US 7172960 B2
A method including introducing a dielectric layer over a substrate between an interconnection line and the substrate, the dielectric layer comprising a plurality of alternating material layers; and patterning an interconnection to the substrate. An apparatus comprising a substrate comprising a plurality of devices formed thereon; and an interlayer dielectric layer comprising a base layer and a cap layer, the cap layer comprising a plurality of alternating material layers overlying the substrate.
1. A method comprising:
introducing an etch stop layer on a substrate;
introducing a base layer on the etch stop layer;
introducing a dielectric cap layer on the base layer between an interconnection line and a contact point on the substrate, the dielectric cap layer comprising alternating different material layers, wherein each respective layer of the alternating different material layers is selectively etchable with respect to the etch stop layer and the number of occurrences of each different material layer is greater than one;
introducing a photoimageable material on the dielectric cap layer; and
patterning an interconnection to the contact point, wherein the dielectric cap layer is configured to suppress substrate reflections during patterning.
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11. A method comprising:
forming a planarized base layer over a substrate having a plurality of devices;
forming a dielectric cap layer over the base layer, wherein the dielectric cap layer is formed by alternating a first material layer and a second material layer a plurality of times, the second material layer formed of a material having a higher dielectric constant than a dielectric constant of a material of the first material layer, wherein collectively the plurality of the first material layer is more than five times thicker than the plurality of second material layer; and
patterning an interconnection to a contact point, wherein the dielectric cap layer is configured to suppress substrate reflections during patterning.
12. The method of
1. Field of the Invention
The invention relates to integrated circuit fabrication and, more particularly, to the definition and alignment of interconnections in integrated circuit structures.
Modern integrated circuits use interconnections to connect the individual devices on a chip or to send and/or receive signals external to the chip. Popular types of interconnections include aluminum or copper interconnections (lines) coupled to devices, including other interconnections (lines) by interconnections through vias.
Fabricating an interconnection structure to a device formed on a circuit substrate, such as an interconnection to a transistor device, typically involves introducing a photoimageable material (e.g., photoresist) over a dielectric layer insulating the device. The photoimageable material is patterned to have an opening to the dielectric above the desired point of contact for the subsequent interconnection. An etch is then used to form an opening or via through the dielectric layer to the device.
One problem with the current state of the art photoimaging technique is the formation of undesired openings in the photoimageable material due to substrate reflections of light.
By creating undesired openings in the photoimageable material, failure modes are introduced into the circuit device processing. When these openings are later filled with interconnection material, electrical shorts may be introduced either between metal lines or on the silicon structure. Further, undesired interconnects coupled to silicon surface introduce a capacitive element in the structure.
Attempts to remedy the problem of creating undesired opening areas include placing an anti-reflective coating over the structure. Such technique, however, involves introducing an additional film which adds process cost and complexity and possibly additional defects in the process flow. Reduction of the light intensity is not a workable solution at this point as it requires approximately 27 millijoules (mJ) to develop positive photoresist with only one to two millijoules margin. Therefore, reducing the light intensity may result in the loss of the desired opening area, such as opening area 150.
What is needed are improved processing techniques and an improved structure that suppresses undesired reflections.
The invention relates to techniques and an apparatus for forming interlayer dielectric material layers that suppress undesired substrate reflections. In one embodiment, a method includes introducing a dielectric layer over a substrate between an interconnection line and a contact point, the dielectric layer comprising a plurality of different material layers, and patterning an interconnection to the contact point. An embodiment of the apparatus includes a substrate comprising a plurality of devices formed thereon and a dielectric layer comprising a plurality of alternating material layers overlying the substrate. The apparatus also includes an interconnection line overlying the dielectric layer and coupled to at least one of the plurality of devices.
Overlying substrate 210 and any devices formed thereon is etch stop layer 240. In one embodiment, etch stop layer 240 is, for example, silicon nitride material deposited by chemical vapor deposition to a thickness on the order of about 500 angstroms (Å). In one sense, etch stop layer 240 protects substrate 210 and devices formed thereon from a subsequent etching operation.
It is appreciated that the introduction of base layer 250 over the substrate may proceed in a conformal manner leaving a non-planar substrate surface. In such cases, following the introduction and possible doping of base layer 250, structure 200 is planarized by, for example, the use of a chemical-mechanical polish. A representative thickness of planarized base layer 250 of, for example, silicon dioxide, is on the order of 1900 angstroms (Å).
It is generally desirable at this point to introduce a dielectric cap over planarized base layer 250. The dielectric cap is included, in one sense, to mask any microdefects caused by the planarization. Referring to
One objective of introducing dielectric cap 255 over base layer 250 is to yield a uniform interlayer dielectric film. One way to target a uniform film of dielectric cap 255 is by introducing the cap layers on a multi-station tool such as a Concept 2 Sequel™, commercially available from Novellus Systems, Inc. of San Jose, Calif. Through the use of a multi-station tool, it is possible to introduce multiple alternating layers or films of dielectric material as dielectric cap 255.
By using a multi-station tool to introduce dielectric cap 255, multiple alternating layers or films of different dielectric materials may be introduced efficiently. By selecting thicknesses of the alternating materials and the number of alternating films, cap layer 255 may be maintained within a suitable thickness range consistent with prior art structures. For example, in one embodiment, it is desired that a dielectric cap 255 has a thickness on the order of about 2,000 Å for the structure described (i.e., an overall dielectric thickness (cap+base layer+etch stop) of approximately 4,000 Å).
The structure represented in each of
One reason for selecting films of silicon dioxide that are more than five times thicker than the silicon oxynitride counterparts is that silicon oxynitride has a higher dielectric constant than silicon dioxide. Measurably increasing the dielectric constant of dielectric cap 255 may impair circuit performance by, for example, introducing undesired capacitance, such as metal to metal capacitance within the structure.
It has been observed that with a dielectric cap that is a two layer or film of 1,000 Å of silicon oxynitride and 1,000 Å of silicon dioxide (one to one relationship) with undesired substrate reflections from, for example, STI 231, are inhibited. Reduction of the amount of silicon oxynitride to silicon dioxide from one to one, to one to five or one to six inhibits some undesired reflections but is not as effective as the inhibiting reflectance of the one to one relationship. It has also been observed by interweaving or alternating the silicon oxynitride and silicon dioxide films as described above using significantly less silicon oxynitride, similar reflection inhibition to the one to one relationship is seen. Therefore, interweaving or alternating as described the structure shown, for example, in
Although the embodiment shown in
In the above embodiment, a dielectric cap of interweaved layers or films of dielectric materials of silicon dioxide and silicon oxynitride is presented. It is appreciated that there may be other materials besides silicon dioxide and silicon oxynitride that may suitably substituted. Other materials may likewise be substituted for the base layer material as well. These dielectric materials include materials having a dielectric constant lower than silicon dioxide (“low k” dielectrics).
In the preceding detailed description, an improved interlayer dielectric is presented that inhibits substrate reflections. The invention is described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.
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