Pattern forming method, semiconductor device manufacturing method and exposure mask set

First, a first exposure process is performed using dipole illumination with only a grating-pattern forming region as a substantial object to be exposed. Next, a second exposure process is performed with only a standard-pattern forming region as a substantial object to be exposed. A development process is then performed to obtain a resist pattern. A mask for the first exposure process is such that a light blocking pattern is formed on the whole surface of a standard-pattern mask part corresponding to the standard-pattern forming region. A mask for the second exposure is such that a light blocking pattern is formed on the whole surface of a grating-pattern mask part corresponding to the grating-pattern forming region.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a pattern forming method, and in particular to a resist pattern forming method including both a grating pattern, which is a fine pattern, and a pattern of arbitrary shape, in a lithography step in the course of a process of manufacturing a semiconductor device.

2. Description of the Background Art

The shrinking of semiconductor circuit patterns in recent years is largely attributable to the progress of optical lithography technique, which mainly results from wavelength shortening of an exposure light source. However, ways of shrinking patterns other than the wavelength shortening have been studied in many fields due to price increases in exposure device. For example, as a result of the progress such as enlargement of the aperture of a lens by scanner-type exposure technique, modified illumination technique, super-resolution mask technique or the like, there is a growing trend to shrink manufacturing dimensions of a pattern while maintaining an exposure wavelength. A reversed phenomenon has taken place from a 0.18 μm (180 nm) generation on down in which manufacturing dimensions are less than an exposure wavelength (KrF Excimer laser: 248 nm).

In forming a fine pattern less than the wavelength of light that is used for exposure, techniques using a half-tone phase shift mask, a phase shift mask, and a modified illumination technique are well known. In techniques using the masks, a special mask is used having a portion thereon for inverting the phase of light of an exposure wavelength, for example, to enhance optical intensity contrast on an image-forming surface by an optical interference effect.

In the modified illumination technique, a mask surface is illuminated by optimizing the shape of illumination such that all complicated circuit patterns designed on the mask are formed with stability in dimensions and two-dimensional shapes thereof, to enhance optical intensity contrast of all the patterns on an image-forming surface.

For example, with a fine circuit pattern that includes a pattern (grating pattern (repetition pattern)) in a lattice having fine lines and spaces being repeated alternately, and a pattern (standard pattern) provided to be partly continuous with the grating pattern and to have larger dimensions than the grating pattern, the shape of illumination has been optimized such that excellent optical contrast is obtained for the fine circuit pattern.

A typical example is the optimization of an outer contour radius (outer diameter R1) and an inner contour radius (inner diameter R2) of annular illumination that blocks light circularly at the center of an illumination optical system. The sizes of four openings of four-lens illumination have been optimized as well.

U.S. Pat. No. 5,858,580 discloses forming a fine circuit pattern by a two-exposure process, in which a wiring portion thinner than an exposure wavelength is formed using a phase shift mask and the other portions are formed using a standard mask. This method is being put to practically use.

In addition, U.S. Pat. No. 5,415,835 and Japanese Patent Application Laid-Open No. 2000-349010 disclose forming a fine circuit pattern by a multiple exposure process including a two-exposure process. U.S. Pat. No. 5,415,835 discloses a technique of fabricating a fine pattern by performing a dual beam interference exposure with a device other than standard reduced projection exposure devices. Further, U.S. Pat. No. 5,858,580, Japanese Patent Application Laid-Open No. 2000-349010, U.S. Pat. Nos. 6,228,539, 6,258,493 and 6,566,023, and United States Patent Application Publication No. 2004-197680 disclose a method in which a standard exposure step and a fine isolated wiring pattern (gate pattern) or fine periodic pattern exposure step are performed without intervention of a development process, the fine isolated wiring pattern or fine periodic pattern exposure step being performed using a Levenson type phase shift mask (Alternative Phase Shift Mask) in which phase-inverted complete transmissive areas are juxtaposed to each other. Furthermore, International Patent Application Publication No. WO99/65066 and Japanese Patent Application Laid-Open No. 2000-021718 disclose a method of forming a periodic pattern using dipole illumination, and forming an isolated pattern by erasing the periodic pattern other than a partial wiring in the periodic pattern with a standard pattern by means of exposure.

