Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2002-08-26
2004-07-06
Versteeg, Steven (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298060, C204S298080, C204S298110
Reexamination Certificate
active
06758948
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the deposition of films, or layers, primarily in the fabrication of integrated circuits, but also in the manufacture of other products.
Integrated circuit fabrication procedures are composed of a variety of operations, including operations for depositing thin films on a semiconductor substrate, or wafer. Typically, a large number of identical integrated circuits are formed on such a wafer, which is then cut, or diced, into individual circuit chips.
Given the small dimensions of these integrated circuits, the quality of each deposited layer or film has a decisive influence on the quality of the resulting integrated circuit. Basically, the quality of a film is determined by its physical uniformity, including the uniformity of its thickness and its homogeneity.
In particular, several process steps require the ability to deposit high quality thin conductive films and to deposit conducting material in both high aspect ratio trenches and vias (and/or contacts).
According to the current state of the art, films, or layers, are deposited on a substrate according to two types of techniques: physical vapor deposition (PVD), which encompasses various forms of sputtering; and chemical vapor deposition (CVD). According to each type of procedure, a layer of material composed of a plurality of atoms or molecules of elements or compounds, commonly referred to collectively as “adatoms”, is deposited upon a substrate in a low pressure region.
In typical PVD procedures, a target material is sputtered to eject adatoms that then diffuse through the low pressure region and condense on the surface of the substrate on which the layer is to be deposited. This material forms a layer on the substrate surface. Continuation of this process leads to the growth of a thin film. The sputtering itself is a physical process which involves accelerating heavy ions from an ionized gas, such as argon, toward the target surface, where the ions act to dislodge and eject adatoms of the target material as a result of momentum exchange which occurs upon collision of the ions with the target surface.
On the other hand, in CVD procedures, two or more gases are introduced into a vacuum chamber where they react to form products. One of these products will be deposited as a layer on the substrate surface, while the other product or products are pumped out of the low pressure region.
Both types of deposition processes are advantageously performed with the assistance of a plasma created in the low pressure region. In the case of PVD processes, it is essential to provide a primary plasma to generate the ions that will be used to bombard the target. However, in these processes, a secondary plasma may be formed to assist the deposition process itself. In particular, a secondary plasma can serve to enhance the mobility of adatoms in proximity to the substrate surface.
Although CVD processes are widely used in the semiconductor fabrication industry, processes of this type have been found to possess certain disadvantages. For example, in order to employ CVD for a particular deposition operation, it is necessary to be able to create a chemical reaction that will produce, as one reaction product, the material to be deposited. In contrast, in theory, any material, including dielectric and conductive materials, can be deposited by PVD and this is the process of choice when deposition must be performed while maintaining the substrate temperature within predetermined limits, and particularly when deposition is to be performed while the substrate is at a relatively low temperature.
A film composed of a dielectric material can be formed by PVD either by directly sputtering a target made of the dielectric material, or by performing a reactive sputtering operation in which a conductive material is sputtered from a target and the sputtered conductive material then reacts with a selected gas to produce the dielectric material that is to be deposited. One exemplary target material utilized for direct sputtering is silicon dioxide. PVD can also be used for conductive layers.
The simplest known PVD structure has the form of a planar diode which consists of two parallel plate electrodes that define cathode constructed to serve as the target and an anode which supports the substrate. A plasma is maintained between the cathode and anode and electrons emitted from the cathode by ion bombardment enter the plasma as primary electrons and serve to maintain the plasma.
While a target made of a conductive material can be biased with a DC power supply, a target made of a dielectric material must be biased with high frequency, and particularly RF power, which can also assist the generation of ions in the plasma. The RF power is supplied to the target by a circuit arrangement including, for example, a blocking capacitor, in order to cause the applied RF power to result in the development of a DC self-bias on the target.
Since the planar diode configuration is not suitable for efficient generation of ions, DC and RF magnetron configurations have been developed for producing a magnetic field having field lines that extend approximately parallel to the target surface. This magnetic field confines electrons emitted from the target within a region neighboring the target surface, thereby improving ionization efficiency and the creation of higher plasma densities for a given plasma region pressure.
Additional configurations followed including the variety of cylindrical magnetrons. Several versions of the cylindrical magnetron variation have appeared in the patent prior art, in particular, the family of U.S. Pat. Nos. 4,132,613, 4,132,612, 4,116,794, 4,116,793, 4,111,782, 4,041,353, 3,995,187, 3,884,793 and 3,878,085.
As described in Thornton in “Influence of Apparatus Geometry and Deposition Conditions on the Structure and Topography of Thick Sputtered Coatings”, J. Vac. Sci. Technol., Vol 11, No 4, 666-670 (1974), the structure of a deposited metal film is dependent on both the temperature of the substrate and the gas pressure within the plasma region. The highest film quality can be achieved when the substrate is at a relatively low temperature and conditions are created to effect a certain level of bombardment of the substrate with ions from the plasma while the film is being formed. When optimum conditions are established, a dense, high quality thin film which is substantially free of voids and anomalies can be achieved.
It is known in the art that bombardment of the substrate with ions having energies under 200 eV, and preferably not greater than 30 eV, and more preferably between 10 and 30 eV, can result in the formation of dielectric films having optimum characteristics. This has been found to be true in the case of, for example, thin films of SiO
2
and TiO
2
.
Achievement of high deposition rates and optimum quality of the deposited layer requires a high energy density in the plasma adjacent both the target and the substrate. Plasma energy flux (with units of J/m
2
-sec) is the product of the ion flux (with units of number of ions/m
2
-sec) and ion energy (with units of J/ion).
However, whereas the highest possible ion energy is desired adjacent the target to maximize the target sputtering rate, it has been found that the ion energy adjacent the substrate, i.e., the energy of ions that bombard the substrate, should be less than the maximum achievable for reasons relating primarily to layer quality.
For example, a reduced ion energy in the plasma adjacent the substrate reduces the rate of implantation of plasma gas ions into the substrate, as well damage to the substrate subsurface, and the creation of voids and mechanical stresses in the layer being formed.
Therefore, while it is desirable to have a high ion density in the plasma adjacent both the target and the substrate, different desiderata exist with respect to plasma ion energy. The plasma density in these systems are quite uniform, ie within +/−20% due to diffusion.
The plasma energy flux to the target and to the substrate are eac
Pillsbury & Winthrop LLP
Tokyo Electron Limited
Versteeg Steven
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