JPS62258352A - Diarylnitrones - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of increasing the contrast of an image of an object, such as a mask for photolithography, for example in the manufacture of integrated circuits (ICs), and to materials used for that purpose.

BACKGROUND OF THE INVENTION Phosphorography in the manufacture of integrated circuits is primarily performed by optical means. In an effort to reduce circuit size, improve performance, and increase yield, optical methods have provided the resolution required in each successive generation of circuit technology.

However, the resolution of projection lithography systems has recently begun to approach physical limits imposed by practical constraints on numerical aperture and wavelength. Although further improvements in lithography technology are expected in the future, no significant improvement is expected in terms of lens resolution. How can we further reduce the minimum feature size achievable by optical techniques?
It is necessary to make further improvements by changing the lithography method used from other aspects.

One area where there is room for further improvement is found in the photoresist process. Each photoresist is characterized by a certain degree of incidence contrast necessary to form a pattern that can be used in subsequent processing.

This minimum required contrast of illumination is called the contrast threshold of the photoresist. Depending on the nature of the substrate, the desired pattern thickness, and the edge profile of the resist, conventional positive photoresists have contrast thresholds between 85% and 90% incident contrast. Currently, most production runs at 90% or higher incidence contrast. When the contrast threshold of a photoresist is lowered, the resolution that can be obtained with a given optical device improves due to the fact that image contrast is a decreasing function of the spatial frequencies present in the image. be done.

SUMMARY OF THE INVENTION The present invention is directed to a photoresist process that enhances the contrast of an aerial image used in the photoresist process prior to application to the photoresist.

One object of the present invention is to reduce the minimum contrast value required to form a usable image in a photoresist.

Another object of the present invention is to provide novel photobleaching compounds and materials.

According to one embodiment of the invention, a layer of photoresist is provided having a first thickness and a predetermined contrast threshold, while an object or mask having opaque areas and transparent areas is provided. An image of an object having a contrast less than a predetermined contrast threshold of the photoresist is formed on the photoresist layer by projecting light of a predetermined wavelength through the object. A layer of photobleachable material containing a photobleachable compound is provided between the object and the photoresist layer and adjacent the surface of the photoresist layer. The photobleaching compound is photosensitive to light of the wavelengths mentioned above and has a photobleaching property of 1
have an absorbance to molecular weight ratio of greater than about 10, expressed in /g-am. The ratio of the absorbance for the unbleached state to the absorbance for the bleached state of the photobleachable material is also greater than about 10. When light of the aforementioned wavelength and predetermined intensity is projected through the object onto the layer of photobleachable material until a reduction in the optical density of the layer of photobleachable material is obtained that is directly proportional to the incident amount of light of the aforementioned wavelength. , whereby the integral contrast of the image transmitted by the layer of photobleachable substance increases with the amount of light transmitted thereby, reaching a maximum value;
Then it decreases.

The parameters of the layer of photobleachable material are selected such that the maximum value of the integrated contrast is greater than a predetermined contrast threshold of the photoresist layer.

The sensitivity and thickness of the photoresist layer is such that the photoresist layer is sufficiently exposed to an amount of light within a predetermined range that is transmitted by the layer of photobleachable material and the integral of the photoresist in this transmitted image is above a predetermined contrast threshold. chosen to provide contrast. Light of the predetermined wavelength is projected through the object for a time sufficient to provide the predetermined amount of light transmitted through the photobleachable layer.

The layer of photobleachable material is removed and the photoresist layer is developed, thereby forming a pattern in the photoresist layer that exhibits an enhancement in the contrast of the reduced contrast image of the object.

The present invention further provides: (A) 100 parts by weight of an organic solvent; (B) 1 to 30 parts by weight, preferably 5 to 15 parts by weight of an inert organic polymer binder; (C) 1 to 30 parts by weight of an arylnitrone, preferably 5
-15 parts by weight; 300-450 nm (nanometer)
It provides a spin-castable mixture capable of forming a photobleachable layer with an absorption maximum in the range of .