The following equation (1) is the Rayleigh equation indicative of optical resolution:
R=k1·(λ/NA)   (1)
where R is pattern resolution, λ is an exposure wavelength, NA is a lens numerical aperture, and k1is a process factor.

It is now assumed that a resist pattern for a fine circuit pattern that includes a grating pattern having a process factor k1of less than “0.3”, and a standard pattern having an arbitrary pattern such as fine isolated space and a process factor k1of “0.5” level, is subjected to patterning. It may be required in some instances that a grating pattern and standard pattern be connected in such resist pattern.

In the conventional techniques described above, it is difficult to resolve this fine circuit pattern with stability no matter how optimized the shape of illumination is. For example, setting the NA to “0.85” with the ArF wavelength (193 nm), the grating pattern of 65 nm L/S will have a process factor k1of “0.28”. In this case, it was extremely difficult even with a phase shift mask technique having a process factor k1of less than “0.3” to form the fine circuit pattern with high accuracy that includes the fine grating pattern and the arbitrary standard pattern having a process factor k1of “0.5” level.

This is because when a phase shift mask suitable for the grating pattern is used, a phase mismatch associated with the principle of phase shift mask occurs inevitably due to the pattern arbitrariness, leaving an unintentional and unnecessary pattern on the standard pattern side. Although a negative type resist is commonly used in order to avoid this problem, a resist material having excellent resolution characteristics for the ArF wavelength is nonexistent, and if it does exist, then the resolution between the same phases will inevitably be insufficient due to the circuit structure.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a pattern forming method capable of forming a fine circuit pattern including a grating pattern having a process factor k1of “0.3” or less and a standard pattern having a process factor k1of “0.5” level with high accuracy.

In an aspect of this invention, a pattern forming method on a resist formed on a predetermined substrate, with the resist including adjacent first and second regions to be patterned, includes the following steps of: (a) performing a first exposure process with a first exposure mask using dipole illumination substantially on the first region of the resist, the first exposure mask having a repetition pattern in which a line and space are repeated alternately; (b) performing a second exposure process with a second exposure mask substantially on the second region of the resist, the second exposure mask having a standard pattern that is a pattern excluding the repetition pattern, the standard pattern at least partially including a connection pattern continuous with the repetition pattern; and (c) performing a development process on the resist having being subjected to the steps (a) and (b).

An exposure process can be performed that is suitable for each of the first and second regions to be provided with the repetition pattern and standard pattern. The result is that a resist pattern including the repetition pattern and standard pattern that are formed continuously with each other through the connection pattern can be obtained with high accuracy.

In another aspect of this invention, a semiconductor device manufacturing method includes the following steps of: (a) forming a resist on a semiconductor substrate or an object to be patterned inside the semiconductor substrate; (b) patterning the resist using the pattern forming method recited in claim1; and (c) patterning the object to be patterned with the resist having been patterned as a mask.

The object to be patterned can be patterned with high accuracy.

In another aspect of this invention, an exposure mask set includes first and second exposure masks. The first exposure mask includes adjacent first and second mask parts, the first mask part having a repetition pattern in which a line and space are repeated alternately. The second exposure mask includes first and second mask parts equivalent to the first and second mask parts of the first exposure mask, the second mask part having a standard pattern that is a pattern excluding the repetition pattern, at least part of the standard pattern including a connection pattern for being continuous with the repetition pattern. The first exposure mask is provided with a light blocking region on the whole surface of the second mask part, and the second exposure mask is provided with a light blocking region on at least part of the first mask part. The first and second exposure masks each include a transmissive part, a half-tone phase shift mask part transmitting light only at a predetermined ratio and inverting a phase of light being transmitted therethrough, and a light blocking part having a smaller transmission factor than the predetermined ratio. The second mask part of the first exposure mask is formed at least of the light blocking part in a region excluding a boundary adjacent region between the first and second mask parts. The first mask part of the second exposure mask is formed at least of the light blocking part in a region excluding the boundary adjacent region.

