Patent Application
20050008983
The present invention relates generally to temperature control of workpiece support chucks for semiconductor processing equipment, and more particularly to rapid heating and cooling of such chucks.
In many semiconductor processing steps, such as etching, deposition, annealing, etc., a workpiece (e.g., a silicon wafer, glass substrate, etc.) is supported within a processing chamber. Gaseous and/or plasma reactants are supplied to the surface of the workpiece while the workpiece is heated to specific temperatures.
Typically, higher temperatures aid in achieving higher reaction rates, and therefore higher workpiece throughput. On the other hand, higher temperatures can sometimes cause damage to structures on partially fabricated integrated circuits. Additionally, certain chemical reactions are most efficiently performed at lower temperatures.
Many structures and methods are known in the art for controlling workpiece temperature within the chamber. For example, radiant heat may be focused onto the workpiece through transparent “cold walls” formed of quartz. Radiant heat is often used in very high temperature processing (e.g., at greater than 500° C.), where it is desirable to raise and lower temperature during the process cycle for each workpiece.
In other arrangements, the temperature of the workpiece can be regulated by heating the workpiece support or chuck. Conventionally, the term “chuck” refers to a support for processing workpieces that is kept at constant temperature as workpieces are transferred in, processed, and transferred out of a processing chamber in cycles.
Some systems, particularly plasma processing systems, require cooling a chuck rather than heating in order to maintain a desired chuck temperature. Depending on the chemistry and process parameters, some plasma processes impart a significant heat load to the chuck. If the chuck does not provide means to remove this heat, the temperature of the chuck can rise above the desired set point. This typically happens in low temperature processes because the chuck temperature is close to the temperature of the surrounding chamber, and the radiative heat transfer between the chuck and the chamber is poor. The situation is made worse when the chamber temperature is even higher than the chuck temperature.
In higher temperature processes, the radiative heat transfer between the chuck and the surrounding chamber is generally sufficient to offset the heat load generated by the process. Using a liquid to both heat the chuck and remove extra heat is common in the industry. Running high temperature processes with liquid heating, however, is dangerous and not economical. Additionally, changing the chuck temperature requires changing the fluid temperature, which can be slow and can reduce throughput.
One method for achieving two temperature levels with a chuck is to use an electrical heat source to run high temperature processes and a liquid heat source to run low temperature processes. Such a system is disclosed, for example, in U.S. Pat. No. 6,461,801. However, in such systems the liquid should be purged from the chuck when running high temperature processes to prevent boiling of the liquid within the chuck. This is typically time consuming and can decrease throughput. Thus, there remains a need for an improved system for providing temperature control of a workpiece support chuck.
Thus, according to one embodiment, a method of processing a workpiece in a processing chamber is provided. The method of this embodiment comprises heating a first chuck to a first temperature, cooling a second chuck to a second temperature below the first temperature, placing a workpiece to be processed on a support surface of the first chuck and controlling a temperature of the first chuck by adjusting a rate of heat transfer between the first chuck and the second chuck.
In one embodiment, adjusting a rate, of heat transfer comprises varying a distance physically separating the first chuck from the second chuck. Varying a distance physically separating the first chuck from the second chuck can comprise placing the chucks in direct physical contact with one another. In another embodiment, adjusting a rate of heat transfer comprises varying a flow of a gas into a space between the first chuck and the second chuck. In yet another embodiment, adjusting a rate of heat transfer comprises varying a parameter affecting a rate at which heat is removed from the second chuck. For example, a flow rate of a cooling fluid circulating through the second chuck can be adjusted.
Another embodiment provides an apparatus for supporting a workpiece in a process chamber. The apparatus of this embodiment comprises a heater coupled to a first chuck having a surface for supporting the workpiece. The apparatus further comprises a second chuck having a cooling device coupled thereto. The second chuck is thermally couplable to the first chuck to vary a rate of heat transfer between the first chuck and the second chuck. In some embodiments, the apparatus further comprises an automatic control system configured to control a temperature of the first chuck by varying a rate of heat transfer between the first and second chucks.