The novel and essential features of the invention are pointed out with particularity in the claims. The structure and implementation method of the present invention, as well as other accompanying objects and advantages, are described in the following detailed description 1. It will become clearer especially when explained with reference to the drawings.

Most photolithography is currently performed by projection techniques that use an aerial image of a mask to expose photoresist. For low-contrast aerial images, even the parts of the image corresponding to the dark gamut of the mask
It has considerable strength. As the contrast decreases, it becomes increasingly difficult to distinguish darker areas from lighter areas. The present invention provides a method for enhancing the contrast of an image incident on a photoresist, thereby improving its identifiability. This contrast enhancement is based on the use of photobleachable materials that are initially relatively opaque but become relatively transparent after exposure to a certain amount of light.

The light transmittance of an idealized photobleachable layer is shown in FIG. When the aerial image of the mask is incident on the photobleachable layer, the areas of the layer exposed to the highest light intensity will be bleached first, while the areas of the layer exposed to the lowest light intensity will be bleached. Bleached at a later point.

In Figures 2A to 2F illustrating the dynamics of this bleaching process, Figure 2A first shows a mask consisting of opaque areas 11 giving 0% transmittance separated by open or transparent areas 12 giving 100% transmittance. It shows the relative transmittance of an object like . IO is the incident light intensity, l is the transmitted light intensity, E,
is the amount of light irradiation required to cause bleaching of the photobleachable layer. FIG. 2B is a graph 13 showing the relative light intensity of an aerial image of a mask as a function of position when placed in an optical projection device to generate an aerial image used, for example, for exposing a layer of photoresist. It is. It is assumed that the wavelength of light used and the dimensions of each area of the mask are such as to produce the contrast shown. (2) is the maximum intensity of the image, and flaX is the minimum intensity of the image, and lff11n is the minimum intensity of the image. FIG. 2C shows a cross-section of an idealized layer 15 of photobleachable material.

FIG. 2D shows the bleaching of layer 15, depicted by dotted line 16, at the end of the first period. FIG. 2E shows the bleaching of layer 15, delineated by dotted line 17, at a later point in time. Figure 2F shows the bleaching of layer 15, delineated by dotted lines 18 and 19, at the end of the exposure and the bleaching is stopped. If the exposure is stopped at a point corresponding to Fig. 2F,
The transmittance of the photobleachable layer corresponds to that of the original mask.

If such a photobleachable material is applied over a conventional photoresist layer, the resulting composite layer can have a contrast threshold that is lower than that of the photoresist layer alone. This may be true if the photoresist is sensitive enough to require a short exposure time compared to the bleaching time. This photobleachable layer essentially forms an in-situ contact mask for the photoresist layer. The net effect of this in-situ contact mask is to increase the contrast incident on the photoresist over the contrast of the aerial image.

Contrast when applying contrast enhancement technology to submicron photolithography! - Some physical and chemical constraints arise in the enhancement layer itself. The contrast-enhancing layer must be thin and at the same time optically dense. The requirement for layer thickness is due to the narrow depth of focus of high-resolution optical systems. This limits the layer thickness to a range of less than about 1 micron. Since the contrast-enhancing layer must also be optically dense, the photochemical component of the layer must have strong light absorption properties. Since the light transmittance after bleaching is determined by the absorbance of the photoproduct, the photoproduct must have a significantly lower absorbance than the parent molecule. The absorbance is defined by the equation: % (1) where A is the absorbance, b is the optical path length (cm), and C is the concentration (mol/1). Absorbance is calculated by the equation: IO A -log+. □ (2)! [In the formula, 1. is the incident light intensity and! is the transmitted light intensity].

The absorbance ε of a substance is determined by measuring the parameters A, b and C of equation (1).

Parameter A is determined from equation (2).

First, a known volume of a substance is dissolved in a known volume of a solvent to determine the concentration C of the substance in the solution. This solution is placed in a cell with known dimensions, placed in the optical path of a spectrophotometer, and the cell is irradiated with light having a known light intensity of 1o. The intensity of transmitted light from this cell is measured. Similarly, only the solvent is placed in another cell with the same known dimensions and placed in the optical path of the spectrophotometer to obtain a known light intensity! . The light is directed towards this cell.

