Patent Application
20250218819
Semiconductor fabrication sometimes involve patterning schemes and other processes in which some regions on a substrate surface are selectively etched. Other fabrication processes employ deposition of materials on a substrate surface. In either case, variations over the face of the substrate in process conditions or in incoming substrates may need to be addressed. As device geometries become smaller, uniformity control has become more important.
The background description provided herein is for the purposes of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Aspects of this disclosure pertain to apparatus for semiconductor processing, which apparatus may be characterized by the following features: (a) a processing chamber including chamber walls that at least partially bound a chamber interior, and a chamber heater configured to heat the chamber walls; and (b) a pedestal positioned within the chamber interior and including: (i) a substrate heater having a plurality of light emitting diodes (LEDs), (ii) a window positioned above the substrate heater comprising a material transparent to light from the LEDs, wherein the window comprises sapphire, spinel, AlON, IR grade fused silica, or a fluoride of an alkaline earth element, and (iii) three or more substrate support pads, each substrate support pad having a substrate support surface vertically offset from the window and configured to support a substrate such that the window and the substrate supported by the three or more substrate support pads are offset by a nonzero distance.
In certain embodiments, the window has thickness of about 5 to 40 mm. In certain embodiments, the window has a diameter of about 250-500 mm. In certain embodiments, a top surface of the window is nonplanar, and/or a bottom surface of the window is nonplanar. In certain embodiments, the window comprises sapphire.
In certain embodiments, the pedestal further includes a sidewall, and an outer region of the window is thermally connected to the sidewall such that heat can be transferred between the outer region and the sidewall.
In certain embodiments, the pedestal includes a bowl in which the substrate heater is positioned, and the bowl includes one or more sidewalls having an exterior surface that comprises reflective material.
In certain embodiments, the pedestal additionally includes a pedestal cooler that is thermally connected to the LEDs such that heat can be transferred between the LEDs and the pedestal cooler. The pedestal cooler may also include at least one fluid channel within the pedestal, and/or be configured to flow a cooling fluid within the at least one fluid channel. In some implementations, the pedestal further includes a pedestal heater configured to heat one or more exterior surfaces of the pedestal.
In certain embodiments, a first set of LEDs are arranged in a first circle having a first radius around a center axis of the substrate heater, and equally spaced apart from each other, and a second set of LEDs are arranged in a second circle having a second radius larger than the first radius around the center axis, and equally spaced apart from each other.
In certain embodiments, a first set of LEDs are electrically connected to form a first electrical zone, a second set of LEDs are electrically connected to form a second electrical zone, and the first and second electrical zones are independently controllable.
In certain embodiments, the apparatus additionally includes a pyrometer having a detector connected to a port and sensor window through a fiberoptic cable. In some implementations, the pyrometer is configured to detect emissions having one or more wavelengths of about 1 to about 4 microns.
In certain embodiments, the apparatus additionally includes (i) a gas distribution unit including: one or more fluid inlets, and a faceplate having a plurality of through-holes fluidically connected to the one or more fluid inlets and to the chamber interior and having a front surface partially bounding the chamber interior; and (ii) a unit heater thermally connected to the faceplate such that heat can be transferred between the faceplate and the unit heater.
Any combination of the above features may be implemented together in apparatus aspects of this disclosure.
Aspects of this disclosure pertain to methods that may be characterized by the following operations: (a) supporting a substrate in a processing chamber having chamber walls using a pedestal having a plurality of substrate support pads that each contact an edge region of the substrate; (b) heating, while the substrate is supported by only the plurality of substrate supports, the substrate to a first temperature by emitting visible light from a plurality of light emitting diodes (LEDs) under the substrate through a window comprising sapphire, spinel, AlON, IR grade fused silica, or a fluoride of an alkaline earth element; and (c) etching, while the substrate is supported by only the plurality of substrate supports and while the substrate is at the first temperature, a surface of the substrate. Any combination of these operations may be implemented using any features of the apparatus aspects of this disclosure.
Aspects of this disclosure pertain to apparatus for semiconductor processing, which apparatus may be characterized by the following features: a processing chamber including chamber walls that at least partially bound a chamber interior, and a chamber heater configured to heat the chamber walls, and a pedestal positioned within the chamber interior. The pedestal may include: (i) a substrate heater having a plurality of light emitting diodes (LEDs), (ii) a window positioned above the substrate heater comprising a material transparent to light from the LEDs, and (iii) three or more substrate support pads, each substrate support pad having a substrate support surface vertically offset from the window and configured to support a substrate such that the window and the substrate supported by the three or more substrate support pads are offset by a nonzero distance, wherein the substrate support pads comprise zirconia or quartz.
In certain embodiments, each substrate support comprises a zirconia. In certain embodiments, each substrate support includes a temperature sensor configured to detect a temperature of a substrate positioned on the substrate support surface. In certain embodiments, a top surface of the window is nonplanar, and/or a bottom surface of the window is nonplanar. In certain embodiments, the substrate support pads comprise yttria-stabilized zirconia.
In certain embodiments, the pedestal further includes a sidewall, and an outer region of the window is thermally connected to the sidewall such that heat can be transferred between the outer region and the sidewall.
In certain embodiments, the pedestal includes a bowl in which the substrate heater is positioned, and the bowl includes one or more sidewalls having an exterior surface that comprises reflective material.
In certain embodiments, the pedestal additionally includes a pedestal cooler that is thermally connected to the LEDs such that heat can be transferred between the LEDs and the pedestal cooler. The pedestal cooler may include at least one fluid channel within the pedestal, and/or be configured to flow a cooling fluid within the at least one fluid channel. In some implementations, the pedestal further includes a pedestal heater configured to heat one or more exterior surfaces of the pedestal.
