The present invention generally relates to a layer structure having a contact hole suitable for dynamic random access memories having fine contact holes, and a method of producing such a layer structure. More particularly, the present invention is concerned with a fin-shaped capacitor having such a layer structure, and a method of forming such a fin-shaped capacitor. Furthermore, the present invention is concerned with a dynamic random access memory having such a fin-shaped capacitor.
Recently, there has been considerable activity as regards the development of 64 Mbit dynamic random access memories (DRAM). There are known DRAMs having three-dimensional stacked capacitor cells capable of providing a storage capacity equal to or higher than 64 Mbits (see Japanese Laid-Open Patent Application Nos. 1-137666, 1-147857 and 1-154549, U.S. Pat. No. 4,974,040 and T. Ema et al., xe2x80x9c3-DIMENSIONAL STACKED CAPACITOR CELL FOR 16M AND 64M DRAMSxe2x80x9d, International Electron Devices Meetings, 592-IEDM 88, Dec. 11-14, 1988). In order to increase the integration density, it is necessary to reduce the two-dimensional size of each memory cell without reducing the capacitance of each stacked capacitor.
In order to fabricate 64Mbit DRAMs, a feature scale approximately equal to 0.3 [xcexcm] is required. However, the conventional photolithography technique can realize a feature scale approximately equal to a maximum of 0.5 [xcexcm]. 64 Mbit DRAMs can be realized by reducing the size of each storage (stacked) capacitor. For this purpose, it is necessary to reduce the size of a contact window (opening) for a storage electrode which is a part of the stacked capacitor. As described above, since the feature scale realized by the conventional photolithography technique is approximately 0.5 [xcexcm], it is impossible to form the contact window having a size approximately equal to 0.3 ([xcexcm]. It is also necessary to reduce the size of a window (contact hole) provided for connecting a word line formed of, for example, polysilicon, and a low-resistance wiring line (word-line shunt layer) formed of Al or Al alloy, directed to preventing the occurrence of a delay in signal transmission in the word line.
Japanese Laid-Open Patent Application No. 63-119239 discloses a method for forming a fine pattern narrower than a feature scale limit of the conventional photolithography technique. The application teaches a process in which polysilicon, PSG or SiO2 is grown on an SiO2 mask having a window through which a substrate is partially exposed, and a grown film on the mask and the exposed substrate surface is anisotropically etched, so that a sidewall is formed on the substrate so that it is formed around the entire inner wall of the window in the mask. The distance between opposite surfaces of the sidewall in the window is less than the feature scale limit. Thus, a surface area of the substrate less than the feature scale limit is exposed through the sidewall in the window. Then, the substrate is etched in such a way that the combination of the sidewall and the mask function as an etching mask, so that a hole is formed in the substrate.
The above-mentioned Patent Application discloses an arrangement in which the mask is formed of SiO2 and a member to be processed is formed of Si. Thus, the removal of the mask material can be easily made. However, when a multilayer structure, such as DRAMS, is produced, it is necessary to consider three layers of a mask material, a material to be processed and a underlying material which is located under the processed material and which is exposed through a hole formed in the processed material. In this case, it is necessary to prevent the exposed portion of the underlaying material from be damaged during a process in which the mask material is removed. Further, if the mask material is left in the finalized products, it is necessary to have no problem arising from the existence of the left mask material. The above-mentioned Japanese Application does not suggest the above matters.
Japanese Laid-Open Patent Application No. 60-224218 discloses the use of a sidewall directed to providing a window (contact hole) smaller than the feature scale limit of the conventional photolithography technique. The sidewall is formed of Al and formed on an SiO2 layer and around an inner wall of a window formed in a silicon nitride (Si3N4) layer also formed on the SiO2 layer. The SiO2 layer is selectively etched in such a way that the Al sidewall and the Si3N4 layer function as mask layers. However, it is very difficult to form the Al sidewall in contact with the inner wall of the window in the Si3N4 layer, since Al has a poor coverage characteristic. Further, it is necessary to form the Si3N4 layer which is sufficiently thick, because the selective etching ratio of Si3N4 to SiO2 is small.
Japanese Laid-Open Patent Application No. 63-116430 (which corresponds to U.S. patent application Ser. No. 924,223 filed on Oct. 28, 1986) teaches the use of a sidewall for forming a hole smaller than the scale limit of the conventional photolithgraphy technique. The just above application shows a lift-off process for removing the mask material. However, the lift-off process has a problem in that some of the mask material separated from the substrate is re-adhered hereto. This frequently causes a pattern fault in a subsequent process. The Japanese application of concern does not disclose an effective step to process the mask material. Further, the Japanese application shows a sidewall formed on the side surface of a photosensitive material. It is necessary to form the sidewall at a low temperature due to the thermal stability of the photosensitive material. Thus, there is a great limitation regarding the selection of mask materials. In addition, the structure shown in the Japanese application of concern is limited to a special application.
It is a general object of the present invention to provide an improved layer structure having a contact hole, in which the above-mentioned disadvantages are eliminated.
A more specific object of the present invention is to provide a layer structure having a contact hole suitable for DRAMs.