The second mask part excluding the boundary adjacent region blocks light during the first exposure process with the first exposure mask, and the first mask part excluding the boundary adjacent region blocks light during the second exposure process with the second exposure mask.

The result is that no part of the repetition pattern is subjected to light transmission during the second exposure process, allowing the repetition pattern to be obtained with high accuracy. In addition, since no part of the standard pattern is subjected to light transmission during the first exposure process, allowing the standard pattern to be obtained with high accuracy.

These and other objects, features, aspects and advantages of this invention will become more apparent from the following detailed description of this invention when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Preferred Embodiment

FIG. 1illustrates a flow chart for a pattern forming method according to a first preferred embodiment of this invention. This method will generally be described.

First, at step S1, a resist is applied to the surface of a predetermined substrate. The predetermined substrate as used herein means a substrate having a silicon wafer and a film subject to pattern formation formed thereon such as polysilicon, tungsten, a silicon oxide film, a silicon nitride film or aluminum, or the substrate itself.

The resist application as used herein means, for example, forming an organic anti-reflection film in a thickness of about 78 nm on the predetermined substrate, and applying a methacrylic-system chemically amplified positive type resist in a thickness of about 180 nm on the organic anti-reflection film.

FIG. 2illustrates the plane shape of a resist pattern (desired pattern) to be finally obtained.

As shown, the desired pattern has a plane shape such that a grating-pattern forming region A1(first region) where a grating pattern100is formed and a standard-pattern forming region A2(second region) where a standard pattern101is formed are separately formed adjacently to each other, while part of the grating pattern100and part of the standard pattern101are connected in a connection region A3adjacent to both the regions A1and A2.

InFIG. 2, line patterns11to14are arranged in a lattice as the grating pattern100, and patterns21to24(21: arbitrary pattern,22and24: pad pattern,23: wiring pattern) are arranged in arbitrary fashion as the standard pattern101. The line pattern12and wiring pattern23are connected, and the line pattern14and pad pattern24are connected. The “standard pattern” as used in this specification means patterns other than the grating pattern.

Subsequently, at step S2, heat treatment before exposure (soft bake) is performed for about 60 seconds at a temperature of about 110° C., for example.

Next, at step S3, a first exposure process is performed with only the grating-pattern forming region A1as a substantial object to be exposed. The ArF Excimer laser (wavelength: 193 nm) is used as an exposure light source in this process. This process will be described later in detail.

Next, at step S4, a second exposure process is performed with only the standard-pattern forming region A2as a substantial object to be exposed. The ArF Excimer laser (wavelength: 193 nm) is used as an exposure light source in this process. This process will be described later in detail.

Then, at step S5, heat treatment after exposure (PEB: Post Exposure Bake) is performed for about 60 seconds at a temperature of about 125° C., for example.

Thereafter, at step S6, a development process is performed to subject the resist to patterning. A 2.38 wt % aqueous solution of tetramethyl ammonium hydroxide may be used as a developer in this process. The result is that the resist is patterned into the desired pattern mentioned above. The development process is followed by heat treatment for dehydration for about 60 seconds at a temperature of about 115° C., for example.

In the first exposure process, the ArF Excimer laser (wavelength: 193 nm) is used as radiation, for example, and dipole illumination is used as illuminating means.

FIG. 3depicts the structure of an illumination system stop for dipole illumination used in the first exposure process. The use of dipole illumination with an illumination system stop31, which is provided with two openings32, allows for dual beam interference exposure by zero-order diffraction light and first-order diffraction light. The two openings32are arranged in a direction in which the lines and spaces of the grating pattern are repeated. That is, when the lines and spaces of the grating pattern100are repeated longitudinally (horizontal-striped pattern) as shown inFIG. 2, the openings32are arranged at the top and the bottom as shown inFIG. 3.

FIG. 4explains an optical interference condition in the first exposure process. How (λ/P) is obtained will be explained with reference to this drawing. InFIG. 4, exposure light36enters an HT (half-tone phase shift) mask35to be diffracted, the HT mask35having a light blocking pattern34that form the grating pattern100being formed on a glass substrate33. The exposure light36having been diffracted is indicated as exposure light37.