Yet another embodiment provides a method of processing a workpiece in an apparatus comprising a first heated chuck and a second cooled chuck. The method of this embodiment comprises placing the workpiece on the first chuck, positioning the second chuck at a first position relative to the first chuck, and performing a first process on the workpiece at a first temperature. The second chuck is then moved relative to the first chuck until the second chuck is at a second position relative to the first chuck, and a second process is performed on the workpiece at a second temperature.
In yet another embodiment, a method of processing a workpiece in an apparatus comprising a first chuck and a second chuck is provided. The method of this embodiment comprises positioning the workpiece on the first chuck, with the second chuck positioned a first distance away from the first chuck. The method comprises initiating a photoresist strip process on the workpiece, changing a temperature of the first chuck by moving the second chuck to a position a second distance away from the first chuck, and continuing to perform the photoresist strip process on the workpiece.
In still another embodiment, a method comprises performing a first photoresist strip process on a first batch of workpieces at a first temperature, moving a second chuck towards the first chuck, and performing a cleaning process on a second batch of workpieces at a second temeperature lower than the first temperature.
Having thus summarized the general nature of the invention, embodiments and modifications thereof will become apparent to those skilled in the art from the detailed description herein having reference to the figures that follow, of which:
With reference to the attached figures, some preferred embodiments of a temperature-controlled apparatus for supporting a workpiece comprise a heat source configured to input heat to a workpiece support and a heat sink configured to remove heat from the support. In one embodiment, illustrated for example in
In general, the first chuck (or “hot chuck”) 10 is configured to be actively heated and is configured to support a workpiece on its upper surface (or on support pins extending upwards therefrom). The second chuck (or “cold chuck”) 20 is generally maintained at a temperature below that of the first chuck 10 and is configured to remove heat from the hot chuck 10 through radiative, convective and/or conductive heat transfer. The rate of heat transfer between the hot chuck and the cold chuck can be varied by adjusting any one of a number of parameters such as a distance separating the chucks 10, 20; a temperature of, or rate of heat transfer from, the cold chuck; a quantity or composition of gas occupying a space between the chucks, or other parameters recognized by the skilled artisan.
In the embodiment illustrated in
The hot chuck 10 can have any suitable construction. For example, the chuck 10 may include vacuum channels for holding the workpiece in place, or the workpiece can be held in place solely by gravity. The hot chuck 10 can be made of any suitable material, typically one having a high thermal conductivity. In one embodiment, the hot chuck 10 is formed of a ceramic material such as aluminum nitride (AlN), and has a mass of between about 700 grams and about 2500 grams, and in one preferred embodiment a mass of about 1200 grams. AlN is a desirable material for use in the present system for its relatively high thermal conductivity, rigidity at high temperatures, and resistance to corrosion. Alternatively, the hot chuck 10 can be made of any other suitable metallic or ceramic material. In the illustrated embodiment, the hot chuck 10 is held stationary or fixed with respect to a chamber 50 (see
The cold chuck 20 can likewise be made of any suitable material. In one embodiment, the material of the cold chuck 20 is selected to have a high thermal conductivity, and in some embodiments, the cold chuck 20 is also selected to have a high mass and a high thermal capacity (i.e. the product of the specific heat and the density of a material) relative to the hot chuck 10, which preferably has a relatively low mass and thermal capacity. In one embodiment, the cold chuck 20 is formed of pure aluminum or an aluminum alloy and has a mass of between about 3,000 grams and about 10,000 grams, and in one preferred embodiment a mass of about 5,000 grams. Thus, in some embodiments, the hot chuck can advantageously have a mass that is between about 20% and about 30% of the mass of the cold chuck. In some preferred embodiments, the hot chuck has a mass of between about 23% and about 28% of the mass of the cold chuck, and in one particular embodiment, the mass of the hot chuck is about 24% of the mass of the cold chuck.
