconductor processing. The high purity dielectric materials further offer improved thermo-mechanical properties.

In one aspect, a plasma chamber of a plasma processing system is provided. The plasma chamber defines a plasma channel having a first side and a second side oppositely disposed along a length of the plasma channel. The plasma chamber comprises a first section constructed from a dielectric material. The first section has (i) a first flange positioned along the first side of the plasma channel and extending beyond the first side by a first width, and (ii) a second flange positioned along the second side of the plasma channel and extending beyond the second side by a second width. The plasma chamber also comprises a second section constructed from the dielectric material. The second section has (i) a third flange positioned along the first side of the plasma channel and extending beyond the first side by the first width, and (ii) a fourth flange positioned along the second side of the plasma channel and extending beyond the second side by the second width. The plasma chamber further comprises an interface that bonds together the first and second sections between the first and third flanges and between the second and fourth flanges.

In another aspect, a method of manufacturing a plasma chamber of a plasma processing system is provided. The plasma chamber defines a plasma channel having a first side and a second side oppositely disposed along a length of the plasma channel. The method comprises constructing a first section from a dielectric material. The first section has (i) a first flange positioned along the first side of the plasma channel and extending beyond the first side by a first width, and (ii) a second flange positioned along the second side of the plasma channel and extending beyond the second side by a second width. The method also comprises constructing a second section from the dielectric material. The second section has (i) a third flange positioned along the first side of the plasma channel and extending beyond the first side by the first width, and (ii) a fourth flange positioned along the second side of the plasma channel and extending beyond the second side by the second width. The method further comprises bonding the first and second sections together to form the plasma chamber having the plasma channel for containing a plasma therein. Bonding the first and second sections comprises forming bonding between the first and third flanges to generate a first bonded flange having the first width and between the second and fourth flanges to generate a second bonded flange having the second width.

Any of the above aspects can include one or more of the following features. In some embodiments, the dielectric material is alumina (Al<NUM>O<NUM>) ceramic. In some embodiments, the dielectric material is an oxide or a nitride of one of a group II element, a group III element, a lanthanide, or a mixture thereof. In some embodiments, the dielectric material is one of Y<NUM>O<NUM>, Sc<NUM>O<NUM> La<NUM>O<NUM>, Ce<NUM>O<NUM>, or MgO. In some embodiments, the dielectric material is one of AlN, BN, or YN.

In some embodiments, a coating is disposed on an inner surface of the plasma chamber that forms at least a portion of the plasma channel exposed to a plasma therein. The coating can comprise one of Al<NUM>O<NUM>, Y<NUM>O<NUM>, Sc<NUM>O<NUM>, La<NUM>O<NUM>, Ce<NUM>O<NUM>, MgO, SiO<NUM>, B<NUM>C or an alloy including YAG.

In some embodiments, the first and second sections are substantially identical. In some embodiments, a thickness of a wall of the first or second section is between about <NUM> (<NUM> inches) and about <NUM> (<NUM> inches). In some embodiments, the first or second section is constructed by machining the dielectric material in a green state.

In some embodiments, the plasma chamber further includes (i) a first bonded flange formed by the bonding of the first and third flanges, where the first bonded flange has the first width, and (ii) a second bonded flange formed by the bonding of the second and fourth flanges, where the second bonded flange has the second width. In some embodiments, the first width of the first bonded flange or the second width of the second bonded flange is between about <NUM> (<NUM> inches) and about <NUM> (<NUM> inch). For example, the first or second width can be about <NUM> (<NUM> inches).

In some embodiments, the bonding interface comprises a bonding agent that is one of a glass frit, a eutectic mixture or an epoxy. For example, the eutectic mixture can comprise one or more of Al<NUM>O<NUM>, Y<NUM>O<NUM>, Sc2O3, Ce2O3, MgO, CaO, or ZrO<NUM>. In some embodiments, the first and second sections are bonded together by sintering the first and second sections together to create a hermetic seal at the first and second bonded flanges. In some embodiments, a layer of alloying agent can be disposed on an inner surface of at least one of the first section or the second section prior to the sintering. The inner surface is adapted to form at least a portion of the plasma channel exposed to the plasma therein. An alloyed coating is created on at least a portion of the inner surface having the layer of alloying agent disposed thereon by the sintering process that bonds the first and second sections.

In some embodiments, the plasma channel forms a toroidal loop. The toroidal plasma channel can be circular, oval, elliptical or polygon in shape. In some embodiments, the plasma channel is linear. In some embodiments, a cross section of the plasma channel is circular, rectangular or oval in shape. An area of the cross section of the plasma channel can be between about <NUM><NUM> and about <NUM><NUM>. chamber typically defines one or more plasma channels having a variety of shapes. For example, a plasma channel can have a linear shape or a loop shape (e.g., to support a toroidal plasma). As shown in <FIG>, the plasma chamber <NUM> can be a toroidal loop, which is defined as forming a looped internal plasma channel (not shown) with a closed path to support plasma current circulation in the closed path.

