US20180005850A1

US20180005850A1 - Selective etch using material modification and rf pulsing

Info

Publication number: US20180005850A1
Application number: US15/197,060
Authority: US
Inventors: Bhargav Citla; Chentsau Ying; Srinivas Nemani; Viachslav BABAYAN; Michael Stowell
Original assignee: Applied Materials Inc
Current assignee: Applied Materials Inc
Priority date: 2016-06-29
Filing date: 2016-06-29
Publication date: 2018-01-04
Anticipated expiration: 2036-06-29
Also published as: US9865484B1; KR102167957B1; US20180082861A1; JP2019526169A; TWI756234B; CN109417028A; CN109417028B; KR20190011328A; TW201810422A; JP6719602B2; WO2018005122A1

Abstract

Semiconductor systems and methods may include methods of performing selective etches that include modifying a material on a semiconductor substrate. The substrate may have at least two exposed materials on a surface of the semiconductor substrate. The methods may include forming a low-power plasma within a processing chamber housing the semiconductor substrate. The low-power plasma may be a radio-frequency (“RF”) plasma, which may be at least partially formed by an RF bias power operating between about 10 W and about 100 W in embodiments. The RF bias power may also be pulsed at a frequency below about 5,000 Hz. The methods may also include etching one of the at least two exposed materials on the surface of the semiconductor substrate at a higher etch rate than a second of the at least two exposed materials on the surface of the semiconductor substrate.

Description

TECHNICAL FIELD

The present technology relates to systems and methods for processing semiconductor materials. More specifically, the present technology relates to semiconductor material modifications and hardware modifications for producing a low-power plasma.

BACKGROUND

Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods for applying and removing material. For removal, chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers, or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process that etches one material faster than another facilitating, for example, a pattern transfer process. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits, and processes, etch processes have been developed with a selectivity towards a variety of materials.
Etch processes may be termed wet or dry based on the materials used in the process. A wet HF etch preferentially removes silicon oxide over other dielectrics and materials. However, wet processes may have difficulty penetrating some constrained trenches and also may sometimes deform the remaining material. Dry etches produced in local plasmas formed within the substrate processing region can penetrate more constrained trenches and exhibit less deformation of delicate remaining structures. However, local plasmas may damage the substrate through the production of electric arcs as they discharge. Additionally, plasma effluents can damage chamber components that may require replacement or treatment.
Thus, there is a need for improved systems and methods that can be used to produce high quality devices and structures. These and other needs are addressed by the present technology.

SUMMARY

Semiconductor systems and methods may include methods of performing selective etches that include modifying a material on a semiconductor substrate. The substrate may have at least two exposed materials on a surface of the semiconductor substrate. The methods may include forming a low-power plasma within a processing chamber housing the semiconductor substrate. The low-power plasma may be a radio-frequency (“RF”) plasma, which may be at least partially formed by an RF bias power operating between about 10 W and about 100 W in embodiments. The RF bias power may also be pulsed at a frequency below about 5,000 Hz. The methods may also include etching one of the at least two exposed materials on the surface of the semiconductor substrate at a higher etch rate than a second of the at least two exposed materials on the surface of the semiconductor substrate.
In embodiments the modifying operation may include forming a plasma from a precursor within the processing chamber with the RF bias power. The precursor may be selected from the group consisting of oxygen, hydrogen, or helium in embodiments. Additionally, each of the at least two exposed materials on the surface of the semiconductor substrate may be selected from the group consisting of silicon oxide, silicon nitride, silicon carbide, and silicon oxycarbide.
For the etching operation, the RF bias power may at least partially form the low-power plasma and operate at a duty cycle below about 50%. Also, forming the low-power plasma may further include utilizing an RF source power below about 100 W. In embodiments, forming the low-power plasma may also include utilizing a pulsed DC power. The pulsed DC power may be applied to a bipolar electrostatic chuck supporting the semiconductor substrate. In embodiments, the pulsed DC power may be applied to a conductive ring embedded in a shield ring of a pedestal supporting the semiconductor substrate or coupled with a showerhead within the processing chamber.
The present technology also includes methods of removing material from a semiconductor substrate. The methods may include modifying a material on a semiconductor substrate having at least two exposed materials on a surface of the semiconductor substrate. The modifying may include forming a plasma from a precursor with an RF bias power to generate plasma effluents that modify the material. The methods may also include forming a low-power plasma within a processing chamber housing the semiconductor substrate. The low-power plasma may be a radio-frequency (RF) plasma in embodiments. The low-power plasma may be formed by a pulsed RF bias power operating at between about 20 W and 50 W at a pulsing frequency between about 500 Hz and about 2,000 Hz. The pulsed RF bias power may be operated at a duty cycle of between about 20% and 50% as well. The methods may include operating a DC pulsed power on an alternating frequency with the RF bias power pulsing. The methods may further include etching one of the at least two exposed materials on the surface of the semiconductor substrate at a selectivity of at least about 20:1 with respect to a second of the at least two exposed materials on the surface of the semiconductor substrate.
In the methods, the modifying operation may include a chemical modification causing a chemical change to the material on the semiconductor substrate. The modifying may also include a physical modification utilizing an inert precursor. In embodiments, the physical modification may include damaging bonds of the material on the semiconductor substrate with ions of the inert precursor. The forming the low-power plasma operation may further include utilizing an RF source power operating up to about 100 W.
The present technology also includes substrate processing chambers including a pedestal configured to support a semiconductor substrate. The chambers may include an RF bias power electrically coupled with the pedestal and configured to generate a plasma within the processing chamber at a power of between about 20 W and about 50 W in embodiments. The RF bias power may be a pulsing power configured to pulse at a frequency below about 5,000 Hz. The substrate processing chambers may further include a DC pulsing power electrically coupled with the substrate processing chamber and configured to produce priming particles for the RF bias plasma. Additionally, the DC pulsing power supply may be configured to pulse at a frequency to produce priming particles without developing a plasma sheath.
In embodiments, the DC pulsing power supply may be configured to be pulsed on for a duration of 100 microseconds or less at a duty cycle of less than about 50%. Additionally, in embodiments the pedestal may be a bipolar electrostatic chuck, and the DC pulsing power may be applied to electrical ground of the bipolar electrostatic chuck. In embodiments the DC pulsing power may be electrically coupled with a conductive ring coupled with the pedestal, and the conductive ring may be electrically decoupled from the electrostatic chuck and the RF bias. In embodiments the DC pulsing power may also be electrically coupled with a conductive ring embedded in a showerhead within the substrate processing chamber.
Such technology may provide numerous benefits over conventional techniques. For example, the technology may allow improved selectivity of etching operations due to, for example, the material modifications. Additionally, the low-power plasmas of the present technology may produce improved feature profiles over conventional techniques, and allow improved front end and back end processing with enhanced plasma control. These and other embodiments, along with many of their advantages and features, are described in more detail in conjunction with the below description and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the disclosed embodiments may be realized by reference to the remaining portions of the specification and the drawings.

