Patent Application
20140263268
1. Field
Embodiments of the present invention generally relate to supporting substrates in processing chambers.
2. Description of the Related Art
During processing, substrates are positioned on a susceptor within a process chamber. The susceptor is supported by a susceptor support shaft, which is rotatable about a central axis. The susceptor support shaft includes multiple arms extending therefrom—usually three to six—which support the susceptor. As the susceptor support shaft is rotated during processing, the arms extending from the susceptor support shaft interrupt a pyrometer beam used to measure a temperature of the susceptor or the substrate, thus causing the interference of pyrometer readings. Even though the arms may be formed from quartz, which is generally optically transparent, at least some amount of light is absorbed by the arms, and thus, is not completely optically transparent. This amount of light absorbed and scattered by the arms affects the amount of light transmitted by the pyrometer beam to the susceptor, and thus, affects the accuracy of the temperature measurement by the pyrometer. As the susceptor support shaft rotates, there are periods when the arm is within the pyrometer beam path, and periods when the arm is adjacent to the pyrometer beam path. Thus, the amount of light from the pyrometer beam reaching the susceptor varies as the susceptor support rotates, resulting in periods of inaccurate temperature measurement.
An IR pyrometry system is normally used for the sensing of radiation emitted from the backside of susceptor or a substrate, the pyrometer reading is then converted to temperature based on the surface emissivity of the susceptor or substrate. A software filter is normally used to reduce interference with temperature ripples (due to the support arms move in and out the pyrometer beam during the rotation mentioned above) to around ±1 degree Celsius. The software filter is also used with an algorithm including average data in sample window a couple of seconds wide.
With the advanced cyclic EPI process, the process temperature will change as per recipe step and recipe step time is getting shorter. Therefore, the time delay of the software filter needs to be minimized and a much narrower sample window is required to improve dynamic response of temperature variations. The temperature ripple needs to be further reduced to less than ±0.5 degree Celsius range for optimum cycle to cycle temperature repeatability.
Therefore, there is a need for an apparatus which enables more accurate temperature measurement.
Embodiments of the invention generally relate to susceptor support shafts and process chambers containing the same. A susceptor support shaft supports a susceptor thereon, which in turn, supports a substrate during processing. The susceptor support shaft reduces variations in temperature measurement of the susceptor and/or substrate by providing a consistent path for a pyrometer focal beam directed towards the susceptor and/or substrate, even when the susceptor support shaft is rotated. The susceptor support shafts also have a relatively low thermal mass which enables fast ramp up and ramp down rates of a susceptor in the process chamber.
In one embodiment, a susceptor support shaft for a process chamber comprises a cylindrical support shaft and a support body coupled the support shaft. The support body comprises a solid disc, a plurality of tapered bases extending from the solid disc, at least three support arms extending from some of the tapered bases, and at least three dummy arms extending from some of the tapered bases. In one example, a custom made refractive element may be removably placed on the top of the solid disc to redistribute secondary heat distributions across the susceptor and/or substrate.
In another embodiment, a process chamber for heating a substrate is disclosed. The process chamber comprises a susceptor disposed within the process chamber for supporting a substrate, a lower dome disposed below the substrate support, and an upper dome disposed opposing the lower dome. The upper dome comprises a central window portion and a peripheral flange engaging the central window portion around a circumference of the central window portion, wherein the central window portion and the peripheral flange are formed of an optically transparent material.
So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized in other embodiments without specific recitation.
Embodiments of the invention generally relate to susceptor support shafts and process chambers containing the same. A susceptor support shaft supports a susceptor thereon, which in turn, supports a substrate during processing. The susceptor support shaft is designed to reduce variations in temperature measurement of the susceptor and/or substrate by providing the susceptor support shaft with a solid disc near the rotation center covering the pyrometer sensing path directed towards the susceptor and/or substrate. As the solid disc covers the pyrometer temperature reading path, the pyrometer reading show less interference, even when the susceptor support shaft is rotated. The solid disc covers only the pyrometer focal beam near the rotation center, so the susceptor support shaft has a relatively low thermal mass, which enables fast ramp up and ramp down rates of a process chamber. In some embodiments, a custom made refractive element can be removably placed on the top of the solid disc to redistribute secondary heat distributions across the susceptor and/or substrate for optimum thickness uniformity of epitaxy process.
