Patent Application
20070045230
The present invention is directed generally toward methods for independently controlling one or more etching parameters in the manufacture of microfeature devices.
Microfeature devices generally have a die (i.e., a chip) that includes a high density of very small components, such as integrated circuitry and an array of very small bond-pads electrically coupled to the integrated circuitry. The bond-pads are the external electrical contacts on the die through which supply voltage, signals, etc., are transmitted to and from the integrated circuitry. In a typical fabrication process, a large number of dies are manufactured on a single workpiece using many different processes that may be repeated at various stages (e.g., implanting, doping, photolithography, deposition, etching, plating, planarizing, etc.) to form trenches, vias, holes, implant regions, and other features on the workpiece that ultimately become semiconductor components, conductive lines, and other microelectronic features (e.g., gates and other structures). Lithographic processes, for example, generally include depositing a layer of radiation-sensitive photoresist material on the workpiece, positioning a patterned mask or reticle over the photoresist layer, and exposing the masked photoresist layer to a selected radiation. After the exposing step, a developing step involves removing one of either the exposed or unexposed portions of photoresist. Complex patterns typically require multiple exposure and development steps.
The workpiece is then subjected to an etching process. In an anisotropic etching process, for example, the etchant removes exposed material, but not material protected beneath the remaining portions of the photoresist layer. Accordingly, the etchant creates a pattern of openings (e.g., trenches, vias, or holes) in the workpiece material or in materials deposited on the workpiece. These openings can be filled with dielectric, conductive, and/or semiconductive materials to build layers of microelectronic features on the workpiece. The dies are then separated from one another (i.e., singulated) by dicing the workpiece and backgrinding the individual dies. After the dies have been singulated, they are typically “packaged” to couple bond-pads on the dies to a larger array of electrical terminals that can be more easily coupled to the various power supply lines, signal lines, and ground lines.
As microfeature devices become more complex, there is a drive to continually decrease the size of the individual features and increase the density of the features across the workpiece. This significantly increases the complexity of processing workpieces because it is increasingly difficult to form such small features on the workpiece. In some processes, the dimensions (referred to as critical dimensions) of selected features are evaluated as a diagnostic measure to determine whether the dimensions of other features comply with manufacturing specifications. Critical dimensions are accordingly most likely to suffer from errors resulting from any of a number of aspects of the foregoing fabrication processes. Such errors can include errors generated by the radiation source and/or the optics used in lithographic processes. The critical dimensions can also be affected by errors in processes occurring before or during the exposure/development process (such as problems with the photoresist material), errors occurring during etching processes, and/or variations in material removal processes (e.g., chemical-mechanical planarization processes).
One area of particular concern in lithographic processing is accurately focusing the pattern onto the surface of the workpiece and maintaining the integrity of the pattern throughout the subsequent processes with little or no critical dimension bias. Critical dimension bias is the difference in a feature's measurement before and after a process flow step, such as comparing the dimension of a feature before etching and after an etch is completed. One problem with conventional lithographic processes is that many photoresist materials do not maintain crisp edges throughout etching and tend to bend, wrinkle, and/or shred. These defects are undesirable because they may be transferred to the underlying layers and often result in significant critical dimension bias. This problem is further exacerbated as the size of microfeature devices (and in turn, the critical dimensions of these features) continues to shrink.
One conventional approach addressing the photoresist material problem is to deposit a carbon-based layer under the photoresist material and use the photoresist material to form a patterned carbon-based layer. The photoresist material is then removed and the carbon-based layer can act as a mask or sacrificial layer when etching the remaining underlying material layers.
One concern with this arrangement is that the pattern of features in the array portion 30 and the periphery portion 40 cannot be changed relative to and independently of each other with conventional etching processes. For example, if the critical dimensions in one portion of the workpiece 10 need to be adjusted or tuned (e.g., because the device has leakage or does not operate fast enough), conventional processes require either (a) multiple lithographic processes to form a pattern in the array portion independently of a pattern in the periphery portion before etching, or (b) a “best fit” adjustment to the critical dimensions across the entire workpiece during etching. One problem with the additional lithographic processes is that such processing is very expensive and time-consuming (e.g., requires additional masks, reticles, and/or requalification of the lithographic tools). The “best fit” approach also includes several drawbacks. Referring to
A. Overview/Summary
The following disclosure describes several embodiments of methods for independently controlling one or more etching parameters in the manufacture of microfeature devices. One aspect of the invention is directed toward a method for fabricating a microfeature device on a microfeature workpiece. The workpiece includes a first portion with features having first critical dimensions and a second portion with features having second critical dimensions different than the first critical dimensions. The workpiece also includes a carbon-based layer over at least a portion of the first portion and the second portion. The method includes setting an etching parameter to control the etching process in the first portion of the workpiece relative to and independently of the etching process in the second portion of the workpiece, and etching the carbon-based layer. The etching parameter can be set before the etching process and held constant while etching the carbon-based layer, or the etching parameter can be set by changing the parameter while etching the carbon-based layer for dynamic etching.
