In the drawings, wherein the same reference number indicates the same element throughout the several views:
Various embodiments of the invention will now be described. The following description provides specific details for a thorough understanding and enabling description of these embodiments. One skilled in the art will understand, however, that the invention may be practiced without many of these details.
To overcome problems associated with film or layer undercutting on a wafer, an improved etching process is performed using a chemical mixture that etches the different layers on a workpiece, such as a silicon semiconductor wafer, at approximately the same rate. While the term “wafer” will be used from this point forward, the processes described herein may be applied to any workpiece including layers or films of different materials on one or more surfaces of the workpiece. These workpieces may include semiconductor wafers, memory disks, optical media, and other substrates on which micro-electronic, micro-mechanical or micro-electromechanical devices are or can be formed.
At the outset of the etching process, the wafer 5 may be loaded into a processing chamber or other suitable vessel in which the wafer 5 may be etched or otherwise processed. The wafer 5 may be loaded via a robot or other suitable loading device, which optionally secures the wafer to a workpiece holder, such as a rotor or chuck, a stationary stage, or another rotatable or fixed support. Once the wafer 5 is secured, the etching process may begin.
A chemical mixture 18 suitable for etching the TiN layer 12 and the TEOS layers 14, 16, at approximately the same rate, is delivered or otherwise applied to the wafer 5. The mixture may be sprayed, jetted, applied in bulk, or applied as a vapor. Immersion, full or partial, may also be used. The chemical mixture 18 preferably etches or strips the chemically different layers at rates that differ by less than 15%, more preferably by less than 10%.
The chemical mixture 18 may be sprayed or otherwise delivered to the wafer 5 from nozzles or another fluid delivery mechanism in the processing chamber. The chemical mixture 18 is preferably delivered at or around the edge region of the wafer 5, as shown in
The chemical mixture 18 preferably includes at least an oxidizing agent and an acid component, such as fluorine or other halogen. Other chemical mixtures suitable for etching the specific chemically different layers or films present on a wafer may alternatively be used. Examples of chemical mixtures suitable for etching the TiN layer 12 and the outer and inner TEOS layers 14, 16, at approximately the same rate, include the following:
In Mixture 1, hydrogen peroxide is the oxidizing agent. The ratio of hydrogen peroxide to ammonium fluoride to hydrofluoric acid in Mixture 1 may be approximately 100:1.0:0.138. This ratio has been found to provide approximately equal etching rates of the chemically different layers on a wafer, such as TiN and TEOS layers. This ratio is exemplary only, however, and may be modified to achieve desired results. For example, each of the ratio numbers given above may be varied by ±5, 10, 20 or 30%. Depending on the water content of these chemical solutions as provided from the manufacturer, de-ionized water may be added as needed to achieve the desired overall concentrations. Surfactants and detergents may also be added.
In Mixture 2, ammonium persulfate is the oxidizing agent. The ratio of deionized water to ammonium persulfate to hydrofluoric acid in Mixture 2 is preferably approximately 100:5.0:0.10. This ratio has been found to provide approximately equal etching rates of the chemically different layers on a wafer, such as TiN and TEOS layers. This ratio is exemplary only, however, and may be modified to achieve desired results. Again, these ratios may be varied in the same way as with mixture 1.
As shown in
In the situation where the TiN layer 12 is encapsulated within two TEOS layers 14, 16, it is acceptable for the chemical mixture 18 to strip the individual TEOS layers 14, 16 up to approximately twice as fast as it strips an individual TiN layer 12. This is because, as the TEOS layers 14, 16 are stripped away at the faster rate, both the upper and lower surfaces of the TiN layer 12 become exposed to the chemical mixture 18. Thus, the combined strip rate of the TiN layer 12 from both sides is essentially double the strip rate of a single side of the TiN layer 12. Accordingly, a chemical mixture 18 that strips the TEOS layers 14, 16 at a higher rate than the TiN layer 12 (up to approximately twice as fast) may be used to increase etching efficiency. For example, a chemical mixture 18 that strips a TEOS film at approximately 600 Å/min, and a TiN film at approximately 300 Å/min, could be used to efficiently remove an encapsulated TiN layer 12 at approximately the same rate as the surrounding TEOS layers 14,16.
By using a chemical mixture that etches away the chemically different layers or films on a wafer at approximately the same rate, undercutting and the resultant flaking away of one or more of the layers is prevented. Furthermore, the use of a single chemical mixture that can be applied in a one-step process for etching chemically different layers or films on a wafer is more efficient than, and reduces system complexity relative to, traditional multi-step etching processes. Indeed, a traditional etching process requiring the application of different etching chemicals, delivered in sequential steps, to remove chemically different layers on a wafer, is generally more time-consuming than the processes described herein. Thus, the described processes can improve etching efficiency and overall processing times.
The processes described here may be used to etch films on one or more sides of a semiconductor wafer or other workpiece. A chemical mixture including an oxidizing agent and a fluorine component may be used for etching certain film combinations, such as a TiN film encapsulated within or sandwiched between two or more TEOS films. Other chemical mixtures may similarly be made suitable for etching a given combination of films or layers at approximately the same rate. Essentially, any chemical mixture suitable for etching a given combination of layers or films of different materials at rates that substantially prevent undercutting of the layers or films, particularly the encapsulated or sandwiched layer or film, is contemplated. Apart from TiN films, the methods may also be used for etching other metal films, including non-aluminum metal films or layers. The methods may also be used for etching multi-layer structures, for example, structures having 2, 3, 4 or more layers. In some applications, an oxide film removing component may be added to the mixture, or separately applied in advance, to remove an oxide layer which might interfere with etching. The process may be performed in spin-spray apparatus, in a single wafer mode, for example as described in U.S. Pat. No. 6,632,292, incorporated herein by reference, or in a batch process mode, as described for example in U.S. Pat. No. 6,871,665 or 6,799,932, both also incorporated herein by reference. The liquid etchant solution may be heated, for example from 25 or 30° C. up to about 99° C. in an ambient pressure process chamber.
The words used here are intended to be interpreted in their broadest reasonable manner, even though they are used with a detailed description of certain specific embodiments of the invention. Any words intended to be interpreted in any restricted way, however, will be specifically defined in this detailed description section.
Where the context permits, singular or plural terms may also include the plural or singular term, respectively. Moreover, unless the word “or” is expressly limited to mean only a single item exclusive from the other items in a list of two or more items, then the use of “or” in such a list is to be interpreted as including (a) any single item in the list, (b) all of the items in the list, or (c) any combination of items in the list.
While several embodiments have been shown and described, various changes and substitutions may of course be made, without departing from the spirit and scope of the invention. Many of the method steps described herein, for example, may be performed in a different order than that which is explicitly described. Moreover, many of the embodiments described herein may be used separately or in combination with one or more additional embodiments. The invention, therefore, should not be limited, except by any claims and their equivalents.