The plasma chamber <NUM>, including the plasma channel, has a first side <NUM> and a second side <NUM> oppositely disposed along the length of the plasma channel. The plasma chamber <NUM> also includes a first bonded flange <NUM> extending from the first side <NUM> by a first width. The plasma chamber <NUM> further includes a second bonded flange <NUM> extending from the second side <NUM> by a second width. Specifically, for the circular toroidal plasma chamber <NUM> illustrated in <FIG>, the first bonded flange <NUM> extends inward from the first/inner side <NUM> by the first width and the second bonded flange <NUM> extends outward from the second/outer side <NUM> by the second width. Generally, the dimensions of the circular toroidal plasma chamber <NUM>, such as the inner radius (i.e., from the center of the circular toroidal plasma chamber <NUM> to the first side <NUM>) and the outer radius (i.e., from the center of the circular toroidal plasma chamber <NUM> to the second side <NUM>), are defined based on the required flow rate of the process gas in the plasma channel and the required plasma power. In some embodiments, the outer radius of the circular toroidal plasma chamber <NUM> is about <NUM> (<NUM> inches).

<FIG> shows an exemplary assembly for forming the plasma chamber <NUM> of <FIG>, according to some embodiments of the present invention. The plasma chamber <NUM> is constructed from several discrete sections, including a first section <NUM>, which can form a bottom half of the plasma chamber <NUM>, a second section <NUM>, which can form a top half of the plasma chamber <NUM>, and a bonding interface <NUM> (shown in <FIG>) that bonds together the first and second sections <NUM>, <NUM> of the plasma chamber <NUM>. The first and second sections <NUM>, <NUM> and the bonding interface <NUM> can be constructed from the same dielectric material or two or more different dielectric materials.

As shown, the first section <NUM> defines (i) a first wall portion <NUM> with an inner surface defining a portion of the plasma channel, (ii) a first flange <NUM> positioned along the first side <NUM> of the plasma channel and extending beyond first side <NUM> by the first width,.

<FIG> shows an exemplary plasma chamber <NUM>, according to some embodiments of the present invention. Generally, a plasma chamber is a container or a portion of a container that contains a gas and/or a plasma and within which a plasma can be ignited and or/maintained. A plasma chamber is adapted to be combined with other components, such as power generation and cooling components, to form a plasma processing system. A plasma and (iii) a second flange <NUM> positioned along the second side <NUM> of the plasma channel and extending beyond the second side <NUM> by the second width. Similarly, the second section <NUM> defines (i) a second wall portion <NUM> with an inner surface defining another portion of the plasma channel, (ii) a third flange <NUM> positioned along the first side <NUM> of the plasma channel and extending beyond the first side <NUM> by the first width, and (iii) a fourth flange <NUM> positioned along the second side <NUM> of the plasma channel and extending beyond the second side <NUM> by the second width. The bonding interface <NUM> is formed by bonding together the first and second sections <NUM>, <NUM> between the first and third flanges <NUM>, <NUM> and between the second and fourth flanges <NUM>, <NUM> of the first and second sections <NUM>, <NUM>, respectively. Specifically, the bonding at the bonding interface <NUM> is adapted to form the plasma chamber <NUM> as a monolithic structure comprising: (i) the first and second wall portions <NUM>, <NUM> cooperatively defining the plasma channel for containing a gas and/or plasma therein, (ii) the first and third flanges <NUM>, <NUM> cooperatively defining the first bonded flange <NUM> with the first width, and (iii) the second and fourth flanges <NUM>, <NUM> cooperatively defining the second bonded flange <NUM> with the second width. In some embodiments, the first width of the first bonded flange <NUM> and/or the second width of the second bonded flange <NUM> are between about <NUM> (<NUM> inches) and about <NUM> (<NUM> inch). For example, both the first or second width can be about <NUM> (<NUM> inches).

Generally, the bond strength for forming the first bonded flange <NUM> or the second bonded flange <NUM> at the bonding interface <NUM> is proportional to the amount of surface area at the bonding interface <NUM>. In the absence of bonded flanges <NUM>, <NUM>, a relatively thin first wall portion <NUM> and/or a second wall portion <NUM> of the plasma chamber <NUM> are adapted to create a thin bonding interface <NUM> that can compromise bonding reliability, even if the thin walls are beneficial for mitigating thermal stress. Hence, the first bonded flange <NUM> and the second bonded flange <NUM> are used to ensure a more reliable and sturdy bond between the first and second sections <NUM>, <NUM> of the plasma chamber <NUM>. This advantageously allows the thickness of the first wall portion <NUM> and second wall portion <NUM> to be independently optimized for minimization of thermo-mechanical stress.

In some embodiments, the first and second sections <NUM>, <NUM> of the plasma chamber <NUM> are substantially identical. In some embodiments, each of the first and second sections <NUM>, <NUM> is formed from a dielectric material and machined in a green state. These two and (iii) a second flange <NUM> positioned along the second side <NUM> of the plasma channel and extending beyond the second side <NUM> by the second width. Similarly, the second section <NUM> defines (i) a second wall portion <NUM> with an inner surface defining another portion of the plasma channel, (ii) a third flange <NUM> positioned along the first side <NUM> of the plasma channel and extending beyond the first side <NUM> by the first width, and (iii) a fourth flange <NUM> positioned along the second side <NUM> of the plasma channel and extending beyond the second side <NUM> by the second width. The bonding interface <NUM> is formed by bonding together the first and second sections <NUM>, <NUM> between the first and third flanges <NUM>, <NUM> and between the second and fourth flanges <NUM>, <NUM> of the first and second sections <NUM>, <NUM>, respectively. Specifically, the bonding at the bonding interface <NUM> is adapted to form the plasma chamber <NUM> as a monolithic structure comprising: (i) the first and second wall portions <NUM>, <NUM> cooperatively defining the plasma channel for containing a gas and/or plasma therein, (ii) the first and third flanges <NUM>, <NUM> cooperatively defining the first bonded flange <NUM> with the first width, and (iii) the second and fourth flanges <NUM>, <NUM> cooperatively defining the second bonded flange <NUM> with the second width. In some embodiments, the first width of the first bonded flange <NUM> and/or the second width of the second bonded flange <NUM> are between about <NUM> inches and about <NUM> inch. For example, both the first or second width can be about <NUM> inches.