The intensity of transmitted light from this cell is measured. The light intensity measurements for the solvent alone are used to correct the transmitted light intensity I for cell and solvent absorption. Thus, using these values for the incident light intensity ■o and the transmitted light intensity ■ in equation (2), the absorbance A is determined. Dimensions are determined from cells of known dimensions. Therefore, the absorbance for the substance is given by substituting the values of c and A into equation (1). Measurement of absorbance of various substances is done by Do
uglas A, Skoog and Donald M,W
est, New York, 11o1d, Rlne.
Published by Hart and Wlnston, Inc.”
Pundamcntals o['Analytic
Chea+1str, 2nd edition (1969), No. 64
Also described on pages 4-652.

Furthermore, the quantum yield of the bleaching reaction must be as high as possible in order to minimize the required increase in exposure time. Also, since photoresists are commonly applied by spin code techniques, it would be advantageous if the contrast enhancement layer could also be applied in a similar manner. The solvent that dissolves the photobleachable material must be compatible with the photoresist layer. Furthermore, it is necessary to be able to apply a contrast-enhancing layer with good optical properties by spin-coating. Finally, the wavelength range in which these photobleaching substances are effective must be the same as the wavelength range in which the optical projection device operates.

Direct writing equipment on wafer (Dlrcct-step
Most of the -on-the-vaf'cr systems>405na operate at 436nm. In this case, OptiMetrix Co., Ltd. (Optia+etrIx Co., Ltd., Mountain View, California, U.S.A.)
) Obtimetric X10:I DS available from
A wavelength of 405n11 was chosen for use on the W instrument. The search for suitable photobleaching materials was based on these constraints. In particular, the search for suitable photobleaching substances was based on absorption maxima within the wavelength range of 300-450 nm.

A model of the photobleaching process was developed and used in the evaluation of photobleachable materials suitable for use in contrast enhancement layers. The parameters of this model are shown in the table below.

Table 1 State quantities Explanation'! :A Absorbance of the molecule in the unbleached state EB Absorbance of the molecule in the bleached state Φ Quantum yield of the bleaching reaction No Initial optical density of the molecule in the unbleached state Fo Density of photons incident on the contrast enhancement layer to Density of photons incident on the contrast enhancement layer Film thickness nf Refractive index of the bleached layer nB Refractive index of the glass substrate on which the contrast enhancement layer is placed Based on the above analysis and the model of the photobleaching process, three criteria were established for the material parameters. These are shown in Table 2.

Table 2 State quantity Numeric value (1) ε/Molecular weight ≧100i'/g -cm(
2) Φ ≧0.2 (3) ε Unbleached state□ □ ≧30 ε Bleached state The first criterion is based on the need for a film with high optical density, and the packing density of absorption centers in the contrast enhancement layer Essentially related. The second criterion is based on the need to achieve the transition from the unbleached state to the bleached state as quickly as possible. The tolerance of a given quantum yield is to some extent related to the first criterion, since improvements in the first criterion can compensate for deficiencies in the second criterion. The third criterion is based on the need for the contrast-enhancing layer to be transparent after the bleaching step. These criteria were used in the initial search for suitable photobleaching materials.

Selection of suitable photobleaching compounds is made by evaluation in the above-described model of the photobleaching process and by tests in which the compound is placed in a layer and the relative transmittance is measured as a function of exposure time or amount of light while keeping the light intensity constant. It has been determined. A large number of different photobleaching compounds with photobleaching properties based on different photobleaching mechanisms were evaluated. Photobleachable compounds based on a photoisomerization mechanism have been found to be particularly suitable. Among these compounds, in particular formula (1): %Formula %(1) (wherein Z is a monovalent group selected from (R3)a-Q-R4- and R5-; Z' is - is a monovalent group selected from 16(X)b; R1R1,
R2 and R3 are -valent atoms or groups selected from hydrogen, C alkyl, (L-8) substituted C alkyl, C aryl hydrocarbon group, and substituted C aryl hydrocarbon group; Q is F, CL Br .

