Optimization of space width for hybrid photoresist

Details Optimization of space width for hybrid photoresist Optimization of space width for hybrid photoresist

1998-10-13

2001-03-13

Baxter, Janet (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Radiation sensitive composition or product or process of making

C430S914000, C430S905000, C430S927000, C430S322000, C430S325000, C430S326000

Reexamination Certificate

active

06200726

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates generally to the field of semi-conductor manufacturing and, more specifically, to optimization of the width of spaces formed in a layer of hybrid resist during lithographic processing.
2. Background Art
The need to remain cost and performance competitive in the production of semiconductor devices has caused continually increasing device density in integrated circuits. To facilitate the increase in device density, new technologies are constantly needed to allow the feature size of these semiconductor devices to be reduced. For the past 20 years, optical lithography has driven the device density and the industry has resorted to optical enhancements to allow increasing densities. As an example, some such enhancements include overexposing/overdeveloping, hard and soft phase shifts, phase edge masks, and edge shadowing. Unfortunately, such enhancements tend to offer only minor increases in density and the limit of optical enhancements appears inevitable in the near future.
Conventional positive and negative tone photoresists used in optical lithography are characterized by a dissolution curve in which there is a single transition from a first dissolution rate to a second dissolution rate as the resist is exposed to varying levels of actinic radiation. In a positive resist, the initially unexposed resist is practically insoluble in developer, while the exposed resist becomes more soluble as the exposure dose is increased above a threshold value. For a negative resist, similar behavior is observed, except that the initially unexposed resist is soluble in developer, and the exposed area is rendered practically insoluble. Because of this differential solubility between the exposed and unexposed resist areas, it is possible to form a pattern in the resist film. Essentially, the soluble areas of the resist dissolve in developer to become spaces in the resist, while the insoluble areas remain as lines of resist material. The pattern thus formed can be used to fabricate integrated circuit devices, and is currently a critical component in their manufacture.
In an ideal situation, the exposure tool would only allow the radiation to expose the resist material through the reticle of the mask, thus providing sharp edges for the lines and spaces. However, diffraction patterns are formed at the edges of the reticle, resulting in partial exposure of the resist about the edges of the reticle. The partial exposure yields a resist profile that exhibits some slope at the transition from a line to a space rather than a sharp, vertical profile at the edge of a line, as would be present in an ideal resist image. Contrast is one indication of the degree to which the profile of a resist image conforms to the ideal resist image. When contrast is high, typically the resist image will possess a more vertical profile. As contrast decreases, the profile exhibits more of a slope at the edge of a line and less conformity to the ideal resist image. Diffraction thus contributes to insufficient contrast since it produces sloped line edges. Limitations in producing high contrast also limit the ability to produce lines and spaces having a small width. As the desired line or space width is decreased, reticle size is typically decreased to produce the smaller dimensions. Diffraction effects are more pronounced with a smaller reticle partly because the resist lines are correspondingly smaller and the sloped line edges become a more significant effect on the resist profile. Thus, it can be said that unless contrast is sufficiently high, a typical resist will not produce small width lines and spaces with sufficiently sharp line edges.
Efforts are being made to improve the contrast of photoresists, however, the basic mechanism of operation of the photoresist continues to be the same, that is, the resists behave as either positive or negative tone systems. It is desirable, therefore, to devise new mechanisms of resist response such that conventional optical lithography can be extended to smaller feature sizes at sufficiently high contrast. It is also desirable to form high contrast, smaller feature sizes without having to develop new tools and reticles to enable the reduction in size. If new tools and reticles happened to be developed later, then any new mechanisms of resist response combined with new tools and reticles will further extend lithographic capability.
Presently, for high performance devices, the control of the image size on the reticle and the control of image size from one batch of wafers to the next comprise the largest contributors to image size variation on the product. Such variation often introduces defects into a chip, lowering the yield of acceptable chips from a given manufacturing process. Chip yield at high performance is also strongly dependent on the uniformity of the image pattern across the chip and the centering of the image pattern at the correct dimension. Uniformity across the chip is typically quantified as the “across chip line width variation” or ACLV. The above circumstances exist currently for all types of lithographic patterning which use a reticle, including: optical, x-ray, and proximity E-beam, for example. The problem of image uniformity across the reticle is especially acute for lithographic techniques that use 1× masks, such as x-ray and proximity E-beam lithography. It is therefore desired to provide a photoresist material that allows very precise resist image control for the image size, independent of the image size control on the reticle.
Therefore, there existed a need to provide increased device density and a low ACLV, wherein the resist image control is preferably independent of the reticle image size control.
DISCLOSURE OF INVENTION
According to the present invention, a photo resist composition is provided containing at least one photoacid generator (PAG), wherein at least two photoacids are produced upon exposure of the photo resist to actinic energy and wherein the photo resist is capable of producing a hybrid response. By way of example, the at least two photoacids may differ in their effectiveness at catalyzing at least one mechanism of the hybrid response. In particular, at least one of the at least two photoacids may be a weaker acid and at least one of the at least two photoacids may be a stronger acid, wherein there exists a difference of at least four orders of magnitude between the acid dissociation constant (K
a
) of the weaker acid and the stronger acid. Further, the at least one PAG may include two PAGs, triphenylsulfonium triflate and di(p-t-butylphenyl)iodonium camphorsulfonate, respectively producing triflic acid and camphorsulfonic acid.
According to the present invention, a method for optimizing space width in a hybrid photo resist is also provided which includes the steps of: 1) selecting a desired space width; 2) selecting at least one photoacid generator (PAG), wherein at least two photoacids will be produced upon exposure to actinic energy in relative proportions sufficient to produce the desired space width in the hybrid photo resist; and 3) forming a hybrid photo resist composition comprising the at least one PAG. By way of example, the step of selecting at least one PAG may include the following steps: a) determining the space width produced alone by each photoacid in a group of candidate photoacids; b) selecting at least two photoacids from the group of candidate photoacids such that at least one photoacid produces alone a space width greater than the desired space width and at least one other photoacid produces alone a space width less than the desired space width; c) determining the relative proportions of the at least two photoacids that will produce the desired space width; and d) determining at least one PAG that will produce the at least two photoacids in the relative proportions.
The foregoing and other features and advantages of the present invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustr

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