Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2000-02-24
2001-07-10
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S238000, C438S252000, C438S253000
Reexamination Certificate
active
06258653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to capacitors formed on conductive surfaces, preferably silicon surfaces, during the construction of integrated circuits. More specifically, the present invention relates to a method of making a capacitor in which silicon nitride barriers are formed between conductive surfaces forming the plates of a capacitor and a capacitor dielectric layer of tantalum oxide located between the conductive surfaces.
2. Description of Related Art
As the memory size of dynamic random access memory (DRAM) devices increases into the gigabit range, the dimensions of all memory structures and the space allotted on the semiconductor substrate for those structures have decreased. To produce capacitors of the necessary value within the limited space available, conventional oxide
itride/oxide stack dielectrics have had to be constructed ever thinner and thinner. Such stack dielectrics are beginning to reach the practical limit of how thin they may be deposited.
One solution to this is to use tantalum oxide to replace oxide
itride/oxide stacks as the capacitor dielectric. Tantalum oxide (Ta
2
O
5
) has a higher dielectric constant and produces a correspondingly higher capacitance in the resulting capacitor.
A problem with the use of tantalum oxide, however, is that the tantalum oxide deposition process results in the formation of a thin silicon oxide interface when the tantalum oxide is deposited directly on a polysilicon bottom electrode.
This silicon oxide interface reduces the overall capacitance and degrades device functionality. To prevent the formation of the undesirable silicon oxide interface, it is known to deposit a thin nitride layer over the polysilicon before depositing the tantalum oxide. This nitride layer has a higher dielectric constant (K
SiN
=7) than the silicon oxide (K
SiO2
=4).
In the prior art implementation of this deposition process, the nitride layer has been deposited using a rapid thermal nitridation (RTN) process. The RTN process, however, is a relatively slow and costly process. This results from the multiple processing steps required. Further, the RTN process results in a nitride layer that is not uniformly thick. This adversely affects the performance of the capacitor being constructed.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of making a capacitor in which the capacitor dielectric layer is separated from the conductive surface by a silicon nitride layer that is uniformly thick.
It is another object of the present invention to provide a method of making a capacitor in which the capacitor dielectric layer is separated from the conductive surface by a silicon nitride layer that can be constructed with fewer steps and less expensively than when constructed with the RTN process.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The present invention uses a high density plasma (HDP) nitridation method to produce a high quality silicon nitride layer for separating a tantalum oxide layer in a capacitor from the conductive surfaces on either side of the tantalum oxide. A particular benefit of using the HDP process is the elimination of the more costly RTN process and the improved wafer throughput.
A further benefit of using HDP is that cleaning of the conductive surface and silicon nitridation can be performed as a single integrated process in a single chamber. The above and other objects and advantages, which will be apparent to ne of skill in the art, are achieved in the present invention which is directed to, in first aspect, a method of making a capacitor including the steps of providing a conductive surface, contamination cleaning the conductive surface in a chamber sing a high density plasma of a first gaseous agent, growing a first silicon nitride layer on the silicon surface using a high density plasma of nitrogen, depositing tantalum oxide on the silicon nitride layer to form a capacitor dielectric layer, growing a second silicon nitride layer on the capacitor dielectric layer using a high density plasma of nitrogen and a silicon containing gaseous agent, and depositing a conductive layer over the second silicon nitride layer to form the capacitor.
The conductive surface forming the lower plate of the capacitor is preferably silicon, and most preferably, polysilicon. The first gaseous agent in the step of contamination cleaning is preferably hydrogen. The high density plasma of nitrogen used in the step of growing a first silicon nitride layer on the conductive surface is formed by heating nitrogen gas with an inductively coupled radio frequency generator.
In the most highly preferred implementation of the method, the steps of contamination cleaning and growing a first silicon nitride layer are both completed in the same chamber without removing the conductive surface from the chamber. This speeds processing as compared to RTN processing.
The first silicon nitride layer is constructed with a thickness of less than 100 Angstroms, and it is preferred to be between about 10 and 40 Angstroms thick. The high density plasma used during the step of growing a first silicon nitride layer on the conductive surface is formed by heating with an inductively coupled radio frequency generator operating at between about 2000 and 4800 watts and the conductive surface is exposed to the nitrogen plasma for a period of time ranging from about 3 to 60 seconds. Similar exposure times and heating temperatures are used during the contamination cleaning step with the high density hydrogen plasma.
During the step of growing the first silicon nitride layer on the silicon surface, argon may be added to the high density plasma of nitrogen. During the step of growing a second silicon nitride layer on the capacitor dielectric layer, silane may be used as the silicon containing gaseous agent.
The invention also includes a capacitor constructed on a conductive surface by a method comprising the steps described above. The resulting capacitor includes a uniform (<2%, 1 sigma) silicon nitride layer on each side of the tantalum oxide layer.
REFERENCES:
patent: 5552334 (1996-09-01), Tseng
patent: 5686337 (1997-11-01), Koh et al.
patent: 5712202 (1998-01-01), Liaw et al.
Chew Kok Heng
Konjuh Kathy
Ravi Tirunelveli Subramaniam
van Cleemput Patrick
DeLio & Peterson LLC
Elms Richard
Luu Pho
Novellus Systems Inc.
Peterson Peter W.
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