Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With plasma generation means remote from processing chamber
Reexamination Certificate
1999-11-12
2004-06-15
Hassanzadeh, Parviz (Department: 1763)
Adhesive bonding and miscellaneous chemical manufacture
Differential fluid etching apparatus
With plasma generation means remote from processing chamber
C156S345480, C118S7230IR, C118S7230IR, C118S7230ME, C118S7230ER
Reexamination Certificate
active
06749717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to integrated circuit manufacturing processes and, more specifically, to a novel process for plasma fabrication procedures for semiconductor substrates using conductive materials.
2. Background
In order to build an integrated circuit, many active devices need to be fabricated on a single substrate. The current practice in semiconductor manufacturing is to use thin film fabrication techniques. A large variety of materials can be deposited using thin films, including metals, semiconductors insulators and the like. The composition and uniformity of these thin layers must be strictly controlled to facilitate etching of submicron features. The surface of the substrate, most often a wafer, must be planarized in some way to prevent the surface topography from becoming increasingly rough with each added thin film level. The formation of such films is accomplished by a large variety of techniques.
Chemical vapor deposition (CVD) processes are often selected over competing deposition techniques because they offer numerous advantages, including the abilities of CVD to deposit films from a wide variety of chemical compositions and provide improved conformality.
In general a CVD process includes the following steps: a selected composition and flow rate of reactant and inert gases are dispatched into a reaction chamber; the gases move to the substrate surface; the reactants are adsorbed on the substrate surface; the species undergo a film-forming chemical reaction and the by-products of the reaction are desorbed from the surface and conveyed away from the surface.
Plasma enhanced CVD (PECVD) uses a plasma or glow discharge with a low pressure gas, to create free electrons which transfer energy into the reactant gases. This allows the substrate to remain at a lower temperature than in other CVD processes. A lower substrate temperature is the major advantage of PECVD and provides film deposition methods for substrates that do not have the thermal stability necessary for other processes that require higher temperature conditions. In addition, PECVD can enhance the deposition rate when compared to thermal reactions alone, and produce films of unique compositions and properties.
In most applications it is desired that thin films maintain a uniform thickness and freedom from cracks or voids. As thin films cross steps that occur on the surface of the underlying substrate, they often suffer unwanted deviations from the ideal conformality, such as thinning or cracking. A measure of how well a film maintains its nominal thickness is referred to as the step coverage of the film. The height of the step and the aspect-ratio (the height-to-spacing ratio of two adjacent steps) of a feature being covered determine the expected step coverage. Step coverage of 100% is ideal, but normally a value less than 100% is specified as acceptable, for any given application.
The semiconductor industry's continuing drive towards closer and smaller device geometries, has placed an increased demand for cost-effective solutions for the problem of higher step coverage and planarization. New plasma sources are being developed because traditional sources cannot extend to the sub-0.5 micron level of processing necessary for the more rigorous device geometries. Fabrication processes that are employed in response to the necessity of good conformality in the face of the submicron geometries include plasma enhanced directional sputtering, plasma enhanced etching and plasma enhanced chemical vapor deposition. CVD processes have been developed for some metals, for example titanium and titanium nitride, both of which can be put to use in 0.35 and 0.25 micron devices. Because these typical back-end-of-the-line (BEOL) fabrication processes must be done at low temperatures (<450° C.) to protect the integrity of previously deposited layers and to ensure that dopants don't diffuse excessively, they are typically based on PECVD, which, as described above, can be achieved at low temperatures. These low temperature, high aspect ratio coverage PECVD process requirements are being met with low pressure, high density plasma (HDP) based processes. To achieve the good step coverage and gap fill desired, HDP CVD systems are run at a high flow rate to achieve adequate deposition. At the same time HDP CVD process pressures need to be relatively low for the plasma to operate properly—that is at high densities.
To deposit or etch conductive or metal films using HDP processes, the plasma must necessarily be generated using inductive coupling. The fabrication by deposition or removal of metal thin films in an inductively coupled high density plasma reactor is desirable because of the advantages it provides, including: lower processing temperatures and higher step coverage, as discussed above, as well as shorter processing times and denser films.
However, in the case of inductively coupled (IC) plasma procedures there is no capacitive coupling to the chamber walls, and any conductive material deposition on the chamber walls blocks the inductive power coupling to the plasma. For the deposition of conductive materials and metal films this means that the reactor chamber walls must be cleaned quite frequently in order to prevent the deposition of conductive materials on the chamber walls which blocks the IC plasma fabrication steps.
Traditionally the only way to remove ionic and metallic contaminants from any plasma reaction chamber or furnace tube has been to clean the tubes with wet etching, often with the simple method of manually rolling them, half submerged, in an acid bath. Cleaning of the reaction chamber in this manner involves removing the dirty quartz tube, install a previously cleaned tube, and cleaning the dirty tube for future use. This method of cleaning is unsatisfactory for many reasons. Tearing down a furnace is a time consuming and difficult process that requires from 4-24 hours and has been likened to “open heart surgery”. It requires not merely a tube change, but also a particle and process requalification of the furnace. The result is that any cleaning regime selected must balance the need to clean the furnace tube with the potential product yield loss and furnace downtime. In addition, a very significant disadvantage of any wet clean process is the increasingly strict regulatory controls placed on wet chemical disposal making it increasingly more costly and troublesome.
Several in-situ cleaning options exist for other CVD systems but metal and other conductive material contamination cannot be removed completely with any of the existing methods. Any conductive deposition on the chamber walls in an IC plasma system blocks the power coupling to the plasma. The significance of this is that in the specific case of inductively coupled plasma chambers, since there is no capacitive coupling to the chamber walls, cleaning by generating a plasma containing an etchant gas to remove conductive material is not possible. With the growing need for more frequent cleaning of furnace tubes, as is the case when using IC PECVD to deposit metals and conductive films an alternative cleaning method is still needed.
SUMMARY OF THE INVENTION
The present invention is a process for plasma enhanced fabrication of conductive materials on a semiconductor substrate comprising the steps of placing the substrate in an inductively coupled (IC) plasma reaction chamber and maintaining the chamber under vacuum pressure while introducing at least a preselected reactant species gas, and optionally a carrier gas into the chamber for a preselected fabrication procedure on the substrate. A plasma is generated from the gas or gases within the chamber using a power source inductively coupled to the reaction chamber. After the consequent fabrication procedure the substrate is removed from the chamber, and any conductive material is in-situ removed from the inside of the chamber to remove any blocking of the inductive power couple to the reaction chamber.
In one embodiment the in-situ removal of con
Sandhu Gurtej S.
Sharan Sujit
Brantley Charles
Hassanzadeh Parviz
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