In some embodiments, the first and second sections <NUM>, <NUM> of the plasma chamber <NUM> are substantially identical. In some embodiments, each of the first and second sections <NUM>, <NUM> is formed from a dielectric material and machined in a green state. These two sections <NUM>, <NUM> of the plasma chamber <NUM> can be bonded by any one of the following bonding approaches including: (i) applying and melting a glass frit at the flanges <NUM>, <NUM>, <NUM>, <NUM> to form a glass joint at the bonded flanges <NUM>, <NUM>, (ii) applying an eutectic mixture comprising one or more of Al<NUM>O<NUM>, Y<NUM>O<NUM>, Sc2O3, Ce2O3, MgO, CaO, or ZrO<NUM> at the flanges <NUM>, <NUM>, <NUM>, <NUM> and sintering the two sections <NUM>,<NUM> together to form the bonded flanges <NUM>, <NUM>, (iii) co-firing the two sections <NUM>,<NUM> together to form the bonded flanges <NUM>, <NUM>, or (iv) applying a high-temperature epoxy at the flanges <NUM>, <NUM>, <NUM>, <NUM> and curing the two sections <NUM>,<NUM> together to form the bonded flanges <NUM>, <NUM>. A strong hermetic seal can be formed at the bonded flanges <NUM>, <NUM>.

As described above, the plasma chamber <NUM>, including the first and second sections <NUM>, <NUM>, can be made from the same dielectric material or different dielectric materials. Typically, the resistance of a particular material to plasma is measured in term of etch rate (e.g., the rate of material removal per unit time measured in microns per minute). In some embodiments, the dielectric material used to construct the plasma chamber <NUM> is a high purity (e.g., about <NUM>% to about <NUM>%) alumina (Al<NUM>O<NUM>) ceramic material that is selected due to its low etch rate in halogen plasmas. Further, alumina has demonstrated good thermal shock resistance, which is another key parameter in terms of material selection for thermal stress applications. The formula for thermal shock resistance is shown in Equation [<NUM>]: <MAT> where R represents the thermal shock resistance, σF represents the flexural strength of a material (MPa), v represents Poisson's ratio, K represents thermal conductivity (W/mK), E represents Young's modulus (GPa), and α represents the coefficient of thermal expansion (µm/mK). Equation [<NUM>] combines several material properties critical to thermal stress resistance by generating a single number that is indicative of how well a material resists thermal stress. The higher the resistance value, the better the material is at handling thermal stress. For example, quartz, which is a dielectric material used in some of the existing plasma chambers, has a thermal shock resistance factor of about <NUM>. In contrast, alumina has a thermal shock resistance of about <NUM>, primarily due to a combination of its high strength and high thermal conductivity. Thus, from a thermal stress handling standpoint, alumina is about <NUM> times better as a structural material than quartz for constructing a plasma chamber.

In some embodiments, the dielectric material for constructing the plasma chamber <NUM> is an oxide or a nitride of one of a group II element, a group III element, a lanthanide, or a mixture thereof. For example, the dielectric material can be one of Y<NUM>O<NUM>, Sc<NUM>O<NUM> La<NUM>O<NUM>, Ce<NUM>O<NUM>, or MgO. As another example, the dielectric material can be one of AlN, BN, or YN.

In some embodiments, plasma resistance of the plasma chamber <NUM> is enhanced by doping or alloying the dielectric material (e.g., Al<NUM>O<NUM>) for forming the plasma chamber <NUM> with a small amount of an oxide of one of a group II or III element, such as Y<NUM>O<NUM>, Sc<NUM>O<NUM> or MgO. It has been shown that mixing Al<NUM>O<NUM> powder with a small amount of Y<NUM>O<NUM> Sc<NUM>O<NUM> or MgO powder and heating the mixture to a temperature of about <NUM> results in the formation of a stoichiometric alloy of the form AlxYyOz, AlxScyOz or AlxMgyOz. Such an alloy has been shown to have lower erosion rates when subject to halogen plasma chemistries, such as F*, Cl* and Br*, as compared to Al<NUM>O<NUM> alone.

In some embodiments, a coating is applied to the inner surface of the first wall portion <NUM> of the first section <NUM> and/or the inner surface of the second wall portion <NUM> of the second section <NUM> of the plasma chamber <NUM> prior to bonding the two sections together at the bonding interface <NUM>. As described above, the two wall portions <NUM>, <NUM> are adapted to form the plasma channel exposed to the plasma therein. Thus, the coating can be applied to the inner surfaces of these two sections such that they directly face the plasma. The coating can comprise one or more of yttria (Y<NUM>O<NUM>), Sc<NUM>O<NUM>, La<NUM>O<NUM>, Ce<NUM>O<NUM>, MgO, SiO<NUM>, B<NUM>C or an alloy of YAG, which have lower etch rates in halogen plasma compared to Al<NUM>O<NUM>. The coating can also comprise Al<NUM>O<NUM>. In general, a thicker coating has a longer life than a thinner one, as a thicker coating takes longer to etch through due to erosion. The adhesion of a coating to the plasma chamber surface, however, is related to the coating thickness. When temperature varies, a mismatch in the thermal expansion coefficients of the coating material and base material creates thermo-mechanical stresses at the interface and in the coating material. Such stresses increase with temperature or temperature gradient, and can cause failure of the coating. The optimal coating thickness is in the range of <NUM> to <NUM> for most of the above-mentioned coating materials. In some embodiments, the preferred coating thickness is between <NUM> and <NUM>.