In this case, an optical path difference Δ between the exposure lights36and37is expressed by the following equation (2):
Δ=d1+d2=P·(sinθi+sinθd)=λ  (2)
where P is a pitch of the grating pattern, θi is an incident angle, θd is a diffraction angle, and as mentioned above, λ is an exposure wavelength. The equation (2) tells that an ideal optical interference condition will be attained when (λ+P)=sinθi+sinθd.

Here, on conditions of λ=193 nm, NA=0.85, P=130 nm (grating pattern in which spaces and lines are arranged with 65 nm-pitches), and iNA=0.81, inner sigma σin and outer sigma σout are obtained by applying (λ+P) obtained from the above equation (2) to the following equations (3) and (4). The iNA is an illumination numerical aperture of an exposure device, and NA is a numerical aperture of a projection lens.
σin={(λ/P)−NA}/NA(3)
σout=iNA/NA(4)

The result is that the inner sigma σin and outer sigma σout of the openings32shown inFIG. 3are obtained as “0.75” and “0.95”, respectively.

An increase in cutting angle of circular arcs of the openings32of the illumination system stop31for dipole illumination shown inFIG. 3will result in deterioration of contrast, but enhancement of illumination. Accordingly, an optimum value for the cutting angle is selected based on a trade-off between them.

In addition, it will be appreciated that the openings32could have other shapes than that inFIG. 3as long as they satisfy the above optical interference condition.

FIG. 5illustrates the plane shape of an HT mask used in the first exposure process. As shown, an HT mask1for the first exposure is such that a light blocking pattern41and transmissive pattern42are formed alternately on a grating-pattern mask part M1(first mask part) corresponding to the grating-pattern forming region A1, and a light blocking pattern43is formed on the whole surface of a standard-pattern mask part M2(second mask part) corresponding to the standard-pattern forming region A2. The light blocking pattern41is provided to form the line patterns11to14shown inFIG. 2. The light blocking patterns41and43of the HT mask1have a transmission factor of 6%.

An HT (half-tone phase shift) mask is described. An HT mask includes a transmissive part (which corresponds to the transmissive pattern42) transmitting high intensity light that contributes to exposure, and a light blocking part (which corresponds to the light blocking pattern41) having a transmission factor of about 6% and inverting the phase of light being transmitted. The adoption of an exposure technique with such HT mask allows for contrast enhancement on an image-forming surface.

With the dipole illumination using the HT mask1, the first exposure process is performed with only the grating-pattern forming region A1as a substantial object to be exposed.

FIG. 6depicts the structure of an illumination system stop for ⅔ annular illumination used in the second exposure process. As shown, an illumination system stop38includes an annular opening39, with the ratio between an inner diameter R1from the center to the opening39and an outer diameter R2from the center to the opening39being set to 2:3. The use of the illumination system stop38thus allows for ⅔ annular illumination. The numerical aperture NA is set to “0.85”. Exposure conditions in the second exposure process including the amount of irradiation and a focus position are respectively optimized.

FIG. 7illustrates the plane shape of an HT mask used in the second exposure process. As shown, an HT mask2for the second exposure is such that a light blocking pattern55is formed on the whole surface of the grating-pattern mask part M1, and light blocking patterns51to54are formed on the standard-pattern mask part M2. In the standard-pattern mask part M2, a region where the light blocking patterns51to54are not formed is a transmissive region. The light blocking patterns51to54are provided to form the patterns21to24of the standard pattern101shown inFIG. 2.

With the ⅔ annular illumination using the HT mask2, the second exposure process is performed with only the standard-pattern forming region A2as a substantial object to be exposed.

Therefore, in the first preferred embodiment, an exposure mask set including the HT mask1for the first exposure and HT mask2for the second exposure is used so that a pattern including the grating pattern100and standard pattern101can be formed on the resist with high accuracy.

As has been described, the desired pattern shown inFIG. 2is obtained by the pattern forming method according to the first preferred embodiment. Observation by an electron microscope of the resist pattern obtained by this pattern forming method confirmed that a pattern including a grating pattern of 65 nm L/S and a peripheral circuit pattern which is a standard pattern that are formed continuously with each other, just like the desired pattern shown inFIG. 2, had been resolved.