FIG. 1 illustrates a method of etching a substrate according to embodiments of the present technology.

FIG. 2 shows a graph illustrating the additive effects of material modification and low-power plasma according to embodiments of the present technology.

FIG. 3 shows imaging of an etch process performed according to embodiments of the present technology.

FIG. 4 shows a chart illustrating etch rates of various materials with and without treatments according to embodiments of the present technology.

FIG. 5 shows a chart illustrating etch rates of silicon oxycarbide and silicon carbide with and without treatments according to embodiments of the present technology.

FIG. 6 shows a partial schematic illustration of a controller providing DC pulse to an electrostatic chuck according to embodiments of the present technology.

FIG. 7 shows a partial schematic illustration of a controller providing DC pulse to a conductor coupled with a pedestal structure within a processing chamber according to embodiments of the present technology.

FIG. 8 shows a partial schematic illustration of a controller providing DC pulse to a conductor coupled with a showerhead of a processing chamber according to embodiments of the present technology.

In the appended figures, similar components and/or features may have the same numerical reference label. Further, various components of the same type may be distinguished by following the reference label by a letter that distinguishes among the similar components and/or features. If only the first numerical reference label is used in the specification, the description is applicable to any one of the similar components and/or features having the same first numerical reference label irrespective of the letter suffix.

