POLISHING METHOD
A polishing method is disclosed, which includes: conditioning a polishing pad, after polishing metal material of a previous wafer; spraying organic acid solution to the polishing pad; spraying deionized water to the polishing pad; performing a water-removing treatment on the polishing pad; and spraying polishing liquid to the polishing pad and polishing metal material of a next wafer. The method can prevent scratches on the surface of metal material of wafers and improve yield rate.
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The present application claims the priority of Chinese Patent Application No. 201010603419.8, entitled “Polishing Method”, and filed on Dec. 23, 2010, the entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing, and particularly relates to a polishing method.
2. Description of Prior Art
With the continuous development of the semiconductor manufacturing process, the critical dimension (CD) of semiconductor devices is getting smaller. Techniques of combining metal gate electrode and gate dielectric layer of High-K material are introduced into the manufacturing of the MOS transistor, to solve the problems caused by small critical dimension devices. Currently, High-K Metal Gate (HKMG) techniques have become the mainstream techniques for 32 nm technology and below, in which chemical mechanical polishing (CMP) on the metal gate electrode is one of the most important step. For the mechanism of CMP, it is described that: a surface layer which is relatively easy to remove is formed by reaction of the surface material of a wafer and polishing liquid, and the surface layer is then mechanically scraped off by polishing pressure and by relative motion between polishing pad and the wafer. Specifically, during the CMP of metal material, polishing liquid is in contact with the surface of the metal material, and metal oxide is generated which is then mechanically scraped off to achieve the effect of polishing.
The most popular material for metal gate electrode is aluminum and Cu—Al alloy (in which aluminum is the major component). Large part of the by-product (i.e. metal oxide, which is mainly alumina and aluminum hydroxide) of the CMP on aluminum is left in the trench of the polishing pad. However, since aluminum has a very low hardness compared with the by-product of the CMP, during the CMP processes on aluminum of follow-up wafers, the surface of the aluminum will be scratched, which affects the functionality and reliability of semiconductor devices. Also the by-product is not dissolved in deionized water; therefore, it is difficult to be totally cleaned by conventional methods (such as spraying deionized water).
SUMMARY OF THE INVENTIONThe present invention is to solve the problem that during the polishing process on metal material of a wafer, by-product left on the polishing pad scratches the surface of the metal material which has a very low hardness compared with the by-product.
To solve the above problem, there is provided a polishing method in the present invention, which includes:
conditioning a polishing pad, after polishing metal material of a previous wafer;
spraying organic acid solution to the polishing pad;
spraying deionized water to the polishing pad;
performing a water-removing treatment on the polishing pad;
spraying polishing liquid to the polishing pad and polishing metal material of a next wafer.
Optionally, the conditioning of the polishing pad is pad ex-situ condition.
Optionally, the spraying organic acid solution to the polishing pad has a flow rate of 100˜1000 ml/min.
Optionally, during the spraying organic acid solution to the polishing pad, a platen has a rotation speed of 10˜150 RPM (Revolutions per Minute).
Optionally, the spraying deionized water to the polishing pad has a flow rate of 100˜1000 ml/min.
Optionally, during the spraying deionized water to the polishing pad, a platen has a rotation speed of 10˜120 RPM.
Optionally, the spraying polishing liquid to the polishing pad includes: polishing liquid covering the entire polishing pad.
Optionally, the spraying polishing liquid to the polishing pad has a flow rate of 100˜1500 ml/min and a spraying time of 5˜100 seconds.
Optionally, the organic acid is oxalic acid, malonic acid, succinic acid, maleic acid, phthalic acid or amino acid.
Optionally, the organic acid solution has a concentration of 0.01˜10 wt %.
Optionally, the metal material is aluminum or aluminum alloy.
In comparison with the conventional technology, the present invention has the following advantages:
By-product, which is generated during the polishing on a previous wafer and is left on the polishing pad, will be dragged out of the trench of the polishing pad during brushing of the polishing pad. In addition, the by-product is dissolved in the organic acid; the dissolved by-product and the organic acid are then removed by spraying deionized water, which effectively removes the by-product left in trenches of the polishing pad and prevents the by-product from scratching the surface of the metal material of a next wafer.
After performing a water-removing treatment on the polishing pad, the spraying polishing liquid to the polishing pad makes the polishing liquid cover the whole polishing pad, which further avoids scratching to the surface of the metal material and improves the yield rate.
Hereunder, the present invention will be described in detail with reference to embodiments, in conjunction with the accompanying drawings.
Embodiments to which the present invention is applied are described, in detail below. However, the invention is not restricted to the embodiments described below.