In one embodiment, it is particularly desirable to provide a hot chuck made of an AlN ceramic with a mass of about 1,200 grams in combination with a cold chuck made of aluminum with a mass of about 5,000 grams. These materials have uniquely desirable physical and thermal properties relative to one another. Alternatively, other materials with substantially large thermal capacities such as beryllium, boron, chromium, copper, etc can also be used in suitable masses. However, metals other than Al are typically provided with a protective plating in order to survive in the plasma environment and to avoid metal contamination during semiconductor processing. In one embodiment as discussed in more detail below, the cold chuck 20 is desirably movable with respect to the hot chuck 10 so as to increase or decrease a separation (or gap) 24 between the hot and cold chucks 10, 20.
In the embodiment illustrated in
Such a fluid-cooled system also typically includes a pump or other device for circulating cooling fluid through the channels 30 in the cold chuck 20. A fluid source (not shown) storing thermal transfer fluid at a relatively low temperature communicates with the fluid channels in the cold chuck 20 via a supply line 42 and a return line 44. A flow control valve (not shown) can be provided in the fluid line to adjust a flow rate of the thermal transfer fluid through the cold chuck 20. Alternatively, a flow rate of the thermal transfer fluid can be controlled by varying a pumping rate or other parameter.
In still further alternative embodiments, the cold chuck 20 can be cooled by other methods or devices as desired. For example, the cold chuck can be cooled by thermoelectric coolers (TEC's) or any other device capable of removing heat from an object.
With reference now to
As shown in
Inlet passages 64 are typically provided through a top of the chamber 50 to allow process gases to enter the chamber 50 through an inlet baffle plate 65 and a shower head plate 66. Exhaust passages 68 can be provided through a bottom of the chamber 50. As shown, a center-draw baffle 70 having a central opening 72 can be provided below the cold chuck 20. The baffle 70 causes process gases to flow more uniformly over the workpiece from the inlet passages 64 to the exhaust passages 68.
In one embodiment as shown in
In the illustrated embodiment, the cold chuck 20 is vertically movable relative to the hot chuck 10. Any suitable motor and position control apparatus can be provided to drive the support column 58 and cold chuck 20 towards or away from the hot chuck 10, as desired. For example, in some embodiments the central column 58 can be raised and lowered by a rack and pinion or a worm screw. Alternatively, the cold chuck 20 can be supported by a plurality of movable supports rather than a single column.
With reference to
In one preferred embodiment, an inert gas is continuously injected into the gap 24 between the chucks. This allows heat to be transferred from the hot chuck to the cold chuck by “free convection” and (to some extent) conduction through the gas. The skilled artisan will recognize that (among other factors), the type of gas and a rate of injection and/or removal of the gas will affect the rate of heat transfer between the chucks. If the chucks 10, 20 are brought into physical contact, conduction becomes the dominant mode of heat transfer between them. The skilled artisan will recognize that conductive heat transfer is dependent on the difference in temperature and the specific heats of the chuck materials as well as other factors. Thus, in one preferred embodiment the temperature of the hot chuck 10 is controlled by increasing or decreasing (possibly to zero) the gap 24 between the chucks 10, 20.
The term “thermally couple” is used herein in its ordinary sense and refers without limitation to the act of increasing a rate of heat transfer between the hot chuck and the cold chuck to or above a desired level. The skilled artisan will recognize that a maximum rate of heat transfer can be achieved by bringing the hot and cold chucks into direct physical contact. However, a desired level of heat transfer sufficient to “thermally couple” the chucks can be less than the maximum possible for a given system. Thus, in some embodiments, the chucks are considered to be “thermally coupled” when they are in proximity (e.g. less than about 2mm) to one another, but are not physically contacting one another. Similarly, the term “thermally decouple” is used in its ordinary sense and refers without limitation to the act of reducing a rate of heat transfer between the hot chuck and the cold chuck to a desired minimum. The skilled artisan will recognize that a desired minimum rate of heat transfer may not necessarily be the absolute minimum that a given system is capable of achieving.
For high temperature processes (e.g., at greater than about 110° C.), the rate of heat transfer from the hot chuck to the cold chuck can be increased by thermally de-coupling the chucks. In some embodiments, the chucks are thermally de-coupled by moving the cold chuck 20 downward away from the hot chuck 10. In one embodiment, the cold chuck 20 is thermally decoupled from the hot chuck 10 when it is moved to a position at least about 0.5 inches (˜1.27 cm) away from the hot chuck 10. In further embodiments, the chucks can be configured to be thermally decoupled when the chucks 10, 20 are separated by a smaller or greater distance, or when another parameter such as a flow rate of a cooling fluid or of a gas injected into a gap between the chucks is adjusted to a particular level.