As described above, in the pattern forming method according to the first preferred embodiment, the first exposure process for forming the grating pattern is performed with only the grating-pattern forming region A1as a substantial object to be exposed, by using dipole illumination suitable for exposure of a fine pattern (having a process factor k1of 0.3 or less, for example). In addition, the second exposure process for forming the standard pattern is performed with only the standard-pattern forming region A2as a substantial object to be exposed, by using isotropic illumination such as annular illumination suitable for exposure of a standard pattern. Namely, the two-exposure process constitutes an optimum exposure process to obtain the desired pattern shown inFIG. 2.

Accordingly, a resist pattern for a circuit pattern that includes both a grating pattern having a process factor k1of less than “0.3”, and a standard pattern having a process factor k1of 0.5 level can be obtained with high accuracy.

The formation with high accuracy of a circuit pattern in which a grating pattern and standard pattern are formed separately while being continuous with each other allows for the designs of circuit patterns having various kinds of shapes.

In addition, in the pattern forming method according to the first preferred embodiment, the light blocking pattern43is provided on the whole surface of the standard-pattern mask part M2during the first exposure process, and the light blocking pattern55is provided on the whole surface of the grating-pattern mask part M1during the second exposure process, so that exposure can be performed only on the grating-pattern forming region A1in the first exposure process and only on the standard-pattern forming region A2in the second exposure process. This attains optimum exposure for each of the grating pattern100and standard pattern101formed on the grating-pattern forming region A1and standard-pattern forming region A2, respectively.

The pattern forming method according to the first preferred embodiment is also a cost-effective method, because it is performed using the existing exposure devices and the like, so no new exposure devices and the like need to be additionally introduced when performing the first and second exposure processes.

The sequence of the first and second exposure processes may be reversed. Namely, the first exposure process may be performed after the second exposure process.

Further, although the resist is exposed to the standard pattern by a single exposure step in the second exposure process according to the first preferred embodiment, the resist may be exposed to the standard pattern by two or more partial exposure steps in the second exposure process. The number of partial exposure steps will be selected in arbitrary fashion depending on the shape of standard pattern, for example.

When performing a plurality of partial exposure steps in the second exposure process, the amount of irradiation and an exposure focus position may naturally be optimized in each partial exposure step. Such optimizations may be performed in the first exposure process as well, as mentioned above.

Thus, appropriate exposure conditions may be set for each pattern to be formed in each partial exposure step in the second exposure process that includes the plurality of partial exposure steps. This allows for resolution enhancement of the whole pattern in order to obtain a desired pattern such as is shown inFIG. 2.

The pattern forming method according to the first preferred embodiment concerns a pattern including a grating pattern in which lines and spaces are repeated only in one direction and a standard pattern. As a modification, exposures are performed based on the assumption that a grating pattern (lines and spaces) is repeated in two directions (first and second directions orthogonal to each other), namely, a grating pattern includes a first partial grating pattern in which lines and spaces are repeated alternately in the above first direction and a second partial grating pattern separately formed in which lines and spaces are repeated alternately in the above second direction.

In this case, it is effective to change a illumination condition of dipole illumination when forming the first and second partial grating patterns by rotating the stops of dipole illumination shown inFIG. 3by 90 degrees. That is, the patterns will be formed on the resist by the following steps:

First, as a first step of the first exposure process for grating pattern, an exposure process is performed under a first illumination condition with the dipole illumination stops in which the two openings32are arranged in the above first direction, using a first partial grating pattern mask having the first partial grating pattern.

Next, as a second step of the first exposure process for grating pattern, an exposure process is performed under a second illumination condition with the dipole illumination stops in which the two openings32are arranged in the above second direction, using a second partial grating pattern mask having the second partial grating pattern.

Then, as a step of the second exposure process, an exposure process is performed under a third illumination condition with isotropic illumination such as annular illumination, using an exposure mask having the standard pattern that includes a connection portion to the grating pattern.