Embodiments disclosed herein may be practiced in the Applied CENTURA® RP EPI chamber, available from Applied Materials, Inc. of Santa Clara, Calif. It is contemplated that other chambers available from other manufacturers may also benefit from embodiments disclosed herein.
The processing chamber 100 includes a plurality of heat sources, such as lamps 135, which are adapted to provide thermal energy to components positioned within the process chamber 100. For example, the lamps 135 may be adapted to provide thermal energy to the substrate 125, a susceptor 126, and/or the preheat ring 123. The lower dome 130 may be formed from an optically transparent material, such as quartz, to facilitate the passage of thermal radiation therethrough. In one embodiment, it is contemplated that lamps 135 may be positioned to provide thermal energy through the upper dome 116 as well as the lower dome 130.
The chamber body 102 includes a plurality of plenums 120 formed therein. For example, a first plenum 120 may be adapted to provide a process gas 150 therethrough into the upper portion 112 of the chamber body 102, while a second plenum 120 may be adapted to exhaust a process gas 150 from the upper portion 112. In such a manner, the process gas 150 may flow parallel to an upper surface of the substrate 125. Thermal decomposition of the process gas 150 onto the substrate 125 to form an epitaxial layer on the substrate 125 is facilitated by the lamps 135.
A substrate support assembly 132 is positioned in the lower portion 114 of the chamber body 102. The substrate support 132 is illustrated supporting a substrate 125 in a processing position. The substrate support assembly 132 includes a susceptor support shaft 127 formed from an optically transparent material and a susceptor 126 supported by the susceptor support shaft 127. A shaft 160 of the susceptor support shaft 127 is positioned within a shroud 131 to which lift pin contacts 142 are coupled. The susceptor support shaft 127 is rotatable. The shroud 131 is generally fixed in position, and therefore, does not rotate during processing.
Lift pins 133 are disposed through openings 280 (shown in
The susceptor support shaft 127 is rotatable in order to facilitate the rotation of the substrate 125 during processing. Rotation of the susceptor support shaft 127 is facilitated by an actuator 129 coupled to the susceptor support shaft 127. Support pins 137 couple the susceptor support shaft 127 to the susceptor 126. In the embodiment
A pyrometer 136 is adapted to measure a temperature of the susceptor 126 and/or the substrate 125 by sensing of radiation emitted from the backside of susceptor 126 or the substrate 125. The pyrometer reading is then converted to temperature based on the surface emissivity of the susceptor or substrate. The pyrometer 136 emits a focal beam 138 directed through the lower dome 130 and through the susceptor support shaft 127. The pyrometer 136 measures the temperature of the susceptor 126 (for example, when the susceptor 126 is formed from silicon carbide) or the temperature of the substrate 125 (for example, when the susceptor 126 is formed from quartz or when a susceptor is absent and the substrate 125 is supported in another manner, such as by a ring). It is to be noted that lift pin contacts 142 are generally positioned adjacent to the focal beam 138, and do not rotate, and thus, do not interfere with the pyrometer focal beam 138 during processing.
The preheat ring 123 is removably disposed on a lower liner 140 that is coupled to the chamber body 102. The preheat ring 123 is disposed around the internal volume of the chamber body 102 and circumscribes the substrate 125 while the substrate 125 is in a processing position. During processing, the preheat ring 123 is heated by the lamps 135. The preheat ring 123 facilitates preheating of a process gas as the process gas enters the chamber body 102 through a plenum 120 adjacent to the preheat ring 123.
The central window portion 115 of the upper dome 116 and the bottom portion 117 of the lower dome 130 may be formed from an optically transparent material such as quartz to direct radiations from the lamps without significant absorption. The peripheral flange 119 of the upper dome 116, which engages the central window portion around a circumference of the central window portion, the peripheral flange 121 of the lower dome 130, which engages the bottom portion around a circumference of the bottom portion, may all be formed from an opaque quartz to protect the O-rings 122 proximity to the peripheral flanges from being directly exposed to the heat radiation.