1, a monovalent, divalent or trivalent atom selected from O, S and N; a is 0.1 or 2; R4 is C(8-1
3) an aryl hydrocarbon group or a substituted C aryl hydrocarbon group, where R5 is an unsubstituted or substituted C aromatic heterocyclic compound residue containing one or more atoms selected from O, N and S; R6 is a C aromatic hydrocarbon group; Any combination according to the value of b of 0°1.2 or 3; n is 0. 1. 2. 3
It has been found that the arylnitrones represented by the formula (or 4) are particularly suitable. The above compounds are for example "methoden der Org"
anlschen CheIlle' (Ilo
Uben-Weyl), Volume 10, Bart 4. Third
15-416 (1968) or Chem by Jan Hamcr and Anthony Hacaluso.
ical Revicvs (1964) Middle tube 476-
It can be manufactured using a method such as that described in "N1troncs" on page 4133.

A variety of aryl ring systems may be formed with a variety of substituents to suit the particular requirements of the optical system used in photoimaging. The arylnitrones have an extinction coefficient of 2 to 5 x 104 f1 molar cm and an extinction coefficient of 0. 1~
0. Photobleach with a quantum yield in the range of 5.

For direct-on-wafer writing systems capable of writing at 405 nm, nitrones of structural formula (2): where A is a C aromatic organic group have been found to be particularly useful. Ta.

This type of p-dialkylaminoaryl nitrones includes, for example, polycyclic compounds such as the compound represented by formula (3).

One preferred group of nitrones represented by formula (2) is the formula: [wherein X is the following group: -C-0R7, -C-R7, -CN (R')2, -CN.

-CF3 is an electron withdrawing group bonded at the ortho or para position selected from halogen, (wherein R7 is a C alkyl group, particularly preferably 1-8) (is a methyl, ethyl, propyl and butyl group) ] are diarylnitrones. Examples of halogen groups included in the above definition of X are fluoro, chloro and bromo groups.

Suitable binders for use in providing spin-castable mixtures for forming photobleachable layers incorporating arylnitrones of formula (1) include, for example, vinyl acetate polymers (homopolymers, and copolymers) and their partially saponified products (e.g. polyvinyl acetate); copolymers of styrene or its derivatives; polymers and copolymers of acrylate or methacrylate esters; acetal resins; acrylonitrile/butadiene copolymers cellulose ethers soluble in ethyl cellulose and other hydrocarbons; cellulose esters soluble in cellulose propionate and other hydrocarbons; poly(chloroprene); poly(ethylene oxide); poly(vinylpyrrolidone); etc. do.

Suitable solvents for use in providing spin-castable mixtures for forming photobleachable layers incorporating arylnitrones of formula (1) include, for example, aromatic hydrocarbons (
(e.g. toluene, xylenes, ethylbenzene, chlorobenzene) alone or in mixtures with aliphatic hydrocarbons (e.g. cyclohexane); halogenated aliphatic compounds (e.g. trichloroethylene, methylchloroform); alcohols (e.g. propatool, butanol). include.

In formula (2), R3 is -CH3CH2- and 1
Diarylnitrone, which is 1 m Q, has been found to be particularly suitable. This nitrone compound, called α-(4-diethylaminophenyl)-N-phenylnitrone, exhibits strong absorption at 405r+m and undergoes monomolecular cyclization at this wavelength to convert into oxacillidine, making it highly efficient and almost transparent. It was found that it can be photobleached.

This nitrone compound is easily soluble in solvents with moderately low polarity (e.g. toluene, ethylbenzene), and is highly soluble in polystyrene, poly(hydroxyethyl methacrylate),
Forms good films at high loading densities with a wide range of polymers such as poly-alpha-methylstyrene, poly(methyl methacrylate), polyvinylpyrrolidone, vinylpyridine/styrene copolymers, and allyl alcohol/styrene copolymers. This nitrone compound, α-(4-diethylaminophenyl)-N-phenylnitrone, is 40
It has an absorbance to weight ratio of 1301/r-cm at 5na+. This compound was incorporated into the contrast enhancement layer by the following method. α-(4-diethylaminophenyl)-N-phenylnitrone (5% by weight of the solution) and styrene/allylic alcohol copolymer (as a binder)
5% by weight of the solution) is dissolved in toluene. A glass substrate is coated with a film thickness of 250 nffl by a spin-coating method.