The above-mentioned objects of the present invention are achieved by a method of forming a structure having a contact hole comprising the steps of:
(a) forming an insulating layer on a first conductive layer;
(b) forming a second conductive layer on the insulating layer;
(c) forming an opening in the second conductive layer;
(d) forming a conductive sidewall around an inner wall of the first conductive layer defining the opening;
(e) selectively etching the insulating layer in a state where the second conductive layer and the conductive sidewall function as etching masks, so that the contact hole having a width smaller than that of the opening and defined by the conductive sidewall is formed, and the first conductive layer is exposed through the contact hole; and
(f) removing the second conductive layer and the conductive sidewall.
The above-mentioned objects of the present invention are also achieved by a method of forming a structure having a contact hole comprising the steps of:
(a) forming an insulating layer on a first conductive layer;
(b) forming a second conductive layer.on the insulating layer;
(c) forming an opening in the second conductive layer;
(d) forming a conductive sidewall around an inner wall of the first conductive layer defining the opening;
(e) selectively etching the insulating layer in a state where the second conductive layer and the conductive sidewall function as etching masks, so that the contact hole having a width smaller than that of the opening and defined by the conductive sidewall is formed on the insulating layer and the first conductive layer is exposed through the contact hole;
(f) forming a barrier layer on the second conductive layer, the conductive sidewall and the first conductive layer exposed through the contact hole; and
(g) forming a third conductive layer on the barrier layer, the barrier layer preventing the third conductive layer from reacting with the second conductive layer and the conductive sidewall.
The above-mentioned objects of the present invention are also achieved by a method of forming a structure having a contact hole comprising the steps of:
(a) forming an insulating layer on a first conductive layer;
(b) forming a second conductive layer on the insulating layer;
(c) forming an opening in the second conductive layer;
(d) forming a conductive sidewall around an inner wall of the first conductive layer defining the opening;
(e) selectively etching the insulating layer in a state where the second conductive layer and the conductive sidewall function as etching masks, so that the contact hole having a width smaller than that of the opening and defined by the conductive sidewall is formed, and the first conductive layer is exposed through the contact hole; and
(f) forming a third conductive layer on the second conductive layer, the conductive sidewall and the member exposed through the contact hole, wherein:
the second conductive layer comprises polysilicon;
the conductive sidewall comprises polysilicon; and
the third conductive layer comprises tungsten.
The aforementioned objects of the present invention are achieved by a method of forming a structure having a contact hole comprising the steps of:
(a) forming an insulating layer on a first conductive layer;
(b) forming a second conductive layer on the insulating layer;
(c) forming a first opening in the second conductive layer;
(d) selectively growing a third conductive layer on the second conductive layer and an inner wall of the second conductive layer defining the first opening, so that a second opening defined by the third conductive layer and having a width smaller than that of the first opening is formed; and
(e) selectively etching the insulating layer in a state where the third conductive layer functions as an etching mask, so that the contact hole having a width substantially identical to the second opening defined by the third conductive layer is formed, and the first conductive layer is exposed through the contact hole.
Another object of the present invention is to provide a layer structure having a contact hole as formed by the above-mentioned methods.
This object of the present invention is achieved by a layer structure comprising:
a first conductive layer;
an insulating layer formed on the first conductive layer and having a contact hole, the first conductive layer being exposed through the contact hole;
a second conductive layer formed on the insulating layer and having an opening having a width larger than that of the contact hole;
a conductive sidewall formed on the insulating layer exposed through the opening and formed around an inner wall of the second conductive layer defining the opening, the conductive sidewall having a width substantially equal to that of the contact hole;
a barrier layer formed on the second conductive layer, the conductive sidewall and the first conductive layer exposed through the contact hole; and
a third conductive layer formed on the barrier layer, the barrier layer preventing the third conductive layer from reacting with the second conductive layer and the conductive sidewall.
The above-mentioned object of the present invention is achieved by a layer structure comprising:
a first conductive layer;
an insulating layer formed on the first conductive layer and having a contact hole, the first conductive layer being exposed through the contact hole;
a second conductive layer formed on the insulating layer and having a first opening having a width larger than that of the contact hole;
a third conductive layer formed on the insulating layer exposed through the first opening and the second conductive layer and formed around an inner wall of the second conductive layer defining the first opening, the third conductive layer defining a second opening having a width substantially equal to that of the contact hole, the second opening being continuously connected to the contact hole;
a barrier layer formed on the third conductive layer and the first conductive layer exposed through the contact hole; and
a fourth conductive layer formed on the barrier layer, the barrier layer preventing the fourth conductive layer from reacting with the third conductive layer and the conductive sidewall.
The above-mentioned object of the present invention is also achieved by a layer structure comprising:
a first conductive layer;
an insulating layer formed on the first conductive layer and having a contact hole, the first conductive layer being exposed through the contact hole;
a second conductive layer formed on the insulating layer and having an opening having a width larger than that of the contact hole;
a conductive sidewall formed on the insulating layer exposed through the opening and formed around an inner wall of the second conductive layer defining the opening, the conductive sidewall having a width substantially equal to that of the contact hole; and
a third conductive layer formed on the second conductive layer, the conductive sidewall and the first conductive layer exposed through the contact hole,
wherein the third conductive layer comprises a material which causes no reaction with the second conductive layer and the conductive sidewall.
According to the present invention, there is also provided a dynamic random access memory having any of the above-mentioned structures.
According to the present invention, there is also provided a fin-shaped capacitor and a method for producing such a fin-shaped capacitor.