In some embodiments, a coating process such as plasma or flame spray is used to deposit a dense coating of material to the inner surface of the first wall portion <NUM> and/or to the inner surface of the second wall portion <NUM>, where the coating thickness is on the order of several microns to hundreds of microns. However, spray coating, also known as line-of-sight coating, requires the coating surface to be well exposed to achieve a relatively uniform coating thickness. The piece-wise structure of the plasma source <NUM>, as illustrated in <FIG>, is particularly suited for spray coating because the inner surfaces of the first wall portion <NUM> and the second wall portion <NUM>, which form the resulting plasma channel of the plasma chamber <NUM>, are easily accessible and well exposed prior to bonding of the two sections <NUM>, <NUM>.

In an exemplary coating process, a thin layer of an alloying agent (e.g., Y<NUM>O<NUM>, Sc<NUM>O<NUM>, or MgO) is deposited on the inner surface of at least one of the first wall portion <NUM> of the first section <NUM> or the second wall portion <NUM> of the second section <NUM>, after the two sections <NUM>, <NUM> are machined in green state, but before the two sections <NUM>, <NUM> are bonded, as shown in <FIG>. When the two sections <NUM>, <NUM> are bonded at the bonding interface <NUM> using a desired bonding process (e.g., co-firing, sintering, etc.), a thin layer of alloyed coating, such as in the form AlxYyOz, AlxScyOz or AlxMgyOz, is generated on at least a portion of the inner surfaces. In some embodiments, the same alloying agent (e.g., Y<NUM>O<NUM>, Sc<NUM>O<NUM> or a mixture of Y<NUM>O<NUM> and Al<NUM>O<NUM>) is also made into a slurry material and applied to the bonding interface <NUM> as a bonding agent to eutectically bond the two sections <NUM>, <NUM> to form the first and second bonded flanges <NUM>, <NUM>. The formation of the eutectic bonding and alloy coating can be achieved in the same bonding process.

In some embodiments, the thickness of the first wall portion <NUM> and/or the thickness of the second wall portion <NUM> of the plasma chamber <NUM> are between about <NUM> (<NUM> inches) and about <NUM> (<NUM> inches). The principal limitation of a dielectric plasma chamber (e.g., the plasma chamber <NUM>) is thermo-mechanical stress resulting from the plasma heat load. There are two competing factors that determine the optimal wall thickness as related to thermo-mechanical stress. On the one hand, the thinner the wall of a plasma chamber, the smaller the thermal gradient through the wall thickness. On the other hand, the wall of a plasma chamber needs to be thick enough to have sufficient mechanical strength to counteract thermal stress and other stresses the plasma chamber is subjected to during assembly. An optimal balance between these two factors (i.e., mechanical strength and low thermal gradients) is therefore desired to mitigate thermal stress. A thickness of the first wall portion <NUM> and/or the second wall portion <NUM> of the plasma chamber <NUM> between about <NUM> (<NUM> inches) and about <NUM> (<NUM> inches) can be chosen to balance these two competing factors.

Even though <FIG> show that the toroidal plasma chamber <NUM> has a toroidal plasma channel that is circular in overall shape, other toroidal channel shapes are possible, such as oval, elliptical or polygon. For example, <FIG> shows a toroidal plasma chamber <NUM> having a toroidal plasma channel that is rectangular in shape, according to some embodiments of the present invention. <FIG> shows a toroidal plasma chamber <NUM> having a toroidal plasma channel that is oval in shape, according to some embodiments of the present invention. The properties and piece-wise manufacturing approaches described above with respect to the toroidal plasma chamber <NUM> are equally applicable to a linear plasma chamber. For example, in an alternative embodiment, a plasma chamber of the present invention is in the form of a linear plasma channel formed by the disclosed bonding process.

The cross section of a plasma channel of the present invention can have different shapes, such as circular, oval, elliptical, polygon or rectangular/square. Moreover, an outer contour and an inner contour of a plasma channel cross section may have the same or different shapes. For example, <FIG> shows a portion of a toroidal plasma chamber <NUM> having a plasma channel <NUM> that has a cross section <NUM> with a rectangular inner contour <NUM> and a rectangular outer contour <NUM>, according to some embodiments of the present invention. <FIG> shows a portion of a toroidal plasma chamber <NUM> having a plasma channel <NUM> that has a cross section <NUM> with a circular inner contour <NUM> and a circular outer contour <NUM>, according to some embodiments of the present invention. <FIG> shows a portion of a toroidal plasma chamber <NUM> having a plasma channel <NUM> that has a cross section <NUM> with a circular inner contour <NUM> and a hexagonal outer contour <NUM>, according to some embodiments of the present invention. In some embodiments, an area of the cross section of a plasma channel is between about <NUM><NUM> and about <NUM><NUM>.

