Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-07-31
2004-02-24
Chaudhari, Chandra (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S270000, C438S545000
Reexamination Certificate
active
06696335
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for forming a diffusion region and in particular to a method for forming a diffusion contact or the like in a semiconductor substrate and in particular for connecting a DRAM memory cell to a vertical MOSFET or the like.
In the case of integrated semiconductor circuits, a large number of components bearing different functions are formed in a very confined space in a semiconductor substrate or the like. In this case, various components must either be connected to one another or adequately insulated from one another.
Certain contacts are made for example as diffusion contacts. In this case, a region of the semiconductor substrate that is initially non-conducting is prestructured and then locally enriched in a targeted manner by a dopant in a doping operation, to thereby increase the conductivity locally in the initially non-conducting subregion of the semiconductor substrate by introducing corresponding charge carriers.
The disadvantage of forming contacts of this type by a diffusion process is that the diffusion process as such generally proceeds more or less isotropically. Therefore, a locally introduced high dopant concentration spreads more or less uniformly in all spatial directions during the thermal outdiffusion or annealing. To be able nevertheless to use the formation of contact regions by diffusion, it is necessary to introduce in the semiconductor substrate a minimum distance between components which absolutely have to be insulated or to form an additional electrical insulation, for example in the form of an oxide region, in order that unwanted instances of contacting or even short circuits are avoided.
The provision of an additional insulating region, for example in the form of an oxide or the like, hinders the individual process steps and consequently increases the costs of production. The maintenance of minimum distances is at odds with the aim and desire of making integrated semiconductor circuits as highly integrated and effective as possible.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for forming a diffusion region that overcomes the above-mentioned disadvantages of the prior art methods of this general type, in which the risk of unwanted instances of contacting or short circuits is particularly low.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for forming a diffusion region. The method includes providing a semiconductor substrate, and forming a first conductivity region and a second conductivity region in the semiconductor substrate. The first conductivity region and the second conductivity region are spatially separated from each other by an intermediate region of the semiconductor substrate. The diffusion region is formed between the first conductivity region and the second conductivity region in the intermediate region by thermally activated diffusion of at least one dopant into the intermediate region. The thermally activated diffusion of the dopant is conducted substantially in a directed manner by an interaction of the dopant with a subregion of the intermediate region. A transformation process is thermally initiated at least in the subregion of the intermediate region.
In the case of the method according to the invention for forming the diffusion region, in particular a diffusion contact or the like, in a semiconductor substrate or the like, in particular for connecting a DRAM memory cell on a vertical MOSFET, a first conductivity region and a second conductivity region are spatially separated from each other by an intermediate region of the semiconductor substrate. The diffusion region or the diffusion contact is formed between the first conductivity region and the second conductivity region, in particular in the intermediate region. The forming of the diffusion region or the diffusion contact takes place by thermally activated diffusion of at least one dopant into the intermediate region of the semiconductor substrate. Furthermore, a transformation process is thermally initiated and/or conducted at least in a subregion of the intermediate region, in particular substantially at the same time as the diffusion, and the thermally activated diffusion of the dopant is thereby carried out substantially in a directed manner, in particular substantially in or along a preferential direction, by interaction of the dopant with the transforming subregion of the intermediate region.
A central idea of the present invention is consequently to control the direction of the thermally activated diffusion of the dopant particles by bringing the dopant particles into specific interaction with the subregion of the intermediate region. The interaction is carried out by initiating and conducting a transformation process of the subregion of the intermediate region. By initiating the transformation processes by thermal activation, the corresponding interaction of the dopant particles with the subregion of the intermediate region and the material present there is also achieved at the same time.
More preferably, a chemical transformation process, a crystallization process and/or the like is/are carried out as the transformation process in the subregion of the intermediate region of the semiconductor substrate.
In this case, an oxidation operation is particularly preferred, in particular an oxidation operation using oxygen or with oxygen.
A particularly strong influence of the transformation process in the subregion of the intermediate region is obtained if, according to a preferred embodiment of the method according to the invention for forming a diffusion region, lattice imperfections, reactive centers and/or the like are produced, provided with increased mobility and/or brought into interaction with the dopant particles by the transformation process.
This measure consequently achieves the particular effect that both the mobility of the dopant particles and the mobility of possible lattice imperfections are increased by thermal activation. As a result, the probabilities of certain mass transfers, for example exchange processes or the like, can be correspondingly increased.
In the case of a particularly preferred embodiment of the method according to the invention, a silicon substrate, in particular a bulk silicon substrate, a p-doped silicon or the like, is provided as the semiconductor substrate, as the intermediate region and/or as the subregion thereof.
In the case of a further embodiment of the method according to the invention, the dopant is chosen to match the material of the intermediate region or of the semiconductor substrate and in particular to match the material of the subregion of the intermediate region, in particular with regard to a particularly high mobility of the dopant particles or of the dopant with respect to a preferential direction.
Particularly advantageous properties are obtained if phosphorus or the like is chosen as the dopant. Phosphorus has, for example in comparison with arsenic, a much stronger tendency to interact with lattice imperfections. It is therefore much easier with phosphorus, in comparison with arsenic or the like, to accomplish a directed diffusion along a preferential direction by local forming of mobile lattice imperfections.
Although the dopant can be introduced subsequently into already existing structures, for example locally by corresponding implantation or the like, it is of particular advantage if the dopant is supplied by a depot region, in particular in the semiconductor substrate. The depot region is advantageously created as a material subregion during the production of the basic structures and is then distributed in a desired way during the thermal outdiffusion from the depot region in a directed manner while interacting with the thermal transformation region.
In this case, the depot region may be provided as a separate region in the region of the semiconductor substrate.
It is also conceivable for the depot region to be provided in
Bonart Dietrich
Voigt Peter
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