A photosensitive layer stack, method, and system are described with respect to improving dimensional resolution by pitch fragmentation during lithographic projection of a layer of an integrated circuit.
A photosensitive layer stack and methods for multiple exposure lithography are disclosed having a bleachable layer with a first absorption switching from absorptive to transmissive upon irradiation and a photochromic layer having a second absorption switching from transmissive to absorptive upon irradiation.
Like reference numerals have been used to identify like elements throughout this disclosure.
Embodiments of photosensitive layer stack for multiple exposure lithography, method and system for multiple exposure lithography are discussed in detail below. It is appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways and do not limit the scope of the invention.
In the following, embodiments of the photosensitive layer stack, method, and system are described with respect to improving dimensional resolution by pitch fragmentation during lithographic projection of a layer of an integrated circuit. The embodiments, however, might also be useful in other respects, e.g., pattern fidelity of two-dimensional structures or manufacturability of a layer of an integrated circuit.
Furthermore, it should be noted that the embodiments are described with respect to line-space-patterns, but might also be useful in other respects, including but not limited to dense patterns, semi dense patterns, patterns with isolated lines or two-dimensional patterns, and combinations between all them. Lithographic projection can also be applied during manufacturing of different products, e.g. semiconductor circuits and thin film elements. Other products, e.g., liquid crystal panels or the like might be produced as well.
In
It should be noted that the term “photochromic” refers to an absorption property of layer 110 where the absorption changes from initially transmissive to absorptive under irradiation. This behavior is known as photochromic effect. Suitable materials will be discussed below. The photochromic layer 110 can be based on a reversible or irreversible photochromic effect.
Utilizing the reversible photochromic effect, an absorption change from initially transmissive to absorptive is followed by a return to the transparent state after a certain time.
In case of irreversible photochromic effect, the photochromic layer 110 remains in the absorptive state. In addition, any intermediate behavior including, for example, a partial absorption without fully recovering into the initial transmissive state is considered to be within the scope of the term “photochromic.”
In the following, the term “bleachable” refers to an absorption property of layer 120 where the absorption changes from initially absorptive to transmissive under irradiation. Suitable materials will be discussed below.
When describing embodiments related to photolithographic structuring, any kind of lithographic projection apparatus using a wide spectrum of different feasible illumination wavelength can be used. Within the described embodiments, a projective optical system using a UV light source of about 193 nm may be employed having a certain demagnification. Other wavelengths, however, may be utilized (e.g., wavelengths of about 248 nm or about 158 nm). Furthermore, lithographic projection means with various projection systems may be used, such as proximity projection, reflective projection, etc. In addition, high NA systems like immersion lithography systems may be employed.
The term “substrate” includes semiconductor wafers having an already structured layer or already structured layer systems being arranged partially or fully covering the substrate. Silicon, germanium or gallium arsenide either doped or undoped are suitable materials. However, other materials of semiconductor wafers are not excluded. Furthermore other substrates like glass, plastic, or the like are also within the scope of term “substrate”.
It should be noted that in the embodiments depicted in
In the photosensitive layer stack 100, the bleachable layer 120 switches from absorptive to transmissive under irradiation with electromagnetic radiation. The electromagnetic radiation can be provided by an exposure device having, e.g., a wavelength in the UV-range (e.g. about 193 nm). Once a first irradiation dose has been reached, the bleachable layer 120 switches from absorptive to transmissive.
A suitable material for bleachable layer 120 includes composites having bleachable characteristics under UV-radiation. By way of example, the bleachable layer may include composites such as Dinitrophenol, Nitrosalicylaldene, m-Nitrophenol, or Ethylorange. It is also possible to use nano-sized particles formed from copper, silicon, germanium, and their various isomers, alloys or oxides.
In general, absorption of the photochromic layer 110 switches from transmissive to absorptive after a specific treatment.
In a first example, a further irradiation can be performed with a wavelength being different to the wavelength of the first irradiation. For example, the first irradiation can use an exposure with electromagnetic radiation having a wavelength of below about 250 nm. Subsequently, a second irradiation uses exposure with electromagnetic radiation having a wavelength higher than that of the first irradiation, e.g., above about 250 nm. Accordingly, the resist film layer 130 can be selected such that it is only sensitive to the first irradiation and not the second irradiation. In general, the absorption conditions of the photosensitive layer stack 100 are adapted to the exposure characteristics of an appropriate resist film material for the resist film layer 130, i.e., by taking into account exposure dose threshold and sensitivity range.
