Abstract:
A method for making an SOI semiconductor device including a silicon substrate includes implanting oxide and Nitrogen into the substrate and then annealing to drive Oxygen and Nitrogen through and below the buried oxide layer. The implanted species interact with the Silicon matrix of the substrate to establish field isolation areas that extend deeper than the buried oxide layer of the SOI device, to ensure adequate component isolation.

Description:
This is a divisional patent application of application Ser. No. 09/479,493, filed Jan. 7, 2000. This application claims the benefit of U.S. Provisional Application for patent application Ser. No. 60/169,695, filed on Dec. 7, 1999 and entitled METHOD FOR ESTABLISHING COMPONENT ISOLATION REGIONS IN SOI SEMICONDUCTOR DEVICE. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the fabrication of-semiconductor devices, and more particularly to isolating components in SOI devices. 
     BACKGROUND OF THE INVENTION 
     Semiconductor chips are used in many applications, including as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices that use semiconductor chips advantageously is minimized, while nevertheless improving the memory capacity and computing power of the devices. Moreover, it is desirable that the devices operate at very fast speeds. 
     Among the things that can limit the speed with which semiconductor devices operate is extraneous capacitances in the devices. More specifically, undesired electrical capacitance can arise from the portions of the source and drain regions that overlap the gate region, as well as from the source and drain junctions. To limit junction depth and, hence, to decrease junction capacitance, so-called “silicon on insulator”, or “SOI”, technology, can be used in which a layer of oxide is buried in the silicon substrate to act as a stop to dopant diffusion (and, hence, to act as a stop to source/drain junction depth). 
     To isolate adjacent components on a semiconductor device, isolation regions are formed in the substrate between the components. In the context of SOI devices, the isolation regions are formed prior to source/drain dopant implantation by forming trenches down to the buried oxide layer and then filling the trenches with dielectric. As understood by the present invention, however, because the depth at which buried oxide layers are typically formed in a substrate can be as close as 1000 Å to the surface of the substrate to limit junction capacitance, at such a depth the isolation trenches can be insufficiently deep to adequately isolate adjacent device components from each other. With the above shortcomings in mind, the present invention makes the critical observation that it is possible to limit the depth of the source/drain junctions in semiconductor devices (and, hence, decrease the junction capacitances) using shallow buried oxide layers, while nevertheless forming isolation regions between adjacent components that are sufficiently deep to adequately isolate the components from each other. 
     BRIEF SUMMARY OF THE INVENTION 
     A method for making an SOI semiconductor device includes implanting Oxygen and/or Nitrogen into the substrate in intended isolation regions. The method also includes heating the substrate to cause the Oxygen and/or Nitrogen to diffuse and interact with the substrate to establish isolation regions, such that the isolation regions extend from the surface of the substrate to below the buried oxide layer of the SOI device. After forming the isolation regions, source and drain regions can be conventionally formed. 
     In a preferred embodiment, the heating act includes annealing the substrate. In this embodiment, to promote a uniform Oxygen concentration in the isolation regions, the Oxygen can be implanted using an implantation energy that increases over time. The substrate can also be annealed in an oxygenated ambient atmosphere to replenish the Oxygen concentration near the surface of the substrate as the Oxygen diffuses into the substrate, to promote a uniform Oxygen concentration in the isolation regions. In still another embodiment, instead of annealing the substrate after Oxygen implantation, the substrate can be oxidized to promote a uniform Oxygen concentration in the isolation regions. 
     In another aspect, an SOI semiconductor device includes a substrate and plural component isolation regions formed in the substrate. The isolation regions include Silicon and at least one of: Oxygen, and Nitrogen. 
     In still another aspect, a method for making an SOI semiconductor includes providing a semiconductor substrate that defines a surface and that has a buried oxide layer, and then establishing component isolation regions in the substrate which extend from the surface to below the buried oxide layer. 