In certain embodiments, the apparatus includes a first set of LEDs are arranged in a first circle having a first radius around a center axis of the substrate heater, and equally spaced apart from each other, and a second set of LEDs are arranged in a second circle having a second radius larger than the first radius around the center axis, and equally spaced apart from each other.
In certain embodiments, the apparatus includes a first set of LEDs are electrically connected to form a first electrical zone, a second set of LEDs are electrically connected to form a second electrical zone, where the first and second electrical zones are independently controllable.
In certain embodiments, the apparatus includes a pyrometer having a detector connected to the port and sensor window through a fiberoptic cable. The pyrometer may be configured to detect emissions having one or more wavelengths of about 1 to about 4 microns.
In certain embodiments, the apparatus additionally includes:
Any combination of the above features may be implemented together in apparatus with the recited substrate support pads.
Aspects of this disclosure pertain to methods that may be characterized by the following operations: (a) supporting a substrate in a processing chamber having chamber walls using only a pedestal having a plurality of substrate support pads that each contact an edge region of the substrate, wherein the substrate support pads comprise zirconia or quartz; (b) heating, while the substrate is supported by only the plurality of substrate supports, the substrate to a first temperature by emitting visible light from a plurality of light emitting diodes (LEDs) under the substrate; and (c) etching, while the substrate is supported by only the plurality of substrate supports and while the substrate is at the first temperature, a surface of the substrate. Any combination of these operations may be implemented using any features of the apparatus aspects of this disclosure.
These and other features of the disclosure will be presented in more detail below, and in some cases, with reference to the associated drawings.
In the following description, numerous specific details are set forth to provide a thorough understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not unnecessarily obscure the disclosed embodiments. While the disclosed embodiments will be described in conjunction with the specific embodiments, it will be understood that it is not intended to limit the disclosed embodiments.
Some semiconductor fabrication processes require careful control of the local temperature of the substrate, over the face of the substrate. In some implementations, temperature control is achieved using a reactor that employs a plurality of heating elements that provide radiant energy to different regions the substrate. Further information about such reactors and the processes they support is provided below. See e.g.,
In some embodiments, apparatuses for conducting semiconductor device fabrication processes that require temperature control employ a window disposed between radiative heat sources (e.g., a plurality of LEDs) and a substrate. Such windows may have multiple functions such as protecting radiative sources from damage caused by aggressive environments around the substrate. In some embodiments, the window separates an atmospheric side of the processing chamber, where the radiative heat source resides, from the vacuum side of the chamber, where the heated substrate is undergoing etch or other process by reactive vapor. During operation, the radiation that heats the substrate passes through the window.
In accordance with some embodiments of this disclosure, a window may have the following features: (1) transparency for the visible radiation emitted by the heat source for substrate heating; (2) little thermal crosstalk between window and wafer; and (3) resistance to attack by the process environment such as an aggressive etchant gas.
The inventors have identified materials that satisfy these requirements and therefore is used as a window material. Examples of such materials include optical grade sapphire (crystalline Al2O3), AlON, and spinel (MgAl2O4).
Quartz has also been used as window material. However, quartz windows have been observed to develop a “haze” over their lifetimes. The haze causes the window to become less effective in transferring power from the radiative heat source to the wafer. A cause of haze is etching of the quartz surface by aggressive process environments such as vapor etch chemistry. The material on the side of the window that contacts the vapor etch chemistry is continuously consumed. Possibly due to etch micro masking effects, the quartz surface, which is being etched develops micro roughness, which manifests as a haze. The haze can absorb and scatter light that passes through it. If the degradation of optical properties of the window is left uncompensated, the on-wafer temperature, and consequently the etch rate, will drift over the lifetime of the quartz window. Eventually, the haze becomes so severe that the window reaches the end of its service life and needs to be replaced.
Additionally, quartz windows may heat up as wafers run through a process tool, and the not window retains its high temperature for a long time after the process ends. This results in undesirable wafer-to-wafer process variation. It may also limit the throughput for high and low temperature cycling recipes. This is due to three physical properties of quartz. The first one is the extremely low heat conductivity of quartz. The second one is the low material strength of quartz, which requires that windows be relatively thick, thereby increasing their thermal mass. And the third one is the high absorptivity of quartz in the infrared spectral range, where a heated substrate emits most of its thermal radiation. Quartz windows therefore retain significant heat at the end of the heating cycle, they absorb more heat at faster rate during the process, and they are inefficient in channeling and dissipating this retained heat after the process is over.
Further, hot quartz windows have high temperature non-uniformity over their surfaces, which may cause within wafer temperature non-uniformity and ultimately within wafer etch rate non-uniformity. This is partly due quartz windows having low thermal conductivity, high thermal mass, and high absorptivity.
Still further, hot quartz is a source of thermal radiation which can confound the measurement of wafer temperature by a radiative pyrometer. To avoid damage by the etch chemistry the pyrometer may be located on the atmospheric side of a window. Thus, when viewing the substrate, the pyrometer receives thermal emission of the window as well as the substrate. Thermal emission of the window is high because it is hot and because the quartz emissivity at a pyrometer's infrared wavelength is high.
By comparison to quartz, other materials such as sapphire (Al2O3) have a beneficial combination of mechanical, thermal, optical, and chemical properties. As a result, windows made from such materials overcome the above problems of quartz windows. Windows fabricated with sapphire are significantly less prone to developing haze problem and have a longer lifetime than quartz windows.