Lastly, the resist is subjected to development.

In this manner, the first and second partial grating patterns are subjected to exposure under different illumination conditions having different contents of the dipole illumination stops, thus setting an optimum illumination condition for each of the first and second exposure processes. Accordingly, a fine pattern that includes a grating pattern (first and second partial grating patterns) having a process factor k1of 0.3 or less both longitudinally and horizontally can be formed with high accuracy.

Second Preferred Embodiment

The finally obtained grating pattern by the pattern forming method according to the first preferred embodiment is thinner than a resist pattern immediately after the first exposure process, and vertically deteriorated in resist shape. This is possibly the consequence of being subjected to half-tone transmitted light (light being transmitted through the light blocking pattern55) during the second exposure process. As a result, the contrast in a composite optical image of the mask for the first exposure and mask for the second exposure deteriorates, further causing deterioration in line edge roughness (straightness of wiring). Improvements are made to these deteriorations in a second preferred embodiment of this invention.

A general process is performed in the same fashion as the first preferred embodiment illustrated inFIG. 1, except the contents of the second exposure process at step S4.

(Study of Various Problems)

FIG. 8illustrates a resist pattern formed when the mask for the first exposure process is overlaid on the mask for the second exposure process with a deviation in a rightward-slanting rear direction. Formed as a result between the grating pattern100and standard pattern101is an unnecessary pattern10that connects the line patterns11to14and the wiring patterns23and24. A short circuit will disadvantageously occur between the line pattern11and the line pattern12(wiring pattern23) when set to different potentials.

FIG. 9illustrates a resist pattern formed when the mask for the first exposure process is overlaid on the mask for the second exposure process with a deviation in a leftward-slanting rear direction. As a result, the line pattern13and pad pattern24get unnecessarily connected.

FIG. 10depicts the plane structure of an imaginary resist pattern focusing only on a grating pattern. An imaginary resist pattern25as shown is assumed to be obtained after being subjected to the first exposure process using the HT mask1shown inFIG. 5, and then a development process. In the imaginary resist pattern25, as shown inFIG. 10, grating pattern edges corresponding to the transmissive patterns42shown inFIG. 5recede (an edge recession phenomenon occurs) from the mask dimensions on the optical principle caused by the shape of pattern, leaving recession residual patterns26.

FIG. 11depicts the plane structure of an assumed resist pattern in view of the edge recession phenomenon shown inFIG. 10. As shown, the recession residual patterns26connects the line patterns11and12,12and13, and13and14, to form an unnecessary electric connection pattern27on each side of the line patterns11to13. The unnecessary electric connection pattern27is disadvantageously further connected to the wiring pattern23and pad pattern24. As such, problems arise not only by the deviations of masks as shown inFIGS. 8 and 9, but also by the edge recession phenomenon shown inFIG. 10.

In view of the various problems mentioned above, improvements are made to the HT mask used in the second exposure process according to the second preferred embodiment.

FIG. 12illustrates the plane structure of an HT mask used in the second exposure process according to the second preferred embodiment.

As shown, an HT mask4for the second exposure is such that a reduced light blocking pattern56that is reduced by a predetermined amount C from each side of the light blocking pattern55of the HT mask2shown inFIG. 7is formed on the grating-pattern mask part M1. That is, the reduced light blocking pattern56is formed on the grating-pattern mask part M1except an extension region E1(first extension region) extending from a boundary line LB2between the grating-pattern mask part M1and the standard-pattern mask part M2toward the grating-pattern mask part M1side by the predetermined amount C (first predetermined amount), and an extension region E2(second extension region) extending inwardly from an edge line LB5by the predetermined amount C (second predetermined amount).

The extension region E2is thus a transmissive region. Imaginary line patterns11vto14vare indicated by dashed lines in order to clarify the size of the reduced light blocking pattern56. The edge line LB5corresponds to edge positions of the imaginary line patterns11vto14v.