The treatment can also include affecting the photochromic layer 110 with a gas or a liquid, performing a wait cycle for a predetermined time following the first irradiation, or performing a thermal cycle, i.e., by heating the layer stack 100 with an appropriate thermal source such as an infrared source, for example.
Furthermore, this treatment can be an irradiation with the same electromagnetic radiation that alters the properties of bleachable layer 120. It should be noted, however, that a second irradiation dose, which can be different to the first irradiation dose of bleachable layer 120, might be necessary. For example, the second irradiation dose can be larger than the first irradiation dose. In this case, photochromic layer 110 shows a saturation behavior, i.e., the absorption reaches the absorptive state after exposure with the second irradiation dose has been performed.
The photochromic layer 110 may include composites having photochromic characteristics. By way of example, the photochromic layer 110 may include compounds such as Vulgin, Spiroxazine, and Chrome. It is also possible to use nano-sized particles formed from copper, silicon, germanium, and their various isomers, alloys or oxides.
A further embodiment is shown with respect to
In general, the photosensitive layer stack 100 with or without the first interface layer 150, the second interface layer 160, and the third interface layer 170 can include composites being soluble in a solvent such as water or a resist developer solution. However, when employing immersion lithography, photochromic layer 110 and/or bleachable layer 120 can include composites being not soluble in water in order to serve as a top coating for immersion lithography.
In the following, the embodiment according to
In the next step, as depicted in
During the first exposure, the photochromic layer 110 is irradiated by UV-photons in first areas 310 that are not blocked by absorbing elements of the first pattern on corresponding parts of the photomask. As a consequence, the photochromic layer 110 switches from transmissive to absorptive irradiating in the first area 310. As long as the photochromic layer 110 is still transmissive, UV-photons also illuminate the bleachable layer 120, which, in turn, switches the absorption from initially absorptive to transmissive. During the transmissive state of the bleachable layer 120, UV-photons irradiate the resist film layer 130 in a first area 310 corresponding to the first pattern.
The above described absorption changes of photochromic layer 110 and bleachable layer 120 are related to the respective irradiation dose. As explained above, the bleachable layer 120 can switch from absorptive to transmissive once a first irradiation dose has been reached. Absorption of the photochromic layer 110 can switch from transmissive to absorptive after a specific treatment, e.g., applying the irradiation which also exposes the bleachable layer 120 and structuring layer 130. After reaching a second irradiation dose, which can be larger than the first irradiation dose of bleachable layer 120, the absorption of the photochromic layer 110 changes after the bleachable layer has already turned its state into transmissive, allowing the resist film to become exposed in first areas 310.
The treatment can also include affecting the photochromic layer 110 with a gas or a liquid, performing a wait cycle for a predetermined time following irradiation, performing a thermal cycle, i.e., by heating the layer stack 100 with (e.g., an infrared source), or performing a further irradiation with a different wavelength, as explained above.
After treatment of the photochromic layer 110 has been performed, the resulting layer structure on substrate 140 is depicted in
After completion of the first exposure with the first pattern, a second exposure using a second pattern is performed. Both first and second pattern can be an alternating line space pattern having the corresponding lines in spaces of the other pattern. When overlaying the first and second pattern, i.e., by performing a multiple exposure, the resulting structure has a finer pitch as compared to the structures of first and second pattern, thus resulting in finer lithographic structures by pitch fragmentation.
The first pattern and the second pattern can be arranged on different areas of a single photomask. It is, however, also conceivable that the first pattern is arranged on a first photomask and the second pattern is arranged on a second photomask. The first photomask can be replaced by the second photomask after performing the first exposure. It should be noted that substrate 140 still remains within the lithographic apparatus. Accordingly, no additional alignment or adjustment steps are necessary for substrate 140. It should be mentioned that usually the mask alignment necessary for exchanging between first and second pattern can be performed with a much higher accuracy as compared to a wafer stage alignment.
Referring to
It should be noted that, according to this embodiment, during the second exposure, no further treatment of photochromic layer 110 is necessary. Below a further embodiment is described wherein the photochromic layer 110 also undergoes a absorption change similar to the first exposure step.
During second exposure, no actinic light under higher diffraction orders or actinic light being scattered at the photomask or stray light can enter the already exposed first areas 310 corresponding to the first pattern. This is due to the fact that the photochromic layer 110 is absorptive in the first areas 310 (or even in an extended area, as described above), so as to serve as a light shield during the second exposure. This greatly improves pattern fidelity, as no unwanted exposure of the resist film layer 130 can take place.
