Patent Application
20150221481
1) Field
Embodiments of the present invention pertain to the field of semiconductor processing equipment and, in particular, to electrostatic chucks with magnetic cathode liners for critical dimension (CD) tuning.
2) Description of Related Art
In a plasma processing chamber, such as a plasma etch or plasma deposition chamber, the plasma density is often an important parameter to control during a process since it can correspond to the amount of ionization available at a location within the plasma.
Often, plasma characteristics can be manipulated by thermal means, where a change in the temperature of the plasma can lead to a change in plasma characteristics. For example, a temperature of a substrate holder, commonly called a chuck or pedestal, may be controlled to heat/cool a workpiece to various controlled temperatures during the process recipe (e.g., to control an etch rate). Similarly, a temperature of a showerhead/upper electrode, chamber liner, baffle, process kit, or other component may also be controlled during the process recipe to influence the processing. Conventionally, a heat sink and/or heat source is coupled to the processing chamber to maintain the temperature of a chamber component at a desired temperature. Often, at least one heat transfer fluid loop thermally coupled to the chamber component is utilized to provide heating and/or cooling power. Long line lengths in a heat transfer fluid loop, and the large heat transfer fluid volumes associated with such long line lengths are detrimental to temperature control response times. Point-of-use systems are one means to reduce fluid loop lengths/volumes. However, physical space constraints disadvantageously limit the power loads of such point-of-use systems.
With plasma processing trends continuing to increase RF power levels and also increase workpiece diameters (with 300 mm now typical and 450 mm systems now under development), temperature and/or RF control and distribution addressing both a fast response time and high power loads is advantageous in the plasma processing field. Temperature-based or temperature-only solutions may not achieve the optimal tunability of plasma density. As such, advances are still needed toward plasma density tunability.
Embodiments of the present invention include with magnetic cathode liners for critical dimension (CD) tuning, where a cathode liner may be included in an electrostatic chuck.
In an embodiment, an electrostatic chuck (ESC) includes a cathode region. A wafer processing region is disposed above the cathode region. A magnetic cathode liner surrounds the cathode region, below the wafer processing region. The magnetic cathode liner is configured to provide magnetic field tuning capability for the ESC.
In another embodiment, a semiconductor processing system includes a chamber coupled to an evacuation device, a gas inlet device, a plasma ignition device, and a detector. A computing device is coupled with the plasma ignition device. A voltage source is coupled with a sample holder that includes an electrostatic chuck (ESC). The ESC is disposed in the chamber and includes a cathode region. The ESC also includes a wafer processing region disposed above the cathode region. The ESC also includes a magnetic cathode liner surrounding the cathode region, below the wafer processing region. The magnetic cathode liner is configured to provide magnetic field tuning capability for the ESC. The magnetic cathode liner includes one or more electromagnets. The semiconductor processing system also includes an electrical source coupled to the one or more electromagnets of the magnetic cathode liner.
In another embodiment, an electrostatic chuck (ESC) includes a ceramic plate having a front surface and a back surface, the front surface for supporting a wafer or substrate. A base is coupled to the back surface of the ceramic plate. A plurality of pixelated elements is disposed in the base. A magnetic cathode liner surrounds the ceramic plate and base. The magnetic cathode liner and the plurality of pixelated elements are configured to provide plasma tuning capability in regions local to the ESC.
Electrostatic chucks with magnetic cathode liners for critical dimension (CD) tuning are described. In the following description, numerous specific details are set forth, such as specific chuck and/or chamber configurations, in order to provide a thorough understanding of embodiments of the present invention. It will be apparent to one skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well-known aspects, such as etch processing in the presence of a wafer supported by a chuck, are not described in detail in order to not unnecessarily obscure embodiments of the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.
One or more embodiments described herein are directed to a magnetic cathode liner for critical dimension (CD) tuning during plasma processing. For example, to offer additional tuning capabilites near the edge of the wafer during plasma processing, an electromagnetic coil is added under the wafer near the wafer edge. The electromagnetic coil is direct current (DC)-powered and can be adjusted in voltage to allow for edge tuning of the etch critical dimensions. In certain embodiments, electromagnets are used, as opposed to permanent magnets, for responsive control. In an exemplary implementation, a chamber having a dual plasma source (DPS) is equipped with a cathode having a liner with an electromagnetic coil provided therein. Electrical wires for the electromagnets may be routed through passageways at atmosphere to the outside of the chamber. In one embodiment, by altering a plasma density and distribution, the plasma impinging the electrostatic chuck (ESC) or chamber wall can be controlled. In one embodiment, with the magnetic field, the charged particle trajectory may be deflected away from the wafer. As such, “fall on” particles that otherwise arrive onto the wafer and cause yield loss may be avoided.
