Patent Application
20060094233
1. Field of the Invention
The present invention relates to coating processes for coating microtechnical structures, in particular during the production of circuit units, and relates in particular to a method for determining an edge coverage (also referred to as edge covering or degree of edge covering) during coating processes, and to a corresponding device.
2. Description of the Related Art
Specifically, the present invention relates to a method for determining an edge coverage, a substrate being provided, a mask layer being deposited on the substrate, the substrate and the mask layer deposited on the substrate being patterned lithographically in such a way that at least one through hole (or a longitudinal groove) is formed in the mask layer deposited on the substrate and at least one first trench-type depression is formed in the substrate, the first trench-type depression being expanded isotropically in such a way that an expanded second trench-type depression is obtained, and a covering layer being deposited in such a way that the through hole formed in the mask layer is closed. In other words, an elongate tunnel is formed in the substrate.
The problem of edge coverage arises in physical and/or chemical vapor deposition processes. Particularly when very thin layers are applied, the disadvantage that results is that edges in the case of microtechnical structures cannot be covered sufficiently and structures having a high aspect ratio cannot be covered as far as the bottom. It is absolutely necessary to evaluate a coating process with regard to the edge coverage. For this purpose, it is necessary to provide a test method for determining an edge coverage which can make a prediction about the quality of a coating process to be used and/or serves for production-accompanying monitoring. Coating processes of this type include, inter alia:
(i) physical vapor deposition (PVD) processes;
(ii) chemical vapor deposition (CVD) processes; and/or
(iii) atomic layer deposition (ALD) processes.
In order to determine the degree of an edge coverage during deposition processes generally from the vapor phase, test structures having an aspect ratio are required. This applies particularly to ALD (atomic layer deposition) processes. It is disadvantageous that in many cases no etching processes exist that can be used to realize the vertical structures with such large aspect ratios.
For determining the edge coverage, the prior art has proposed etching vertical holes having a high aspect ratio into silicon. It is disadvantageous that such etching processes in silicon require very complicated trench etching procedures (Trench Etch Processes).
It is an object of the present invention to provide a method and a device for determining an edge coverage during coating processes which are relatively simple and cost-effective and which do not require structures having a high aspect ratio.
The object is achieved in accordance with the invention by dispensing with vertical structures in silicon wafers or structures having high aspect ratios by forming trenches laterally, extending parallel to a silicon (wafer) surface, which trenches are covered from above with a covering layer and opened laterally. This affords the advantage that it is possible to estimate an edge coverage on the basis of a penetration of coating material into one lateral opening of the trenches (or both lateral openings of the trenches).
Preferably, the trench-type depressions may be oriented in a direction parallel to the surface of the substrate, the trench-type depressions having a trench opening at at least one lateral end region, through which trench opening the coating material can penetrate laterally into the trench-type depression.
This affords the advantage that, in the case of arranging parallel trenches offset in the lateral direction, in a cross section through the wafer, an edge coverage can be estimated in a simple manner.
In accordance with one general aspect, the inventive method for determining an edge coverage during coating processes essentially has the following steps:
a) provision of a substrate;
b) deposition of a mask layer on the substrate;
c) patterning of the substrate and of the mask layer deposited on the substrate lithographically in such a way that at least one through hole is formed in the mask layer deposited on the substrate and at least one first trench-type depression is formed in the substrate;
d) isotropic expansion of the first trench-type depression in such a way that an expanded second trench-type depression is obtained; and
e) deposition of a covering layer in such a way that the through hole formed in the mask layer is closed, the second trench-type depression extending in a direction parallel to the surface of the substrate, and having a lateral trench opening at at least one lateral end region, through which trench opening a coating material can penetrate laterally into the second trench-type depression.