Meanwhile, a light blocking pattern53of the HT mask4includes the light blocking pattern53of the HT mask2shown inFIG. 7, and additionally a light blocking pattern extension part53cextending toward the (inside of) grating-pattern mask part M1side in the extension region E1, while a light blocking pattern54includes the light blocking pattern54of the HT mask2shown inFIG. 7, and additionally a light blocking pattern extension part54cextending toward the grating-pattern mask part M1side in the extension region E1. That is, the extension parts53cand54cof the light blocking patterns53and54serving as connection patterns of the standard pattern101are provided in the extension region E1.

As such, in the HT mask4used in the second exposure process according to the second preferred embodiment, the light blocking pattern53includes a light blocking pattern main part53m(which corresponds to the light blocking pattern53of the HT mask2) and the light blocking pattern extension part53cthat are formed continuously with each other, while the light blocking pattern54includes a light blocking pattern main part54m(which corresponds to the light blocking pattern54of the HT mask2) and the light blocking pattern extension part54cthat are formed continuously with each other.

The predetermined amount C is determined based on the amount of recession due to the edge recession phenomenon, and a tolerance of the overlay deviation (simple sum of the amount of recession and the tolerance of the overlay deviation, for example).

A wiring width LW of the light blocking pattern extension parts53cand54cis determined as follows: when a line dimension of the grating pattern is set to 65 nm, for example, a simple sum of a overlay tolerance of 15 nm (vertical and horizontal directions in the plane structure shown inFIG. 12) and a dimensional accuracy tolerance of 10 nm (tolerance of finished dimensional deviation) leads to the wiring width LW of 115 nm. The tolerances may be obtained by a simple sum or by a root sum square. The dimensions of wiring with a thickness tolerance as defined herein should not be regarded as design dimensions of a mask, but may be regarded as the dimensions of a resist pattern obtained after exposure and development.

As described above, in the pattern forming method according to the second preferred embodiment, the second exposure process is performed using the HT mask4instead of the HT mask2of the first preferred embodiment.

FIG. 13illustrates a resist pattern obtained by the pattern forming method according to the second preferred embodiment, where the edge recession phenomenon occurs with an amount of recession dc1(<C).

As described above, the HT mask4includes the reduced light blocking pattern56reduced by the predetermined amount C, and the light blocking pattern extension parts53cand54cextending by the predetermined amount C, from the boundary line LB2toward the grating-pattern mask part M1side. Accordingly, the unnecessary electric connection patterns27(seeFIG. 11) not located under the light blocking pattern extension parts53cand54care completely erased during the second exposure process.

The result is that wiring pattern extension parts23cand24care formed extending from a boundary line LB1between the grating-pattern forming region A1and the standard-pattern forming region A2toward the grating-pattern forming region A1side only by the amount of recession dc1, as shown inFIG. 13. The wiring pattern extension part23cconnects the wiring pattern23and line pattern12, and the wiring pattern extension part24cconnects the pad pattern24and line pattern14. Therefore, a pattern equivalent to theFIG. 2pattern in terms of electrical connection relationship is obtained even in the event of the edge recession phenomenon.

FIG. 14illustrates a resist pattern obtained by the pattern forming method according to the second preferred embodiment, where the mask overlay deviation phenomenon in a rightward-slanting direction occurs with an amount of deviation dc2(<C) to the right (direction in which the line pattern11is formed (first direction)).

As described above, the HT mask4includes the reduced light blocking pattern56, and the light blocking pattern extension parts53cand54c. Accordingly, the unnecessary pattern10(seeFIG. 8) not located under the light blocking pattern extension parts53cand54cis completely erased during the second exposure process.

The result is that wiring pattern extension parts23cand24care formed extending from the boundary line LB1toward the grating-pattern forming region A1side only by the amount of deviation dc2, as shown inFIG. 14. The wiring pattern extension part23cconnects the wiring pattern23and line pattern12, and the wiring pattern extension part24cconnects the pad pattern24and line pattern14. Therefore, a pattern equivalent to theFIG. 2pattern in terms of electrical connection relationship is obtained even in the event of the mask overlay deviation phenomenon in a rightward-slanting direction.