To provide context, demand for very uniform wafer temperature and plasma density tunability on an electrostatic chuck is ever increasing. In general, wafer clamping by means of electrostatic chucking has been used to provide temperature control during etch processing. The wafer is clamped to a ceramic or multi-layer surface with a heat sink or heater (or both) depending on application. Due to inherent non-uniformities and auxiliary hardware (e.g., lifter pins, RF/DC electrode(s), etc.) the ceramic surface temperature is not uniform. This non-uniformity translates to the wafer, affecting the etch process. Conventional chuck designs have concentrated on coolant layout optimization and introduction of multiple (up to 4 zones) heaters. Such chuck designs have not been useful for solving issue related to, or caused by, auxiliary hardware (e.g., lifter pins, RF/DC electrode(s), etc.).
More specifically, conventional electrostatic chuck temperature control is typically based on a cooling base and one or more electrical heaters included in the electrostatic chuck. Such an arrangement, however, can have flaws or drawbacks that lead to some level of temperature non-uniformity. For example, bond imperfection between the ceramic layer of the electrostatic chuck and an underlying cooling base which results in thickness variation between the ceramic plate and cooling base can lead to the formation of cold or hot spots across the check. In an example of particular significance to the present disclosure, plasma density variation, e.g., in a plasma etch or deposition chamber, can lead to the formation of hot or cold spots across a wafer or substrate supported by the chuck or pedestal. In accordance with an embodiment of the present invention, as described herein, a magnetic cathode liner is included to surround an electrostatic chuck in order to provide capability to provide a finely tuned magnetic field for the plasma near the chuck. The finely tuned magnetic field can be used to tune plasma density and, hence, plasma uniformity at or near a sample. Embodiments described herein may be directed to next generation etch chamber ESCs with active magnetic field control.
It is appreciated that magnetron reactive ion etching (RIE) has been employed to provide global magnetic field control over an associated plasma density. However, control in on a localized level is not achievable with such processes or associated apparatuses. By contrast, as described in association with embodiments herein, an ESC having a magnetic cathode liner provides fine tuned magnetic field tuning capability for controlling plasma ionization more local to the chuck.
In accordance with one or more embodiments described herein, an electromagnetic tuning feature is provided to tune critical dimension uniformity (CDU) at the wafer level. In one such embodiment, one or more electromagnets are included in a cathode liner. The resulting magnetic cathode liner may be provided as part of an electrostatic chuck used to hold a wafer during plasma processing, such as plasma etching.
For comparative purposes,
As is also depicted in
In an embodiment, the electromagnets are powered by a direct current (DC) voltage and do not require an RF filter. In one embodiment, the electromagnets are composed of a magnetic material such as, but not limited to, metal wires, metal coils, ferrites and ferromagnetic materials. In an embodiment, the material of the cathode liner 208 housing the electromagnets is composed of a material such as, but not limited to, Alumina based ceramics, quartz and Yttrium based materials. It is to be appreciated that, in addition to the embodiments described above, the magnetic cathode liner 208 can house one or more than two electromagnets.
In an embodiment, use of a magnetic cathode liner such as the magnetic cathode liners described above can be beneficial since it has been determined that ion flux is influenced by the presence of a magnetic field. For example,
In another aspect, one or more embodiments described herein relate to electrostatic chucks with magnetic cathode liners for CD tuning and having additional variable magnetic control within the surface area of the processing region of the chuck. In particular, variable pixelated magnetic field generation may be incorporated into a bonded electrostatic chuck using individualized electrical wiring and a control system to power the individualized wiring for each element in a pixelated arrangement. Applications may include increased plasma density uniformity control for pedestals or electrostatic chucks, e.g., as included in semiconductor processing chambers. Particular embodiments involve the incorporation of a plurality of electromagnets as embedded in an electrostatic chuck for independent and local process control at the wafer level.