The relative transmittance of this sample was tested at 405 nm and was found to have the relative transmittance versus time characteristics shown in FIG. 3 at 405 nm.

The photobleaching model was used to calculate the contrast improvement as a function of exposure time for the contrast enhancement layer of FIG. This is accomplished by calculating the degree of bleaching for two representative points in a given pattern. In this example, we choose two incident light intensities that correspond to the maximum and minimum values of the line and spatial grid patterns. The contrast C that these two light intensity levels sign is defined as follows: ■ff1ax-Iff11n C-(3)! wax ''Ia+in. The model of the photobleaching method is used to measure the transmitted light intensity as a function of the amount of incident light for both the maximum and minimum values. From these quantities, the instantaneous contrast and the integral contrast can be calculated. can be calculated as a function of the amount of incident light. Figure 4 shows a graph of the light intensity and calculations for a 30% contrast pattern incident on the layer of the sample described above. Graph 21 shows the incident light intensity in Joules. Graph 22 shows the relative transmittance at the relative maximum as a function of the amount of light. Graph 23 shows the relative transmittance at the minimum as a function of the amount of incident light. Graph 23 is determined from graphs 21 and 22 using equation (3). Graph 24 shows the instantaneous contrast as a function of the amount of incident light applied.Graph 24 shows I and lff instead of instantaneous contrast values.
The integral contrast obtained from equation (3) using the integral value aX of 11n is shown. Since photobleaching is a dynamic process, the contrast obtained from transmitted light is also a function of the amount of light. A more useful graph than Figure 4 is shown in Figure 5. In FIG. 5, a graph corresponding to FIG. 4 is plotted as a function of the amount of transmitted light. This graph allows estimation of contrast enhancement as a function of the sensitivity of the photoresist used in conjunction with the contrast enhancement layer. Graph 2
6 shows the relative transmittance at the relative maximum as a function of the amount of transmitted light. Graph 27 shows the relative transmittance at the relative minimum as a function of the amount of transmitted light.

Graph 28 shows the instantaneous contrast obtained from graphs 26 and 27 as a function of the amount of transmitted light using Equation 3. Graph 29 shows I and ■1I as a function of the amount of transmitted light.
The integral contrast obtained from equation (3) using the integral value of 11n is shown.

The method used to utilize the contrast-enhancing layer is described below and the results obtained therefrom are compared with those obtained under the same conditions but without the use of a contrast-enhancing layer. Section 6A describes various steps of a method of forming a pattern of photoresist on a suitable substrate.
Referring to FIGS. 6E-6E, FIG. 6A shows a substrate 31 and a suitable photoresist formed thereon.
Figure 3 shows a layer 32 of the Shipley 1400 series, a positive photoresist available from the Company. Such positive-acting photoresists are made of a novolac resin or poly(vinylphenol), a diazonaphthoquinone ester and a solvent (e.g. cellosolve acetate, xylene).
Consisting of This liquid photoresist is placed on the surface of the substrate,
It is then spun to form a layer of desired thickness. After baking the photoresist layer to remove the solvent, a contrast enhancement layer 33 is formed on the surface of the photoresist. This contrast-enhancing layer 33 consists of a styrene/allylic alcohol copolymer binder (
5 mm% of the solution) and α-(4-diethylaminophenyl)-N-phenylnitrone (5% by weight of the solution). Apply this solution to photoresist 3.
2, spun and then baked to remove the solvent, forming a layer 33 of the desired thickness as shown in FIG. 6B. 1r'? The photoresist layer is then sensitized and sufficiently exposed to an irradiation pattern consisting of an irradiation area 35 and a non-irradiation area 36 located below an arrow 37 indicating light irradiation, as shown in FIG. 6C. Exposure is performed at a range of light levels and for a time sufficient to form a contrast-enhanced image. Thereafter, the contrast enhancement layer 33 is removed, as shown in FIG. 6D, using a suitable stripping solvent, such as trichlorethylene, which removes only the contrast enhancement layer without affecting the photoresist. Further thereafter, as shown in FIG. 6E, unexposed or underexposed areas 38, 39 and 40
Remove the exposed portion of the photoresist leaving behind.

