Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1999-08-12
2001-04-03
Kunemund, Robert (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S710000, C438S712000, C438S713000, C438S770000
Reexamination Certificate
active
06211091
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application serial no. 88109594, filed Jun. 9, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device, and more particularly, to a self-aligned etching process.
2. Description of the Related Art
When the deep sub-micron process is used in semiconductor manufacturing, the size of a device becomes smaller so that the operating speed of the integrated circuit is efficiently enhanced. Regarding semiconductor devices with the same circuit pattern, the operating speed of the circuit depends on the density of interior devices. In the case of the high density of devices, such as a DRAM (Dynamic Random Access Memory), the space between a bit line and a node contact of a capacitor must decrease, and thus the insulation between them becomes a hard-to-solve problem.
One solution is to form a self-aligned contact. A cap and spacers, both made of silicon nitride, are formed on the top and sidewalls of a bit line, and then a silicon oxide layer is formed thereon. Second, due to different chemical properties of silicon nitride and silicon oxide, by selectively etching silicon oxide, the silicon oxide layer is etched in a self-aligned fashion to form a node contact opening between adjacent bit lines. The bit line is protected during etching because of the silicon nitride cap and spacers, which therefore maintain a good insulation between the bit line and the node contact.
However, in the above case, the dielectric constant of silicon nitride is relatively high, about 7 to 8; thus, a higher bit line capacitance arises (because a capacitor comprising the node contact, a dielectric layer and the bit line in sequence is formed) and a severe coupling effect between adjacent bit lines is induced. This situation seriously affects the accuracy of data reading. For example, in the case of a 64 Mbits DRAM, the general selection principal for using a material or a combination of materials as an insulator between adjacent bit lines is that the induced equivalent bit line capacitance of a section having a capacity of 512 bits must be less than 120 fF; i.e., the equivalent bit line capacitance of each bit must be less than 0.23 fF, which can thereby prevent the data address in a memory from being misjudged.
In addition, greater thermal stress exists between silicon nitride and silicon, and exists between silicon nitride and tungsten silicide as well, which increases the difficulty with which the process is controlled.
Therefore, a need exists for a method of forming a node contact in a self-aligned fashion to prevent the above problems.
SUMMARY OF THE INVENTION
In accordance with the above, the invention provides a method of forming a node contact in a self-aligned fashion. A first insulating layer is formed on a substrate, and a plurality of node contact plugs are then formed within the first insulating layer. A second insulating layer, a conductive layer and a third insulating layer are formed on the first insulating layer in sequence. The third insulating layer and the conductive layer are subsequently patterned to form a plurality of bit line stacks on the second insulating layer. A fourth insulating layer corresponding to the second insulating layer is formed over the substrate, and an anisotropic removal process is then performed to remove portions of the fourth and second insulating layers in order to form spacers on sidewalls of the bit line stacks and to expose upper surfaces of the node contact plugs. A stop layer and a planarized fifth insulating layer are formed on the resulting structure. Portions of the fifth insulating layer are removed to form a plurality of openings and to expose portions of the stop layer above the node contact plugs. The exposed stop layer is removed to expose upper surfaces of the node contact plugs, and then a conductive material fills openings to form a plurality of node contacts.
According to the invention, since the materials used as the third and fourth insulating layers in contact with the conductive layer have a low dielectric constant and good thermal stability, the bit line capacitance is reduced and the accuracy of data reading is enhanced. Furthermore, the thermal stress is reduced so that process control is improved. In addition, since the selected material used as the fifth insulating layer is different from that used as the stop layer, a method can be chosen to remove the fifth insulating layer more efficiently than the stop layer; i.e. the removal can be self-aligned.
The invention provides a self-aligned etching method. The method is performed as following. A conductive layer and a first insulating layer are formed on a substrate. The conductive layer and the first insulating layer are patterned to form a plurality of stacks in desired regions. Second, spacers are formed on sidewalls of each stack, and then a stop layer and a planarized second insulating layer are formed on the substrate. Third, the second insulating layer is etched to form a plurality of openings and to expose portions of the stop layer between spacers, and then the exposed stop layer is etched to expose the substrate.
According to the invention, the materials used as the first insulating layer and spacers in contact with the conductive layer have low dielectric constants and good thermal stability in order to prevent parasitic capacitance and thermal stress from arising. Furthermore, the material used as the stop layer is different from that used as the second insulating layer so that the second insulating layer is etched more efficiently than the stop layer and the process therefore is self-aligned.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
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Cherng Meng-Jaw
Lien Wan-Yih
Huang Jiawei
J C Patents
Kunemund Robert
Vinh Lan
Worldwide Semiconductor Mfg. Corp.
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