<FIG> show views of an exemplary plasma processing system <NUM>, according to some embodiments of the present invention. <FIG> shows an exemplary plasma processing system <NUM> including the plasma chamber <NUM> of <FIG>. <FIG> shows a cutaway view of the plasma processing system <NUM> of <FIG>. <FIG> shows a side view of the exemplary plasma processing system <NUM> of <FIG>. As shown, the plasma processing system <NUM> includes the plasma chamber <NUM> having at least one gas inlet <NUM> and at least one gas outlet represented by an exit flange <NUM>.

The plasma chamber <NUM> is surrounded by a heat sink <NUM> for removing heat from the plasma chamber <NUM>. The heat sink <NUM> can be formed from multiple segments, such as at least two segments 810a, 810b that substantially enclose the plasma chamber <NUM>. Segmentation of the heat sink <NUM> can aid the assembly of the system <NUM>, especially when the plasma chamber <NUM> has a complex shape, such as a toroidal shape. In some embodiments, the heat sink <NUM> is divided into two segments along the azimuthal plane (i.e., the X-Z plane as indicated in <FIG>). The resulting two heat sink segments 810a, 810b can be substantially identical and aligned along the y-axis to form the overall heat sink <NUM>. In some embodiments, the heat sink <NUM> is formed as a single monolithic component.

The plasma processing system <NUM> includes a power transformer <NUM> that couples electromagnetic energy into the plasma chamber <NUM>. The power transformer <NUM> includes a high permeability magnetic core <NUM>, a primary coil <NUM>, and plasma chamber <NUM>. The plasma chamber <NUM> allows plasma to form a secondary circuit of the transformer <NUM>. The magnetic core <NUM> can be supported and cooled by a supporting structure <NUM>. The power transformer <NUM> can include additional magnetic cores and conductor coils that form additional primary or secondary circuits. For example, the system <NUM> shown in <FIG> shows the plasma chamber <NUM> encircled by four transformer cores (e.g., magnetic core <NUM> and three additional magnetic cores (not labeled)).

<FIG> shows a cross-sectional view of the plasma processing system <NUM> along the A-A section line shown in <FIG>. The plasma processing system <NUM> includes an assembly that includes the plasma chamber <NUM> and the heat sink <NUM>, which is placed within the transformer <NUM>. The transformer <NUM>, which includes the magnetic core <NUM> and one or more primary coils <NUM> (not shown), is adapted to couple (e.g., inductively couple) electrical power into a plasma generation volume defined by the plasma channel <NUM> of the plasma chamber <NUM>. The magnetic core <NUM> together with the primary coils induce an electric field and a current aligned with the plasma channel <NUM>, which allow a plasma in the plasma channel <NUM> to be ignited and sustained to form a secondary circuit of the transformer <NUM>.

Specifically, in operation, a gas can be fed into the plasma channel <NUM> via the gas inlet <NUM> until a pressure between, for example, about <NUM> Torr and about <NUM> Torr, is reached. The transformer <NUM> induces an electric field that ionizes the gas in the plasma channel <NUM> of the plasma chamber <NUM> to form a plasma that completes the secondary circuit of the transformer <NUM>. At least a portion of the plasma or the activated gas in the plasma channel <NUM> can be delivered away from the system <NUM> via the exit flange <NUM>. In some embodiments, prior to induced electrical power being coupled to the plasma, the gas inside of the plasma channel <NUM> is ignited by electric fields applied to the plasma channel <NUM> to create initial electrical breakdown. Several igniton schemes are described in <CIT>, <CIT> and<CIT> and assigned to MKS Instruments, Inc. of Andover, MA.

In some embodiments, the heat sink <NUM> substantially encapsulates/surrounds the plasma chamber <NUM> with a thermal interface <NUM> disposed between the heat sink <NUM> and the plasma chamber <NUM>. The heat sink <NUM>, which is configured to remove heat from the plasma chamber <NUM>, can be formed from an electrically conductive material, such as copper. In some embodiments, cooling fluid is supplied to the cooling jacket via the fluid inlet <NUM> and removed via the fluid outlet <NUM>. The thermal interface <NUM> can be a compliant, thermally-conductive pad or a potting compound. The thermal interface <NUM> has one or more mechanical properties, which permit it to accommodate pressure induced by thermal deformation of the plasma chamber <NUM> inside the heat sink <NUM> when the dielectric chamber is subject to heat load from the plasma. The thermal interface <NUM> can have varying degrees of compliance, such as being easily deformable, which can help to accommodate thermally-induced dimensional changes of the system <NUM>. The thermal interface <NUM> can also have sufficiently high thermal conductivity to effectively conduct the heat away from the dielectric plasma chamber <NUM> toward the heat sink <NUM>. The thermal interface <NUM> can be made compressible by introducing a small amount of porosity (<NUM>-<NUM>% in volume) in the material. In some embodiments, a gap between the plasma chamber <NUM> and the heat sink <NUM> is filled with the thermal interface <NUM>, and the gap is about <NUM> (<NUM> inches) in width.