For low temperature processes (e.g., at less than about 110° C.), the cold chuck 20 is moved upwardly, or towards the hot chuck 10. Preferably, the cold chuck 20 is movable into contact with the hot chuck 10 to increase a rate of heat transfer between the hot chuck 10 and the cold chuck 20. In still further alternative embodiments, intermediate thermally conducting or insulating structures or materials can be placed between the hot and cold chucks in order to vary a rate of heat transfer therebetween.
In one embodiment, a desired temperature of the hot chuck 10 is controlled by an external closed-loop temperature controller (not shown) configured to receive a temperature measurement from a thermocouple 80 and to control parameters affecting the heat transfer rate as discussed above. If the measured temperature of the hot chuck 10 is higher than a desired temperature, the controller can reduce or turn off the power to the heating elements 36. The controller can also raise the cold chuck 20 upwardly towards the hot chuck 10 to thermally couple the chucks 10, 20.
In some embodiments, the cold chuck 20 is thermally coupled to the hot chuck 10 when the cold chuck is moved to a position less than 0.5 inches (12.7 mm) away from the hot chuck 10. In one particular embodiment, the cold chuck 20 is thermally coupled to the hot chuck 10 when it is moved into contact with the hot chuck 10. When the cold chuck 20 contacts the hot chuck 10, the temperature of the hot chuck 10 typically drops sharply due to its low mass and thermal capacity in comparison to that of the cold chuck 20. The temperature of the cold chuck 20 rises only moderately due to its high mass and high thermal capacity.
As discussed above, an inert gas can be supplied between the hot chuck 10 and the cold chuck 20 to increase the rate of heat transfer between the chucks 10, 20 when a gap exists therebetween. For example, even when the chucks 10, 20 are in physical contact with one another, gaps may exist as a result of rough variations in the mating surfaces of the chucks. The skilled artisan will recognize that heat will be transferred across any gap faster if a gas is present than would be the case in a vacuum. Therefore, in some embodiments, an inert gas can be selected to have as high a thermal conductivity as possible. Temperature equilibrium between the chucks 10, 20 can thus be reached relatively quickly.
In order to maintain the temperature of the hot chuck 10 within a desired range, the controller can adjust system parameters to increase or decrease the rate at which heat is transferred from the hot chuck 10 and thereby to increase or decrease the temperature of the hot chuck 10. According to one embodiment, if the measured temperature of the hot chuck 10 is less than the desired temperature, the controller reactivates the heating elements 36 of the hot chuck 10 to increase the temperature of the hot chuck 10. The desirably low mass and thermal capacity of the hot chuck 10, allows the temperature of the hot chuck 10 to be changed rapidly. If the measured temperature is greater than the desired temperature of the hot chuck 10, the heating elements 36 can remain deactivated while the thermal transfer fluid circulates through the cold chuck 20 to remove additional heat from the chucks 10, 20.
In some embodiments, the illustrated workpiece support apparatus can be employed within a microwave plasma asher for stripping organic photoresist from integrated circuit workpieces. The asher can employ a remote microwave plasma source which produces oxygen and/or fluorine radicals upstream of the process chamber. Alternatively, the apparatus can employ an internal radio frequency (RF) plasma generator within the process chamber 50.
As previously noted, some embodiments of the illustrated apparatus are particularly useful for photoresist stripping and/or cleaning operations. Photoresist is applied and removed from a workpiece at various stages of semiconductor fabrication. As described in the following examples, the illustrated apparatus has utility in many resist strip contexts. For example, the illustrated apparatus is particularly useful for two-step photoresist strip processes in which one processing step is carried out at a higher temperature than another. By adjusting a rate of heat transfer between the hot and cold chucks 10, 20, one processing step can be carried out immediately after another without having to remove the workpiece from the process chamber 50. In addition, different batches of workpieces can be processed at different temperatures using the illustrated apparatus. A first batch of workpieces can be processed in the chamber 50 at a first temperature. Then, by adjusting the distance between the chucks 10, 20 (or another parameter affecting the rate of heat transfer between the chucks), a second batch of workpieces can be processed in the chamber 50 at a second temperature immediately thereafter.