Sapphire has a considerably higher mechanical strength than quartz (flexure strength is greater by greater than 11 times), which allows a thinner (e.g., 3 times thinner) window design. The thermal conductivity of sapphire is about 30 times greater than quartz. Furthermore, sapphire absorbs less IR than quartz.
Certain other materials also compare favorably to quartz as window materials. These include AlON, calcium fluoride, and spinel (MgAl2O4).
In some embodiments, apparatuses for conducting semiconductor device fabrication processes that require temperature control employ support contacts for holding a substrate in position while the process takes place. Such contacts may be positioned to contact the substrate at multiple locations around its perimeter. These contacts sometimes take the form of fingers, pads, or tabs that extend inwardly from a ring or other structure, disposed outside the substrate perimeter, toward the substrate. During processing, the substrate rests on these pads.
These support pads may be constructed from many different materials. Examples of such materials include aluminum, including anodized aluminum, quartz, and zirconia, including yttria-stabilized zirconia.
In some disclosed embodiments, support pads impart (1) little or no perturbation to a substrate's temperature through heat conduction and/or blockage of thermal energy to the via, e.g., LED light, and (2) chemical resistance of support pad material toward the aggressive reactor conditions (e.g., etchant gas).
Hard-anodized aluminum has excellent chemical compatibility with certain vapor etch chemistries, and the anodization protects the interior bulk aluminum from the aggressive chemistry of the reactor. However, it has been observed that, when used in support pads, the heat conductivity of aluminum metal can produce wafer temperature uniformity, which translates into process non-uniformity such as etch rate non-uniformity.
In some embodiments, the support pads comprise zirconia (ZrO2) or yttria-stabilized zirconia. In some cases, such material may be a ceramic. As a material for support pads, zirconia provides a useful combination of mechanical, thermal, and chemical properties. Its high mechanical strength enables fabrication of long parts with small cross-sections, at least by comparison to aluminum alloys. Furthermore, by comparison to aluminum and quartz, zirconia can provide a small contact area with the substrate. Further, the relatively low heat conductivity of zirconia, allows support pads to provide good thermal uniformity on the substrate. Still further, zirconia's chemical properties enable long service life of these parts, without degradation, in the aggressive environment of, e.g., a selective vapor etch reactor.
Support pads fabricated from quartz (SiO2) provide an alternative implementation. Quartz has very low heat conductivity, and hence enables comparable thermal performance to zirconia. However, quartz is more likely to be etched in some environments. Therefore, quartz support pads may be consumable parts. Given the relatively low cost of quartz, this is acceptable for some applications. The periodic replacement of support pads may not have a large negative impact to the cost of ownership.
The support pads may have many different sizes and shapes. Some designs leverage the advantages of zirconia and/or quartz. Such designs may have relatively small contact areas with the substrate, fingers that are relatively long, and/or fingers that have a relatively large cross-section (in the direction of potential heat transfer).
Provided herein are methods and apparatuses for semiconductor processing, for example to etch a semiconductor substrate using thermal energy, rather than, or in addition to, plasma energy. In certain embodiments, etching that relies upon chemical reactions in conjunction with primarily thermal energy, not a plasma, to drive the chemical reactions may be considered “thermal etching”. In various embodiments, apparatuses described herein are designed or configured to rapidly heat and cool a substrate, and precisely control a substrate's temperature. In some embodiments, the substrate is rapidly heated and its temperature is precisely controlled using, in part, visible light emitted from light emitting diodes (LEDs) positioned in a pedestal under the substrate. The visible light may have wavelengths that include and range of about 400 nanometers (nm) to 800 nm. The pedestal may include various features for enabling substrate temperature control, such as a transparent window that optionally has lensing for directing or focusing the emitted light, reflective material also for directing or focusing the emitted light, and/or temperature control elements that assist with temperature control of the LEDs, the pedestal, and the chamber.
Such apparatuses are sometimes implemented as selective vapor etch reactors, such as the Lam Research Prevos™. Such reactors are used to fabricate advanced logic devices. For example, they are used in the IC fabrication industry's transition from finFET to gate all around (GAA) transistor devices. They are also used to fabricate 3D DRAM devices. In such reactors, a substrate such as a silicon wafer under process is immersed in a reactive gas environment, while being heated from below by a multi-source LED heater. The LED heater allows fast, accurate, and controllable temperature ramp up and ramp down cycles, thus making possible precise, atomic level control of etch reactions.
In some embodiments, the apparatuses herein thermally isolate, or thermally “float,” the substrate within the processing chamber so that only the smallest thermal mass is heated, the ideal smallest thermal mass being just the substrate itself, which enables fast heating and cooling. The substrate may be rapidly cooled using a cooling gas and/or radiative heat transfer to a heat sink, such as a top plate (or other gas distribution element) above the substrate, or both. In some instances, the apparatus also includes temperature control elements within the processing chamber walls, pedestal, and top plate (or other gas distribution element), to enable further temperature control of the substrate and processing conditions within the chamber, such as prevention of unwanted condensation of processing gases and vapors.
