This Application claims priority from Japanese Application 2006-319728, filed on Nov. 26, 2006.
This invention relates to a method of manufacturing a semiconductor device and, in particular, to a manufacturing method for removing undesirable nitride regions by using a sacrificial oxide film.
In the process of manufacturing semiconductor devices such as field effect transistors, the semiconductor devices on the silicon substrate are separated by a field insulation film or an STI (Shallow Trench Isolation) film.
JP H8-107205A discloses a technique for separating the semiconductor devices by the field oxide film which is formed by the LOCOS (Local Oxidation of Silicon) method. During the field oxidation process, nitride films are also oxidized so that nitrogen atoms (N) or ammonium molecules (NH3) are produced and form undesirable nitride regions in field regions. In order to remove the undesirable nitride regions, a sacrificial oxide film is formed on the silicon substrate. Then, the silicon substrate is soaked in hydrofluoric acid solution to remove the undesirable nitride regions together with the sacrificial oxide film.
According to JP H8-107205A, the sacrificial oxide film is formed in the atmosphere comprising ozone. However, the temperature of the atmosphere should be lower than 800° C. because the thermal-resistivity of ozone is very poor.
The semiconductor devices on the silicon substrate may be separated by the STI film. During the process of forming the STI film, undesirable nitride regions are also formed on the silicon substrate. One of existing methods of removing the nitride region is to carry out dry or wet oxidation. However, during the dry or wet oxidation, the oxidizing species may diffuse into the STI film and oxidize the silicon substrate in the trench.
The oxidized STI film will expand and apply stresses to the device formation regions adjacent thereto. Such stresses may result in the increase of the junction leakage current.
According to one aspect of the present invention, a method of manufacturing a semiconductor device comprises at least two processes. Under an atmosphere comprising hydrogen and oxygen, a sacrificial oxide film is formed on a silicon substrate that is provided with at least one nitride region. Then, the sacrificial oxide film and the nitride region are removed from the silicon substrate.
An appreciation of the objectives of the present invention and a more complete understanding of its structure may be had by studying the following description of the preferred embodiment and by referring to the accompanying drawings.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
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The STI film 17 defines a plurality of device formation regions 18 into the silicon substrate 10. The undesirable nitride regions 15 are exposed on the edges of the device formation regions 18. If gate oxide films are formed without removing the undesirable nitride regions 15, the undesirable nitride regions 15 inhibit the formation of the gate oxide films. As the result, the gate oxide films have thinner regions on the undesirable nitride regions 15, respectively; the thinner regions of the gate oxide films cause withstand voltage failures of the gate oxide films.
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H2 and O2 react with each other in the reaction chamber to form water. During this process, H2 and O2 generate radical species which contain oxygen (O) atomic radicals and hydroxyl (OH—) molecular radicals. In comparison with the conventional wet or dry oxidation, the radical species according to this embodiment need a shortened time to oxidize exposed regions of the silicon substrate 10, i.e., the device formation regions 18 with no oxide film. In addition, the radical species will lose their energy at the thick oxide region such as the STI film 17 and turn into the oxide species which have the oxidation characteristic same as that of the oxide species generated by wet or dry oxidization. In other words, according to the present embodiment, only the surfaces of the device formation regions 18 can be oxidized without further oxidizing the inner surface of the trench 13 in the silicon substrate 10.
The thickness of the sacrificial oxide film 19 may be adjusted so that it is proportional to the thickness of the liner oxide film 14, in order to ensure complete removal of the undesirable nitride regions 15. Specifically, it is preferable that the thickness of the sacrificial oxide film 19 is 6 nm, 9 nm, and 12 nm when the thickness of the liner oxide film 14 is 10 nm, 15 nm, and 20 nm, respectively. It is more preferable that the thickness of the sacrificial oxide film 19 is three-fifth of the thickness of the liner oxide film 14.
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For evaluation of the effect of the present embodiment, two samples were fabricated and measured, wherein one of the samples was formed in accordance with the earlier technique, while the other was formed in accordance with the present embodiment. Each of the samples had a structure similar to that of
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The present application is based on Japanese patent applications of JP2006-319728 filed before the Japan Patent Office on Nov. 28, 2006, the contents of which are incorporated herein by reference.
While there has been described what is believed to be the preferred embodiment of the invention, those skilled in the art will recognize that other and further modifications may be made thereto without departing from the spirit of the invention, and it is intended to claim all such embodiments that fall within the true scope of the invention.
Number | Date | Country | Kind |
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2006-319728 | Nov 2006 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
4531282 | Sakai et al. | Jul 1985 | A |
4545114 | Ito et al. | Oct 1985 | A |
4555842 | Levinstein et al. | Dec 1985 | A |
4583106 | Anantha et al. | Apr 1986 | A |
4722908 | Burton | Feb 1988 | A |
20070218624 | Satake et al. | Sep 2007 | A1 |
Number | Date | Country |
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8-107205 | Apr 1996 | JP |
2004-186359 | Jul 2004 | JP |
2004-311487 | Nov 2004 | JP |
2004-363121 | Dec 2004 | JP |
Number | Date | Country | |
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20080124892 A1 | May 2008 | US |