The present invention relates to a semiconductor memory device; and, more particularly, to a method for forming noble metal electrodes.
Recently, an oxidation layer including a noble metal such as platinum(Pt), iridium(Ir), ruthenium(Ru), iridium oxidation layer(IrO), ruthenium oxidation layer(RuO), Pt-alloy or the like has been employed as a top/bottom electrode to increase a capacitance of a capacitor.
A chemical vapor deposition(CVD) or an atomic layer deposition(ALD) having an improved step coverage in comparison with a physical vapor deposition(PVD) must be employed to utilize a noble metal as a capacitor electrode of a high density memory device.
Referring to FIG. 1, there is shown a diagram representing a supply of gas for a CVD of a noble metal in accordance with a conventional method. The drawing represents a reaction gas, a base gas and a noble metal precursor flowing into a reactor during the operation of the CVD.
Referring to FIG. 1, the noble metal precursor and the reaction gas are continuously injected into the reactor during a deposition process for depositing a noble metal thin film.
However, in the CVD, to react the noble metal precursor with the reaction gas sufficiently, it is necessary to increase a temperature of a substrate to be deposited thereon the noble metal thin film; accordingly this means that the CVD must be implemented at a high temperature.
Therefore, a roughness of a surface of the noble metal thin film is increased; and particularly, there is a problem of an agglomeration effect during a thermal process due to a deterioration of the thin film density. And also, a throughput is decreased since a deposition speed is reduced for securing sufficient step coverage.
An ALD has been introduced in order to overcome the above-described shortcomings of the CVD.
Referring to FIG. 2, there is shown a diagram representing a supply of gas for the ALD of a noble metal in accordance with a conventional method. The drawing represents a noble metal precursor flowing into a reactor, a reaction gas and a base gas during the operation of the CVD.
Referring to FIG. 2, a reaction gas and a noble metal precursor flowing into a reactor follow to a pulse type supplying method, which is one of special features of the ALD.
But, in the ALD, a combination between the noble metal precursor and the reaction gas or a condition is selected to obtain a sufficient reactivity; and further, since an advantage of the ALD does not implement if the noble metal precursor and the reaction gas are mixed in a vapor phase, it is necessary to insert a purge time between flowing pulses of the noble metal precursor and the reaction gas, as a result, there is a limit in throughput.
Accordingly, since there does not exist an appropriate gas substituted for the noble metal precursor, a possibility of realization is low, and although the appropriate gas is detected, a throughput becomes low since the purge time between flowing pulses of the noble metal precursor and the reaction gas becomes long to mix with the noble metal precursor and the reaction gas.
It is, therefore, an object of the present invention to solve the above-described problems of the conventional method and to provide a method for forming a noble metal thin film suitable for suppressing the deterioration of a throughput according to enlarging a purge time to prevent the noble metal precursor from mixing with a reaction gas in a reactor during the deposition of an atomic layer.
In accordance with one aspect of the present invention, there is provided a method for forming a metal thin film, the method including the steps of: flowing a reaction gas into a reactor loaded therein a substrate; flowing a metal precursor in a pulse form into the reactor; activating the reaction gas by exciting a plasma in a pulse form to change with a pulse of the metal precursor in the reactor, alternately; and depositing a metal thin film in a unit of an atomic layer by reacting the activated reaction gas with the metal precursor.
In accordance with another aspect of the present invention, there is provided a method for forming a metal thin film, the method including the steps of: loading a substrate in a reactor; flowing a reaction gas and a base gas into the reactor; supplying a metal precursor solved in an organic solvent in a form of a pulse into the reactor; activating the reaction gas by exciting a plasma in a pulse form to change with a pulse of the metal precursor in the reactor, alternately; and depositing a metal thin film in a unit of an atomic layer by reacting the activated reaction gas with the metal precursor.
In accordance with another aspect of the present invention, there is provided a method for forming a metal thin film, wherein the deposition method is implemented by alternately repeating a pulse to inflow the metal precursor and a pulse to excite the plasma and the reaction gas is continuously introduced during the repetitions of the pulse to inflow the metal precursor and the pulse to excite the plasma.