The apparatuses may also be configured to implement various control loops to precisely control the substrate and the chamber temperatures (e.g., with a controller configured to execute instructions that cause the apparatus to perform these loops). This may include the use of various sensors that determine substrate and chamber temperatures as part of open loops and feedback control loops. These sensors may include temperature sensors in the substrate supports which contact the substrate and measure its temperature, and non-contact sensors such as photodetectors to measure light output of the LEDs and a pyrometer configured to measure the temperature of different types of substrates. As described in more detail below, some pyrometers determine an item's temperature by measuring emitted infrared light or other optical signals from the item. However, many silicon substrates cannot be measured by some pyrometers because the silicon can be optically transparent at various temperatures and with various treatments, e.g., doped or low doped silicon. For example, a low doped silicon substrate at a temperature less than about, e.g., 300° C. is transparent to infrared signals. Certain pyrometers provided herein are able to measure multiple types of silicon substrates at various temperatures.
The processing chamber 102 includes sides walls 112A, a top 112B, and a bottom 112C, that at least partially define the chamber interior 114, which may be considered a plenum volume. It may be desirable in some embodiments to actively control the temperature of the processing chamber walls 112A, top 112B, and bottom 112C in order to prevent unwanted condensation on their surfaces. Some semiconductor processing operations deliver vapors, such as water and/or alcohol vapor, onto the substrate where they adsorb, but they may also undesirably adsorb onto the chamber's interior surfaces. This can lead to unwanted deposition and etching on the chamber interior surfaces which can damage the chamber surfaces and cause particulates to flake off onto the substrate thereby causing substrate defects. In order to reduce and prevent unwanted condensation on the chamber's interior surfaces, the temperature of chamber's walls, top, and bottom may be maintained at a temperature at which condensation of chemistries used in the processing operations does not occur.
This active temperature control of the chamber's surfaces may be achieved by using heaters to heat the chamber walls 112A, the top 112B, and the bottom 112C. As illustrated in
The chamber walls 112A, top 112B, and bottom 112C, may also be comprised of various materials that can withstand the chemistries used in the processing techniques. These chamber materials may include, for example, an aluminum, anodized aluminum, aluminum with a polymer, such as a plastic, a metal or metal alloy with a yttria coating, a metal or metal alloy with a zirconia coating, yttria-stabilized zirconia, and a metal or metal alloy with aluminum oxide coating; in some instances the materials of the coatings may be blended or layers of differing material combinations, such as alternating layers of aluminum oxide and yttria, or aluminum oxide and zirconia. These materials are configured to withstand the chemistries used in the processing techniques, such as anhydrous HF, water vapor, methanol, isopropyl alcohol, chlorine, fluorine gases, nitrogen gas, hydrogen gas, helium gas, and mixtures thereof.
The apparatus 100 may also be configured to perform processing operations at or near a vacuum, such as at a pressure of about 0.1 Torr to about 100 Torr, or about 20 Torr to about 200 Torr, or about 0.1 Torr to about 10 Torr. This may include a vacuum pump 184 configured to pump the chamber interior 114 to low pressures, such as a vacuum having a pressure of about 0.1 Torr to about 100 Torr, including about 0.1 Torr to about 10 Torr, and about 20 Torr to about 200 Torr, or about 0.1 Torr to about 10 Torr.
Various features of the pedestal 104 will now be discussed. The pedestal 104 includes a heater 122 (encompassed by the dashed rectangle in
A heater's plurality of LEDs may be arranged, electrically connected, and electrically controlled in various manners. Each LED may be configured to emit a visible blue light and/or a visible white light. In certain embodiments, white light (produced using a range of wavelengths in the visible portion of the EM spectrum) is used. In some semiconductor processing operations, white light can reduce or prevent unwanted thin film interference. For instance, some substrates have backside films that reflect different light wavelengths in various amounts, thereby creating an uneven and potentially inefficient heating. Using white light can reduce this unwanted reflection variation by averaging out the thin film interference over the broad visible spectrum provided by white light. In some instances, depending on the material on the back face of the substrate, it may be advantageous to use a visible non-white light, such as a blue light having a 450 nm wavelength, for example, in order to provide a single or narrow band of wavelength which may provide more efficient, powerful, and direct heating of some substrates that may absorb the narrow band wavelength better than white light.
Various types of LED may be employed. Examples include a chip on board (COB) LED or a surface mounted diode (SMD) LED. For SMD LEDs, the LED chip may be fused to a printed circuit board (PCB) that may have multiple electrical contacts allowing for the control of each diode on the chip. For example, a single SMD chip may have three diodes (e.g., red, blue, or green) that can be individually controllable to create different colors, for instance. SMD LED chips may range in size, such as 2.8×2.5 mm, 3.0×3.0 mm, 3.5×2.8 mm, 5.0×5.0 mm, and 5.6×3.0 mm. For COB LEDs, each chip can have more than three diodes, such as nine, 12, tens, hundreds or more, printed on the same PCB. COB LED chips typically have one circuit and two contacts regardless of the number of diodes, thereby providing a simple design and efficient single-color application. The ability and performance of LEDs to heat the substrate may be measured by the watts of heat emitted by each LED; these watts of heat may directly contribute to heating the substrate.
In some embodiments, the LEDs may also be arranged along circles around the center of the substrate heater. In some instances, some LEDs may be arranged along circles while others may be arranged along arcs.