Processing continues by removing the photochromic layer 110 and the bleachable layer 120, as shown in
As shown in
A further embodiment is now described with respect to
Referring to
This fact can now be exploited to perform a third exposure outside the previously exposed region 810. It should be noted that a layout pattern used in manufacturing of different kinds of memory circuits (for example. DRAMs, FeRAM, NROM or the like) include a so-called cell array, which is located at the position of the individual memory cells. The cell array consists of very dense individual elements in order to arrive at high density memory cells. The cell array is surrounded by periphery structures which are used to select certain memory cells during operation of the memory chip. While the cell array consist of a regular pattern, the periphery structures quite often are represented by different patterns having line elements both in vertical and horizontal directions.
For lithographic projection, the imaging conditions can not usually be simultaneously optimized so as to precisely image the cell array and the periphery structures. According to this embodiment, the cell array can be printed in high resolution due to pitch fragmentation during the first and second exposure steps, while the periphery structures are transferred into resist film layer 130 during the third exposure.
Furthermore, it is possible to select the imaging conditions differently for each of the first and second exposure, as well as for the third exposure such that a pattern transfer form structuring device to the substrate can be achieved with a large process window and improved pattern fidelity as compared to a projection where a compromise between the cell array and the periphery structures has to be chosen. For example, the first and second exposure steps can be performed with polarized off-axis illumination and the third exposure can be performed with unpolarized on-axis illumination.
The projection of the third pattern is schematically shown in
Processing continues by removing the photochromic layer 110 and the bleachable layer 120, as shown in
As shown in
A further embodiment is now described with reference to
In the next step, as depicted in
During the first exposure, UV-photons do not irradiate the resist film layer 130 in the first area 310 as UV-photons are absorbed within the bleachable layer 120. It should be noted that “absorbed” means that the resist film layer 130 does not be exposed above its exposure dose threshold or well below the exposure dose threshold. Blocking of substantially all UV-photons is not required although possible and within the scope of the term “absorbed”.
Absorption of the photochromic layer 110 can switch from transmissive to absorptive after a specific treatment, which includes affecting the photochromic layer 110 with a gas or a liquid, performing a wait cycle for a predetermined time following irradiation, performing a thermal cycle, i.e. by heating the layer stack 100 with e.g. an infrared source, or performing a further irradiation with a different wavelength, as explained above. The treatment of photochromic layer 110 can also affect the dimensions of the corresponding absorptive areas on photochromic layer 110. As shown in
After treatment of photochromic layer 110 has been performed, the resulting layer structure on substrate 140 is depicted in
With respect to
Processing continues by removing the photochromic layer 110 and the bleachable layer 120, as shown in
As shown in
In
In step 1850, a second exposure using a second pattern is performed, which irradiates the photochromic layer such that it switches from transmissive to absorptive, the bleachable such that it switches from absorptive to transmissive, and the resist film layer in a second area corresponding to the second pattern.
In
In step 1940, a first exposure using a pattern on a photomask is performed, which irradiates the photochromic layer in a first area. In step 1950, a treatment of the photochromic layer is performed so as to switch the photochromic layer from transmissive to absorptive at least in the first area. Afterwards, in step 1960, a second exposure is performed, which irradiates the bleachable layer so as to switching from absorptive to transmissive and the resist film layer in a second area.
In
The projection apparatus 2000 furthermore includes a light source 2030, which is, e.g., an excimer laser with 193 nm wavelength. An illumination optic 2040 projects the light coming from the light source 2030 through the photomask 2020 into an entrance pupil of a projection system 2060. The photomask 2020 can include the first pattern and the second pattern, which can be arranged on different areas of a single photomask. It is, however, also conceivable that the first pattern is arranged on a first photomask and the second pattern is arranged on a second photomask. The first photomask can be replaced by the second photomask after performing the first exposure.
Accordingly, the substrate 140 remains within the lithographic apparatus. Consequently, no additional alignment or adjustment steps are necessary for the substrate 140. It should be mentioned that mask alignment in mask holder 2025 necessary for exchanging between first and second pattern can be performed with a much higher accuracy as compared to a wafer stage alignment in substrate holder 2010.
Having described embodiments of the invention, it is noted that modifications and variations can be made by persons skilled in the art in light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments of the invention disclosed which are within the scope and spirit of the invention as defined by the appended claims.