Patent Application
20060000551
The present invention relates to fabrication of semiconductor integrated circuits and, more particularly, to temperature control of plasma processing systems.
In the fabrication of semiconductor-based devices, e.g., integrated circuits or flat panel displays, layers of materials may alternately be deposited onto and etched from a substrate surface. During the fabrication process, various layers of material, e.g., borophosphosilicate glass (BPSG), polysilicon, metal, etc. are deposited on the substrate. The deposited layers may be patterned with known techniques, e.g., a photoresist process. Thereafter, portions of the deposited layers can be etched away to form various features, e.g., interconnect lines, vias, trenches, and etc.
As can be appreciated by those skilled in the art, in the case of semiconductor processing such as etch processes, a number of parameters within the processing chamber must be tightly controlled to maintain high quality results. Temperature is one such parameter. Because etch quality (and resulting semiconductor-based device performance) may be highly sensitive to temperature fluctuations of components in a plasma processing system, accurate control therefore is required. Moreover, as feature sizes continue to get smaller, there is an ever increasing need to provide plasma processing apparatus with better temperature control in order to provide consistent and precise fabrication of semiconductor devices.
In particular,
As an example, a substrate holding mechanism 126 can be an electrostatic chuck (ESC). The surface of a substrate 122 is etched by an appropriate plasma processing source gas that is released into a processing chamber 132. Plasma source gases may be released by a variety of mechanisms, including a showerhead or a gas distribution plate. A vacuum plate 116 maintains a sealed contact with chamber walls 118 of plasma processing chamber 132. Coils 134 provided on the vacuum plate 116 may be coupled to a radio frequency (RF) power source (not shown) and used to create plasma from plasma source gases released into plasma processing chamber 132. A substrate holding mechanism 126 is also often RF powered during the etch processes using a RF power supply (not shown). A pump 130 is also included to draw process gases and gaseous products from plasma processing chamber 132 through a duct 136.
A combination heating and cooling plate 104 placed on the top of the apparatus operates to control the temperature of vacuum plate 116 of the plasma processing apparatus 100 such that an inner surface of a vacuum plate 116, which is exposed to plasma during operation, may be maintained at a controlled temperature. Heating and cooling plate 104 may be constructed using several physical layers comprising in providing both heating and cooling operation. More particularly, heating and cooling plate 104 includes a thermal gasket 138 that thermally couples heating and cooling plate 104 with vacuum plate 116.
Thermal gasket 138 may be configured to provide a conformal thermal interface between vacuum plate 116 and a heating and cooling plate 104. Heating and cooling plate 104 also includes a heater block 112. Heater block 112 includes resistive elements that output thermal energy to heater block 112 when elements are supplied with electrical current. A thermal break 140 may be provided between heater block 112 and cooling block 108. Thermal break 140 may provide a thermal separation zone between a hot surface created by heater block 112 and a cold surface created by cooling block 108. A cooling block 108 includes a plurality of cooling elements in thermal communication with cooling block 108. Accordingly, a heating and cooling plate 104 can be viewed as a sandwich structure including thermal gasket 138, heater block 112, thermal break 140, and cooling block 108. Accordingly, temperature of the vacuum plate 116 may be controlled through activation of either heater elements of heater block 112 or cooling elements of cooling block 108.
Most top piece designs, however, are optimized for operational performance within the chamber itself, and not for other considerations such as general thermal performance. Historically, since the manufacturing cost of the top piece was just a relatively small portion of the overall system cost, there has been no incentive to re-design with smaller amount of material, hence a smaller thermal mass. Subsequently, the larger thermal mass of the top piece tends to resist rapid temperature adjustment, often creating substantially long wait intervals in order to bring the system to the desired temperature—in some cases as long as 15 minutes or more. In addition, thermal excursions, once detected, cannot generally be quickly stabilized due to the thermal inertia of the mass.
A common plasma chamber design incorporates aluminum, which exhibits high thermal conductivity.
In addition, since many temperature control systems often incorporate the heating and cooling elements, comprising plastic and stainless steel materials, directly into the chamber structure itself, preventive maintenance may be an issue. The presence of plastic and stainless steel often limits the types of available cleaning techniques, and hence the effectiveness of preventive maintenance. That is, although a particular cleaning chemical may effectively clean the residue from the chamber walls, the same chemical may also substantially damage the plastic materials or stainless steel.