In some embodiments, the plurality of LEDs may include at least about 1,000 LEDs, including about 1,200, 1,500, 2,000, 3,000, 4,000, 5,000, or more than 6,000, for instance. Each LED may, in some instances, be configured to uses about 4 watts or less at 100% power, including about 3 watts at 100% power and about 1 watt at 100% power. These LEDs may be arranged and electrically connected into individually controllable zones to enable temperature adjustment and fine tuning across the substrate. In some instances, the LEDs may be grouped into at least 20, for instance, independently controllable zones, including at least about 25, 50, 75, 80, 85 90, 95, or 100 zones, for instance. These zones may allow for temperature adjustments in the radial and azimuthal (i.e., angular) directions. These zones can be arranged in a defined pattern, such as a rectangular grid, a hexagonal grid, or other suitable pattern for generating a temperature profile as desired. The zones may also have varying shapes, such as square, trapezoidal, rectangular, triangular, obround, elliptical, circular, annular (e.g., a ring), partially annular (e.g., an annular sector), an arc, a segment, and a sector that may be centered on the center of the heater and have a radius less than or equal to the overall radius of the substrate heater's PCB. For example, in
In certain embodiments, the substrate heater 122 is configured to heat the substrate to multiple temperatures and maintain each such temperature for various durations. The substrate heater may be configured to heat the substrate to between about 50° C. and 600° C., including to any temperature or range between these temperatures. Additionally, in some embodiments, the substrate heater 122 is configured to heat the substrate to any temperature within these ranges in less than about 60 seconds, less than about 45 seconds, less than about 30 seconds, or less than about 15 seconds, for instance. In certain embodiments, the substrate heater 122 is configured to heat a substrate at one or more heating rates, such as between at least about 0.1° C./second and at least about 20° C./second, for example.
The substrate heater may increase the temperature of the substrate by causing the LEDs to emit the visible light at one or more power levels, including at least about 80%, at least about 90%, at least about 95%, or at least about 100% power. In some embodiments, the substrate heater is configured to emit light between about 10 W and 4000 W, including at least about 10 W, at least about 30 W, at least about 0.3 kilowatt (kW), at least about 0.5 kW, at least about 2 kW, at least about 3 kW, or at least about 4 kw. The apparatus is configured to supply between about 0.1 kw and 9 kW of power to the pedestal; the power supply is connected to the substrate heater through the pedestal but is not depicted in the Figures. During temperature ramps, the substrate heater may operate at the high powers, and may operate at the lower power levels (e.g., including between about 5 W and about 0.5 kW) to maintain the temperature of a heated substrate.
The pedestal may include reflective material on its internal surfaces that, during operation, reflects and directs the light emitted by the LEDs onto the backside of the substrate supported by the pedestal. In some such embodiments, the substrate heater may include such reflective material positioned on a top surface 140, as shown in
In some embodiments, the substrate heater may also include a pedestal cooler that is thermally connected to the LEDs such that heat generated by the plurality of LEDs can be transferred from the LEDs to the pedestal cooler. This thermal connection allows heat to be conducted from the plurality of LEDs to the pedestal cooler along one or more heat flow pathways between these components. In some instances, the pedestal cooler is in direct contact with one or more elements of the substrate heater, while in other instances other conductive elements, such as thermally conductive plates (e.g., that comprise a metal) are interposed between the substrate heater and the pedestal cooler. Referring back to
As provided herein, it may be advantageous to actively heat the exterior surfaces of the processing chamber 102. In some instances, it may similarly be advantageous to heat the exterior surfaces of the pedestal 104 to prevent unwanted condensation and deposition on its external surfaces. As illustrated in
The pedestal may also include a window to protect the substrate heater, including the plurality of LEDs, from damage caused by exposure to the processing chemistries and pressures used during processing operations. As illustrated in
With the window 150 positioned above the substrate heater 122, the window 150 gets heated by the substrate heater 122 which can affect the thermal environment around the substrate. Depending on the material or materials used for the window 150, such as quartz, the window may retain heat and progressively retain more heat over the course of processing one or more substrates. This heat can get radiatively transferred to the substrate and therefore directly heat the substrate. In some instances, that the window can cause a temperature increase of between 50° C. and 80° C. above the heater temperature. This heat may also create a temperature gradient through the thickness, or in the vertical direction, of the window. In some instances, the top surface 152 is 30° C. hotter than the bottom surface 154. It may therefore be advantageous to adjust and configure the chamber to account for and reduce the thermal effects of the window. This may include detecting the substrate's temperature and adjusting the substrate heater to account for the heat retained by the window.
This may also include various configurations of the pedestal, such as actively cooling the window. In some embodiments, like that shown in
In some embodiments, the window may be placed in direct, thermal contact with the substrate heater and the pedestal cooler may be configured to cool both the PCB and the window. In some embodiments, as also shown in
Further discussion of certain embodiments, including materials of fabrication appears below. Judicious choice of the window material and/or the contact pad construction can mitigate some of the issues discussed above.
As shown in
The pedestal 104 is therefore configured, in some embodiments, to support the substrate 118 by thermally floating, or thermally isolating, the substrate within the chamber interior 114. The pedestal's 104 plurality of substrate supports 108 are configured to support the substrate 118 such that the thermal mass of the substrate 118 is reduced as much as possible to the thermal mass of just the substrate 118. Each substrate support 108 may have a substrate support surface 120 that provides minimal contact with the substrate 118. The number of substrate supports 108 may be at least 3, at least 6 or more. The surface area of the support surfaces 120 may also be the minimum area required to adequately support the substrate during processing operations (e.g., to support the weight of the substrate and prevent inelastic deformation of the substrate). Further embodiments relating to substrate supports (also referred to as pad supports are described below).
The substrate supports are also configured to prevent the substrate from being in contact with other elements of the pedestal, including the pedestal's surfaces and features underneath the substrate. As seen in
The substrate 118 is also offset from the substrate heater 122 (as measured in some instances from a top surface of the substrate heater 122 which may be the top surface of the LEDs 124) by a distance 160. This distance 160 affects numerous aspects of heating the substrate 118. In some embodiments, a distance 160 of about 10 mm to 90 mm, or about 5 mm to 100 mm, including about 10 mm to 30 mm. The offset may be chosen to provide a substantially uniform heating pattern and acceptable heating efficiency.
