The present invention relates to integrated circuit structures and, in particular, to a method for economically fabricating extremely fine pitch, self-aligned, alternating n-type and p-type stripes that form the voltage blocking region of a superjunction power device.
As discussed in U.S. Pat. No. 5,216,275, which issued on Jun. 1, 1993, it is well known that, in conventional semiconductor power devices, the reverse voltage applied across the n+ region(s) and p+ region(s) is sustained by a lightly doped semiconductor layer, typically referred to as the voltage sustaining layer. For high voltage power devices, the on-resistance of the device is determined primarily by the voltage sustaining layer, since the breakdown voltage of the device depends primarily on the doping concentration and thickness of this layer. The lower the doping concentration and/or the greater the thickness of the voltage sustaining layer, the higher the breakdown voltage, but also the higher the on-resistance.
The '275 patent discloses the utilization of a so-called composite buffer layer just below the active region of a superjunction power device for a vertically configured device, or adjacent to the active region for a laterally configured device. The composite buffer layer contains alternating regions with opposite conductivity types, i.e. alternatingly arranged n-type regions and p-type regions, that improve the relationship between the breakdown voltage and the on-resistance of the device.
Xu et al., “120 V Interdigitated-Drain LDMOS (IDLDMOS) on SOI Substrate Breaking Power LDMOS Limit”, IEEE Transactions on Electron Devices, Vol. 47, No. 10, October 2000, disclose a device structure of the type discussed in the '275 patent. The Xu et al. device, shown in
Although superjunction power device structures of the type disclosed in the '275 patent and in the Xu et al publication are well known, it would be highly desirable have available a low cost method of fabricating fine pitch n-type and p-type stripes for utilization in these structures. Xu et al. demonstrate that the finer the pitch, the lower the on-state resistance obtainable for a given breakdown voltage.
The present invention provides a method for fabricating extremely fine pitch, alternating n-type and p-type stripes that form the voltage blocking region of a superjunction device. The stripes are self-aligned and do not suffer from alignment tolerances. The self-aligned fine pitch enables improvements in on-state resistance, while ensuring that the device is fully manufacturable. In contrast with past fabrication techniques for these structures, only one masking step is required to fabricate the n-type and p-type stripes.
An embodiment of a method of fabricating fine-pitch, self-aligned n-type and p-type stripes for a superjunction device will now be described in conjunction with the partial cross-section drawings provided in
With reference to
Referring now to
Next, as shown in
Next, referring the
The conformal material 108 is then planarized by, for example, by etching the conformal material 108 back or chemically mechanically polishing (CMP) the conformal material 108 to the top surface of the remaining dielectric “pillars”, as shown in
Referring to
Referring to
The remaining conformal material 108 is then stripped, as is the remaining dielectric material 104, resulting in the structure shown in
It should also be understood that the particular embodiments of the invention described above have been provided by way of example and that other modifications may occur to those skilled in the art without departing from the scope and spirit of the invention as expressed in the appended claims and their equivalents.
Number | Name | Date | Kind |
---|---|---|---|
5216275 | Chen | Jun 1993 | A |
6512267 | Kinzer et al. | Jan 2003 | B2 |
6528849 | Khemka et al. | Mar 2003 | B1 |
6576935 | Onishi et al. | Jun 2003 | B2 |
6621122 | Qu | Sep 2003 | B2 |
6673679 | Miyasaka et al. | Jan 2004 | B1 |
6768180 | Salama et al. | Jul 2004 | B2 |
6787872 | Kinzer et al. | Sep 2004 | B2 |
6835993 | Sridevan et al. | Dec 2004 | B2 |