To further demonstrate the concepts at hand, when applying a magnetic field at the wafer level, electrons gyrate around the magnetic field lines and are trapped as a local ionization source. The trapping leads to higher plasma density locally. In addition, the recombination with an associated chamber wall with a magnetic field may be reduced. The gyrofrequency of an electron is provided by equation 1 (eq. 1):
(ω=qB/me. (eq. 1)
Simulation results indicate that a magnetic field of approximately 4 Gauss is strong enough to deviate the ion flux by ±5%, even in the presence of bias in a Cl2 plasma. For example,
In principle, as described above, with a magnetic field at the wafer level, the plasma undergoes gyration motion. The magnetic field can be controlled or tuned using the above described magnetic cathode liner. Additionally, in an embodiment, plasma density is further tuned (e.g., increased) locally by using localized electromagnets included in an electrostatic chuck. Together, the magnetic field introduced around the wafer can cause the local electron accelerated in cyclic motion, leading to locally enhanced molecular dissociation.
As a general example,
In an embodiment, the plurality of electromagnets 850 is disposed in the cooling based 808 at a level approximately 1 centimeter or less below the electrostatic chuck top portion 802. In one such embodiment, the plurality of electromagnets 850 is disposed in the cooling based 808 at a level approximately in the range of 5-8 mm below the electrostatic chuck top portion 802. In an embodiment, the cooling base 808 includes a chiller plate with an aluminum (Al) body and capability for fluid flow there through.
In another aspect, one or more embodiments described herein relate to electrostatic chucks with magnetic cathode liners for CD tuning and having additional variable temperature control within the surface area of the processing region of the chuck. In particular, variable pixelated heat generation may be incorporated into a bonded electrostatic chuck using individualized electrical wiring and a control system to power the individualized wiring for each element in a pixelated arrangement. Applications may include increased plasma density uniformity control for pedestals or electrostatic chucks, e.g., as included in semiconductor processing chambers. Particular embodiments involve the incorporation of a plurality of light pipes as embedded in an electrostatic chuck for independent and local process control at the wafer level. As such, light energy may be used instead of or in addition to thermal resistance for fine tuning of temperature uniformity. One or more advantages of implemental discrete temperature control by light heating include, but are not limited to, (1) the ability to heat specific area(s) of a pedestal or electrostatic chuck, (2) special perforated bonding can allow direct heating of a back side of a ceramic chuck or pedestal, (3) RF interface issue mitigation as heating is light based, (4) a control system which allows only specific fibers are used for heating based on cold spot mapping.
In an exemplary embodiment,
Referring again to
In another embodiment, in place of a plurality of fibers/light carrying medium 912, a plurality of resistive heaters may be provided to enable pixilated temperature control of the electrostatic chuck.
As described above, magnetic field tunability may be provided for an electrostatic chuck by including a magnetic cathode liner for the electrostatic chuck. As an example,
The substrate support 1000 may include a body 1004. The body 1004 may have an interior volume 1006 that is separated from a processing volume 1008 of the process chamber. The interior volume 1006 may be held at atmosphere, for example, about 14.7 pounds per square inch (psi), or be held under an inert atmosphere, such as nitrogen (N2) or the like. The interior volume 1006 is further isolated from, and protected from, any gases that may be present in the processing volume 1008 of the process chamber. The process volume 1008 may be held at atmospheric or sub-atmospheric pressures.
The interior volume 1006 may be enclosed by an electrostatic chuck 1010 at an upper end 1005 of the body 1004 and by a feed through structure 1011, which may be welded or brazed to a lower opening 1014 of the body 1004. For example, as illustrated in
The bellows 1012 may be coupled to the body 1004 at the lower opening 1014, for example, by welding or brazing. An opposing lower end 1016 of the bellows 1012 may be coupled to an opening 1018 in the chamber wall 1002. For example, as illustrated in
The substrate support 1000 may include a cooling plate 1034 disposed in the interior volume 1006 below the electrostatic chuck 1010. For example, in some embodiments, the cooling plate 1034 may be directly contacting an interior volume facing surface of the electrostatic chuck 1010. However, this embodiment of the cooling plate 1034 is merely exemplary and the cooling plate may not directly contact the electrostatic chuck 1010. The cooling plate 1034 may include a plurality of cooling channels (not shown) for circulating a coolant there through. The coolant may include any suitable liquid or gas coolant. In some embodiments, the coolant may be supplied to the cooling plate 1034 via a coolant source 1036 coupled to the cooling plate 1034 via the feed through structure 1011. For example, the cooling plate 1034 may be engaged to the electrostatic chuck 1010 by one or more springs 1035 or any suitable engagement mechanism.