As stated, the substrate supports 108 are configured to support the substrate 118 above the window. In some embodiments, these substrate supports are stationary and fixed in position; they are not lift pins or a support ring. In some embodiments, at least a part of each substrate support 108 that includes the support surface 120 may be comprised of a material that is transparent at least to light emitted by LEDS 124. This material may be, in some instances, quartz or sapphire. The transparency of these substrate supports 108 may enable the visible light emitted by the substrate heater's 122 LEDs to pass through the substrate support 108 and to the substrate 118 so that the substrate support 108 does not block this light and the substrate 118 can be heated in the areas where it is supported. This may provide a more uniform heating of the substrate 118 than with a substrate support comprising a material opaque to visible light.
In some embodiments, such as those shown in
In some embodiments, the substrate supports may each contain a temperature sensor that is configured to detect the temperature of the substrate positioned on the support surface of the substrate supports.
Referring back to
The gas distribution unit 110 is configured to flow process gases, which may include liquids and/or gases, such as a reactant, modifying molecules, converting molecules, or removal molecules, onto the substrate 118 in the chamber interior 114. As seen in
The through-holes 178 may be configured in various ways to deliver uniform gas flow onto the substrate. In some embodiments, these through-holes may all have the same outer diameter, such as between about 0.03 inches and 0.05 inches, including about 0.04 inches (1.016 mm). These faceplate through-holes may also be arranged throughout the faceplate in order to create uniform flow out of the faceplate.
Referring back to
In some embodiments, the gas distribution unit 110 may include a second unit heater 182 that is configured to heat the faceplate 176. This second unit heater 182 may include one or more resistive heating elements, fluid conduits for flowing a heating fluid, or both. Using two unit heaters 180 and 182 in the gas distribution unit 110 may enable various heat transfers within the gas distribution unit 110. This may include using the first and/or second unit heaters 180 and 182 to heat the faceplate 176 in order to provide a temperature-controlled chamber, as described above, in order to reduce or prevent unwanted condensation on elements of the gas distribution unit 110.
The apparatus 100 may also be configured to cool the substrate. This cooling may include flowing a cooling gas onto the substrate, moving the substrate close to the faceplate to allow heat transfer between the substrate and the faceplate, or both. Actively cooling the substrate enables more precise temperature control and faster transitions between temperatures which reduces processing time and improves throughput. In some embodiments, the first unit heater 180 that flows the heat transfer fluid through fluid conduits may be used to cool the substrate 118 by transferring heat away from the faceplate 176 that is transferred from the substrate 118. A substrate 118 may therefore be cooled by positioning it in close proximity to the faceplate 176, such as by a gap 186 of less than or equal to 5 mm or 2 mm, such that the heat in the substrate 118 is radiatively transferred to the faceplate 176 and transferred away from the faceplate 176 by the heat transfer fluid in the first unit heater 180. The faceplate 176 may therefore be considered a heat sink for the substrate 118 in order to cool the substrate 118.
In some embodiments, the apparatus 100 may further include a cooling fluid source 173, which may contain a cooling fluid (a gas or a liquid), and a cooler (not pictured) configured to cool the cooling fluid to a desired temperature, such as less than or equal to about 90° C., less than or equal to about 70° C., less than or equal to about 50° C., less than or equal to about 20° C., less than or equal to about 10° C., less than or equal to about 0° C. less than or equal to about −50° C., less than or equal to about −100° C., less than or equal to about −150° C., less than or equal to about −190° C., about −200° C., or less than or equal to about −250° C., for instance. The apparatus 100 includes piping to deliver the cooling fluid to the one or more fluid inlets 170, and the gas distribution unit 110 which is configured to flow the cooling fluid onto the substrate. In some embodiments, the fluid may be in liquid state when it is flowed to the processing chamber 102 and may turn to a vapor state when it reaches the chamber interior 114, for example if the chamber interior 114 is at a low pressure state, such as described above, e.g., between about 0.1 Torr and 10 Torr, or between about 0.1 Torr and 100 Torr, or between about 20 Torr and 200 Torr, for instance. The cooling fluid may be an inert element, such as nitrogen, argon, or helium. In some instances, the cooling fluid may include, or may only have, a non-inert element or mixture, such as hydrogen gas. In certain embodiments, the apparatus may be configured to cool a substrate at one or more cooling rates, such as at least about 5° C./second, at least about 10° C./second, at least about 15° C./second, at least about 20° C./second, at least about 30° C./second, or at least about 40° C./second.
In some embodiments, the apparatus 100 may actively cool the substrate by both moving the substrate close to the faceplate and flowing cooling gas onto the substrate. In some instances, the active cooling may be more effective by flowing the cooling gas while the substrate is in close proximity to the faceplate. The effectiveness of the cooling gas may also be dependent on the type of gas used.
In some embodiments, the apparatus 100 may include a mixing plenum for blending and/or conditioning process gases for delivery before reaching the fluid inlets 170. One or more mixing plenum inlet valves may control introduction of process gases to the mixing plenum. In some other embodiments, the gas distribution unit 110 may include one or more mixing plenums within the gas distribution unit 110. The gas distribution unit 110 may also include one or more annular flow paths fluidically connected to the through-holes 178 which may equally distribute the received fluid to the through-holes 178 in order to provide uniform flow onto the substrate.
