Etching a substrate: processes – Nongaseous phase etching of substrate – Using film of etchant between a stationary surface and a...
Reexamination Certificate
1998-03-03
2001-01-09
Lund, Jeffrie R (Department: 1763)
Etching a substrate: processes
Nongaseous phase etching of substrate
Using film of etchant between a stationary surface and a...
C216S088000, C438S692000, C438S693000
Reexamination Certificate
active
06171514
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a polishing method for planarizing a substrate and, more particularly, to a polishing method for planarizing a substrate which is applied to fabrication of a multi-layer thin film substrate.
The multi-layer thin film substrate is formed by stacking a plurality of layers on a substrate base. A polishing process is performed each time a single layer is formed so that each layer is formed with a high degree of precision. In order to improve productivity of such a multi-layer thin film substrate, it is desired to reduce the process time of a polishing process which takes a relatively long time as compared to that of other processes.
2. Description of the Related Art
When an attempt is made to provide a wiring layer to have a multi-layered structure, thickness is varied between an area where a via or a wiring is formed and an area where such a via or a wiring is not provided. This makes it difficult to provide a multi-layered wiring layer. Accordingly, a wiring layer can be formed in a three-layered structure at the maximum. If the number of layers is increased, a yield or production rate of the multi-layer thin film substrate is considerably decreased. In order to achieve a multi-layered structure having more layers, a method is used in which surface planarization is performed after each layer is formed. Such planarization is accomplished by a polishing referred to as chemical-mechanical polishing (CMP).
However, in order to increase the number of layers or improve the yield rate, polishing by CMP alone is not sufficient, and a further planarization technique is needed. Such a planarization technique is disclosed in “CHEMICAL MECHANICAL POLISHING (CMP) OF COPPER/POLYIMIDE WITH POLISH STOP FOR MICROELECTRONIC INTEGRATION” for the Proceedings of the technical program for the Pan Pacific Microelectronics Symposium, Honolulu, Hi., Feb. 6-8, 1996. In this technique, a photoresist layer is formed on an upper surface of a ceramic substrate base on which a first-layer wiring pattern and pads are formed. An aperture is formed in the photoresist layer at a position corresponding to each of the pads. Then, a copper interconnecting post is formed within each aperture by using a CVD method or a plating method. Thereafter, the photoresist layer is removed, and a dielectric (polyimide) layer is formed. After that, a hard mask layer (stop layer) of tungsten is formed on the dielectric layer. The thus formed structure is polished by CMP using a slurry having a low polishing capability when used on tungsten. According to this method, a fairly good planar layer can be provided. The slurry having a PH value of 3 is used in this method so as to decrease the polishing capability when used on tungsten so that the tungsten layer serves as a stop layer. Additionally, silica (SiO
2
), which is suitable for selectively polishing high points, is added to the slurry. The polishing is performed by a single stage process.
However, in order to selectively form the mask layer at a level to stop the polishing, non-planar areas must be masked, resulting in a decrease of productivity. Accordingly, such decrease of the productivity is prevented by forming the mask layer on the entire surface including high points and selectively polishing the high points by using CMP. In order to polish the hard tungsten in a short time, the polishing capability must be increased in a chemical manner by increasing the PH value of the slurry to an alkaline level, or a polishing powder having a high polishing speed must be added to the slurry. However, such a slurry removes even the tungsten layer which is required to serve as a stop layer, and the stop layer may be completely removed before the copper studs and the polyimide layer are planarized by polishing. As a result, a surface of the layer which must be planarized cannot be a planer surface. Accordingly, in order for the stop layer to function well, a silica slurry having a PH value of 3 must be used in the conventional method. However, the conventional method has a low capability for polishing the tungsten on the high points. Additionally, since alumina (Al
2
O
3
) which can polish copper and polyimide at a high speed is not added to the slurry, a time needed for polishing to achieve a planarized surface is increased, that is, about 90 minutes. This becomes an obstacle to increased productivity of a multi-layer thin film substrate.
SUMMARY OF THE INVENTION
It is a general object of the present invention to provide an improved and useful polishing method for planarizing a substrate in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide a polishing method for planarizing a substrate which provides efficient polishing so that a time needed for the polishing is reduced as compared to the conventional method.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a polishing method for planarizing a substrate having a surface to be polished covered by a polish stop layer, the surface including at least one high area and a low area surrounding the high area, the polishing method comprising:
a first polishing process for removing a portion of the polish stop layer which covers the high area by using a first slurry having a high polishing capability for polishing the polish stop layer; and
a second polishing process, subsequent to the first polishing process, for removing the high area by using a second slurry having a high polishing capability for polishing a material covered by the polish stop layer, a polishing capability of the second slurry for polishing the polish stop layer being lower than the polishing capability of the first slurry for polishing against the polish stop layer.
According to the above-mentioned invention, the portion of the polish stop layer covering the high area can be selectively removed at a fast removal rate. Then, the high area from which the polish stop layer has been removed can be easily removed at a fast removal rate until a height of the high area is reduced to be equal to a height of the low area which is still covered by the polish stop layer stopping further abrasion in the second polishing process. Thus, the polished surface is planarized with high accuracy at a uniform height corresponding to a height of the low area. By selectively removing the high area in the first polishing process, a total time for planarizing the surface is greatly reduced as compared to that of the conventional method. Thus, a process time for fabricating a multi-layer thin film substrate can be greatly reduced, which increases productivity of the multi-layer thin film substrate.
In the polishing method according to the present invention, the first polishing process may include providing the first slurry as an alkalized slurry, and the second polishing process may include providing the second slurry as an acidified slurry.
Additionally, the first polishing process may include providing the first slurry containing powder having an average diameter less than 0.1 &mgr;m, and the second polishing process may include providing the second slurry containing powder having an average diameter greater than 0.1 &mgr;m.
Further, the first polishing process may include providing the first slurry containing powder having a hardness higher than powder contained in the second slurry.
Additionally, in the polishing method according to the present invention, the first polishing process may include providing the first slurry as an alkalized slurry, the first slurry containing powder having an average diameter less than 0.1 &mgr;m, the powder contained in the first slurry having a hardness higher than powder contained in the second slurry; and the second polishing process may include providing the second slurry as an acidified slurry, the powder contained in the second slurry having an average diameter greater than 0.1 &mgr;m.
Additionally, there is provided according to anothe
Hara Kouichi
Ozaki Norikazu
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Lund Jeffrie R
Powell Alva C
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