The object is also achieved in accordance with the invention by a device for determining an edge coverage during the coating processes, comprising:
a) a substrate;
b) a mask layer deposited on the substrate, the substrate and the mask layer deposited on the substrate being patterned lithographically in such a way that at least one through hole is formed in the mask layer deposited on the substrate and at least one trench-type depression is formed in the substrate; and
c) a covering layer deposited in such a way that the through hole formed in the mask layer is covered, the trench-type depression extending in a direction parallel to the surface of the substrate and the trench-type depression having a lateral trench opening at at least one lateral end region, through which trench opening a coating material can penetrate laterally into the trench-type depression.
The deposition of the mask layer may be carried out by means of chemical vapor deposition (CVD) and/or by means of physical vapor deposition (PVD) and/or by means of atomic layer deposition (ALD).
The isotropic expansion of the first trench-type depression may be carried out in such a way that an expanded second trench-type depression is obtained selectively with respect to the mask layer deposited on the substrate. For this purpose, use is preferably made of an isotropic etching process either wet-chemically or dry-chemically.
The deposition of the covering layer is effected either conformally or non-conformally. In accordance with yet another preferred development of the present invention, the deposition of the covering layer is carried out by means of chemical vapor deposition (CVD) and/or by means of physical vapor deposition (PVD) and/or by means of atomic layer deposition (ALD).
In a restricted version of the inventive method, the substrate is provided as a silicon wafer (Si), and the mask layer is provided for example from silicon dioxide (SiO2).
The mask layer may be formed as a hard mask. The mask layer preferably comprises a silicon nitride material (Si3N4). The covering layer may preferably be provided from a silicon oxide material (SiO2) or a silicon nitride material (Si3N4) or an aluminum oxide material (Al2O3)
At least two trench-type depressions may be formed in parallel fashion and in a manner offset in the longitudinal direction in the substrate.
For determining the edge coverage in a simplified manner, the at least two trench-type depressions are arranged parallel and in a manner offset in each case by a constant amount with respect to one another in the longitudinal direction.
Respective lateral trench openings may be provided at both lateral end regions of the trench-type depression.
In this way, it is possible to obtain a method and a device which enable an edge coverage during coating processes in a simple and cost-effective manner without having to etch deep structures having a high aspect ratio into the substrate.
FIGS. 1(a) to (d) show process steps for producing a covered trench-type depression running in the substrate in accordance with a preferred exemplary embodiment of the present invention;
In the figures, identical reference symbols designate identical or functionally identical components or steps.
FIGS. 1(a), (b), (c) and (d) illustrate sectional views through a trench structure formed by the method according to the invention. Specifically,
If a deposition is then effected onto the substrate, that is to say onto the structure shown in
It should be pointed out that, although this is not illustrated in
Depending on the edge coverage capability—that is to say depending on the magnitude of the sticking coefficient—of the coating process, the coating material used in a test penetrates more or less laterally into the second trench-type depressions 105-105n which are in each case covered with the covering layer 106. The penetration of coating material into the tunnel (channel) open toward one side thus represents a measure of the edge coverage capability of the coating process.
In this way, the method according to the present invention avoids complicated “trench etch processes” which are associated with etching vertical holes into a substrate. The device according to the invention has substantially shallow, but in return very long trenches which are etched into the substrate 101 and subsequently covered with the covering layer 106. This gives rise to long tunnels which are used, during an ALD, CVD and/or PVD deposition, to determine the edge coverage capability of the coating process.
The ascertaining of the depth or the sequential number i of a second trench-type depression 105a-105n up to which a coating has taken place is known to the person skilled in the art. For this purpose, the person skilled in the art uses for example a wafer breaking technique with subsequent SEM (scanning electron microscopy) examination. For this reason, such an examination method is not discussed in the present invention.
It should be pointed out, however, that through the possibility of using standardized SEM (scanning electron microscopy) methods, an investigation of the edge coverage capability of coating processes is facilitated and/or can be standardized. What is used as a measure of the deposition depth, as illustrated in
Although modifications and changed may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted heron all changes and modifications as reasonable and properly come within the scope of their contribution to the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102004052626.5 | Oct 2004 | DE | national |