DETAILED DESCRIPTION

In semiconductor processing, etching may be performed for a number of reasons. In dry etching, precursors may be flowed through plasma to produce radical plasma effluents for etching various semiconductor materials. The plasma effluents include ions directed to the surface of the substrate and materials to be etched. In certain etching operations, such as with reactive-ion etching, the ions are directed to the surface of the materials, and based on the energy involved can sputter the materials from the surface of the substrate. Other etching operations are designed with a goal towards removing one material faster than a second material, often called a selective etch. In order to enhance selectivity, one approach may include reducing the sputtering component of an etching operation. This may be achieved in part by reducing the plasma power in order to reduce the electron temperature. Selectivity may become increasingly critical as feature size reduces. The higher the selectivity, the less material that is meant to be maintained may be formed as a buffer for the target dimensions of the final product. Even conventionally higher selectivities may be unsuitable as feature sizes continue to reduce. For example, if even a few nanometers is removed from materials meant to be maintained, device performance may be negatively impacted.
Plasma may be produced in a number of ways including, for example, with a radio-frequency (“RF”) bias electrically connected to a pedestal supporting a substrate. This bias power may be used in conjunction with or alternatively to an RF source coupled with portions of the chamber, or may work in conjunction with an inductively-coupled plasma source, a capactively-coupled plasma source, a microwave source, or any other plasma source that may additionally be used to produce plasma effluents. By utilizing a bias power in lieu of or in addition to a source power, directionality may be provided to the ions to provide more of an anisotropic, or orientation dependent etch. However, as ion energy increases, sputtering may also increase. Because sputtering may be more material independent, it can reduce selectivity between materials where only one is desired to be removed. Accordingly, a goal may be to reduce the plasma power on bias to reduce sputtering in an attempt to improve selectivity.
Conventional technologies may reduce the plasma power at the source or the bias, but are limited in the degree to which the bias power may be reduced both from the perspective of striking a plasma as well as in producing an etch. In order to strike a plasma, the power must exceed the breakdown voltage of the fluid from which plasma is produced. For conventional sputtering and pulsed-etch operations, glow discharge is often produced around, for example, 500 V and at a power of several thousand Watts in a low current, medium voltage regime. These power levels, however, will provide increased ion energy and concomitant sputtering of materials, which may lead to lower selectivity. If plasma power is lowered to further reduce sputtering, it may be difficult to generate or sustain a plasma at all, especially with a pulsed plasma power. Additionally, if the bias power is reduced too far, although sputtering may be resolved, overall etching may be reduced to zero.
The present technology overcomes many of these issues by producing a low-power RF plasma that is pulsed. Conventional so-called low-power plasmas may be produced at up to a few hundred Watts of source power and at a pulsing frequency in the megahertz range. These power ranges are unable to produce the selectivities of the present technology because the sputtering component of these plamsas is still too pronounced. The present technology, on the other hand, may produce plasmas at a variety of chamber conditions with a pulsed RF bias operating below 100 Watts, at a duty cycle down to about 20%, and at a pulsing frequency down to about 500 Hz. In this operating regime, sputtering may be reduced or substantially eliminated and etch selectivies may be produced that may be up to an order of magnitude improvement over conventional technologies. The present technology may involve a combination of enhancing selectivity via material modification and performing a low-power etch. These processes may enhance overall selectivity by reducing the amount of materials meant to be maintained both by reducing the amount etched in relation to other materials, as well as by reducing any plasma effects that may sputter or impact the materials negatively.
Although the following description will routinely identify etching operations, it is to be understood that the techniques may be applied more broadly. The system and operating methods may additionally by applied to deposition, cleaning, or any other plasma operations that may benefit from a low-power plasma as described. Accordingly, the description is not intended to limit the applications only to the examples described throughout the specification.
FIG. 1 illustrates a method 100 of etching a substrate according to embodiments of the present technology. Optional operations may be performed prior to the noted method operations including patterning, film formation, or a variety of other known process operations. The method may include modifying a material on a semiconductor substrate at operation 110. The substrate may have at least two exposed materials on a surface of the semiconductor substrate, and may have three, four, five, six, or more different materials exposed. Additionally, one or more materials may be initially covered prior to the selective etching method 100 but then exposed by the operations, and thus one or more of the exposed films may be exposed during the etching operation in embodiments. In embodiments, removal of one or more of these materials may be sought.
The method may also include forming a low-power plasma within a processing chamber housing the semiconductor substrate at operation 120. The low-power plasma may be a radio-frequency (“RF”) plasma in embodiments, although other plasma formations may similarly be encompassed. The low-power plasma may be at least partially formed by an RF bias power operating at between about 10 W and 100 W in embodiments. The RF bias power may be pulsed, and may be operated at a pulsing frequency below about 5,000 Hz in embodiments. The method may further include etching one or more of the at least two exposed materials on the surface of the semiconductor substrate at operation 130. The etching of one or more of the at least two exposed materials may be at a higher rate than a second of the at least two exposed materials on the surface of the semiconductor substrate in embodiments.
