Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-05-27
2001-06-12
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S317000, C216S041000
Reexamination Certificate
active
06245489
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to the patterning of organic polymer films comprising phenyl groups. These polymer films are used, e.g., as inter- or intra-dielectric layers in semiconductor device fabrication for isolation purposes in multi-metal layer structures.
BACKGROUND OF THE INVENTION
The increasing complexity of integrated circuits, the growing number of metal levels and the focus on increasing speed of these circuits have created demands for low permittivity materials, particularly for use as inter-metal layers, i.e., used to isolate two metal levels from one another, or intra-metal layers, i.e., used to isolate metal patterns possibly formed within the same metal level one from another. Conventionally, metal interconnects, mostly aluminum layers, with silicon dioxide as a dielectric are used, but this conventional solution will not be able to meet the stringent specifications resulting from the above mentioned trends. Therefore, to avoid a large portion of the total circuit delay caused by the resistance and, particularly, the capacitance of the interconnect system, it is desirable to reduce the permittivity of the dielectric used. This is stated in numerous publications, e.g., in Table 1 of R. K. Laxman, “Low ∈ dielectric: CVD Fluorinated Silicon Dioxides”, Semiconductor International, May 1995, pp. 71-74. A low ∈ material, a low K material and a material with a low permittivity are all alternative expressions for a material with a low dielectric constant, at least for the purposes of this disclosure. Therefore, miniaturization has lead to an intensified search for new low K materials. The most desirable material should have a low K value, low mechanical stress, high thermal stability and low moisture absorption. Furthermore, the desired material should be selected based on the compatibility with state-of-the-art semiconductor processing steps and tools.
Part of the search for new low K materials was directed to changing the properties of silicon dioxide as deposited. Deposited silicon dioxide is the most widely used dielectric inter- or intra-metal material having a K value of about 3.9. Several publications have indicated that the K value of silicon dioxide films can be reduced by introducing increasing amounts of fluorine in said films. A wide variety of processes to deposit fluorinated silicon oxide films are known, like, e.g., Plasma Enhanced Chemical Vapor Deposition (PECVD) process as in the U.S. Pat. No. 5,641,581. Using these processes K values in the range between 3 and 3.5 are reported to be dependent on the amount of fluorine atoms incorporated, i.e., an increasing amount of fluorine leads to a decrease in the K value.
Besides the focus on changing the properties of silicon oxide, there is an ongoing search for new low K materials amongst others because a K value of 3 is still too high. These new materials can be divided roughly in two groups: the inorganic low-K materials and the organic low-K materials. The inorganic low-K materials have mostly interesting K values below 2 or even below 1.5 like, e.g., xerogels, but these materials are mostly not compatible with the fabrication process of integrated circuits. The organic low-K materials, especially the organic spin-on materials, however, have a K-value typically in the range from 2.5 to 3. These organic materials are of particular interest because they feature simplified processing, excellent gap-fill and planarization.
The benefits of using such organic low-K spin-on materials are partly nullified by the need to introduce an inorganic hard mask layer for the patterning of an organic low-K spin-on material. For the purpose of this disclosure, a hard mask layer is defined as a layer which can be etched selectively to another layer and which therefore can be used as an etch mask to etch said other layer. Traditional lithographic resists are not suited to be used as hard mask layers for patterning organic low-K spin-on materials because these resists are also based on organic polymers resulting in an insufficient etch selectivity with regard to the organic low-K spin-on material. Conventionally, inorganic hard mask layers like silicon oxide or silicon nitride layer are used as described in, e.g., M. Schier, “RIE of BCB using a silicon nitride dielectric etch mask”, J. Electrochem. Soc., v. 142, n9, p. 3238, 1995 and E. A. Lagendijk, et al., MRS Symp. Proc., v. 443, p. 177, 1997. These conventional inorganic hard mask layers have a rather high K value, i.e., typically in the range of 3.9 and above, which makes them less suitable for interconnect or isolation structures wherein the hard mask layers cannot be removed. Examples of such structures are damascene structures, where the hard mask layer can be positioned in-between two dielectric layers. If these dielectric layers are low-K organic layers part of the benefit of using such low-K layers is nullified because the K value of the inorganic hard mask layer contributes significantly to the mean value of the K value of the total dielectric stack comprising the hard mask layer and the two low K layers.
SUMMARY OF THE INVENTION
An aim of the present invention is to form a hard mask layer in an organic polymer layer by modifying at least locally the chemical composition of a part of an exposed organic low-K polymer. The polymer comprises phenyl groups. This modification starts from an exposed surface of the polymer and extends into the polymer thereby increasing the chemical resistance of the polymer. As a result, this modified part can be used as a hard mask for plasma etching. This modification is performed by exposing the low-K polymer to an ambient comprising fluorine, substantially without changing the film thickness, i.e., substantially without etching the low-K polymer. By doing so, the use of an extra hard mask layer, particularly an inorganic hard mask layer, can be avoided or at least removed subsequently. Furthermore, the mean K value even decreases due to the fluorination.
In one aspect of the invention a method is disclosed to form a hard mask layer in an organic polymer layer by modifying at least partly the chemical composition of a first region of an organic polymer film. The first region is uncovered. This modification is performed by exposing a surface of the organic polymer film to an environment comprising fluorine substantially without changing the thickness of the first region of the organic polymer film. As a result a part of the first region of the organic polymer film is fluorinated leading to an increase in chemical resistance and a decrease in the K value of that part. That part starts at a surface of the first region and extends in the polymer film with elapsing exposure time. Thereafter, a layer, forming a diffusion barrier for fluorine and covering the surface of a second region, is removed from the second region, yielding the organic polymer film comprising the first region and the second region, wherein a surface of the first region and a surface of the second region are exposable. Thereafter, an etching procedure can be applied on the organic polymer film to remove selectively at least a part of the second region using the first region as a hard mask.
According to this aspect of the invention, a method for patterning an organic polymer film is disclosed. The method comprises the steps of: defining at least one first region and at least one second region in an organic polymer film formed on a substrate, the first region being uncovered and the second region being covered with a layer forming a diffusion barrier for fluorine; exposing the first and the second region to an ambient comprising fluorine resulting in the fluorination of at least a part of the first region; removing the barrier layer; selectively removing at least a part of the second region by etching, using the first region as a mask.
In an embodiment of the invention the exposure of the organic polymer film to fluorine is performed in a plasma ambient comprising fluorine. The conditions of the plasma ambient are such that damagin
Baklanov Mikhail Rodionovich
Declerck Gilbert
Maex Karen
Vanhaelemeersch Serge
Waeterloos Joost
Duda Kathleen
IMEC vzw
Knobbe Martens Olson & Bear LLP
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