To measure the improvement in contrast threshold achieved by using a composite layer of contrast-enhancing layer and photoresist according to the present invention, α-(4-diethylaminophenyl)-N-phenylnitrone and styrene/allyl alcohol bonds Various patterns were formed using the photobleachable materials described above in combination with a Shipley 1400 series positive photoresist. One silicon wafer or substrate is coated with only a 1.6 micron thick photoresist layer, and the other silicon wafer is coated with a 1.6 micron thick photoresist layer and then a layer of the photobleaching material described above. It was coated with a thickness of 0.25 microns. An opaque line with a width of 2 microns, a transparent space with a width of 2 microns, an opaque line with a width of 0.8 micron, and a width of 0.8 micron.
An object consisting of a micron-sized transparent space was projected using an Obtimetrics 10:1 projection device at 405 nm.
, using a light intensity in a range that forms a large number of patterns in the photoresist in the wafer 71 that has only a photoresist layer, and also writes a large number of patterns in the photoresist on the wafer 71 that has a photoresist layer and a contrast enhancement layer. Drawing was performed using a light amount within the range that forms the pattern. The photoresist on each wafer was developed to obtain a pattern of lines and spaces formed in the photoresist. A pattern is formed in a wafer having only a photoresist layer using the minimum exposure amount required to create a space of 0.8 micron width at the interface of the photoresist and the substrate using the minimum exposure amount required to create a space of 0.8 micron width at the interface of the photoresist and the substrate. A comparison was made with a pattern formed in wafer 71 having a photoresist layer and a contrast enhancement layer using the lowest exposure required to open the voids. Width 2. The θ micron lines and 2.0 micron wide spaces were accurate for both wafers with only a photoresist layer and wafers with a photoresist layer and a contrast enhancement layer thereon. Width 0. The 8 micron line was significantly overexposed on a wafer with only a photoresist layer using an exposure dose that created a 0.8 micron wide void in the photoresist. On the other hand, in a photoresist on a wafer having both a photoresist layer and a contrast enhancement layer using an exposure dose that forms a 0.8 micron wide space in the photoresist, a 0.8 micron wide line part is properly exposed. A line portion with a width of 0.8 microns was formed. Moreover, the wall profile of the pattern obtained using the contrast-enhancing layer was vertical. The pattern formed in the photoresist is poorer without the use of a contrast-enhancing layer because the aerial image contrast obtained at a given output of an Obtimetrics projection device is less than the light image or illumination pattern obtained from the device. This is because the higher the spatial frequency that exists within, the lower it becomes.

Although the invention has been described above in connection with a particular positive-working photoresist, it will be appreciated that other positive-working and negative-working photoresists may also be utilized. Further, as an example for explaining the present invention, a case where a photoresist with a specific thickness and a contrast enhancement layer with a specific thickness is used is shown, but it is of course possible to use photoresists and contrast enhancement layers with other thicknesses. That's true. Preferably, the photoresist layer should have a thickness of less than about 3 microns and the contrast enhancement layer should have a thickness of less than about 1 micron.

Furthermore, although equal weight proportions of a photobleaching compound and a binder therefor are used as an exemplary composition of the contrast-enhancing layer, other proportions may of course be used if desired.

Regarding photoresists, we have mentioned that they have a characteristic so-called contrast threshold; this characteristic depends on the conditions of the photoresist itself as well as the conditions of use of the photoresist, such as the type of substrate on which it is coated and its reflectance. It should be noted that it is a function of .

Preferably, the ratio of the absorbance in the unbleached state to the molecular weight of the photobleachable compound is greater than about 100, and the ratio of the absorbance in the unbleached state to the absorbance in the bleached state of the photobleachable compound is preferably greater than about 30. Although it is preferable that the ratio be large, a numerical value of about 10 may be satisfactory.

