Semiconductor memory

Abstract

Manufacturing processes for phase change memory have suffered from the problem of chalcogenide material being susceptible to delamination, since this material exhibits low adhesion to high melting point metals and silicon oxide films. Furthermore, chalcogenide material has low thermal stability and hence tends to sublime during the manufacturing process of phase change memory. According to the present invention, conductive or insulative adhesive layers are formed over and under the chalcogenide material layer to enhance its delamination strength. Further, a protective film made up of a nitride film is formed on the sidewalls of the chalcogenide material layer to prevent sublimation of the chalcogenide material layer.

Description

TECHNICAL FIELD [0001] The present invention relates to a technique that is effective when applied to semiconductor integrated circuit devices which employ phase change memory cells formed of a phase change material such as chalcogenide. BACKGROUND ART [0002] Mobile devices, typified by cellular phones, use a semiconductor memory such as a DRAM, SRAM, or flash memory. A DRAM provides large capacity but its access speed is low. A SRAM, on the other hand, is high-speed memory, but is not suitable for forming a large capacity memory, since each cell requires a number of transistors (4 to 6 transistors) and hence it is difficult to produce highly integrated SRAM. DRAM and SRAM must continuously receive power to retain data; that is, they are volatile memories. Flash memory, on the other hand, is a nonvolatile memory; it does not need to continuously receive power to electrically retain data. However, the flash memory is disadvantageous in that its program / erase count is limited to a max...

AI Technical Summary

Benefits of technology

[0018] The major effects of the present invention will now be briefly described.

[0019] The adhesive layers formed over and under the chalcogenide material layer can prevent delamination of the chalcogenide material layer during the manufacturing process. Further, the protective film formed on the sidewalls of the chalcogenide material layer can prevent sublimation of the chalcogenide material layer during the manufacturing process. These arrangements improve the phase change memory manufacturing process in such a way as to reduce variations in the electrical characteristics of the phase change memory, as well as preventing reliability degradation.BEST MODES FOR CARRYING OUT THE INVENTION

[0020] A first means of the present invention is to form adhesive layers over and under the chalcogenide material (layer) so as to enhance the adhesive strength of the chalcogenide material (at its interfaces with the overlying and underlying layers).

[0021] First, the effects of these adhesive layers will be described. We formed GeSbTe films on SiO2 films to a thickness of 100 nm, and performed a scratch test on these GeSbTe films to compare their delamination strength. In a scratch test, a thin film surface of a sample is scratched by an indenter while applying a load to the sample in the vertical direction, in order to determine the minimum load that cause delamination (referred to as the “critical delamination load”). The higher the critical delamination load, the higher the delamination strength. FIG. 8 shows the (critical delamination load) measurement results. As shown in FIG. 8, the delamination strength of the GeSbTe film was extremely low when an adhesive layer was not inserted (between the GeSbTe film and the SiO2 film). Further, insertion of a W layer did not lead to any improvement in the delamination strength of the GeSbTe film. This reflects the fact that chalcogenide material has low adhesion to high melting point metals. On the other hand, inserting an Al material layer increased the delamination strength of the GeSbTe film by a factor of 7-9, and inserting a Ti material layer enhanced the delamination strength by a factor of 10-15.

[0022] These results indicate that insertion of an adhesive layer may be effective in enhancing the adhesive properties of the chalcogenide material. As can be seen from FIG. 8, Ti material is superior to Al material as an adhesive layer. Further, nitrides have higher adhesion to chalcogenide material than oxides, and individual metals have higher adhesion than oxides and nitrides.

[0023] An exemplary manufacturing process of the present invention will be described with reference to FIG. 1. First, an interlayer insulating film 1 and a plug 2 are formed by a conventional technique. Then, the following layers are sequentially deposited: an adhesive layer 7 of, for example, titanium; a chalcogenide material layer 3 of, for example, GeSbTe; an adhesive layer 8 of, for example, titanium; an upper electrode 4 of, for example, tungsten; and a hard mask 5 made up of, for example, a silicon oxide film. Then, the hard mask 5, the upper electrode 4, the adhesive layer 8, the chalcogenide material layer 3, and the adhesive layer 7 are processed by a known lithographic technique and dry etching technique, forming the structure shown in FIG. 1.

Problems solved by technology

A DRAM provides large capacity but its access speed is low.

A SRAM, on the other hand, is high-speed memory, but is not suitable for forming a large capacity memory, since each cell requires a number of transistors (4 to 6 transistors) and hence it is difficult to produce highly integrated SRAM.

However, the flash memory is disadvantageous in that its program / erase count is limited to a maximum of approximately 105 and its reprogramming speed is a few orders of magnitude lower than those of other memories.

Since each memory (described above) has its disadvantage, it is current practice to select suitable memory depending on the application.

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