Patent Application
20140211175
1. Technical Field
This invention relates generally to the field of lithography and, more particularly, to approaches for enhancing resolution in lithographic processes using high refractive index fluids (e.g., in immersion lithography).
2. Related Art
Lithography is a common technique utilized in semiconductor processing. Although there are many types of lithographic processes, a common type of lithography is known as dry optical lithography whereby a wafer is irritated (e.g., via a laser) through a series of lenses and a mask. One type of laser is an argon fluoride laser (ArF laser), which is a particular type of excimer laser, that may also be referred to as an exciplex laser. With a certain wavelength, an ArF laser is a deep ultraviolet laser that is commonly used in the production of semiconductor integrated circuits. The term excimer is an abbreviation for ‘excited dimer’, while exciplex is short for ‘excited complex’. An excimer laser typically uses a mixture of a noble gas (e.g., argon, krypton, or xenon) and a halogen gas (e.g., fluorine or chlorine), which, under suitable conditions of electrical stimulation and high pressure, emits coherent stimulated radiation (laser light) in the ultraviolet range. In any lithographic process, resolution of the system is a constant variable desired to be optimized. Specifically, improved resolution yields improved patterning results.
In general, aspects of the present invention relate to an approach for enhancing resolution in a lithographic process (e.g., an immersion lithographic process). Specifically, a material having a high reflexive index (e.g., water) is provided on opposite sides of an objective lens. This allows a set of light rays (e.g., high intensity) to be directed/passed from a light source, through a condenser lens, over a mask, through the material positioned on one side of the objective lens, through the objective lens, through the material on the opposite side of the objective lens, and to a wafer that is then patterned. Positioning the material on both sides of the objective lens allows for improved resolution and lithographic patterning of the wafer for both on-axis illumination and off-axis illumination techniques.
A first aspect of the present invention provides a method for enhancing resolution in a lithographic process, comprising: providing a material having a high refractive index between a mask and an objective lens and between the objective lens and a wafer; and passing a set of light rays from a light source through a condenser lens and over the mask, wherein the set of light rays further passes through the material and the objective lens to the wafer.
A second aspect of the present invention provides a method for enhancing resolution in a lithographic process, comprising: passing a set of light rays from a light source through a condenser lens and over a mask; passing the set of light rays from the mask through a material having a high reflexive index positioned between the mask and an objective lens; passing the set of light rays through the objective lens; and passing the set of light rays through a material having a high reflexive index positioned between the objective lens and a wafer.
A third aspect of the present invention provides a lithographic system, comprising: a light source; a condenser lens positioned proximate the light source; a mask positioned proximate the condenser lens; and a material having a high refractive index positioned between the wafer and an objective lens and between the objective lens and a wafer.
These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings in which:
The drawings are not necessarily to scale. The drawings are merely representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting in scope. In the drawings, like numbering represents like elements.
Illustrative embodiments will now be described more fully herein with reference to the accompanying drawings, in which embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. As used herein, the singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms “a”, “an”, etc., do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced items. The term “set” is intended to mean a quantity of at least one. It will be further understood that the terms “comprises” and/or “comprising”, or “includes” and/or “including”, when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.
Reference throughout this specification to “one embodiment,” “an embodiment,” “embodiments,” “exemplary embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” “in embodiments” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The terms “overlying” or “atop”, “positioned on” or “positioned atop”, “underlying”, “beneath” or “below” mean that a first element, such as a first structure (e.g., a first layer) is present on a second element, such as a second structure (e.g. a second layer) wherein intervening elements, such as an interface structure (e.g. interface layer) may be present between the first element and the second element.
Immersion lithography is a photolithography resolution enhancement technique for manufacturing integrated circuits (ICs) that replaces the usual air gap between the final lens and the wafer surface with a liquid medium that has a refractive index greater than one. The resolution is increased by a factor equal to the refractive index of the liquid. Current immersion lithography tools use highly purified water for this liquid, achieving feature sizes below 45 nanometers.
As indicated above, aspects of the present invention relate to an approach for enhancing resolution in a lithographic process (e.g., an immersion lithographic process). Specifically, a material having a high reflexive index (e.g., water) is provided on opposite sides of an objective lens. This allows a set of light rays (high intensity) to be directed/passed from a light source, through a condenser lens, over a mask, through the material on one side of the objective lens, through the objective lens, through the material on the other side of the lens, and to a wafer. Positioning the material on both sides of the objective lens allows for improved resolution and lithographic patterning of the wafer for both on-axis illumination and off-axis illumination techniques.
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In various embodiments, design tools can be provided and configured to create the data sets used to pattern the semiconductor layers as described herein. For example, data sets can be created to generate photomasks used during lithography operations to pattern the layers for structures as described herein. Such design tools can include a collection of one or more modules and can also include hardware, software, or a combination thereof. Thus, for example, a tool can be a collection of one or more software modules, hardware modules, software/hardware modules, or any combination or permutation thereof. As another example, a tool can be a computing device or other appliance on which software runs or in which hardware is implemented. As used herein, a module might be implemented utilizing any form of hardware, software, or a combination thereof. For example, one or more processors, controllers, application-specific integrated circuits (ASIC), programmable logic arrays (PLA)s, logical components, software routines, or other mechanisms might be implemented to make up a module. In implementation, the various modules described herein might be implemented as discrete modules or the functions and features described can be shared in part or in total among one or more modules. In other words, as would be apparent to one of ordinary skill in the art after reading this description, the various features and functionality described herein may be implemented in any given application and can be implemented in one or more separate or shared modules in various combinations and permutations. Even though various features or elements of functionality may be individually described or claimed as separate modules, one of ordinary skill in the art will understand that these features and functionality can be shared among one or more common software and hardware elements, and such description shall not require or imply that separate hardware or software components are used to implement such features or functionality.
While the invention has been particularly shown and described in conjunction with exemplary embodiments, it will be appreciated that variations and modifications will occur to those skilled in the art. For example, although the illustrative embodiments are described herein as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events unless specifically stated. Some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes that fall within the true spirit of the invention.