Although we have used the particular type of photobleaching compounds described above that are based on monomolecular cyclization, namely arylnitrones, other photobleaching compounds that are based on monomolecular cyclization or based on other photobleaching mechanisms, e.g. Compounds may also be used in accordance with the present invention.

The α-(4-diethylaminophenyl)-N-phenylnitrone mentioned above and also shown in Table 3 is p-diethylaminobenzaldehyde (18°5g, 0.1
mol) and freshly prepared phenylhydroxyamine (
11°l, 0.1 mol) was prepared by condensation reaction in 40 ml of absolute ethanol at room temperature for 18 hours.

Evaporation of the solvent gave a red oil which was crystallized twice from toluene/petroleum ether to give the nitrone 13. Og
(0.05 mol) was obtained. Melting point 103-105°C.

Further recrystallization of an analytical sample of this compound increased the melting point to 110-112°C.

Other nitrones with absorption maxima in the wavelength range of 300-450 nm are also shown in Table 3. In Table 3, λ (n
m) indicates the absorption maximum ax in nanometers, ε indicates the absorption ax light gravity at the wavelength of maximum absorption, and lap indicates the melting point in degrees Celsius ('C).

These other nitrones were also produced by condensing the corresponding aldehydes and phenylhydroxyamines in polar solvents using a method similar to the method for producing the nitrones.

B -
2w! Mahachi 1 A I A 16 verses
The el size
In the method of the invention, the photobleachable layer is present in the form of an in-situ contact mask on the photoresist layer.

Formation of such composite structures offers numerous advantages.

The photobleachable layer perfectly conforms to the topography of the surface of the photoresist layer, thus preventing the formation of voids between hypoindoids on the surface of the photoresist layer and the photobleachable layer. Such voids may be formed if the two layers are formed on separate supports and then combined. Such voids are especially important when the features to be imaged are on the order of 2.3 microns and when the field depth of the projection device is 2.3 microns.
3 microns would be significantly detrimental to the resolution of the image formed in the photoresist. Additionally, when a layer of photobleachable material is brought into close contact with a layer of photoresist and then separated, the breaks in one layer will stick to the other layer;
This creates the risk of damaging the photoresist layer.

Although the present invention has been described in a specific embodiment, where the contrast-enhancing layer is provided in close contact with the photoresist layer, the contrast-enhancing layer may be formed separately from the photoresist layer if desired, e.g., in situ. They can also be separated by thin conformal layers of neutral material.

Although the present invention has been described with particular reference to particular embodiments, it will be apparent to those skilled in the art that various modifications, such as those described above, may be made. It is intended to include such variations and modifications without departing from the technical idea of the invention as set forth in the claims.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relative transmittance of an idealized photobleachable layer as a function of the amount of light impinging on the incident surface of the layer. Figures 2A-2F are diagrams useful in explaining the kinetics of the photobleaching process used in the present invention. FIG. 3 is a graph showing the relative transmittance of a particular contrast-enhancing layer as a function of response time when the layer is exposed to a particular amount of incident light. FIG. 4 is a set of graphs showing the relative transmittance of a 30% contrast image and the resulting instantaneous and integrated contrast values for the maximum and minimum transmittance cases as a function of the amount of incident light. FIG. 5 is a set of graphs showing the relative transmittance and contrast as a function of transmitted light for the graph of FIG. 6th
Figures A-6E are cross-sectional views of a structure showing a series of successive steps in one embodiment of the method of the present invention.

Claims (1)

[Claims] 1. Formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [In the formula,
There are tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ -CN, -CF_3 and halogen, (However, R^7 is C
is an electron-withdrawing group present in the ortho or para position selected from _1_-_8 representing an alkyl group]. 2. The compound according to claim 1, which is α-(4-diethylaminophenyl)-N-phenylnitrone. 3, α-(4-diethylaminophenyl)-N-(4-
The compound according to claim 1, which is ethoxycarbonylphenyl)nitrone. 4, α-(4-diethylaminophenyl)-N-(4-
The compound according to claim 1, which is butoxycarbonylphenyl)nitrone.