Patent Application
20110189855
1. Field of the Invention
The present invention generally relates to a method for cleaning a surface including Cu. In particular, the present invention is directed to a method for cleaning a surface including Cu by means of a chemical buffing procedure on a substrate using a specially formulated chemical solution which has a pH value approximately between 6 and 8 to remove undesirable residues on the substrate after a main chemical mechanical polishing procedure in order to facilitate a post clean procedure which is later performed on the substrate.
2. Description of the Prior Art
Because Cu has lower electrical resistance than Al, the techniques to form circuits in a semiconductor wafer have changed from etching a bulky conductive material to depositing a conductive material into pre-determined vias and/or trenches. This is generally known as the “damascene method”.
The advantages of Cu damascene method reside in a lower resistance capacitance (RC) delay due to higher electrical conductivity of Cu and its superior electro-migration performance, compared with Al. After the deposition procedure filling the pre-determined vias and trenches, the damascene method in later steps further involves removing superfluous metal by using a chemical mechanical polishing (CMP) for field Cu and barrier removal. Standard Cu CMP process involves two steps. The first one polishes Cu and stops on the barrier layer. The second one requires further removal of the underlying barrier layer and planarization of the entire surface. In some cases, benzotriazole (BTA) and its derivatives such as benzotriazole-5-carboxylic acid, 5-methyl-1H-benzotriazole are used as an inhibitor to facilitate Cu removal. This formulation indeed demonstrates a high planarization efficiency. After the CMP process, the substrate is subject to a post-clean step to completely remove all the residues on the surface.
The high planarization efficiency of this formulation is theoretically based on the formation of a strong BTA-Cu complex located on the surface of the substrate during polishing. Unfortunately, the formation of the strong BTA-Cu complex on the surface also inevitably inhibits the hydrophilic property of the surface of the substrate, and as a result impedes the following post-clean step in order to completely remove all the residues on the surface of the substrate. In the presence of a strong BTA-Cu complex on the surface of the substrate, the relatively hydrophobic surface of the substrate makes the workload of the post-clean step heavy or impossible. In other words, in such a way the post-clean step highly possibly fails to completely remove all the residues on the surface of the substrate as expected. Consequently, the failure of the post-clean step eventually jeopardizes the quality and yield of the semiconductor wafers.
Accordingly, a novel method for cleaning a surface including Cu is still needed to solve the problems in this field and to improve the quality and yield of the semiconductor wafers as well.
The present invention therefore proposes a novel method for cleaning a surface including Cu. The method of the present invention on one hand may solve the problems as described above, and on the other hand the method of the present invention may also improve the quality and yield of the semiconductor wafers.
The present invention proposes a method for cleaning a surface. First, a substrate including Cu and a barrier layer is provided. Second, a first chemical mechanical polishing procedure is performed on the substrate to partially remove Cu. Then, a second chemical mechanical polishing procedure is performed on the substrate. The second chemical mechanical polishing procedure includes at least two steps. The first step is to perform a main chemical mechanical polishing procedure on the substrate to partially remove the barrier layer. The second step is to perform a chemical buffing procedure on the substrate. A chemical solution which has a pH value around 6 to 8 may be used in the second step to remove undesirable residues on the substrate after the main chemical mechanical polishing procedure. Later, a water rinsing procedure is performed on the substrate. Afterwards, a post clean procedure is performed on the substrate after the second chemical mechanical polishing procedure. Optionally, before the second chemical mechanical polishing procedure, a pre-clean procedure which uses the chemical solution may be performed on a polishing pad which is for use in the second chemical mechanical polishing procedure.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
The present invention provides a novel method for cleaning a surface including Cu, preferably for use in a damascene method. The method of the present invention in one aspect may substantially completely remove all the undesirable residues on the surface, and on the other hand the method of the present invention may also facilitate the following post-clean step to completely remove all the residues on the surface of the substrate as expected.
Then, as shown in
Later, as shown in
The second step, as shown in
For example, if the chemical formulation containing benzotriazole (BTA) and its derivatives is employed in the first chemical mechanical polishing procedure, it is believed that a strong BTA-Cu complex is formed on the surface of the copper layer during the procedure. This BTA-Cu complex residue potentially jeopardizes the hydrophilic property of the surface of the substrate 101 and makes the following water rinsing procedure and the post clean procedure difficult or impossible to achieve the predetermined purposes. In other words, the chemical buffing procedure may increase the hydro-affinity of the substrate 101 as well.
The second step uses a specially formulated chemical solution to facilitate and to remove most of undesirable residues left on the surface of the substrate 101. The specially formulated chemical solution generally has a mild pH range, about 6 to about 8 for example. Further, the specially formulated chemical solution may have various ingredients, for example at least one of an oxidizing agent, an organic amine, a chelating agent, a corrosion inhibitor and an amino acid.
For example, the oxidizing agent may be hydrogen peroxide. The organic amine may be a water-soluble or water-miscible organic amine or imine. The chelating agent may be at least one 1,3-dicarbonyl compound. The amino acid may be molecules containing an amine group, a carboxylic acid group and a side chain of different chemical functions, such as an alpha-amino acid. As known to persons of ordinary skills in the art, the specially formulated chemical solution may be optionally a concentrated solution or a diluted solution. The concentration of the chemical solution is at the discretion of persons of ordinary skills in the art when the chemical solution is used. The specially formulated chemical solution may be originally a concentrated solution with or without an organic solvent, or with or without water for the convenience of transportation or long term storage. Water or at least one organic solvent may be added into the specially formulated chemical solution to obtain a desirable concentration.
After the second chemical mechanical polishing procedure, as shown in
Optionally, before the following procedure, a pre-clean procedure may be carried out, as shown in
Afterwards, as shown in
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
