This invention relates generally to methods of cleaning and etching silicon surfaces, and more specifically to the use of NF to preclean wafers at low temperatures. During the fabrication of semiconductor devices using silicon wafers , formation may occur on the silicon surfaces of the silicon wafers. Contaminants and impurities, such as epitaxial silicon deposition or oxide layer growth, after removing the contaminants, if wafer is exposed to oxygen, the silicon atoms on the wafer surface immediately combine with oxygen to form a thin SiO film (approximately 20A), this natural oxide SiO may interfere with the deposition process, for example, an polycrystalline film may be formed when epitaxial film deposition is required, resulting in device noise or performance degradation.
In addition, natural oxides reduce the yield of semiconductor devices. As device geometries become smaller, the formation of natural oxides and the presence of various contaminants on the silicon surface become increasingly serious problems. This Natural oxides reduce control and reproducibility in semiconductor device manufacturing processes. Therefore, in the manufacturing process of semiconductor device , the natural oxide film and contaminants must be removed before depositing and growing certain films, so that the silicon surface of wafer does not contain oxides and contaminants before epitaxial deposition. Traditional cleaning methods use the process chamber of a chemical vapor deposition (CVD) reactor to clean the native oxides on the wafer and for wafer processing, which is the deposition of thin films onto the wafer. A method called hydrogen bake uses hydrogen to reduce the natural oxides in the silicon layer. For hydrogen bake, the wafer is brought to a high temperature, such as 1150°C. Hydrogen is pumped into the chamber where it interacts with the wafer surface. reaction, reducing the natural oxides in the silicon, thereby removing the natural oxides, and then cooling the chamber and/or wafer to the temperature at which the silicon was deposited; another cleaning method is to use a hydrochloric acid etch, often combined with a hydrogen bake, In this method, the wafer is brought to temperature in the reaction chamber (i.e., 1150°C. or more) and then subjected to a conventional hydrochloric acid etch (e.g., 1-5% hydrochloric acid in H2) to remove the wafer formed by Silicon and metal contamination that damages the wafer surface caused by polishing. Therefore, the natural oxides and damage on the silicon surface are removed, and then the temperature of the wafer is lowered for epitaxial deposition or oxide growth. These cleaning techniques require the wafer to reach high temperatures in the epitaxial deposition process chamber, which is higher than normally required. At high temperatures, the strength of silicon wafers decreases, leading to defects such as slippage, which leads to an increase in yield loss.
The high temperatures at which the wafer is placed inside the programming chamber can also lead to undesirable self-doping. The wafer typically includes a semiconductor substrate, usually silicon, in which n-type and p-type regions are formed. During semiconductor manufacturing processes, the substrate The heavily doped part is usually covered by a lightly doped epitaxial layer to achieve a sharp connection between the heavily doped substrate and the lightly doped epitaxial layer. However, when the wafer temperature rises to the cleaning temperature, the dopants from the heavily doped areas evaporate and are deposited on the chamber walls and other parts of the wafer. After cleaning the wafer, a lightly doped epitaxial layer is deposited on the wafer. , during this deposition process, dopants on the chamber walls may fall off and contaminate the epitaxial layer, causing unwanted and unpredictable changes in the dopant concentration in the epitaxial layer.
During the semiconductor manufacturing process, the heavily doped part of the substrate is usually covered by a lightly doped epitaxial layer to achieve a sharp connection between the heavily doped substrate and the lightly doped epitaxial layer. However, when the wafer temperature rises to At cleaning temperature, dopants from the heavily doped areas evaporate and are deposited on the chamber walls and other parts of the wafer. After cleaning the wafer, a lightly doped epitaxial layer is deposited on the wafer. During this deposition process , dopants on the chamber walls may fall off and contaminate the epitaxial layer, causing unwanted and unpredictable changes in the dopant concentration in the epitaxial layer.
Another disadvantage of traditional cleaning methods using process chambers is that the throughput of the system is reduced due to the time required to clean the wafers. Both cleaning and epitaxial deposition are completed in the process chamber, so these processes must be performed in sequence. , throughput can be increased by adding more process chambers to the system, however, since process chambers are expensive, using more process chambers to increase throughput will increase the cost of the system. Therefore, a method to clean the silicon surface is needed to overcome the above drawbacks.
uses fluorine-containing raw gas (preferably NF) to clean the silicon surface of the wafer to generate fluorine atoms, which react with natural oxide and silicon in a separate pre-cleaning chamber. The wafer to be processed is first Cleaning is performed in a separate pre-cleaning chamber. NF gas is used to generate fluorine atoms and then enters the pre-cleaning chamber. Once the fluorine atoms contact the silicon surface of the wafer, the natural oxides and contaminated silicon will be removed. During the cleaning process , the wafer and pre-clean chamber can be kept at room temperature, or their temperature can be increased for smoother surfaces and higher etch rates. Therefore, the natural oxides and contaminated silicon on the wafer surface are removed in the pre-cleaning chamber. After cleaning, the wafers are transferred from the pre-cleaning chamber to the process chamber for classified deposition. In some embodiments, the pre-cleaning chamber can be configured to move to both sides. One or more process chambers provide wafers.
By pre-cleaning at temperatures significantly lower than the process temperature or temperatures used in previous cleaning methods, the method according to the present invention reduces self-doping, slip problems associated with high temperatures, and in addition uses a separate pre-cleaning chamber with In sharp contrast to traditional technology, in which the process chamber of the CVD reactor is used to clean the native oxides on the wafer and for wafer processing, that is, the deposition of thin films on the wafer, by providing a separate pre-cleaning chamber, it can be improved Throughput, because the process chamber does not need to double as a cleaning chamber and can therefore be used to process wafers continuously, the pre-cleaning chamber and processing chamber can now also be optimized to individually clean and process wafers.
This article provides a method and structure for using NF gas to clean the silicon surface of the wafer at reduced temperatures by placing the wafer in a separate pre-cleaning chamber before epitaxial deposition. The ability to reduce slip and self-doping issues associated with high-temperature cleaning processes. Additionally, by cleaning the wafers in a separate pre-clean chamber, the system can increase throughput at minimal cost because cleaning and deposition can now be performed in parallel. performed, and because pre-cleaning chambers are much more expensive than procedure chambers.
The use of separate cleaning chambers allows the deposition chamber to be dedicated only to the epitaxial deposition process, so the cleaning and epitaxial growth processes can be performed in parallel on separate wafers, and therefore, throughput is increased. Because preclean chambers are much less expensive than deposition chambers, this increases the cost efficiency of the system. Typically, the cost of a preclean chamber can be greater than the cost of a deposition chamber, in part because preclean chambers require complex heating, cooling, gas flow, and monitoring. The requirement, therefore, is to use NF gas in a separate pre-clean chamber to etch and clean silicon wafers at low temperatures, improving throughput and system cost efficiency while reducing slip, self-doping and other high-temperature issues.