     Other features of the present invention are disclosed or apparent in the section entitled DETAILED DESCRIPTION OF THE INVENTION. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     For understanding of the present invention, reference is made to the accompanying drawing in the following DETAILED DESCRIPTION OF THE INVENTION. In the drawings: 
     FIG. 1 is a flow chart of the present process; 
     FIG. 2 is a side view of a portion of a semiconductor device made in accordance with the present in invention, after masking and before isolation species implantation; 
     FIG. 3 is a side view of a portion of a semiconductor device made in accordance with the present invention after implantation of the isolation species; and 
     FIG. 4 is a side view of a portion of a semiconductor device made in accordance with the present invention, after stripping away the mask and annealing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention are equally applicable to a wide range of semiconductor and integrated circuit design and manufacture regimens, including but not necessarily limited to the production of non-volatile memory devices. All such implementations are specifically contemplated by the principles of the present intention. 
     Referring initially to FIGS. 1 and 2, at block  10  in FIG. 1 a semiconductor device  12  (FIG. 2) is provided which includes a silicon substrate  14 . In one preferred embodiment, the device  10  is an SOI device. Accordingly, a buried oxide layer  16  is disposed in the substrate  14  at a depth “d” from the surface  18  of the substrate  14  of about one thousand Angstroms (1000 Å). 
     Proceeding to block  20  of FIG.  1  and still referring to FIG. 2, the surface  18  is oxidized such that a surface oxidation layer  22  is formed thereon. Also, intended source/drain regions  24  of the substrate  14  are masked with, e.g., photoresist layers  26  in accordance with masking principles known in the art. Intended isolation regions  28  of the substrate  14 , however, are not masked. 
     Proceeding to block  30  of FIG.  1  and now referring to FIG. 3, Nitrogen and/or Oxygen are implanted into the intended isolation regions  28 , as indicated by the arrows  32 . Preferably, both Nitrogen and Oxygen are implanted at block  30 . 
     Moving to block  34  of FIG.  1  and referring to FIG. 4, the mask layers  26  are stripped away and the substrate  14  is annealed, to drive the implanted species below the buried oxide layer  16 . In other words, a bottom boundary  36  of each isolation region  28  is spaced further from the surface  18  of the substrate  14  than is the buried oxide layer  16 , i.e., the isolation regions  28  extend from the surface  18  of the substrate  14  to a depth that is deeper in the substrate  14  than the buried oxide layer  16 . As intended by the present invention, the Oxygen and/or Nitrogen diff-use and interact with the Silicon matrix of the substrate  14  to establish the isolation regions  28  during the annealing step. 
     In one preferred embodiment, to promote a uniform Oxygen and/or Nitrogen concentration in the isolation regions  28 , the implanted species, and in particular the Oxygen, is implanted using an implantation energy that increases over time. In other words, the implantation energy is varied as appropriate to establish a uniform Oxygen concentration profile from the surface  18  of the substrate  14  to the bottom boundaries  36  of the isolation regions  28 . Or, the substrate  14  can be annealed in an oxygenated ambient atmosphere, such that the concentration of Oxygen near the surface  18  of the substrate  14 , which otherwise could be depleted of Oxygen as the Oxygen diff-uses deeper into the substrate  14  during annealing, is fortified, thereby promoting a uniform Oxygen concentration profile. Or yet again, the annealing step at block  34  can be replaced by simply oxidizing the substrate  14  to promote a uniform Oxygen concentration in the isolation regions. 
     Once the isolation regions  28  have been formed, the process moves to block  38 , wherein the surface oxidation layer  22  is etched away by means known in the art. Manufacturing is conventionally completed at block  40 , wherein appropriate barrier oxides and nitrides are formed, source and drain dopants are implanted into the substrate  14 , gate stacks are formed on the surface  18  of the substrate  14 , and contacts and interconnects are formed. 
     The present invention has been particularly shown and described with respect to certain preferred embodiments of features thereof However, it should be readily apparent to those of ordinary skill in the art that various changes and modifications in form and detail may be made without departing from the spirit and scope of the invention as set forth in the appended claims. In particular, the use of: alternate layer deposition or forming methodologies; etching technologies; masking methods; lithographic methods, passivation and nitridization techniques; as well as alternative semiconductor designs, as well as the application of the technology disclosed herein to alternate electronic components are all contemplated by the principles of the present invention. The invention disclosed herein may be practiced without any element which is not specifically disclosed herein. The use of the singular in the claims does not mean “only one”, but rather “one or more”, unless otherwise stated in the claims.