The modifying operation may be tuned in any number of ways based on the materials on the surface of the substrate, and may be based on an identification of properties of the materials and how they may differ from other materials on the substrate surface. For example, the modifying operations may initially identify differences in density, chemical structure, reactive nature, or any other characteristics between films that may be utilized. The modification to one or more of the materials may be performed to enhance or produce differences between the films that may be exploited in an etching operation. The modification may be performed in embodiments by exposing the materials to one or more precursors. In embodiments, the precursors may or may not be excited prior to interacting with the exposed materials. In embodiments, the modifying may include forming a plasma from a precursor within the processing chamber. The plasma may be from between about 50 W to about 300 W depending on the film being modified. For example, films exhibiting a higher density may benefit from a higher plasma power in embodiments. The plasma may be produced with a source power or a bias power in embodiments, as well as with a combination of the two in order to generate plasma effluents that modify one or more of the exposed materials. In embodiments, the plasma may be formed with an RF bias power.
The precursor utilized in the operation may include one or more precursors based on the type of modification being performed. The precursors may include one or more precursors intended to react with the materials in one form or another, or may include one or more precursors intended to physically alter one or more of the exposed materials. A combination of precursors having either or both of these effects may also be utilized in embodiments. In examples, the precursors may be selected from the group of elements including noble or inert elements, such as helium, neon, argon, krypton, xenon, and radon. The precursors may also be selected from halogens including fluorine, chlorine, bromine, iodine, and astatine, in embodiments. The precursors may also be selected from the chalcogens including oxygen, as well as a variety of other reactive and non-reactive precursors including hydrogen, for example.
As noted above, the modifying operation may include either or both of a chemical modification or a physical modification. A chemical modification may cause a chemical change to one or more of the materials on the semiconductor substrate. The chemical change may include a reaction such as, for example, producing an oxide of a material layer in embodiments. The chemical change may also adjust bonding structures of the materials, or may chemically alter atoms or molecules of the material, such as, for example, by removing electrons. The chemical modification may also involve densifying a material or film that is to be maintained on the surface of the substrate in relation to an additional material to be removed. Physical modification may be performed with an inert precursor that does not react with exposed materials on the substrate. For example, physical modification may involve damaging bonds of one or more of the materials on the semiconductor substrate with ions of the inert precursor. It is to be understood that the modification may involve a combination of chemical and physical modification, and individual precursors utilized may cause an amount of both physical and chemical modification to occur.
The materials on the surface of the semiconductor substrate may include a variety of materials used in various semiconductor processing. The materials may include metals, dielectrics, etch stop layers, and substrate materials that may include any of a number of elements commonly understood in semiconductor processing. For example, the materials may include metals such as copper, tungsten, titanium, or other metals or metal-containing layers. The materials may also include silicon-containing materials such as silicon oxide, silicon nitride, polysilicon, silicon carbide, silicon oxycarbide, silicon carbonitride, or materials based on other semiconductor base materials, such as, for example, gallium.
In embodiments, the low-power plasma utilized in the etching operation may be at least partially produced from an RF bias power electrically coupled with a pedestal on which the substrate is supported. The bias power may be operated at a power of from about 1 W to about 500 W in embodiments. The bias power may also be operated from about 10 Watts to about 250 Watts, from about 15 Watts to about 200 Watts, from about 20 Watts to about 150 Watts, from about 20 Watts to about 100 Watts, or from about 20 Watts to about 50 Watts in embodiments. The bias power may be operated in this range which may provide benefits of reducing sputtering, while still striking a plasma and producing etch results. For example, as power levels increase, sputtering may increase as well due to increased ion energy, and so the power level may be maintained below about 100 Watts in embodiments. On the other hand, the power level may be maintained above about 20 Watts in embodiments, as levels below this threshold may have reduced etching capacity or ability to strike a plasma. These parameters may also be dependent to a degree on chamber conditions including pressure and temperature, but may still generate stable plasma under pulsing conditions utilizing the technology discussed in more detail below.
The RF bias power may be operated at a low duty cycle and pulsing frequency in order to generate the low-power plasma. The duty cycle may be below about 75% in embodiments, and may be below about 70%, below about 65%, below about 60%, below about 55%, below about 50%, below about 45%, below about 40%, below about 35%, below about 30%, below about 25%, below about 20%, below about 15%, or below about 10% in embodiments. The RF bias pulsing duty cycle may also be operated with a duty cycle between about 10% and about 60%, or between about 20% and 50% in embodiments for similar reasons of maintaining lower ion energy while still having enough on-time to generate stable plasma.
The frequency of pulsing for the RF bias may be below about 10 kHz in embodiments. The frequency of pulsing for the RF bias may also be below about 9,000 Hz, below about 8,000 Hz, below about 7,000 Hz, below about 6,000 Hz, below about 5,000 Hz, below about 4,500 Hz, below about 4,000 Hz, below about 3,500 Hz, below about 3,000 Hz, below about 2,500 Hz, below about 2,000 Hz, below about 1,500 Hz, below about 1,000 Hz, below about 750 Hz, or below about 500 Hz in embodiments. The pulsing frequency may also be maintained between about 500 Hz and about 5,000 Hz in embodiments or about 500 Hz and about 2,000 Hz in embodiments. The frequency of the bias pulsing may affect the dissociation of the plasma precursors, and thus by adjusting the frequency, the dissociation may be adjusted.
In addition to the RF bias power, an RF source power may be used in embodiments. The RF source power may be used in the etching operation with a power up to about 1,000 W or less, and may be operated with a power up to about 500 W, or up to about 100 W in embodiments. The RF source power may be operated below about 100 W in embodiments, and may be operated between about 0 W and 100 W in embodiments. Different precursors may benefit from the addition of RF source, while other precursors may benefit from the lack of RF source power. For example, RF source may increase polymer dissociation, so for certain precursors including, for example C₄F₈and C₄F₆, source power may dissociate the polymer and deposit carbon material on the substrate impeding the etch operation. Accordingly, using a low or no RF source may improve etching in some embodiments. In embodiments a variety of precursors may be utilized in the etching operation depending on the type of film being etched. Exemplary precursors that may be used include C₄F₈, C₄F₆, CF₄, Cl₂, CH₂F₂, O₂, N₂, as well as any other precursors that may provide etchant characteristics to remove the target material.