In view of foregoing, there is a need for methods and apparatus for optimal temperature control in plasma processing systems.
The invention relates, in one embodiment, in a plasma processing system, to a temperature control device for controlling temperature of an upper chamber of a plasma processing apparatus. The temperature control device includes a thermally conductive body having an inner surface and an outer surface removably connected with and in thermal communication with the upper chamber of the plasma processing apparatus. The temperature control device also includes a plurality of thermal interface layers in thermal communication with the thermally conductive body wherein at least one layer is a heating element; and a cooling element connected with the banded thermally conductive body and thermally coupled with the upper chamber of the plasma processing apparatus wherein the cooling element is configured to conduct a fluidic medium. The temperature control device further includes at least one temperature sensor for sensing temperature of the upper chamber of the plasma processing apparatus; a temperature control unit for controlling the heating element and the cooling element; and a latching mechanism for securing the temperature control device to the upper chamber.
The invention relates, in another embodiment, in a plasma processing system, to a method of using a temperature control device, including a latching mechanism, for controlling the temperature of an upper chamber of a plasma processing apparatus comprising. The method includes providing a combination heating and cooling band wherein the cooling portion of the band is configured to conduct fluidic flow having a constant temperature. The method also includes adjusting the volume of the fluidic flow in response to temperature variation within the upper chamber; and adjusting the heat output of the heating element in response to temperature variation within the upper chamber.
These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention.
While not wishing to be bound by theory, it is believed by the inventor herein that an agile temperature management system may achieve substantially accurate temperature control in a plasma processing system.
In one embodiment, a temperature management system and method may operate to achieve optimal temperature control of an upper chamber of a plasma processing apparatus during fabrication of semiconductor devices. An optimal temperature control system, as contemplated by the present invention, provides greater process control for plasma processing apparatuses which is becoming more and more important as feature size continues to shrink. Furthermore, in a non-obvious way, the present invention provides for rapid response temperature control of a plasma processing system.
In another embodiment, the temperature control system includes a heating and cooling unit that is coupled to an outer surface of an upper chamber of a plasma processing apparatus to be temperature controlled. A heating and cooling unit serves to transport heat into or away from the surface(s) being controlled through the same thermal interface.
In another embodiment, the temperature control system includes a heating and cooling unit that is coupled via a latching mechanism to an outer surface of an upper chamber of a plasma processing apparatus to be temperature controlled.
In another embodiment, the latching mechanism is a clamp assembly.
In another embodiment, the clamp assembly is integrated directly into the heating and cooling unit.
Additional embodiments of the invention are discussed below. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. Furthermore, those skilled in the art will readily understand that the illustrations are not necessarily scale drawings, but are intended to assist in describing the embodiments herein.
Temperature spikes generally represent points at which plasma is extinguished. That is, because plasma releases heat energy, temperature rises until plasma is extinguished. One skilled in the art will appreciate that temperature may continue to rise for period of time after plasma is extinguished due to heat buildup in a process chamber and due to use of large thermal masses in constructing process chambers. When plasma is extinguished, temperature continues to fall as heat is dissipated into the atmosphere. Temperature dips represent points at which plasma is ignited. As noted above, a lag time may occur in some systems due, in part, to thermal mass. A dramatic drop in temperature illustrated at 210, where time is approximately equal to 70 minutes, is representative of temperature drop occurring during an idle state of the plasma processing chamber.