Several different etching parameters (e.g., flow of Cl2, bias power) can be selected to control the etching process in the first portion relative to the second portion. For example, increasing the flow of Cl2 can increase the second critical dimensions in the second portion of the workpiece while holding the first critical dimensions in the first portion of the workpiece generally constant. Likewise, decreasing the flow of Cl2 during etching can decrease the second critical dimensions in the second portion of the workpiece while holding the first critical dimensions in the first portion generally constant. Increasing the bias power during etching decreases the first critical dimensions in the first portion of the workpiece while keeping the second critical dimensions in the second portion generally constant, while decreasing the bias power increases the first critical dimensions in the first portion of the workpiece while keeping the second critical dimensions in the second portion generally constant.
Another embodiment of a method for etching material during the fabrication of a microfeature device includes providing a microfeature workpiece having an array portion, a periphery portion, and a carbon-based layer. The carbon-based layer on the workpiece is over at least a portion of the array portion and the periphery portion of the workpiece. The method further includes etching the carbon-based layer using an etchant including O2/Cl2/SiCl4, and selectively setting and/or varying one or more etching parameters to control the etching process in the array portion relative to and independently of the etching process in the periphery portion.
Still another embodiment of the invention is directed to a method for etching material on a workpiece in the formation of a gate structure. The workpiece can include an array portion, a periphery portion at least partially surrounding the array portion, and a carbon-based layer. The carbon-based layer is over at least a portion of the array portion and the periphery portion. The method includes etching the carbon-based layer using an etchant including O2/Cl2/SiCl4. The method further includes tuning the etching process in the array portion relative to and independently of the etching process in the periphery portion by selectively varying one or more etching parameters while etching the carbon-based layer.
Additional embodiments of the invention are directed toward an apparatus for etching a microfeature workpiece. The apparatus includes an etching chamber and a workpiece positioned in the chamber for etching. The workpiece can include a first portion with features having first critical dimensions, a second portion with features having second critical dimensions different than the first critical dimensions, and a carbon-based layer. The carbon-based layer is over at least part of the first and second portions of the workpiece. The apparatus also includes a controller operably coupled to the etching chamber. The controller can include a computer-readable medium containing instructions to perform a method comprising (a) etching the carbon-based layer, and (b) setting an etching parameter to control the etching process in the first portion of the workpiece relative to and independently of the etching process in the second portion of the workpiece. The etching parameter can be set before the etching process and held constant while etching the carbon-based layer, or the etching parameter can be set by changing the parameter while etching the carbon-based layer for dynamic etching.
The term “microfeature workpiece” is used throughout to include substrates upon which and/or in which microelectronic circuits or components, data storage elements or layers, vias or conductive lines, micro-optic features, micromechanical features, optics, and/or microbiological features are or can be fabricated. For example, microfeature workpieces can be semiconductor wafers, glass substrates, dielectric substrates, or many other types of substrates. Microfeature workpieces generally have at least several features with critical dimensions less than or equal to 1 μm, and in many applications the critical dimensions of the smaller features on microfeature workpieces are less than 0.25 μm or even less than 0.1 μm. Many specific details of certain embodiments of the invention are set forth in the following description and in
B. Methods for Independently Controlling One or More Etching Parameters in the Manufacture of Microfeature Devices
The first columns 222a-c are at a first portion 206 (e.g., an array portion) over the workpiece 200 and the first columns 222d and 222e are at a second portion 207 (e.g., a periphery portion) over the workpiece 200. Microfeature devices (e.g., memory devices) such as those being formed using the workpiece 100 can include both an array of memory cells and peripheral circuits. The array of memory cells store information, and may be referred to as an array or a storage aspect of a memory device. The array may require a high density of components so that a large amount of information can be stored within a limited amount of space. The peripheral circuits often need to quickly process signals, such as timing, address, and data, so as to access the array to read or to write information. Such peripheral circuits may be referred to as a periphery or a logic aspect of a memory device. The periphery may require high speed to operate with the demand of a fast central processing unit. Accordingly, both high speed and high density are required for memory devices. In the illustrated embodiment, for example, the array portion 206 can include a number of devices or first features, such as memory cells, that coexist in close proximity with each other. The periphery portion 207 can include a number of devices or second features that operate at high speed, such as timing circuits and decoders. For purposes of illustration, only three devices (represented by first columns 222a-c) are shown in the array portion 206 and only two devices (represented by first columns 222d and 222e) are illustrated in the periphery portion 207. Although only five first columns 222 are shown in
The individual first columns 222a-c in the array portion 206 have a critical dimension of A1 and the first columns 222d and 222e in the periphery portion 207 have a critical dimension of P1. As discussed below in more detail, several embodiments of the present invention allow the critical dimension A1 and/or the critical dimension P1 to be adjusted or “tuned” relative to and independently of each other by selectively changing one or more etching parameters before and/or while etching the carbon-based layer 216.
