1. Field of the Invention
The present invention relates to a method of forming a metal layer using atomic layer deposition and a semiconductor device having the metal layer as a barrier metal layer or the upper or lower electrode of a capacitor.
2. Description of the Related Art
As the integration density of semiconductor devices increases, high dielectric materials having a large dielectric constant have been developed to obtain large capacitance in a small area. For example, a BST (BaSrTiO3) film having a perovskite crystal structure has a dielectric constant of about several hundreds through one thousand in a bulk state, which is different to a silicon nitride film, a silicon oxy-nitride film and a tantalum oxide (Ta2O5) film which are conventionally used for a capacitor. A BST film is advantageous in that a thin dielectric film can be implemented such that an equivalent oxide thickness is less than 10 xc3x85 even when the thickness of the BST film is more than 500 xc3x85. An electrode such as platinum (Pt) which is not oxidized may be used for a BST electrode. An electrode such as ruthenium (Ru) or iridium (Ir), which holds the characteristics of a conductor even if it is oxidized and forms oxide ruthenium (RuO2) or oxide iridium (IrO2), may also be used for a BST electrode.
To obtain a high dielectric BST film having excellent capacitance and leakage current characteristics, a thermal process needs to be performed at a high temperature after depositing BST film. At this time, a barrier metal layer needs to be formed to prevent oxidation of an ohmic layer and a polysilicon plug due to diffusion of oxygen. The barrier metal layer is interposed between the polysilicon plug and a lower electrode.
Conventionally, a titanium nitride (TiN) film is usually used for the barrier metal layer, but the TiN film is oxidized at a temperature of more than 450xc2x0 C. When a high temperature thermal process is performed in an oxygen atmosphere after depositing a BST film, a TiN film and a polysilicon plug are oxidized because platinum (Pt) lets oxygen easily pass through. Especially, a non-conductive TiO2 film is formed when the TiN film is oxidized. In addition, platinum (Pt) and silicon (Si) is diffused into the TiN film, and thus the TiN film cannot act as a barrier metal layer. It is known that the diffusion of Pt and Si is caused by the columnar structure of TiN. Accordingly, it is necessary to restrain the diffusion of oxygen by implementing an amorphous structure which dose not have a grain boundary acting as a path of diffusion.
From this necessity, compounds containing a refractory metal have been studied. A barrier metal layer formed of a compound containing a refractory metal has a problem that adjustability and reproducibility of composition is decreased when the compound is deposited by chemical vapor deposition, due to the complexity of the composition. Accordingly, a reactive sputtering process is usually performed in a nitrogen atmosphere when forming a barrier metal layer of a compound containing a refractory metal. However, a barrier metal layer formed by a sputtering process has a poor step coverage so that it cannot be suitable for a barrier metal layer in a capacitor, the structure of which becomes more complex as the integration density of a semiconductor device increases, for example, a barrier metal layer which is formed at the lower portion of a trench having a high aspect ratio in a trench type capacitor.
To solve the above problems, it is the first object of the present invention to provide a method of forming a metal layer using atomic layer deposition, which has an excellent step coverage and prevents diffusion of oxygen, by which method the composition of the metal layer can be appropriately adjusted so as to easily provide a desirable resistance and conductivity.
It is the second object of the present invention to provide a semiconductor device having the metal layer formed by the above method as a barrier metal layer or the upper or lower electrode of a capacitor.
Accordingly, to achieve the first object, the present invention by a first aspect provides a method of forming a metal layer having an A-B-N structure in which a plurality of atomic layers are stacked by individually injecting pulsed source gases for a reactive metal (A), an amorphous combination element (B) for preventing crystallization of the reactive metal (A) and nitrogen (N), and nitrogen (N) and allowing the source gases to be chemically adsorbed to a semiconductor substrate.
In particular, the source gases are alternately injected in a predetermined order to alternately arrange the atomic layers, and the number of injection pulses of each source gas is adjusted to determine the composition of the metal layer.
The reactive metal (A) may be titanium (Ti), tantalum (Ta), tungsten (W), zirconium (Zr), hafnium (Hf), molybdenum (Mo) or niobium (Nb). The amorphous combination element (B) for preventing crystallization of the reactive metal (A) and the nitrogen (N) may be aluminum (Al), silicon (Si) or boron (B). In addition, the electrical conductivity and resistance of the metal layer may be determined by adjusting the number of injection pulses of a source gas for the amorphous combination element. The content of Al with respect to Ti may be 10-35% in a TiAlN layer when the metal layer is the TiAlN layer.