The RF bias conditions previously discussed may pose difficulties in controlling the plasma sheath or maintaining homogeneity of the sheath in embodiments. However, the conditions may aid in minimizing sputtering during the etching processes. Accordingly, the present technology further seeks to gain control over operating plasmas at low power that may not be assisted by magnetics or associated components. As pressures and operating conditions are adjusted for particular processes, plasmas may be more difficult to strike under these conditions. Plasma generation or gas discharge may in part depend on priming particles or creating energized particles as a precursor to breakdown. These energized particles are generated to accelerate discharge, which may reduce the needed firing voltage. During a pulsing power operation such as that previously discussed, including an additional energy source to produce priming particles and to maintain electrons in the plasma feedback loop may aid in the control of plasma generation at low power during a variety of processing conditions. By providing the additional energy source, plasma may then be struck at low or lower than normal power levels such as those described above. The present technology provides additional sources of energy in embodiments to return energetic particles back into the plasma priming loop.
A variety of additional energy sources may be utilized in the present technology, and in one example may include a pulsed DC power. The pulsed DC power may be connected to a variety of locations in the chamber in order to help prime the plasma before the low-power plasma is struck with the RF bias power. However, this pulsed DC power is fundamentally different from conventional DC bias. In some conventional processing, DC bias is applied in the system, including as a bias on the pedestal. When the DC pulse is applied, the plasma will form all the way from the bulk and will be maintained long enough for current to be accommodated in a plasma sheath at the pedestal. Accordingly, it will collapse down to the surface of the pedestal creating a sheath with a certain amount of DC potential. This plasma sheath and potential produces ion energies for the process and will produce sputtering of the materials at the surface of the cathode due to high ion energies associated with the DC plasma. The present technology, however, may cycle the DC pulse prior to forming a plasma sheath.
In embodiments of the present technology, the pulsed DC potential may be initiated to prime the plasma, and then cycled off to prevent the formation of a high-voltage DC plasma sheath at the substrate surface. Thus, conventional DC bias maintains the pulse long enough to develop a sheath, which is at a high voltage and affects the ion energies. The present technology may utilize the pulsed DC power to create priming particles to allow a low RF power to ignite a plasma each time it is pulsed on. The low RF power, which may be below a typical breakdown voltage, provides lower ion energies than would be produced in a high-voltage DC plasma sheath, such as produced by a conventional DC bias. The pulsed DC power of the present technology instead produces the priming particles that allow avalanche breakdown and development of the sheath when the RF bias cycles on, despite the low power of the RF bias. The result is a plasma sheath at lower ion energies, which may reduce or substantially reduce sputtering over conventional technologies. By reducing the sputtering, higher selectivity may be afforded as previously explained.
To produce the functionality of the pulsed DC power, the duty cycle of the pulsed DC power may be very low, and may be associated with an on time of 1 microsecond to about 100 microseconds in embodiments. In embodiments the on time may be less than about 75 microseconds, less than about 50 microseconds, less than about 30 microseconds, less than about 25 microseconds, less than about 20 microseconds, less than about 15 microseconds, less than about 10 microseconds, less than about 5 microseconds, or less than about 1 microsecond.
In terms of duty cycle, while conventional DC bias may include a duty cycle of above 50%, above 75%, or above 90% in order to generate a plasma sheath, the present technology may utilize a duty cycle of the pulsed DC power that is less than about 50% in embodiments. The duty cycle of the pulsed DC power may also be less than about 40%, less than about 30%, less than about 25%, less than about 20%, less than about 15%, less than about 10%, less than about 5%, or less than about 1% in embodiments. The DC power may also be pulsed at a duty cycle between about 1% and about 50%, between about 1% and about 25%, between about 1% and about 10%, or any other range between or within these values.
The pulsed DC power may also be operated on an alternating or semi-alternating frequency with the RF bias pulsing. For example, the frequency of the pulsed DC power may be such that it is in the on cycle while the RF bias is in the off cycle and vice versa. Depending on the duty cycles of the two powers, either one of the two powers may be operating at a given time or neither of the two powers may be operating at a given time. In embodiments both may also be operating at a given time. By utilizing the reduced duty cycles of the present technology, a plasma sheath may not be formed at the substrate surface while the pulsed DC power is operating. Thus, the pulsed DC power maintains priming particles available for discharge breakdown and to stabilize the impedance to improve the operating conditions of the system, while not forming a sheath or breakdown until the RF power is cycled on. In this way, a variety of pressure ranges may be accommodated by the present technology including pressure regimes below about 50 mTorr as well as pressure regimes up to several hundred mTorr or above. Put another way, the present technology controls the impedance for glow discharge breakdown to remove the conventional impedance limitations of configuration, orientation, pressure, chemistry, etc.
The pulsed DC power may be coupled with the system in a number of ways further described below in relation to the other figures. For example, and as described in detail below, the pulsed DC power may be applied to a bipolar electrostatic chuck supporting the semiconductor substrate. Additionally, the pulsed DC power may be applied to a conductive ring embedded in or coupled with a shield ring of a pedestal supporting the semiconductor substrate. Still further, the pulsed DC power may be applied to a conductive ring embedded in or connected with a showerhead within the processing chamber.
Turning to FIG. 2 is shown a graph illustrating the additive effects of material modification and low-power plasma according to embodiments of the present technology. As illustrated, an exemplary process may include removing an oxide film relative to a carbide film on the surface of a substrate. As shown by the first bar, a reactive-ion etching or continuous waveform process may provide a selectivity below 10:1 for the oxide material with respect to the carbide material. This may be due in part to the sputtering caused by the ion process, which is more aggressive to all materials thereby increasing both etch rates. Moreover, the reactive-ion etch may also produce rounded corners in the etch profile and may also etch an underlying layer due to ion bombardment once the desired film has been removed. Accordingly, a reactive-ion etch may be unsatisfactory for selective processing and maintaining features of the substrate.
