Patent Application
20140187051
The present disclosure relates generally to methods for forming semiconductor devices using wet etch technologies.
Advanced semiconductor devices continue to shrink in size. This increases the density and performance of the devices. Additional benefits of increased manufacturing efficiency and lower costs are also realized. As the size of the devices shrink, the processing sequences become more challenging.
One of the critical elements of the semiconductor devices is the gate structure. The design, materials, size, and process sequence details of the gate structure determine attributes such as power consumption, speed, and reliability. As the size of the semiconductor devices has continued to shrink, the gate dielectric material has changed from silicon dioxide to high k dielectric material such as hafnium oxide and the like. Additionally, the conductive materials used as gate electrodes have been selected to have the proper work function for n-type and p-type devices.
Traditionally, the manufacturing of semiconductor devices has employed a “gate first” manufacturing process sequence wherein the gate structure is formed and the remaining elements are formed subsequent to the gate structure formation. The gate structure can be damaged during some of the subsequent processing steps and this has limited the process window (e.g. temperature) of some of the subsequent processing steps. An alternate manufacturing process sequence known as “gate last” or “replacement gate” forms the gate structure and the surrounding elements using a “dummy gate” that is used as a structural surrogate for the gate during the manufacturing process. The dummy gate structure is then removed and the final gate materials are deposited. This allows a broader process window during the manufacturing and does not expose the final gate materials to potential damage during the processing. The removal of the dummy gate structure is a critical step in this manufacturing process sequence.
The following summary of the disclosure is included in order to provide a basic understanding of some aspects and features of the invention. This summary is not an extensive overview of the invention and as such it is not intended to particularly identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented below.
In some embodiments, poly-silicon structures are removed using an ammonium hydroxide-hydrogen peroxide-water (APM) mixture with concentrations between 1:10:20 and 1:1:2 and at temperatures between 20 C and 80 C for times between 1 minute and 60 minutes.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings are not to scale and the relative dimensions of various elements in the drawings are depicted schematically and not necessarily to scale.
The techniques of the present invention can readily be understood by considering the following detailed description in conjunction with the accompanying drawings, in which:
A detailed description of one or more embodiments is provided below along with accompanying figures. The detailed description is provided in connection with such embodiments, but is not limited to any particular example. The scope is limited only by the claims and numerous alternatives, modifications, and equivalents are encompassed. Numerous specific details are set forth in the following description in order to provide a thorough understanding. These details are provided for the purpose of example and the described techniques may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the embodiments has not been described in detail to avoid unnecessarily obscuring the description.
In the first step, 100, of the method described in
The portion of the device illustrated in
The portion of the device illustrated in
The portion of the device illustrated in
At this point in the manufacturing of the device, the dummy gate layer, 212, and the dummy gate dielectric layer, 214, need to be removed so that the high k gate dielectric and the gate electrode materials can be formed. In the next step, 102, of the method of
Traditionally, the dummy gate dielectric layer, 212, is formed from poly-silicon. A common etchant used to remove the poly-silicon is tetramethylammonium hydroxide (TMAH). Although effective at removing poly-silicon, the TMAH process is sensitive to issues such as the pre-doping levels of the poly-silicon. The TMAH is ineffective at removing silicon nitride, so if silicon nitride residues are present, the poly-silicon removal will be incomplete. Additionally, the TMAH etch process is sensitive to the crystal orientation of the poly-silicon. Therefore, the etch may be non-uniform and may result in poly-silicon residues left at the bottom or the sidewall of the opening, 316, illustrated in
In some embodiments, a solution of ammonium hydroxide-hydrogen peroxide-water (APM) is used to remove the dummy gate dielectric layer, 212. The ratio of the constituents of the solution can range from 1:10:20 (ammonium hydroxide : hydrogen peroxide : water) to 1:1:2, such as 1:1:5 or 1:5:20. In some embodiments, the concentration of the ammonium hydroxide is less than or equal to the concentration of water and the ratio of the ammonium hydroxide to water constituents can range from 1:1 to 1:20. The APM solution may be used to remove the poly-silicon at temperatures between 20 C and 80 C, such as between 60 C and 65 C. The time required for the APM solution to remove the poly-silicon can vary between 1 minute and 60 minutes and will depend on parameters such as APM solution concentration, APM solution temperature, poly-silicon thickness, etc. In some embodiments, time required for the APM solution to remove the poly-silicon can vary between 5 minutes and 60 minutes, such as 15 minutes, 25 minutes, or 50 minutes. After the dummy gate layer, 212, is removed, the sample may be rinsed in deionized water.
In some embodiments, the APM solution includes a ratio of ammonium hydroxide:hydrogen peroxide:water of 1:1:5 at a temperature between 60 C and 65 C. In some embodiments, the APM solution includes a ratio of ammonium hydroxide:hydrogen peroxide:water of 1:5:20 at a temperature between 60 C and 65 C.
After the poly-silicon dummy gate layer, 212, is removed, the dummy gate dielectric layer, 214, is removed, typically using a dilute hydrofluoric acid solution, as is well known in the art.
In some embodiments, a thin native oxide forms on top of the dummy gate dielectric layer, 214. As noted previously, the etch rate of silicon oxide in the APM solution is very slow. Therefore, the thin native oxide can be removed by exposing the substrate to a dilute hydrofluoric acid solution prior to the removal of the poly-silicon. This will produce a clean, oxide free poly-silicon surface that can be removed using the APM solution described previously. Alternately, it may be possible to add a small amount of hydrofluoric acid to the APM solution. The hydrofluoric acid constituent would serve to etch the native oxide layer and allow the APM solution to remove the poly-silicon. The concentration of the hydrofluoric acid is maintained at a low level so that it does not result in significant loss of spacer or ILD layer material.
Returning to
Although the foregoing examples have been described in some detail for purposes of clarity of understanding, the invention is not limited to the details provided. There are many alternative ways of implementing the invention. The disclosed examples are illustrative and not restrictive.