The apparatus 100 may include one or more optical sensors 198 to detect one or more features of the visible light emitted by the LEDs. In some embodiments, these optical sensors may be one or more photodetectors configured to detect the light and/or light intensity of the light emitted by the LEDs of the substrate heater. In
The apparatus 100 may also include one or more additional non-contact sensors for detecting the temperature of the substrate. Such sensors may include pyrometers, for instance. Although conventional pyrometers are not able to detect certain substrates within particular temperature ranges, the pyrometer described here overcomes these problems. For instance, the pyrometer is configured to detect multiple emission ranges to detect multiple types of substrates, e.g., doped, low doped, or not doped, at various temperature ranges. This includes a configuration to detect emission ranges of about 0.95 microns to about 1.1 microns, about 1 micron, about 1 to about 4 microns, and/or about 8 to 15 microns. The pyrometer is also configured to detect the temperature of a substrate at a shorter wavelength to differentiate the signal from the thermal noise of the chamber.
The pyrometer may include an emitter configured to emit infrared signals and a detector configured to receive emissions. Referring to
As explained, the window material can have a significant impact on process reliability as well as the window's durability. For example, if a window becomes less transparent—such as by formation of a haze—it reduces the amount of power transferred from radiative heat elements to the substrate surface. As a consequence, the substrate temperature decreases, which may cause the process to shift. For example, the lower temperatures may cause a higher thermal etch rate. Additionally, the window may need to be replaced frequently.
The following includes some comparative information about quartz and sapphire as window materials. In aggressive etch vapor environments, it has been observed that the mass change of quartz is more than 10000 times that of sapphire. It has been observed that AlON and spinel (MgAl2O4) are also more resistant than quartz to such environments. Additionally, sapphire has over 28 times higher thermal conductivity than quartz. And sapphire has greater than 11 times the mechanical strength of quartz. Further, sapphire absorbs less thermal IR than quartz.
The table below provides a comparison of physical properties of quartz and certain other window materials.
Other materials that may be used in a window include IR Grade fused silica, magnesium fluoride (MgF2), calcium fluoride (CaF2), barium fluoride (BaF2).
A sapphire window can also improve the accuracy of wafer thermometry.
By contrast, a sapphire window does not significantly interfere with pyrometer readings. This is partly because a sapphire window runs cooler than a quartz window. It can have a smaller size, higher specific heat, and consequently hold less heat at a given temperature. Additionally, sapphire has a lower emissivity at a typical pyrometer wavelength (e.g., 2.3 um) than quartz.
The thermal properties of quartz coupled with the need to make quartz windows relatively large (due to quartz's mechanical properties) cause quartz windows to emit more radiation during cooling than during heating. This difference further complicates interpretation of pyrometer readings.
In certain embodiments, a sapphire, AlON, or spinel window has thickness of about 5 to 40 mm or about 7 to 15 mm for, e.g., a 300 mm diameter window. The thickness may scale the window diameter. In certain embodiments, a sapphire, AlON, or spinel window has diameter of about 250 to 500 mm or about 300 to 400 mm.
As indicated, a substrate undergoing processing is supported by support pads, of which pads 108 provide one example. In some embodiments, the support pads should introduce little or no perturbation of substrate temperature. Such perturbation can be caused by heat conduction and/or blockage of LED light by the support pads. Additionally, in some embodiments, support pads comprise a material that exhibits chemical resistance to the chamber environment such as an aggressive etchant gas.
The inventors have observed that some the perimeter region of a wafer substrate may exhibit cold spots where support pads are located. In some cases, the cold spot may be about 5° C. or greater, and sometimes 20° C. or greater. These cold spots may be distributed azimuthally around the perimeter of the substrate, corresponding to the locations of the support pads. Such substrate temperature non-uniformity directly translates into high process rate non-uniformity (e.g., high etch rate non-uniformity), which is not acceptable for many applications.
Such non-uniformity has been found to occur with aluminum or anodized aluminum support pads. These support pads may have a generally triangular shape on or proximate to a contact point with the substrate.
The source of the cold spots may be heat conduction away from (or to) the substrate via the support pads. Considering the relevant heat transfer physics, one may consider the heat conduction equation:
where
To minimize heat transfer, the contact area A between the support pad and the substrate should be small, the thermal conductivity k of the support pad material should be low, and the length of heat transfer path Δx (e.g., the length of the support pad) should be large. Example materials having relatively low thermal conductivity values include alumina (about 25 W/mK), yttria-stabilized zirconia (about 3 W/mK), and quartz (about 1.5 W/mK).
In tests, it has been observed that quartz support pads and zirconia support pads have significantly less effect on substrate temperature (e.g., they do not produce significant cold spots on substrates) than aluminum support pads and even alumina support pads.
In addition to having a low thermal conductivity, zirconia has comparatively good mechanical strength. The high flexural strength of zirconia enables fabrication of small cross-section support pads, which reduces the contact area between the substrate and the support pad. Further, the high hardness of zirconia allows a relatively small contact area, A, between the support pad and the substrate. Because the mechanical properties of zirconia compare favorably with those of quartz, support pads fabricated with zirconia can provide lower thermal conduction than those fabricated with quartz.
Further, because zirconia is relatively chemically inert (at least in comparison to some other materials such as quartz), it can provide long-lived, dimensionally stable support pads even in aggressive environments. In some tests, zirconia was found to be thousands of times more resistant to vapor etch than quartz.
However, support pads fabricated from quartz may still be suitable as a support pad material. Quartz has very low heat conductivity, and hence enables comparable thermal performance to zirconia. While quartz is more likely to be etched in some environments, it can still be used in support pads in such environments, so long as the quartz support pads are treated as consumable parts.