As shown in the second bar, by simply utilizing the pulsing low-power RF bias plasma described above, such as with the pulsed DC power, selectivity may be improved over the conventional reactive-ion etch process. The process may also reduce or eliminate the corner rounding and underlying layer etch produced by reactive-ion etching. The third bar, however, illustrates the synergistic benefits of performing a material modification prior to performing the low-power pulsing. By utilizing both film modification as well as the low-power plasma RF pulsing process, selectivity increases by almost an order of magnitude over the reactive-ion etching process. Additionally, the etch profile is much improved with reduced corner rounding and underlying layer etching.
FIG. 3 illustrates imaging of an etch process performed according to embodiments of the present technology. As shown in the image on the left, regions of silicon nitride 305 are disposed between regions of silicon carbide 310. After a material modification and low-power RF etching operation as previously discussed are performed, the silicon carbide sections are removed, as illustrated in the figure on the right. The layers of silicon nitride 305 are substantially maintained, and only minimal corner rounding can be observed. Additionally, silicon oxide layer 315 underlying the silicon carbide sections 310 was exposed during the etch process, but the film was able to act as an etch stop to the process, as opposed to a reactive-ion process that would have etched into the trench due to bombardment of the silicon oxide. The measured effects illustrate that the present technology was able to produce an etch selectivity of silicon carbide to silicon nitride of over 50:1 with minimal corner rounding of the silicon nitride. The present technology was also able to produce an etch selectivity of silicon carbide to silicon oxide of over 70:1.
FIG. 4 shows a chart illustrating etch rates of various materials with and without a treatment according to embodiments of the present technology. The present example shows a material modification that utilized an oxygen precursor in plasma to modify silicon oxycarbide, silicon oxide, silicon carbide, and silicon nitride exposed on a substrate surface. A low-power pulsed RF etching process was performed on similar materials with and without the oxygen treatment. As illustrated, all four films etched with low selectivity during the low-power etch process without the material modification. On the other hand, after the oxygen treatment, silicon oxycarbide and silicon carbide continued to etch, while the silicon oxide and silicon nitride films were essentially maintained and buffered by the oxygen treatment providing a surface enhancement to those films.
FIG. 5 shows a chart illustrating etch rates of silicon oxycarbide and silicon carbide with and without treatments according to embodiments of the present technology. Although the oxygen modification performed in the example illustrated in FIG. 4 was successful for the carbon-containing films with respect to silicon oxide and silicon nitride, the two carbon-containing films did not have high selectivity with respect to each other. In FIG. 5, a physical modification was performed that exploited the higher porosity of the silicon oxycarbide film. Silicon oxycarbide is a more porous film than silicon carbide, and the chemical bonding is weaker as well. The physical modification of this example included utilizing a helium precursor in plasma, and then exposing the films to those plasma effluents. Because helium is inert to the two films, it did not chemically react with the materials, although the impact of the helium ions was of a sufficient capacity to damage the chemical bonds of the silicon oxycarbide. This further weakened the film, after which a low-power RF pulsing etch was performed. As illustrated by the figure, the modification followed by the low-power etch removed the silicon oxycarbide material while essentially maintaining the silicon carbide.
The examples illustrated by FIGS. 4 and 5 are exemplary only, and are not intended to limit the present technology. These examples merely show the types of material modifications encompassed by the present technology. One of skill will readily understand by these examples how the material modifications and low-power etch operations may be applied to a variety of materials to enhance selectivity and improve etch profiles. By utilizing the present technology, greater than 20:1 selectivity may be achieved for silicon oxycarbide with respect to silicon oxide and silicon nitride. Greater than 20:1 selectivity may also be achieved for silicon oxide with respect to silicon oxycarbide, silicon nitride, and silicon carbide using various material modifications and etching according to the present technology. Greater than 20:1 selectivity may also be achieve for silicon carbide with respect to silicon oxide, silicon nitride, and silicon oxycarbide using various material modifications and etching according to the present technology. Additionally, greater than 20:1 selectivity may be achieved for silicon nitride with respect to silicon oxide, silicon oxycarbide, and silicon carbide using various material modifications and etching according to the present technology. In embodiments the selectivity of any of these operations may also be greater than or about 25:1, greater than or about 30:1, greater than or about 35:1 , greater than or about 40:1, greater than or about 45:1, greater than or about 50:1, greater than or about 55:1, greater than or about 60:1, greater than or about 65:1, greater than or about 70:1, greater than or about 75:1, greater than or about 80:1, greater than or about 85:1, greater than or about 90:1, greater than or about 95:1, or greater than or about 100:1.
Turning to FIG. 6 is shown a partial schematic illustration of a controller providing DC pulse to an electrostatic chuck according to embodiments of the present technology. The system may be included with a substrate processing chamber according to embodiments of the present technology. An exemplary chamber may be the Mesa™ Etch System produced by Applied Materials, Inc. of Santa Clara, Calif. The components may include a pedestal 605 configured to support a semiconductor substrate. The system may also include a pulsed RF bias power 610 electrically coupled with the pedestal and configured to generate a plasma as previously described. The pulsed RF bias power 610 may be configured to generate a plasma within the processing chamber at a power of between about 20 W and about 50 W, and the pulsed RF bias power may be pulsed at a frequency below about 5,000 Hz. The system may also be configured to operate at any of the other levels previously described.