In some cases, the entire upper dome 116, including the peripheral flange 119, may all be formed of an optically transparent material such as quartz. In certain examples, both the upper and lower domes 116, 130 and respective peripheral flanges 119, 121 may all be formed of optically transparent material such as quartz. Having the peripheral flanges 119, 121 made optically transparent may be advantageous. Epitaxial deposition is a complex process of laying down atoms such as Si, Ge or dopants on a substrate surface to create a single crystalline layer. The very nature of the upper and lower dome constructions may incur a high thermal temperature gradient from the edge of the domes to the peripheral flanges if clear quartz domes and opaque peripheral flanges were used. This is because at elevated deposition temperatures, the dome temperature may raise up to about 342° C. over the substrate while the area near the peripheral flange may drop off by about 100° C. and rapidly decreases from such area, which causes appreciable deposition particles and is undesirable for epitaxy processes that demand very tight temperature controls.
An all-clear dome provides for thermal uniformity within a delta of 10° C. for the dome/flange in the area of chamber gases. By constructing the upper and lower domes out of all clear quartz, the thermal conductivity of the quartz is quite high, resulting in a very uniform temperature profile across the surface. For example, it has been observed that at elevated deposition temperatures, a dome temperature of 342° C. was measured at the center while 335° C. measured at the inner edge of the peripheral flange. Thermal transient stabilization times is therefore greatly improved by 2-3× due to the improved conductance. This will allow for better process control for ZII/V as well as SiGe and SiC applications, among others.
The support system 104 includes components used to execute and monitor pre-determined processes, such as the growth of epitaxial films in the processing chamber 100. The support system 104 includes one or more of gas panels, gas distribution conduits, vacuum and exhaust sub-systems, power supplies, and process control instruments. A controller 106 is coupled to the support system 104 and is adapted to control the processing chamber 100 and support system 104. The controller 106 includes a central processing unit (CPU), a memory, and support circuits. Instructions resident in controller 106 may be executed to control the operation of the processing chamber 100. Processing chamber 100 is adapted to perform one or more film formation or deposition processes therein. For example, a silicon carbide epitaxial growth process may be performed within processing chamber 100. It is contemplated that other processes may be performed within processing chamber 100.
The support arms 270 may include an opening 280 formed therethrough. The opening 280 may be located adjacent to a connecting surface 278 that connects to one of the tapered bases 274. The opening 280 allows the passage of a lift pin therethrough. A distal end 281 of a support arm 270 may also include an opening 282 for accepting a pin 137 (shown in
The support body 264 may also include a plurality of dummy arms 272. Each dummy arm is coupled to a tapered base 274 and extends linearly therefrom. The dummy arms 272 are spaced at equal intervals from one another, for example, about 120 degrees. In the embodiment shown in
During processing, the susceptor support shaft 127 absorbs thermal energy from lamps utilized to heat a susceptor and/or substrate. The absorbed heat radiates from the susceptor support shaft 127. The radiated heat radiated by the susceptor support shaft 127, particularly the support arms 270, is absorbed by the susceptor and/or substrate. Because of the relatively close position of the support arms 270 to the susceptor or substrate, heat is easily radiated to the susceptor or support shaft causing areas of increased temperature adjacent to the support arms 270. However, utilization of the dummy arms 270 facilitates a more uniform radiation of heat from the susceptor support shaft 270 to the susceptor and/or substrate, and thus, the occurrence of hot spots is reduced. For example, the utilization of dummy arms 272 results in a uniform radiation of a susceptor, rather than three local hot spots adjacent the support arms 272.
Additionally, the absence of a supporting ring adjacent to a susceptor, as is used in some prior approaches, increases thermal uniformity across a substrate. The susceptor support shaft 127 does not include an annular ring coupling the terminal ends of the susceptor support shaft, thus improving thermal uniformity. The utilization of such a ring can result in an increased temperature gradient adjacent to the ring (e.g., near the perimeter of the susceptor). Moreover, the absence of material from between the support arms 270 and the dummy arms 272 reduces the mass of the susceptor support shaft 127. The reduced mass thus facilitates rotation of the susceptor support shaft 127, and also reduces the amount of undesirable thermal radiation from the susceptor support shaft 127 to a susceptor (e.g., due to a reduction in thermal mass). The reduced mass of the susceptor support shaft 127 also assists in achieving faster ramp up and cool down on substrate. The faster ramp up and cool down facilitates increased throughput and productivity.