Further, according to a second aspect of the present invention, a plurality of oxygen diffusion preventing layers, e.g., aluminum oxide layers, may be formed in alternation with a plurality of metal layers so as to form a multiple metal layer including a plurality of metal layers and a plurality of oxygen diffusion preventing layers. Here, the oxygen diffusion preventing layer may be formed by alternately applying pulsed injections of source gases for a metal element and oxygen to the semiconductor substrate including the metal layer. The oxygen diffusion preventing layer may be formed by performing the steps of forming a material layer containing oxygen on the metal layer using atomic layer deposition and thermal-processing the semiconductor substrate including the metal layer and the material layer.
To achieve the second object, the present invention also provides a semiconductor device including an insulating film including a contact hole in a semiconductor substrate, a conductive material film formed on the bottom of the contact hole, and a capacitor including a lower electrode formed on the conductive material film in the contact hole, a high dielectric film formed on the lower electrode and an upper electrode formed on the high dielectric film.
In particular, the semiconductor device has a barrier metal layer between the conductive material film in the contact hole and the lower electrode. The barrier metal layer may be a metal layer formed in an A-B-N structure in which a plurality of atomic layers are stacked by alternately depositing a reactive metal (A), an amorphous combination element (B) for preventing crystallization of the reactive metal (A) and nitrogen (N), and nitrogen (N). The composition ratio of the barrier metal layer may be determined by the number of depositions of each atomic layer.
The reactive metal (A) may be titanium (Ti), tantalum (Ta), tungsten (W), zirconium (Zr), hafnium (Hf), molybdenum (Mo) or niobium (Nb). The amorphous combination element (B) for preventing crystallization of the reactive metal (A) and the nitrogen (N) may be aluminum (Al), silicon (Si) or boron (B). In addition, the electrical conductivity and resistance of the barrier metal layer may be determined by the number of injection pulses of an atomic layer of the amorphous combination element (B) to the total number of injection pulses used for the barrier metal layer.
The semiconductor device of present invention may also include an oxygen diffusion preventing layer, e.g., an aluminum oxide layer, on the metal layer. Accordingly, the barrier metal layer may be formed of a multiple metal layer including a plurality of metal layers and a plurality of oxygen diffusion preventing layers. In addition, a material layer containing oxygen may be formed on the oxygen diffusion preventing layer.
Further, to achieve the second object, the present invention provides a semiconductor device including a semiconductor device having a capacitor including a lower electrode formed on a predetermined material film on a semiconductor substrate, a high dielectric film formed on the lower electrode and an upper electrode formed on the high dielectric film.
In particular, the lower electrode may be formed in an A-B-N structure in which a plurality of atomic layers are stacked by alternately and sequentially depositing atomic layers of a reactive metal (A), an amorphous combination element (B) for preventing crystallization of the reactive metal (A) and nitrogen (N), and nitrogen (N). The composition of the lower electrode can be determined by the number of depositions of each atomic layer. The upper electrode may be formed in the same manner as the lower electrode.
The reactive metal (A) may be titanium (Ti), tantalum (Ta), tungsten (W), zirconium (Zr), hafnium (Hf), molybdenum (Mo) or niobium (Nb). The amorphous combination element (B) for preventing crystallization of the reactive metal (A) and the nitrogen (N) may be aluminum (Al), silicon (Si) or boron (B). In addition, the electrical conductivity and resistance of the lower electrode may be determined by the number of injection pulses of an atomic layer of the amorphous combination element (B) to the total number of injection pulses used for the lower electrode.
As described above, a metal layer (a multiple metal layer) formed by atomic layer deposition of the present invention has a high thermal resistant and high oxidation resistant characteristics. Since the metal layer is formed by individually depositing atomic layers, the step coverage thereof is excellent even in a very compact region. In addition, since individual atomic layers are adsorbed and formed in a predetermined order, the composition ratio of each element contained in the metal layer can be easily adjusted. A metal layer formed by atomic layer deposition of the present invention may be employed as a barrier metal layer, a lower electrode or an upper electrode in a semiconductor device.