In some embodiments, the cooling plate 1034 may include an inner and outer cooling plate. In some embodiments, the inner cooling plate may be disposed about a center gas line, and the outer cooling plate may be disposed about a plurality of outer gas lines. For example, the inner and outer cooling plates may be used to adjust cooling capacity depending on how the electrostatic chuck 1010 is utilized, such as how electrical power is provided to the electrode(s) 1026 and/or the one or more heaters 1023 or the like. Further, the inner and outer cooling plates may be utilized to improve substrate temperature control or cool down the substrate support 1000 from high temperatures. For example, the inner and outer cooling plates may be modulated to control heat transfer between the one or more heaters 1023 and the substrate 1001.
In some embodiments, the cooling plate 1034 may include an upper and a lower cooling plate. The upper and lower cooling plates may be utilized to provide similar benefits as discussed above for the inner and outer cooling plates. The upper and lower cooling plates may be stacked such that upper cooling plate contacts the electrostatic chuck 1010 via a foil while lower cooling plate contacts upper cooling plate. By independently controlling the flow of coolant to the upper and lower cooling plates, variable heat transfer is achieved between ceramic body 1020 and cooling plate assembly 1034. In some embodiments, each of the upper and lower cooling plates may provide uniform cooling over the entire diameter of cooling plate 1034. In other embodiments, each of upper and lower cooling plates may provide different cooling to inner and outer regions of cooling plate 1034. That is, in some embodiments, upper and lower cooling plates may be combined with inner and outer cooling plates.
The electrostatic chuck 1010, thus, may include a ceramic plate 1020. As illustrated in
As described above, the electrostatic chuck 1010 may further include one or more heaters 1023. The one or more heaters 1023 may be coupled to one or more power supplies 1025 and may be independently controllable. In some embodiments, the one or more heaters 1023 may include a plurality of heaters 1023, as illustrated in
An electrostatic chuck having a magnetic cathode liner may be included in processing equipment suitable to provide an etch plasma in proximity to a sample for etching. For example,
Referring to
Chamber 1102 and sample holder 1104 may include a reaction chamber and sample positioning device suitable to contain an ionized gas, i.e. a plasma, and bring a sample in proximity to the ionized gas or charged species ejected there from. Evacuation device 1106 may be a device suitable to evacuate and de-pressurize chamber 1102. Gas inlet device 1108 may be a device suitable to inject a reaction gas into chamber 1102. Plasma ignition device 1110 may be a device suitable for igniting a plasma derived from the reaction gas injected into chamber 1102 by gas inlet device 1108. Detection device 1116 may be a device suitable to detect an end-point of a processing operation. In one embodiment, system 1100 includes a chamber 1102, a sample holder 1104, an evacuation device 1106, a gas inlet device 1108, a plasma ignition device 1110 and a detector 1116 similar to, or the same as, a Conductor etch chamber or related chambers used on an Applied Materials® AdvantEdge system.
It is to be appreciated that although an etch chamber is described above, electrostatic chucks such as those described herein may instead be included in other semiconductor processing chambers. Examples of other suitable semiconductor processing chambers include, but are not limited to, chemical vapor deposition (CVD) or physical vapor deposition (PVD) process chambers.
Embodiments of the present invention may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the present invention. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium (e.g., read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory devices, etc.), a machine (e.g., computer) readable transmission medium (electrical, optical, acoustical or other form of propagated signals (e.g., infrared signals, digital signals, etc.)), etc.
The exemplary computer system 1200 includes a processor 1202, a main memory 1204 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 1206 (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory 1218 (e.g., a data storage device), which communicate with each other via a bus 1230.
Processor 1202 represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processor 1202 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processor 1202 may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processor 1202 is configured to execute the processing logic 1226 for performing the operations discussed herein.
The computer system 1200 may further include a network interface device 1208. The computer system 1200 also may include a video display unit 1210 (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device 1212 (e.g., a keyboard), a cursor control device 1214 (e.g., a mouse), and a signal generation device 1216 (e.g., a speaker).
The secondary memory 1218 may include a machine-accessible storage medium (or more specifically a computer-readable storage medium) 1231 on which is stored one or more sets of instructions (e.g., software 1222) embodying any one or more of the methodologies or functions described herein. The software 1222 may also reside, completely or at least partially, within the main memory 1204 and/or within the processor 1202 during execution thereof by the computer system 1200, the main memory 1204 and the processor 1202 also constituting machine-readable storage media. The software 1222 may further be transmitted or received over a network 1220 via the network interface device 1208.
While the machine-accessible storage medium 1231 is shown in an exemplary embodiment to be a single medium, the term “machine-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “machine-readable storage medium” shall also be taken to include any medium that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present invention. The term “machine-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media.
Thus, electrostatic chucks with magnetic cathode liners for critical dimension (CD) tuning have been disclosed.