The solid disc 262 may have a surface area (one side) that is less than the surface area (one side) of the substrate. For example, the solid disc 262 may have a surface area that is about 90% less, about 80% less, about 70% less, about 60% less, about 50% less, about 40% less, about 30% less, about 20% less, or about 10% less than that of the substrate. In one example, the solid disc 262 has a surface area (one side) about 30% to 80% less than the surface area (one side) of the substrate. In one example, the solid disc 262 may have a radius of about 60 millimeters to ensure passage of a pyrometer focal beam therethrough. In such an embodiment, the pyrometer focal beam passes through the sidewall 384, which has a substantially constant thickness.
In contrast, prior known susceptor supports had arms which interrupted the pyrometer focal beam. Thus, when the susceptor support rotates, the beam would experience areas of differing transmission path (e.g., either through a susceptor support arm, or adjacent thereto). The differing path of prior methods resulted in periods of inaccurate temperature measurement, because it is difficult to accurately calibrate a pyrometer for use through transmissions of different mediums. In contrast, the susceptor support shaft 127 facilitates a consistent path of the pyrometer focal beam transmission, and thus, the accuracy of temperature measurement using the pyrometer focal beam 138 is increased.
The support body 264 also includes a plurality of tapered bases 274 extending from the outer circumference 273 the solid disc 262. As the width 386 of the tapered bases 274 decreases (e.g., as the tapered bases 274 extend outward from the solid disc 262), the height or thickness 387 of the tapered bases increases. The increase in the thickness 387 of the tapered base compensates for a reduced structural strength of the tapered base attributable to the decreasing width 386. Additionally, a similar bending moment of inertial is maintained. In one example, the thickness 385 is about 3 millimeters to about 5 millimeters, such as about 3.5 millimeters. The thickness 387 may be within a range of about 3 millimeters to about 12 millimeters. It is contemplated that the thicknesses 387 and 385 may be adjusted as desired.
The refractive element 502 is sized to substantially match the circumference of the solid disc 262 so that the refractive element 502 is fully supported and securely positioned on the solid disc 262 without movement while the susceptor support shaft 127 is rotated during the process. The refractive element 502 may have any desired dimension. The refractive element 502 may be configured to sufficiently cover the pyrometer temperature reading path to avoid any possible interference of pyrometer readings. The refractive element 502 can be replaced for maintenance. The refractive element 502 may be a simple add-on to any susceptor support shafts using multiple arms. In various examples, the refractive element 502 may be formed of clear quartz or any suitable material such as glass or transparent plastic.
Referring to
During the process, the heat radiation from the lamps (e.g., lamps 135 of
The convex surface of the refractive element 502 may have a desired radius of curvature of, for example, about 200 mm to about 1200 mm, plus or minus 300 mm. The concave surface of the refractive element 502 may have the same or different radius of curvature as that of the convex surface. The radius of curvature of the refractive element may vary depending upon the susceptor and/or the substrate. The diameter and/or radius of curvature of the convex surface of the refractive element 502, or even the shape and diameter of the solid disc 262, or their combinations, may be independently adjusted to manipulate the heat distribution for effective heating of the entire substrate, or the specific radius zone on the substrate.
Benefits of the invention generally include more accurate temperature measurement of susceptors and substrates during processing, particularly when using a rotating susceptor support shaft. The susceptor support shafts of the present invention facilitate consistent pyrometer beam transmission as the susceptor support shaft rotates. Thus, temperature measurement variations attributed to a change in transmission path of the pyrometer beam are reduced. Moreover, the reduced mass of the disclosed susceptor support improves substrate temperature uniformity and enhances process ramp up and ramp down times.
While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. provisional patent application Ser. No. 61/798,503, filed Mar. 15, 2013 which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61798503 | Mar 2013 | US |