In certain embodiments, a zirconia or quartz support pad has contact surface with the substrate and a finger that extends from the contact surface to a ring or other attachment structure to which the fingers are attached. As examples, the finger shape may be generally rod-shaped, generally rectangular-shaped, or generally triangular-shaped. In some embodiments, the shape may be configured as a thermal choke.
In certain embodiments, fingers of zirconia or quartz support pads have a length (distance between the contact surface and the attachment structure of at least about 10 mm or at least about 15 mm. In some embodiments, the distance is about 18 to 25 mm.
In certain embodiments, a contact surface of a zirconia or quartz support pad has a contact area with a substrate that is no greater than about 10 mm2 or no greater than about 5 mm2.
In some embodiments, the apparatuses described herein may include a controller that is configured to control various aspects of the apparatus in order to perform the techniques described herein. For example, referring back to
In some implementations, a controller is part of a system, which may be part of the above-described examples. Such systems can comprise semiconductor processing equipment, including a processing tool or tools, chamber or chambers, a platform or platforms for processing, and/or specific processing components (a wafer pedestal, a gas flow system, etc.). These systems may be integrated with electronics for controlling their operation before, during, and after processing of a semiconductor wafer or substrate. The electronics may be referred to as the “controller,” which may control various components or subparts of the system or systems. The controller, depending on the processing requirements and/or the type of system, may be programmed to control any of the processes disclosed herein, including the delivery of processing gases, temperature settings (e.g., heating and/or cooling), pressure settings, vacuum settings, power settings, radio frequency (RF) generator settings, RF matching circuit settings, frequency settings, flow rate settings, fluid delivery settings, positional and operation settings, wafer transfers into and out of a tool and other transfer tools and/or load locks connected to or interfaced with a specific system.
Broadly speaking, the controller may be defined as electronics having various integrated circuits, logic, memory, and/or software that receive instructions, issue instructions, control operation, enable cleaning operations, enable endpoint measurements, and the like. The integrated circuits may include chips in the form of firmware that store program instructions, digital signal processors (DSPs), chips defined as application specific integrated circuits (ASICs), and/or one or more microprocessors, or microcontrollers that execute program instructions (e.g., software). Program instructions may be instructions communicated to the controller in the form of various individual settings (or program files), defining operational parameters for carrying out a particular process on or for a semiconductor wafer or to a system. The operational parameters may, in some embodiments, be part of a recipe defined by process engineers to accomplish one or more processing steps during the fabrication of one or more layers, materials, metals, oxides, silicon, silicon dioxide, surfaces, circuits, and/or dies of a wafer.
The controller, in some implementations, may be a part of or coupled to a computer that is integrated with, coupled to the system, otherwise networked to the system, or a combination thereof. For example, the controller may be in the “cloud” or all or a part of a fab host computer system, which can allow for remote access of the wafer processing. The computer may enable remote access to the system to monitor current progress of fabrication operations, examine a history of past fabrication operations, examine trends or performance metrics from a plurality of fabrication operations, to change parameters of current processing, to set processing steps to follow a current processing, or to start a new process. In some examples, a remote computer (e.g. a server) can provide process recipes to a system over a network, which may include a local network or the Internet. The remote computer may include a user interface that enables entry or programming of parameters and/or settings, which are then communicated to the system from the remote computer. In some examples, the controller receives instructions in the form of data, which specify parameters for each of the processing steps to be performed during one or more operations. It should be understood that the parameters may be specific to the type of process to be performed and the type of tool that the controller is configured to interface with or control. Thus as described above, the controller may be distributed, such as by comprising one or more discrete controllers that are networked together and working towards a common purpose, such as the processes and controls described herein. An example of a distributed controller for such purposes would be one or more integrated circuits on a chamber in communication with one or more integrated circuits located remotely (such as at the platform level or as part of a remote computer) that combine to control a process on the chamber.
Without limitation, example systems may include a plasma etch chamber or module, a deposition chamber or module, a spin-rinse chamber or module, a metal plating chamber or module, a clean chamber or module, a bevel edge etch chamber or module, a physical vapor deposition (PVD) chamber or module, a chemical vapor deposition (CVD) chamber or module, an atomic layer deposition (ALD) chamber or module, an atomic layer etch (ALE) chamber or module, an ion implantation chamber or module, a track chamber or module, and any other semiconductor processing systems that may be associated or used in the fabrication and/or manufacturing of semiconductor wafers.
As noted above, depending on the process step or steps to be performed by the tool, the controller might communicate with one or more of other tool circuits or modules, other tool components, cluster tools, other tool interfaces, adjacent tools, neighboring tools, tools located throughout a factory, a main computer, another controller, or tools used in material transport that bring containers of wafers to and from tool locations and/or load ports in a semiconductor manufacturing factory.
In some embodiments, the apparatus may further be configured to generate a plasma and use the plasma for some processing in various embodiments. This may include having a plasma source configured to generate a plasma within the chamber interior, such as a capacitively coupled plasma (CCP), an inductively coupled plasma (ICP), an upper remote plasma, and a lower remote plasma.
The apparatuses described herein may be used for various etching techniques including, but not limited to, continuous etching methods and cyclic methods such as atomic layer etching.
Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present embodiments. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein.
A PCT Request From is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request From is incorporated by reference herein in their entireties and for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2023/016762 | 3/29/2023 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63362327 | Mar 2022 | US | |
| 63362329 | Mar 2022 | US |