The system may also include a DC pulsing power 615 electrically coupled with the substrate processing chamber. The DC pulsing power 615 may be as previously described, and configured to produce priming particles for the RF bias plasma. In embodiments, the DC pulsing power may be configured to pulse at a frequency to produce priming particles without developing a plasma sheath. The DC pulsing power may be operated for any of the times or at any of the duty cycles previously described, and may be configured to be pulsed for a duration of 100 microseconds or less at a duty cycle of less than about 50%. The DC pulsing power may also be configured to be operated for a pulse duration of less than about 50 microseconds at a duty cycle of less than about 20%. The DC pulsing power may also be configured to be operated for a pulse duration of less than about 10 microseconds at a duty cycle of less than about 10% in embodiments.
As illustrated in FIG. 6, the pedestal 605 may be an electrostatic chuck. A chamber controller 620 may provide instructions to the electrostatic chuck controller 625, including the input/output module 630 for the bipolar electrostatic chuck. The DC pulsing power 615 may be electrically coupled with electrical ground of the bipolar electrostatic chuck 630 as illustrated in the figure. In many processing chambers the electrodes may be biased to DC voltages, and heavy filtering may be included at the output of the DC power supplies to block RF power. Consequently, when the supplies are pulsed as shown in the configuration, the waveform may begin to be distorted and attenuated. Accordingly, to overcome this issue, the electrostatic chuck power may be floated at the voltage of the pulsed DC. Thus, the electrostatic chuck electrodes are then referenced to the high voltage of the pulsed DC. Put another way, the electrostatic chuck power supply may then be floating electrically isolated from the machine ground, and ground of the electrostatic chuck essentially may be at high voltage. The electrostatic chuck can then output positive and negative polarity with respect to the high voltage.
Thus, if the pulsed DC is cycled off or grounded, then the electrostatic chuck electrodes would be referenced to the ground, plus or minus. However, when the DC is applied or pulsed, then the electrostatic chuck electrodes would be referenced to the power of the applied DC power. As a non-limiting example of such a configuration for the purposes of explanation, and not as a particular process scenario, if the pulsed DC power operates at 1 kV, and the electrostatic chuck operates at +/−500 volts, when the DC power supply is cycled on to assist with plasma generation as previously described, then the electrodes would be at 1500 volts and 500 volts respectively. A benefit of this configuration may be that an additional conductor for the pulsed DC power may not be required inside the chamber. Additionally, in embodiments the DC and RF pulses may be alternated, and thus the DC and RF supplies may be decoupled from one another despite that they are each biasing the same pedestal base.
An additional coupling option that may be decoupled from the electrostatic chuck is illustrated in FIG. 7, which shows a partial schematic illustration of a controller providing DC pulse to a conductor coupled with a pedestal structure according to embodiments of the present technology. As illustrated in the figure, a substrate processing chamber 701 is shown having a showerhead 703 and a pedestal 705 configured to support a substrate. The system may include a pulsed RF bias 710 as previously discussed, as well as a DC power 715 for electrostatic chucking. An additional DC pulsing unit 720 may be included that provides pulsed DC power as previously discussed for producing priming for a plasma ignited by the RF bias. In this example, the DC pulsing power is electrically coupled with a conductive ring 725 embedded in or coupled with the pedestal. This conductive ring 725 may be decoupled from the electrostatic chuck and from the RF bias in embodiments. For example, the conductive ring 725 may be included in a dielectric shield ring, including a quartz shield ring of the pedestal 705 as shown. The conductive ring may be any conductive material including a metal or silicon carbide in embodiments. In this scenario, although an additional conductor is included in the system, because the conductive ring is decoupled from the other power supplies, the components do not require electrical floating with respect to one another.
Another coupling option that may be decoupled from the electrostatic chuck is illustrated in FIG. 8, which shows a partial schematic illustration of a controller providing DC pulse to an embedded conductor within a showerhead of a processing chamber according to embodiments of the present technology. As illustrated, components similar to those discussed with respect to FIG. 7 are shown, including a substrate processing chamber 701, including showerhead 703, and pedestal 705, for example. The system similarly includes a pulsed RF bias 710, a DC power 715 for electrostatic chucking, and a DC pulsing unit 720. The figure additionally includes a conductive ring 825 which may be a similar material as discussed above, but may be coupled with showerhead 703 in embodiments. This coupling option also decouples the pulsed DC from the other power supplies.
The coupling ring may also be included coupled with or embedded in a chamber wall in embodiments, or other components of the chamber system. By providing the pulsed DC power with any of these options or alternative options as would be readily understood to be similarly encompassed, the system may produce lower power plasma than conventional systems. By providing energy to produce energetic particles allowing the low-power, pulsing RF bias to more easily strike a plasma at lower voltages with lower ion energies, improved plasma processing may be provided for etching, deposition, cleaning, or any other process that may benefit from a low-power plasma.
In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.
Having disclosed several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the embodiments. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present technology. Accordingly, the above description should not be taken as limiting the scope of the technology.
Where a range of values is provided, it is understood that each intervening value, to the smallest fraction of the unit of the lower limit, unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Any narrower range between any stated values or unstated intervening values in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of those smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included. Where multiple values are provided in a list, any range encompassing or based on any of those values is similarly specifically disclosed.
As used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural references unless the context clearly dictates otherwise. Thus, for example, reference to “a material” includes a plurality of such materials, and reference to “the precursor” includes reference to one or more precursors and equivalents thereof known to those skilled in the art, and so forth.
Also, the words “comprise(s)”, “comprising”, “contain(s)”, “containing”, “include(s)”, and “including”, when used in this specification and in the following claims, are intended to specify the presence of stated features, integers, components, or operations, but they do not preclude the presence or addition of one or more other features, integers, components, operations, acts, or groups.

