Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Forming nonplanar surface
Reexamination Certificate
2000-02-22
2004-01-06
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Forming nonplanar surface
C430S313000, C430S314000, C430S315000, C430S322000, C430S323000, C430S325000
Reexamination Certificate
active
06673525
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains generally to a method for manufacturing integrated circuits that satisfy narrow design rules and more particularly to an improved thin layer imaging process for photoresist patterning in systems having low radiation flux and highly energetic, strongly attenuated radiation.
As integrated circuits have become smaller the demands to achieve submicron resolution with satisfactory line width control have become increasingly important. Design rules of 0.5 &mgr;m are being replaced by design rules that require feature sizes of 0.25 to 0.18 &mgr;m and significant effort is presently being put into achieving 0.1 &mgr;m resolution.
Integrated circuits are manufactured using lithographic processes. Energy (generally electromagnetic radiation, i.e., light) is caused to interact selectively with an energy sensitive resist material deposited onto a substrate in such a way that a pattern or image is produced on the resist material. The resist material is developed and the pattern is transferred by etching onto the substrate.
The energy used to expose the resist material, the composition of the resist material, the thickness of the resist material, and many other factors affect the ability of a lithographic process to delineate a feature on a substrate. The smaller the design rule (feature size) the more precisely the feature must be delineated. This requirement, coupled with the demand for smaller feature sizes has driven the wavelength of radiation needed to produce the desired pattern to ever shorter wavelengths. Shorter wavelength light is strongly absorbed by the resist material and thus unable to penetrate much below the surface of the resist material. By way of example, the characteristic attenuation length for 13.4 nm radiation (the wavelength desired for 0.1 &mgr;m feature size) is on the order of 0.1-0.2 &mgr;m for most organic films. If a standard 0.5-0.8 &mgr;m thick resist material is required for further processing it will result in a wall profile significantly less than 80 degrees and hence unacceptable critical dimension control.
The topography of the substrate surface may also adversely affect the ability of the lithographic process to define features on the substrate. When a single layer of resist material is applied over a nonplanar substrate pattern, light scattering by the resist material and substrate, as well as the potential inability of the light to completely penetrate and uniformly expose the resist material can result in errors in the defined lithographic pattern. Consequently, surface imaging lithographic processes have been developed that do not require that the resist material be exposed throughout its entire thickness. These processes are referred to as surface imaging processes because they define features only in the near surface region of the resist.
While surface imaging is absolutely required for patterning advanced integrated circuits using highly attenuated radiation, the technology may also offer advantages in any case of narrow design rules where standard lithographic processes are difficult due to severe wafer topography or radiation reflection or depth of focus (DOF) limitations since imaging just the surface of the resist relaxes DOF requirements. High numerical aperture steppers, while capable of printing smaller features at a given wavelength, often have small DOF and this can preclude focused exposure through the thickness of the film. By providing a planarizing layer disposed between the surface of the substrate and the imaging layer, it is possible to deposit a uniform imaging layer having minimum thickness, thereby reducing problems associated with variations in DOF.
Four basic surface imaging technologies are well known in the art; single layer silylation processes, bilayer processes, trilayer processes, and a variation of the standard bilayer process in which the topmost resist layer is reactive to a silylation reagent.
In the standard bilayer process a relatively thick layer of resist material (typically 1.5-4 times the height of the highest step on the substrate) is deposited on the surface of a substrate as a planarizing processing layer. A second imaging resist layer is spin cast onto the surface of the planarizing layer. A circuit pattern is produced on the surface of the resist material which is subsequently developed, exposing portions of the underlying planarizing layer. The mask pattern is transferred from the imaging layer directly onto the surface of the substrate by etching through the planarizing layer by standard device processing. Bilayer systems have not found ready acceptance for high volume applications due to their processing complexity and expense.
Trilayer resist processes incorporate a highly etch resistant layer i.e., “hard” layer, between the two resist layers of the bilayer process. Typically, this intervening hard layer is composed of a sputtered metal or a refractory material such as silicon dioxide, which can either be applied through a conventional chemical vapor deposition processes or by a liquid deposition process wherein silicon dioxide particles or silicon containing polymer, oligomers or clusters are suspended or dissolved in a liquid that desirably evaporates quickly to leave a glass-like layer referred to as spin-on-glass (SOG). While the trilayer process has eliminated many of the problems encountered with the bilayer process, other complications are associated with this process. For example, the susceptibility of the silicon dioxide hard mask layer to internal and surface defects caused by agglomeration of silicon dioxide particles or cracking of the hard mask layer due to internal stresses limit the usefulness of this process. The defect density associated with the application of a very thin imaging layer over an often rough middle layer is also a major issue for the trilayer process.
Another approach to imaging a circuit pattern onto a substrate involves introducing silicon into the surface layer of a resist material after exposure as described by Coopmans, et al. “DESIRE: A New Route to Submicron Optical Lithography”,
Solid State Technology
, pp. 93-97, June 1987. In this process a resist material is coated onto a substrate or an intervening planarizing layer and a circuit pattern is produced on the resist material by a standard UV exposure. The exposed wafer is subjected to silylation by either a gaseous or liquid silicon containing compound such as hexamethyldisilizane (HMDS) or silicon tetrachloride, whereby silicon is incorporated into the polymer. Depending upon the changes in the resist material caused by exposure to UV the silylating reagent can be incorporated either into the exposed or unexposed regions of the resist material. Silicon which has been incorporated into the resist material will be converted to an etch protective oxide when exposed to the oxygen etch process of the pattern transfer step. Consequently, the silylated regions of the polymer will etch at a significantly slower rate than the unsilylated regions.
Exposure to UV light can cause reactive groups to form in the resist material which react selectively with a silylating reagent such as disclosed in U.S. Pat. No. 4,751,170. Depending upon the composition of the resist material, exposure to UV light can cause the resist material to crosslink and/or form groups that react selectively with silylating agents as disclosed in U.S. Pat. Nos. 5,487,967 and 5,550,007. Diffusion of the silylating reagent is inhibited by the crosslinked regions of the resist material. Thus, those areas of the resist material that are crosslinked will be more easily etched. A modification of this process is disclosed in U.S. Pat. No. 4,931,351, wherein the resist material is first conventionally exposed to radiation, then developed by contacting the exposed resist material with a suitable developer known to those skilled in the art, such as tetramethylammonium hydroxide (TMAH) and the like, and then exposed to UV light to enhance reaction of the resist material with a silylating reagent to produce an
Baxter Janet
EUV LLC
Nissen Donald A.
Thornton Yvette C.
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