Thus, in one example of a resist strip process, the hot and cold chucks are thermally coupled 110 while thermal transfer fluid circulates through the cold chuck 20, and an initial strip is first conducted 120 at low temperature until the trapping crust is removed from the photoresist. Workpiece temperatures during the initial step are preferably kept between about 100° C. and 140° C., more preferably between about 110° C. and 125° C. Reaction gases can include an oxidant to aid oxidation of the resist (e.g., O2, preferably converted to oxygen radicals); a fluorine source to aid removal of the implanted portion (e.g., NF3 or CF4, preferably converted to fluorine radicals); and a diluting gas (such as He or Ar) and/or forming gas (H2/N2) to serve as a carrier. Reactants can be supplied to the workpiece surface in any suitable fashion. Radicals can be generated in a remote microwave plasma generator or any other suitable plasma source. The implanted upper portion of the resist is typically removed in about thirty (30) seconds.
Once the crust has been removed, the hot and cold chucks are thermally de-coupled 130, the temperature of the hot chuck 10 rises 140 and the reaction continues 150. Preferably, the temperature is raised to between about 150° C. and 300° C. and more preferably between about 200° C. and 250° C. During this higher temperature step, the cold chuck 20 is preferably thermally decoupled from the hot chuck 10. For example, the cold chuck 20 can be moved at least about 0.5 inches (12.7 mm) away from the hot chuck 10. Once the hot chuck 10 is separated from the cold chuck 20, the electrical heating elements 36 cause the temperature of the hot chuck 10 to rise. The same reactant chemistry can continue to flow during the second stage of the strip. However, in some embodiments N2 (or forming gas) flows with O2 and fluorine flow can be discontinued. The raised temperature results in a significantly increased etch rate, thereby improving workpiece throughput. In particular, a temperature of about 250° C. results in a strip rate of about 7 μm/min. A typical photoresist mask of about 1 μm can therefore be removed within about 5 to 10 seconds.
With reference now to
After via formation, the photoresist mask is removed. Unfortunately, the process of forming the via creates an organic residue within the via, which is often difficult to remove. The residue is often referred to in the industry as a polymer “veil,” and is particularly problematic following reactive ion etching of vias for back-end or metallization stages of fabrication. While relatively vigorous cleaning chemistries are often employed to remove this polymer residue, over-etching of the structure risks damage to the exposed features within the via. Accordingly, it is advantageous to conduct the post-via formation cleaning after rapid resist stripping at relatively low temperatures.
With the hot and cold chucks thermally de-coupled 210, and with the hot workpiece chuck 10 at an elevated temperature (e.g., 200° C. to 250° C.), a high temperature resist strip 220 can be conducted at rapid rates, as disclosed above with respect to the second stage of the post-implant process. Reactants can also be provided as discussed in previous examples above, with optional fluorine flow. In one embodiment, the thermal decoupling is achieved by moving the cold chuck 20 at least 0.5 inches (12.7 mm) away from the hot chuck 10.
The illustrated two-chuck system allows the post-via cleaning to be conducted within the same process chamber as the high temperature resist strip 220. Accordingly, after the high temperature resist strip 220, the hot and cold chucks can be thermally coupled 230 and the “hot” chuck 10 can be cooled 240 for a low temperature cleaning process 250. During the post-strip clean process, the workpiece temperature is typically kept between about room temperature and about 100° C., more preferably between about 50° C. and 80° C. The chemistry during this process preferably includes an oxidant (e.g., O2), a diluting gas (e.g., He, Ar, and/or forming gas such as N2/H2), and a fluorine source gas (e.g., NF3 or CF4). The fluorine, while aiding removal of the polymer, also attacks the oxide sidewalls of the via. The oxidant and fluorine reactants can comprise radicals formed upstream of the reaction chamber.