Claims

1. A method of performing a selective etch, the method comprising:

modifying a material on a semiconductor substrate having at least two exposed materials on a surface of the semiconductor substrate;

forming a low-power plasma within a processing chamber housing the semiconductor substrate, wherein the low-power plasma is a radio-frequency (RF) plasma, and wherein the low-power plasma is at least partially formed by an RF bias power operating at between about 10 W and 100 W and at a pulsing frequency below about 5,000 Hz; and

etching one of the at least two exposed materials on the surface of the semiconductor substrate at a higher rate than a second of the at least two exposed materials on the surface of the semiconductor substrate.

2. The method of claim 1, wherein the modifying comprises forming a plasma from a precursor within the processing chamber with the RF bias power.

3. The method of claim 2, wherein the precursor is selected from the group consisting of oxygen, hydrogen, or helium.

4. The method of claim 1, wherein each of the at least two exposed materials on the surface of the semiconductor substrate are selected from the group consisting of silicon oxide, silicon nitride, silicon carbide, and silicon oxycarbide.

5. The method of claim 1, wherein the RF bias power at least partially forming the low-power plasma operates at a duty cycle below about 50%.

6. The method of claim 1, wherein forming the low-power plasma further comprises utilizing an RF source power below about 100 W.

7. The method of claim 1, wherein forming the low-power plasma further comprises utilizing a pulsed DC power.

8. The method of claim 7, wherein the pulsed DC power is applied to a bipolar electrostatic chuck supporting the semiconductor substrate.

9. The method of claim 7, wherein the pulsed DC power is applied to a conductive ring embedded in a shield ring of a pedestal supporting the semiconductor substrate or embedded in a showerhead within the processing chamber.

10. A method of removing material from a semiconductor substrate, the method comprising:

modifying a material on a semiconductor substrate having at least two exposed materials on a surface of the semiconductor substrate, wherein the modifying comprises forming a plasma from a precursor with an RF bias power to generate plasma effluents that modify the material;

forming a low-power plasma within a processing chamber housing the semiconductor substrate, wherein the low-power plasma is a radio-frequency (RF) plasma, and wherein the low-power plasma is formed by a pulsed RF bias power operating at between about 20 W and 50 W at a pulsing frequency between about 500 Hz and about 2,000 Hz at a duty cycle of between about 20% and 50%;

operating a DC pulsed power on an alternating frequency with the RF bias power pulsing; and

etching one of the at least two exposed materials on the surface of the semiconductor substrate at a selectivity of at least about 20:1 with respect to a second of the at least two exposed materials on the surface of the semiconductor substrate.

11. The method of claim 10, wherein the modifying comprises a chemical modification causing a chemical change to the material on the semiconductor substrate.

12. The method of claim 10, wherein the modifying comprises a physical modification utilizing an inert precursor.

13. The method of claim 12, wherein the physical modification comprises damaging bonds of the material on the semiconductor substrate with ions of the inert precursor.

14. The method of claim 10, wherein forming the low-power plasma further comprises utilizing an RF source power operating up to about 100 W.

15. A substrate processing chamber comprising:

a pedestal configured to support a semiconductor substrate;

an RF bias power electrically coupled with the pedestal and configured to generate a plasma within the processing chamber at a power of between about 20 W and about 50 W, wherein the RF bias power is a pulsing power configured to pulse at a frequency below about 5,000 Hz; and

a DC pulsing power electrically coupled with the substrate processing chamber and configured to produce priming particles for the RF bias plasma.

16. The substrate processing chamber of claim 15, wherein the DC pulsing power supply is configured to pulse at a frequency to produce priming particles without developing a plasma sheath.

17. The substrate processing chamber of claim 16, wherein the DC pulsing power supply is configured to be pulsed on for a duration of 100 microseconds or less at a duty cycle of less than about 50%.

18. The substrate processing chamber of claim 15, wherein the pedestal comprises a bipolar electrostatic chuck, and wherein the DC pulsing power is applied to electrical ground of the bipolar electrostatic chuck.

19. The substrate processing chamber of claim 15, wherein the pedestal comprises an electrostatic chuck, and wherein the DC pulsing power is electrically coupled with a conductive ring coupled with the pedestal, wherein the conductive ring is electrically decoupled from the electrostatic chuck and the RF bias.

20. The substrate processing chamber of claim 15, wherein the DC pulsing power is electrically coupled with a conductive ring embedded in a showerhead within the substrate processing chamber.