Referring next to
Referring next to
The carbon-based layer 216 can be etched using an etchant including O2/Cl2/SiCl4. The flow rate of O2 can be approximately 40-200 standard cubic centimeters per minute (sccm), the flow rate of Cl2 can be approximately 10-100 sccm, and the flow rate of SiCl4 can be approximately 0.5-5 sccm. The proper ratio of materials in the etchant can provide a generally anisotropic etch (i.e., the sidewalls of the etched carbon-based layer 216 will be generally normal to the first side 202 of the workpiece 200). In one embodiment, for example, the etchant may include a ratio of O2 to Cl2 to SiCl4 of approximately 1/2/0.03. In other embodiments, the ratio may be different.
In additional processing steps not described in detail herein, the dielectric layer 214 can be etched using the carbon-based layer 216 as a mask. The carbon-based layer 216 can then be removed from the workpiece 200 and the workpiece can undergo further processing to complete the construction of gates or other structures in the workpiece 200.
One aspect of the method described above for etching the carbon-based layer 216 is that the critical dimensions in a first area can been controlled relative to and independently of the critical dimensions in a second area by selectively varying or otherwise selecting one or more of the etching parameters to achieve a desired result.
The following table illustrates selectively setting and/or changing an etching parameter relative to a prior setting for the etching parameter to control the etching process of a carbon-based layer in a first portion of a workpiece having features with first critical dimensions relative to and independently of a second portion of the workpiece having features with second critical dimensions. The feature sizes in the first portion can be less than 90 nm and the feature sizes in the second portion can be less than 110 nm, although the features in the first and second portions may have different sizes in different embodiments. The carbon-based layer can be etched with an etchant including O2/Cl2/SiCl4 and the above-described ranges of etching parameters (e.g., chamber pressure, TCP power, substrate bias, and chemical flow rates).
One feature of the methods described above is that selecting one or more etching parameters for etching the carbon-based layer 216 can provide independent control of the critical dimensions in a first portion of the workpiece 200 with respect to the critical dimensions in a second portion of the workpiece 200 where the features have different sizes in the first and second portions. An advantage of this feature is that if the critical dimensions in one portion of the workpiece 200 need to be tuned or adjusted (e.g., because the device has leakage or does not operate fast enough), the critical dimensions can be independently adjusted in that portion without negatively affecting the critical dimensions in other portions of the workpiece 200. This feature can make processing of the workpieces more efficient because precisely tuning the critical dimensions during fabrication in accordance with various manufacturing tolerances and specifications can significantly reduce the time and expense of fabrication and increase throughput.
Another feature of the methods described above is that the proper ratio of materials in the etchant provides a generally anisotropic etch. Many conventional etching processes result in non-anisotropically sloped sidewalls, which can be problematic because they alter the critical dimensions of the device features. One advantage of the methods described above is that anisotropic etches allow for greater precision during the etching process and, accordingly, greater device density. This feature is particularly helpful in further reducing the footprint of microfeature devices.
C. Additional Embodiments of Systems and Methods for Independently Controlling One or More Etching Parameters in the Manufacture of Microfeature Devices
In additional embodiments, the critical dimensions in the array portion 206 can be controlled when etching the carbon-based layer 216 while keeping the critical dimensions in the periphery portion 207 generally constant. Referring to
In still further embodiments, the critical dimensions in both the array and periphery portions 206 and 207 (i.e., the absolute critical dimensions) of the workpiece 200 can be increased/decreased while holding the array to periphery critical dimension ratio generally constant. Referring to
An example of an etching process using the system 500 can include etching a first workpiece, measuring the features on the first workpiece, and selecting/changing an etching parameter based on the measured feature size of the first workpiece. The method can further include etching a second workpiece with the changed etching parameter. This process can be manual or automatic. Another example of an etching process utilizing the system 500 can include an operator inputting a desired outcome (e.g., feature size) into the computer-operable medium 540 and letting the computer select the appropriate parameter set. The computer can then execute the etching process with the preselected settings.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the invention. For example, in alternative embodiments the workpiece 200 may be etched in a different type of etching system, such as a low density system. Additionally, in several embodiments the workpiece 200 may be positioned on a controllable electrostatic chuck during processing to help increase critical dimension uniformity. Furthermore, while the foregoing embodiments are generally related to forming gate structures in microfeature workpieces, the methods described above can also be used in the formation of other microelectronic features or structures. Aspects of the invention described in the context of particular embodiments may be combined or eliminated in other embodiments. For example, several etching parameters may be changed simultaneously to provide more precise control while tuning the critical dimensions. Further, while advantages associated with certain embodiments of the invention have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