In some embodiments, the two heat sink segments 810a, 810b are electrically separated/isolated from each other by one or more dielectric breaks <NUM> located along the second/outer side <NUM> and/or the first/inner side <NUM> of the plasma channel <NUM>. For example, the dielectric breaks <NUM> can be placed along the first/inner bonded flange <NUM> and/or the second/outer bonded flange <NUM> of the plasma chamber <NUM>. These dielectric breaks <NUM> also provide spacing for the thermal interface <NUM>. For example, the dielectric breaks <NUM> can be configured to contain the thermal interface material within the gap between the plasma chamber <NUM> and the heat sink <NUM> and prevent the thermal interface material from leaking away from the space between the heat sink <NUM> and the plasma chamber <NUM>.

In some embodiments, the two heat sink segments 810a, 810b are further electrically separated along the toroidal direction of the plasma chamber <NUM>. Such segmentation of the heat sink <NUM> in the toroidal direction prevents an electric current from being induced in the heat sink <NUM> that can short the transformer secondary formed by the plasma in the plasma channel <NUM>.

<FIG> shows another cross-sectional view of the plasma processing system <NUM> that is along the B-B section line shown in <FIG>. As shown, the plasma chamber <NUM> is surrounded by azimuthally-segmented heat sinks 810a and 810b, and is encircled by the magnetic cores (e.g., magnetic core <NUM>). The B-B section line goes across the joints of the toroidally-segmented heat sink <NUM>, with cooling fluid being conducted between the segmented heat sink sections through dielectric fluid couplings <NUM>. In some embodiments, the dielectric fluid couplings <NUM> are made of high temperature plastics. Similar heat sink segmentation arrangements are described in <CIT> and <CIT>, assigned to MKS Instruments, Inc. of Andover, MA.

In addition to enabling a strong bond between the two sections <NUM>, <NUM> of the plasma chamber <NUM> (see <FIG>), the first and second bonded flanges <NUM>, <NUM> provide benefits in terms of reducing temperature and thermal stress. Specifically, because the first and second bonded flanges <NUM>, <NUM> extend beyond the first and second sides <NUM>, <NUM> of the plasma channel <NUM>, respectively, they increase the amount of contact surface area between the body of the plasma chamber <NUM> and the heat sink <NUM>, as illustrated in <FIG> and <FIG>. This additional contact surface can result in a peak temperature reduction in the dielectric plasma chamber <NUM>.

<FIG> shows simulated temperature profiles of the plasma chamber <NUM> of <FIG> with the first and second bonded flanges <NUM>, <NUM> according to an embodiment of the present invention. <FIG> shows simulated temperature profiles of a plasma chamber <NUM> without bonded flanges. The first and second bonded flanges <NUM>, <NUM> used in the simulation of <FIG> both have a width of <NUM> (<NUM> inches). The simulation uses an inlet cooling water temperature of <NUM> and an operating power load of <NUM> kilowatts (kW). As shown, the peak temperature is about <NUM> in plasma chamber <NUM> without bonded flanges, while the peak temperature is about <NUM> with the bonded flanges <NUM>, <NUM> according to the exemplary embodiment of the present invention. It shows that the use of bonded flanges <NUM> and <NUM> can reduce peak temperature rise in the plasma chamber <NUM> by about <NUM>%.

Further, the first and second bonded flanges <NUM>, <NUM> function as stiffening ribs around the first/inner and second/outer sides <NUM>, <NUM> of the plasma chamber <NUM>, which can reduce deformation and thermal stress of the plasma chamber <NUM> under a heat load.

In another aspect, the electrical separation/isolation of the two heat sink segments 810a, 810b provided by the dielectric breaks <NUM> and the bonded flanges <NUM>, <NUM> of the plasma chamber <NUM> allow them to be biased at opposite voltages for plasma ignition. <FIG> shows a cross-sectional view of an assembly including the plasma chamber <NUM> encapsulated by the heat sink segments 810a, 810b shown in <FIG>, <FIG>, <FIG>. The heat sink segments 810a, 810b can serve as ignition electrodes that are capacitively coupled to the plasma chamber <NUM>, and to which a voltage can be applied for ignition of a gas <NUM> in the plasma chamber <NUM>. As shown, the two heat sink segments 810a, 810b can be biased at opposite polarities when connected to a power supply <NUM>, which can be a DC, RF or pulsed power supply, and the applied voltage can be on the order of several hundred volts to a few kilovolts. As an example, the ignition electrodes in the form of the heat sink segment 810a, 810b can be biased using a <NUM> RF power supply at about <NUM>-5kV peak-to-peak voltage. Once the voltage is applied, an electrical breakdown (e.g., electrical breakdown <NUM>) is created inside the gas <NUM> contained in the plasma channel of the plasma chamber <NUM>. Because the ignition electrodes in the form of the heat sink segment 810a, 810b cover substantially the entire second/outer side <NUM> of the plasma channel, the electrical breakdown <NUM> is adapted to cover a large volume of the process gas <NUM>. This feature, in combination with the use of an induced electric field in the toroidal direction of the plasma chamber <NUM>, enables a toroidal plasma to be formed in the plasma chamber <NUM>.