The post-strip clean process can utilize RF plasma generation within the chamber, compensating for reduced temperatures during the process. N2 or forming gas aid maintenance of the plasma discharge. Additionally, an optional physical sputter etch can be briefly applied immediately after treatment with the oxygen and fluorine sources.
Upon completion of the via cleaning step 250, the workpiece is removed 260 from the chamber 50. The cold chuck 20 and the hot chuck 10 are then thermally de-coupled 270 and the hot chuck 10 is again heated 280 in preparation for processing another workpiece.
Thus, in the embodiment illustrated in
The skilled artisan will recognize that workpieces can be processed according to the processes described herein in a “batch mode” or an individual mode. For example, in one embodiment, a single wafer can be processed through the method illustrated in
With reference again to
Integrated circuits include many dielectric elements for electrical isolation of conductive elements. A common material for such dielectric elements is silicon oxide in various forms, although silicon nitride is also popular for many applications.
In forming electrical contacts among conductive elements, the contact holes or openings are formed through insulating layers known as interlevel dielectrics (ILDs). Opening contact holes to active areas within semiconductor substrates often exposes insulative sidewall spacers over transistor gate electrodes. Such contact etches typically also expose sacrificial oxide over the substrate. In each of these examples, masks are employed to define the hole or via, and an etch process exposes oxide surfaces.
Such oxide surfaces define dimensions selected by a circuit design. As device packing density continues to increase in pursuit of faster integrated circuit (IC) operating speeds and lower power consumption, it becomes ever more important to maintain these dimensions, and tolerance for overetch is commensurately reduced. Thus, it is increasingly important that cleaning the openings after removal of the photoresist mask be carefully controlled to avoid overetch of the exposed insulating surfaces, particularly oxide surfaces.
Accordingly, one embodiment of a method of reducing oxide loss comprises thermally de-coupling 210 the hot and cold chucks and then conducting a first stage of post-contact etch resist stripping 220 at high temperatures (preferably between about 100° C. and 300° C., more preferably between about 200° C. and 250° C.). An exemplary reactant flow includes 1:10 ratios of N2:O2.
After the post-contact etch resist strip 220, the dual-chuck apparatus can be employed to perform a lower temperature post-strip clean. Accordingly, the hot and cold chucks are thermally coupled 230, the hot chuck is cooled 240 to a desired temperature, and a post-strip clean process is performed 250. As noted with respect to the post-via cleaning, fluorine aids in cleaning oxide surfaces of lithography by-products. Desirably, a relative small percentage of fluorine gas source (e.g., less than about 5% CF4) is added to the flow.
Advantageously, employing an RF plasma, in addition to the remote plasma generator, lowers the required process temperature for a given etch rate. The temperature of the hot chuck 10 is preferably maintained between about 15° C. and 100° C., more preferably between about 20° C. and 100° C., and most preferably between about 25° C. and 50° C. during the low temperature cleaning step 250. Despite rapid etch rates, the post-strip clean can be strictly controlled by limiting the time for which the RF electrodes are powered (e.g., for about 15 seconds).
In addition to the examples of two stage processes discussed above, the two-chuck apparatus of
For such processes, illustrated for example in
Accordingly, several advantages inhere in the described apparatus. For example, processes that require two-step processing at different temperatures can be efficiently conducted within the same process chamber. Furthermore, workpiece throughput can be increased by eliminating a separate cooling station conventionally used for cooling workpieces prior to placement in a low-cost storage cassette.
Although certain embodiments and examples have been described herein, it will be understood by those skilled in the art that many aspects of the methods and devices shown and described in the present disclosure may be differently combined and/or modified to form still further embodiments. Additionally, it will be recognized that the methods described herein may be practiced using any structure suitable for performing the recited steps. Such alternative embodiments and/or uses of the methods and devices described above and obvious modifications and equivalents thereof are intended to be within the scope of the present disclosure. Thus, it is intended that the scope of the present invention should not be limited by the particular embodiments described above, but should be determined only by a fair reading of the claims that follow.
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/469,050, filed on May 7, 2003.
| Number | Date | Country | |
|---|---|---|---|
| 60469050 | May 2003 | US |