Typically, sidewall(s) may be constructed using aluminum. Sidewall(s) may be constructed as a single planar surface having a circular profile, or may be constructed as multiple planar surfaces having 2 or more planar surfaces. A temperature control device 308 is attached with and in thermal communication with sidewall(s) 312. Temperature control device 308 is described in further detail below for
In many cases, defects in the mechanical bond due to material aberrations, manufacturing defects, or physical deformity due to warping or mishandling, for example, may be present. Thus, the need for an interface material that can account for these differences ensuring efficient thermal conductivity. In this manner, thermal loads may be effectively conducted in a vector perpendicular to the interface layer. In one embodiment, thermally conductive material 344 is a thermal pad. In other embodiments, thermally conductive material 344 is thermal grease. A dissipation band 348 comprises another of the plurality of physical interface layers. Without being bound by theory, it is believed that the dissipation band 348 functions to distribute thermal loads evenly over the surface of thermally conductive body 334. The dissipation of thermal loads by a dissipation band differs from conduction of thermal loads by a thermally conductive material in that dissipation is substantially radial with respect to interface layer surfaces whereas conduction is substantially perpendicular with respect to interface layer surfaces. Dissipation band material may be chosen from any of a number of suitable thermally dissipative materials well-known in the art. In one embodiment, dissipation band 348 is series 6000 aluminum.
A heater layer 350 comprises another of the plurality of thermal interface layers. In one embodiment, heater layer 350 is a kapton etched foil heater. The capacity of the heater is selected based upon the process demand parameters. Referring briefly back to
A thermal barrier layer 352 comprises another of the plurality of thermal interface layers. Without being bound by theory, thermal barrier layer 354 may function as a heat sink selected to make fluidic medium less efficient. In any thermal system, one skilled in the art will appreciate that balanced thermal loading is desirable. In one embodiment, where fluidic medium is provided at an uncontrolled flow rate, the efficiency of the fluidic medium may exceed the thermal output of the process. In this example, an apparatus configured in this manner might never reach a desired operating temperature or might only reach sub-optimal operating temperature only upon input of excess energy from a heater layer (e.g., heater layer 350) resulting in a coordinate increase in production costs. In other examples, the flow of fluid may experience perturbations such as temperature differences or flow rate differences during processing. Thermal barrier layer 352, in those examples, may diminish perturbation effects on process temperatures by acting as a thermal cushion to those effects. In one embodiment the thermal barrier is Mylar Polycarbonate available from various manufacturers.
A final layer (not shown) may be bonded to an outer surface of the thermally conductive body 334. This final layer, in some embodiments, is a thermal arrestor. A thermal arrestor may insulate a thermal control device from ambient temperature changes thus resulting in better process control of the device. Each of the layers discussed may be bonded to each other using any thermally conductive adhesive well known in the art. In some embodiments, double sided thermal adhesive tape such as THERMATTACH® (T412 from Chomerics may be used. Those skilled in the art will recognize that the layers illustrated are not scale representations of actual embodiments. Rather, the layers are for illustrative purposes only. Material selection and design constraints will dictate layer sizing.
Referring to
In one embodiment, the clamp assembly may be integrated with the temperature control device; such that a screwdriver, socket, or nut driver may be used to rotate a screw coupled to a band having serrations, in order to secure the temperature control device to the plasma processing chamber. As the screw is rotated, the screw threads advance the serrations causing a reduction in the inside diameter of the band.
In another embodiment, the removable clamp may be integrated with the temperature control device, such that a pair of pliers or a special tool may be employed to secure the temperature control device to the plasma processing chamber. Generally made from an elastically deformable material, when a compressive force is applied to tabs extending from the clamp, the inside diameter of the clamp is increased. Removal of the compressive force causes the inside diameter of the clamp to decrease, thereby applying a compressive force to a hose inserted therein
In another embodiment, the clamp assembly may be integrated with the temperature control device, such that an upper clamp half, a lower clamp half, a hinge pin connecting the halves, and a fastener are employed secure the temperature control device to the plasma processing chamber. The fastener may comprise a bolt carried by a rotatable pivot pin mounted in the lower clamp half. Slots may be provided in the upper clamp half and the lower clamp half so that the bolt can swing in and out of engagement with the clamp halves to permit the assembly to be opened for mounting the tubular, and then closed and locked by tightening the bolt to retain the tubular in the clamp assembly.
Tension imparted on the device must be sufficient to maintain the position of temperature control device 308, but not excessive so as to damage or distort temperature control device 308 and its associated structures. In selecting a clamping method, uniform and repeatable contact pressure when temperature control device 308 is mounted is desirable.
Second, mounting blocks 432 may serve as attachment points for cooling conduit 420/424. At least one inlet 420 and one outlet 424 may be mounted on either of mounting blocks 432. Any number of suitable fittings well known in the art may be utilized as attachment points for the cooling conduit.