As discussed in the background, in a conventional polishing process, by-product of CMP of aluminum (i.e. metal oxide generated in oxidation of aluminum by polishing agent, which is mainly alumina and aluminum hydroxide) will be left in trenches of the polishing pad. Since aluminum has a very low hardness compared with the by-product, for example the hardness of aluminum is 160 Mpa while the hardness of aluminum hydroxide is 20000 Mpa, the by-product which is left in the trenches of the polishing pad will scratches the surface of the aluminum during the CMP of a next wafer. The by-product which is left in trenches of the polishing pad can not be found by naked eyes, and is all over the trenches of the polishing pad under a scanning electron microscope (SEM). It is found that the scratches of different sizes on the surface of the metal material are generated by the left by-product. If the metal gate electrode is scratched, the functionality and reliability of semiconductor devices will be affected. Since the by-product is not dissolved in deionized water, it can not be cleaned well even with large amount of deionized water.
To prevent by-product from scratching the surface of the metal material, there is provided a polishing method in an embodiment of the present invention.
S101, conditioning a polishing pad, after polishing metal material of a previous wafer;
S102, spraying organic acid solution to the polishing pad;
S103, spraying deionized water to the polishing pad;
S104, performing a water-removing treatment on the polishing pad; and
S105, spraying polishing liquid to the polishing pad and polishing metal material of a next wafer.
The polishing method will be described in detail with reference to another embodiment, in conjunction with
As discussed above, the metal oxide is the by-product during the polishing of Al, and a large part of the by-product is left in the trenches of the polishing pad 102. If not cleaned well, the by-product in the trenches will scratch the surface of the Al of a next wafer during polishing, which will affect the device performance.
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In the above embodiments, the metal material is aluminum or aluminum alloy. In other embodiments of the present invention, the polishing method provided can also apply to polishing process in which metal material has a low hardness.
In comparison with the conventional technology, the present invention has the following advantages:
By-product, which is generated during the polishing on a previous wafer and is left on the polishing pad, will be dragged out of the trench of the polishing pad during brushing of the polishing pad. In addition, the by-product is dissolved in the organic acid; the dissolved by-product and the organic acid are then removed by spraying deionized water, which effectively removes the by-product left in trenches of the polishing pad and prevents the by-product from scratching the surface of the metal material of a next wafer.
After performing a water-removing treatment on the polishing pad, the spraying polishing liquid to the polishing pad makes the polishing liquid cover the whole polishing pad, which further avoids scratching to the surface of the metal material and improves the yield rate.
Although the present invention has been illustrated and described with reference to the preferred embodiments of the present invention, those ordinary skilled in the art shall appreciate that various modifications in form and detail may be made without departing from the spirit and scope of the invention.
Claims
1. A polishing method, comprising:
- conditioning a polishing pad, after polishing metal material of a previous wafer;
- spraying organic acid solution to the polishing pad;
- spraying deionized water to the polishing pad;
- performing a water-removing treatment on the polishing pad; and
- spraying polishing liquid to the polishing pad and polishing metal material of a next wafer.
2. The polishing method of claim 1, wherein the conditioning of the polishing pad is pad ex-situ condition.
3. The polishing method of claim 1, wherein the spraying organic acid solution to the polishing pad has a flow rate of 100˜1000 ml/min.
4. The polishing method of claim 3, wherein during the spraying organic acid solution to the polishing pad, a platen has a rotation speed of 10˜150 RPM.
5. The polishing method of claim 1, wherein the spraying deionized water to the polishing pad has a flow rate of 100˜1000 ml/min.
6. The polishing method of claim 5, wherein during the spraying deionized water to the polishing pad, a platen has a rotation speed of 10˜120 RPM.
7. The polishing method of claim 1, wherein the spraying polishing liquid to the polishing pad includes: polishing liquid covering the entire polishing pad.
8. The polishing method of claim 7, wherein the spraying polishing liquid to the polishing pad has a flow rate of 100˜1500 ml/min and a spraying time of 5˜100 seconds.
9. The polishing method of claim 1, wherein the organic acid is oxalic acid, malonic acid, succinic acid, maleic acid, phthalic acid or amino acid.
10. The polishing method of claim 1, wherein the organic acid solution has a concentration of 0.01˜10 wt %.
11. The polishing method of claim 1, wherein the metal material is aluminum or aluminum alloy.
Type: Application
Filed: Jul 8, 2011
Publication Date: Jun 28, 2012
Applicant: Semiconductor Manufacturing International (Beijing) Corporation (Beijing)
Inventors: Li Jiang (Shanghai), Mingqi Li (Shanghai)
Application Number: 13/178,968
International Classification: B24B 1/00 (20060101);