<FIG> illustrates an exemplary process <NUM> for manufacturing the plasma chamber <NUM> of <FIG>, according to some embodiments of the present invention. The plasma chamber <NUM> defines an internal plasma channel with a first side <NUM> (i.e., an inner side if the plasma channel is toroidal) and a second side <NUM> (i.e., an outer side if the plasma channel is toroidal). At step <NUM>, the first section <NUM> of the plasma chamber <NUM> is constructed from a dielectric material by, for example, machining the dielectric material in a green state. At step <NUM>, the second section <NUM> of the plasma chamber <NUM> is constructed from the same dielectric material or a different dielectric material by, for example, machining the dielectric material in a green state. The first or second section <NUM>, <NUM> can be the top or bottom half of the plasma chamber <NUM>. The first section <NUM> has (i) a first flange <NUM> positioned along the first side <NUM> of the plasma channel and extending beyond the first side <NUM> by a first width and (ii) a second flange <NUM> positioned along the second side <NUM> of the plasma channel and extending beyond the second side <NUM> by a second width. Similarly, the second section <NUM> has (i) a third flange <NUM> positioned along the first side <NUM> of the plasma channel and extending beyond the first side <NUM> by the first width, and (ii) a fourth flange <NUM> positioned along the second side <NUM> of the plasma channel and extending beyond the second side <NUM> by the second width.

In some embodiments, after step <NUM>, but before the first and second sections <NUM>, <NUM> are bonded at step <NUM>, a coating is applied at step <NUM> on an inner surface of the first wall portion <NUM> and/or the second wall portion <NUM> of at least one of the first section <NUM> or the second section <NUM>, respectively, where the inner surface of the first or second wall portion <NUM>, <NUM> form at least a portion of the plasma channel exposed to the plasma therein. In some embodiments, the coating is a layer of alloying agent deposited on an inner surface of the first wall portion <NUM> and/or the second wall portion <NUM> of at least one of the first section <NUM> or the second section <NUM>.

At step <NUM>, the first and second sections <NUM>, <NUM> are bonded to form the plasma chamber <NUM>. Bonding the first and second sections <NUM>, <NUM> involves (i) forming a bond between the first and third flanges <NUM>, <NUM> of the first and second sections <NUM>, <NUM>, respectively, to generate the first bonded flange <NUM>, and (ii) forming a bond between the second and fourth flanges <NUM>, <NUM> of the first and second sections <NUM>, <NUM>, respectively, to generate the second bonded flange <NUM>. During this bonding process, if a layer of alloying agent has been disposed in the inner surface of the first wall portion <NUM> and/or the second wall portion <NUM>, an alloyed coating on the inner surface can be created from the layer of alloying agent by the same bonding process. Even though the manufacturing process <NUM> is explained with respect to a toroidal plasma chamber having a toroidal plasma channel, the same process <NUM> is also applicable to plasma chambers of other shapes, such as a plasma chamber with a plasma channel that is linear.

In some embodiments, the first section <NUM> and second section <NUM> can be joined together using high temperature low vapor pressure epoxy or glass frit bonding. In such an embodiment the first and second sections <NUM>, <NUM> would be fired/sintered prior to bonding. An epoxy or glass frit can be applied to at least the first and second flanges <NUM>, <NUM> of the first section <NUM>. The bonding of the first and third flanges <NUM>, <NUM> and second and fourth flanges <NUM>, <NUM> would be accomplished by heating the first and second sections cooperatively to either cure the epoxy or melt the glass frit to form the bonding interface <NUM>. A curing temperature of an epoxy is typically between approximately <NUM>-<NUM> and melting temperature of glass is approximately <NUM>-<NUM>, both of which are substantially lower than the sintering temperature of high temperature ceramic materials. For example, sintering temperature of alumina (Al<NUM>O<NUM>) ceramic is on the order of <NUM>. Due to the difference between the epoxy curing/glass melting temperature and ceramic sintering temperature in such an embodiment the sintering and bonding steps must be separate.

<FIG>show another exemplary assembly for forming a plasma chamber according to some embodiments of the present invention. The plasma chamber <NUM> is constructed from two discrete sections, including a first section <NUM> and a second section <NUM>, as illustrated in <FIG>. Each of the first section <NUM> and the second section <NUM> can comprise a half of the plasma chamber <NUM>, with one section including a gas inlet and the other section including a gas outlet of the plasma chamber <NUM>. The two sections can be bonded together at flanges <NUM> and <NUM> using a bonding agent. In some embodiments, section <NUM> and section <NUM> are geometrically identical. In some embodiments, section <NUM> and section <NUM> have different geometries for accommodating or creating gas flow patterns along the plasma chamber <NUM>. Section <NUM>, section <NUM>, and the bonding interface <NUM> can be constructed from the same dielectric material, or from two or more different dielectric materials. In some embodiments, a coating is disposed on an inner surface of the plasma chamber that forms at least a portion of the plasma channel exposed to a plasma therein. The coating can comprise one of Al<NUM>O<NUM>, Y<NUM>O<NUM>, Sc2O3, La<NUM>O<NUM>, Ce<NUM>O<NUM>, MgO, SiO<NUM>, B<NUM>C or an alloy including YAG. The inner surfaces of the inlet and outlet sections can be coated with different materials for optimization of plasma performance.

In another aspect, the plasma chambers and plasma processing systems of the present invention can be used in a variety of applications, such as in semiconductor wafer processes that require halogen plasmas. One exemplary semiconductor wafer process called atomic layer etch (ALE) requires the use of Cl* plasma and pulsed operation of the plasma source. The dielectric plasma chambers of the present invention (e.g., the plasma chamber <NUM>) are compatible with both of these requirements as they have low erosion rates in Cl* plasma and can be used in pulsed modes due to their ability to quickly ignite in-process gas.