Handles 416 are provided to assist in the handling of temperature control device 308. Handles 416 may be thermally isolated from temperature control device 308 so as to reduce or eliminate thermal noise in the system. Additional handles may be added as required without departing from the present invention. A temperature sensing device is shown at 404. Temperature sensing device 404 may be used to interlock a plasma control system in the event of an over-temperature condition. In one embodiment, a resistance temperature detector (RTD) may be used to sense temperature. A heater attachment point 408 is connected with thermally conductive body 334. Heater attachment point 408 provides stress relief for heater layer 350 (
Temperature Control: Constant Fluidic Flow/Variable Heat
In some embodiments, heat output may be regulated by a power limiting circuit (not shown). The method proceeds to query whether the process is complete at step 614. If the process is complete, the method continues at step 514 (
If the method determines, at a step 604, that temperature is not too low (e.g., temperature is higher than set point), the method queries whether a heating element is on at step 608. If the heating element is on and temperature is above a desired set point, then the query of step 608 is answered in the affirmative and the heating element is turned off at step 610. The method proceeds to query whether the process is complete at step 614. If the process is complete, the method continues at step 514 (
If the query of step 608 is answered in the negative, the method then queries whether an over-temperature condition exists at step 612. If the answer to step 612 is no (i.e., no over-temperature condition), then the method proceeds to query whether the process is complete at step 614. If the process is complete, the method terminates. If the process is not complete, the method continues to step 602 and continues cycling until the process is complete. If an over-temperature condition exists at step 612, then the method stops. Notably, each cycle requires a query to determine whether the process is complete as illustrated by step 614.
Temperature Control: Variable Fluidic Flow/Constant Heat
If the method determines, at step 624, that temperature is not too low, the method queries whether an over-temperature condition exists at step 628. If an over-temperature condition does not exist, then fluidic medium flow may be increased at step 630. The method proceeds to query whether the process is complete at step 632. If the process is complete, the method continues at step 514 (
Temperature Control: Variable Fluidic Flow/Variable Heat
The determination of which element is activated in response to a low temperature condition is user determinable and may depend on a variety of conditions for example, implementation cost, resource availability, or desired speed of reaction (i.e. system agility). Thus, a user may select a heating element response where additional fluidic flow is not available or cost effective. In like manner, a user may select to decrease fluidic medium flow response where additional energy for activating a heat element is not available or cost effective. In contrast, where maximum system agility is desirable and both availability and cost are not limited, both elements (e.g., heating element activated, fluidic medium flow decreased) may be activated. The method proceeds to query whether the process is complete at step 652. If the process is complete, the method continues at step 514 (
If the method determines, at step 644, that the temperature is not too low, then the method queries whether an over-temperature condition exists at step 648. If an over-temperature condition does not exist, the method proceeds to step 650 where one of three conditions are activated: a) a heating element is deactivated; b) fluidic medium flow is increased; or c) a heating element is deactivated and fluidic flow is increased. As noted above, the determination of which element is activated in response to a high temperature condition is user determinable and may depend on a variety of conditions including, for example, implementation cost, resource availability, or desired speed of reaction (i.e. system agility). Thus, a user may select a heating element response where increased fluidic flow is not practical or cost effective.
In like manner, a user may select increasing fluidic medium flow response where selecting a heating element response is not practical or cost effective. In contrast, where maximum system agility is desirable and both availability and cost are not limited, both elements (e.g., heating element OFF, increase fluidic flow) may be activated. The method proceeds to query whether the process is complete at step 652. If the process is complete, the method continues at step 514 (
As presented herein, the present invention provides agile temperature control for plasma processing systems. In addition, the present invention provides ergonomic benefits due in part to its efficient design.
While his invention has been described in terms of several preferred embodiments, there are alterations, permutations, modifications and various substitute equivalents, which fall within the scope of this invention. For example, the TCP 2300 plasma processing type system manufactured by Lam Research Corporation of Fremont, Calif. may be used to practice the present invention.
It should also be noted that there remain many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, modifications, and various substitute equivalents as fall within the true spirit and scope of the present invention.
