1. Field of the Invention
The present invention provides a cleaning method following an opening etch, and more particularly, to a cleaning method that utilizes an in-situ nitrogen (N2) treatment process.
2. Description of the Prior Art
To meet the needs of high integration and high processing speed in integrated circuits (ICs) and in semiconductor fabrication of 0.13 micrometer (μm) or below, a copper (Cu) dual damascene technology in company with low dielectric constants (k values) (low-k; k≦2.9) dielectric layer has now become an effective metal interconnection solution. The reason is because Cu has the features of lower resistance (approximately 30% lower than aluminum) and better electro-migration resistance and so on. Besides, the use of low-k materials as dielectric layers can help to reduce Resistance-Capacitance Time Delay. Therefore, low-k dielectric layer in company with Cu dual damascene in ICs fabrication has become more and more significant.
Low-k dielectric layer is made of carbon doped silicon oxide materials among which at least a portion of the oxygen atoms bonded to the silicon atoms are replaced by one or more organic functional groups such as, for example, an alky group (CH3—), etc. The low-k materials comprise organo-silicate-glasses (OSGs), fluorinated silica glasses (FSGs), hydrogen silsequoxiane (HSQ), methyl silsequoxiane (MSQ), etc. The dielectric constants of those materials are all smaller than about 2.5.
The substitution of one or more organic functional groups for some of the oxygen atoms bonded to the silicon atoms in silicon oxide dielectric materials has a beneficial effect in lowering of the dielectric constant of the carbon doped silicon oxide materials. However, it has been found that the bond formed between the silicon atoms and the organic groups is not as stable as the silicon-oxygen bond formed in conventional silicon oxide materials. Therefore, the bond formed between the silicon atoms and the organic groups is easily damaged during some processes of the Cu dual damascene fabrication such as an opening etch, which is performed to etch the low-k dielectric layer to form opening structures (i.e. trench or via hole), or an ashing process used for removing photoresist layers, etc.
Radicals, which are formed while the bonds formed between the silicon atoms and the organic groups are cleaved, will react with reactive gases used in etch or ashing processes to produce lots of polymers having carbon-fluorine (C—F) bonds remaining on the bottom or the sidewall of the dual damascene structure. Besides, as the improvement of the semiconductor fabrication technology, hard mask layers containing metal layers such as titanium nitride (TiN), etc, are used as etching mask to replace the conventional photoresist layer in the Cu dual damascene fabrication. However, the use of the hard mask layer containing metal layers as an etching mask results in metal residues, which are more difficult to remove than conventional organic photoresist layers, remaining on the bottom or the sidewall of the dual damascene structure. Accordingly, if the dual damascene structure having those polymers or residues were directly filled with a metal conductive layer such as a Cu layer to form a metal interconnection, the resistance would increase.
Accordingly, there are plenty of patents that have disclosed how to clean polymers having carbon-fluorine bonds or metal residues. In U.S patent publication No. 2006/0246717 A1, entitled “Method for fabricating a dual damascene and polymer removal”, a dry clean process is disclosed in which a cleaning gas with hydrogen (H2), oxygen (O2), or carbon tetrafluoride (CF4) is introduced into a reaction chamber, where the etching process has been performed to form the dual damascene structure, to remove the residues resulting form etching the low-k dielectric layer.
In addition, in U.S. Pat. No. 6,713,406, entitled “Method for polymer removal following etch-stop layer etch”, an extra process is disclosed in which the semiconductor substrate is moved to a plasma cleaning chamber for introducing a hydrogen-containing plasma to remove the residue polymers.
However, the aforesaid cleaning methods of using H2/O2/CF4 plasma or only H2-containing plasma still can't remove polymers or metal residues effectively; therefore, the aim of increasing yield hasn't made a breakthrough. Accordingly, after performing the conventional plasma cleaning methods, many times wet cleaning processes are needed to achieve removing polymers or metal residues clean. As increasing in the times of wet cleaning processes, the throughput is decreased and the cost is increased. Furthermore, the cleaning methods using reactive gases such as H2 or CH4, etc, as plasma sources usually result in damaging the low-k dielectric layer or changing the dielectric constant of the low-k dielectric layer so as to affect the capacitances of the corresponding devices.
Accordingly, how to remove the residues resulting from the opening etch with a more effective method without destroying the dual damascene structures or changing the constant value of the low-k dielectric layer is still an important issue that needs to be investigated.