In some embodiments, the plasma processing systems of the present invention, such as the plasma processing system <NUM>, have low ion bombardment energy in high-density plasma environments, thus offering an advantage over other capacitively or inductively coupled sources that suffer from erosion of their plasma-facing surfaces due to ion bombardment from the plasma. Thus, the plasma processing systems of the present invention have low particle generation and long life (e.g., measured in RF hours) under high plasma power densities. Lower particle defects enable higher yields in semiconductor device manufacturing, which is generally sensitive to sub-microscopic particles that can create defects on the devices.

Traditional plasma processing systems are typically made from metals (e.g., aluminum) with dielectric coatings on the inside surfaces to provide sufficient heat conduction to maintain the temperature of the plasma chamber within reasonable limits under high power plasma operating conditions. This material choice is made due to the excellent (e.g., greater than <NUM> times) thermal conductivity of aluminum in comparison to typical dielectric materials. For a given heat flux (Q W/m2), the temperature difference across a solid is calculated as ΔT = Q*Thx/k, where k is the thermal conductivity of the solid and Thx is the thickness of the solid across which heat is conducted. Thus, to minimize the temperature difference across the solid, k/Thx needs to be maximized. This implies that the choice of material needs to be either metallic with high thermal conductivity or a thinner material of dielectric with lower thermal conductivity. The advantage of using a pure dielectric plasma chamber is that it is able to handle large voltages (e.g., up to tens of kVs) necessary to quickly ignite a plasma in-process gas while a metallic plasma chamber is limited in such capability and typically requires benign ignition conditions (such as argon gas as ignition gas) and further requires a transition to process chemistry to sustain the plasma.

This advantage in the ignition capability of a dielectric plasma chamber enables the dielectric plasma chamber to be filled with electronegative gases (e.g., O<NUM>, NF<NUM>, F<NUM>, Cl<NUM> etc.) during ignition without additional transitioning associated with changing over from noble/electropositive gases to process gases. Such capability also enables plasma to be pulsed (i.e., toggle between ON and OFF states) that is critical for atomic layer processing applications, such as ALE and ALD. Thus, a dielectric plasma chamber becomes the optimal architecture for use in a remote plasma source for pulsed radical delivery applications in comparison to alternatives, such as remote inductively coupled plasma sources or microwave or dielectric barrier discharge based plasma sources.

Further, the transformer-coupled plasma processing systems of the present invention, such as the plasma processing system <NUM>, can be operated to deliver specific chemical reactants over a short period of time. <FIG> show various exemplary pulsed operations using the plasma processing system <NUM> of <FIG> as a remote plasma source, according to some embodiments of the present invention. Specifically, <FIG> shows an exemplary pulsed operation when the remote plasma source <NUM> is only operated (i.e., turned on) when precursor B is flown into the plasma chamber <NUM> through either the remote plasma source <NUM>, an inlet downstream of the remote plasma source <NUM>, or directly into the plasma chamber <NUM>. Other modes of operating the plasma processing system <NUM> as a remote plasma source are possible, such as turning on the remote plasma source only for Precursor A, as illustrated in <FIG>, or for both Precursors A and B, as illustrated in <FIG>.

The same principles can be used if there is a single precursor with constant flow and only the remote plasma source is toggled to allow for radical based processing of certain duration within the overall process, where precursor based processes are used to modulate the rate and type of reactions downstream of the remote plasma source. One such example is an ALE process, as illustrated in <FIG>, where the precursor flowing through the remote plasma source can include Cl<NUM> or other halogen gases, which is converted to radicals including atomic chlorine and excited chlorine molecules for high reactivity at a periodic interval with some ionic bombardment on the substrate in the intermittent times using an independent bias on the substrate to activate the surface. Generally, there are many ways to optimize these combinations to enable specific applications. One common feature is the ability to have a low particle generating remote plasma source that can provide the radical flux needed for the chemical reactions at the atomic level and the remote plasma source can be toggled on and off quickly based on the process needs to allow for ignition within process gas. Such capability can be achieved by the plasma chambers and plasma processing systems of the present invention. For example, the plasma chambers of the present invention can be formed from a dielectric material and bonded from a clamshell geometry that enables new coating materials to be integrated into the plasma-facing surfaces compatible with desired process chemistries.

Claim 1:
A plasma chamber (<NUM>) of a plasma processing system (<NUM>), the plasma chamber (<NUM>) defining a plasma channel having a first side (<NUM>) and a second side (<NUM>) oppositely disposed along a length of the plasma channel, the plasma chamber (<NUM>) comprising:
a first section (<NUM>) constructed from a dielectric material;
a second section (<NUM>) constructed from the dielectric material;
characterized by the first section (<NUM>) having (i) a first flange (<NUM>) positioned along the first side (<NUM>) of the plasma channel and extending beyond the first side (<NUM>) by a first width, and (ii) a second flange (<NUM>) positioned along the second side (<NUM>) of the plasma channel and extending beyond the second side (<NUM>) by a second width;
the second section (<NUM>) having (i) a third flange (<NUM>) positioned along the first side (<NUM>) of the plasma channel and extending beyond the first side (<NUM>) by the first width, and (ii) a fourth flange (<NUM>) positioned along the second side (<NUM>) of the plasma channel and extending beyond the second side (<NUM>) by the second width; and
an interface (<NUM>) that bonds together the first and second sections (<NUM>, <NUM>) at between the first and third flanges (<NUM>, <NUM>) and between the second and fourth flanges (<NUM>, <NUM>).