Moreover, because the wiring width LW of the light blocking pattern extension parts53cand54cis set wider than the forming width of the line patterns11to14in view of the overlay tolerance and dimensional accuracy tolerance, the line pattern12and wiring pattern extension part23c, and the line pattern14and wiring pattern extension part24ccan respectively be connected with reliability even in the event of a overlay deviation in a vertical direction (second direction).

In this manner, in the pattern forming method according to the second preferred embodiment, the second exposure process is performed using the HT mask4shown inFIG. 12, thus forming a resist pattern free from problems even in the event of the edge recession phenomenon, mask overlay deviation phenomenon, and so on.

FIG. 15illustrates a resist pattern formed by the pattern forming method according to the second preferred embodiment. As shown, a grating pattern102including line patterns61to69and a standard pattern103including patterns71to75are formed adjacently to each other as a desired pattern. The wiring pattern71and line pattern63, the wiring pattern73and line pattern66, and the wiring pattern75and line pattern68, are respectively continuous with each other.

FIG. 16illustrates an HT mask for the first exposure process in obtaining a resist pattern60shown inFIG. 15. As shown, an HT mask3for the first exposure is such that a light blocking pattern44and transmissive pattern45are formed alternately on the grating-pattern mask part M1, and a light blocking pattern46is formed on the whole surface of the standard-pattern mask part M2.

FIG. 17illustrates an HT mask for the second exposure process in obtaining the resist pattern60shown inFIG. 15. As shown, in an HT mask6for the second exposure, a reduced light blocking pattern86reduced by the predetermined amount C from each side of the grating-pattern mask part M1is formed on the grating-pattern mask part M1, and light blocking patterns81to85are formed on the standard-pattern mask part M2.

The light blocking patterns81,83and85additionally include light blocking pattern extension parts81c,83cand85c, respectively, extending from the boundary line LB2between the grating-pattern mask part M1and the standard-pattern mask part M2toward the grating-pattern mask part M1side by the predetermined amount C. As described above, the wiring width LW of the light blocking pattern extension parts81c,83cand85cis set in view of the overlay tolerance and dimensional accuracy tolerance.

FIG. 18illustrates a resist pattern obtained by the pattern forming method according to the second preferred embodiment, with the resist pattern60shown inFIG. 15as a desired pattern. InFIG. 18, the edge recession phenomenon occurs with the amount of recession dc1(<C).

As described above, the HT mask6includes the reduced light blocking pattern86reduced by the predetermined amount C, and the light blocking pattern extension parts81c,83cand85cextending by the predetermined amount C, from the boundary line LB2toward the grating-pattern mask part M1side. Accordingly, unnecessary electric connection patterns (such as the unnecessary electric connection patterns27shown inFIG. 11that are caused by the edge recession phenomenon) not located under the light blocking pattern extension parts81c,83cand85care completely erased during the second exposure process.

The result is that wiring pattern extension parts71c,73cand75care formed extending from the boundary line LB1between the grating-pattern forming region A1and the standard-pattern forming region A2toward the grating-pattern forming region A1side only by the amount of recession dc1, as shown inFIG. 18. The wiring pattern extension part71cconnects the wiring pattern71and line pattern63, the wiring pattern extension part73cconnects the wiring pattern73and line pattern66, and the wiring pattern extension part75cconnects the wiring pattern75and line pattern68. Therefore, a pattern equivalent to the resist pattern60inFIG. 15in terms of electrical connection relationship is obtained even in the event of the edge recession phenomenon.

FIG. 19illustrates a resist pattern obtained by the pattern forming method according to the second preferred embodiment, where the mask overlay deviation phenomenon in a rightward-slanting direction occurs with the amount of deviation dc2to the right.

As described above, the HT mask6includes the reduced light blocking pattern86, and the light blocking pattern extension parts81c,83cand85c. Accordingly, unnecessary patterns (which correspond to the unnecessary pattern10inFIG. 8) not located under the light blocking pattern extension parts81c,83cand85care completely erased during the second exposure process.

The result is that the wiring pattern extension parts71c,73cand75care formed extending from the boundary line LB1toward the grating-pattern forming region A1side only by the amount of deviation dc2, as shown inFIG. 19. The wiring pattern extension part71cconnects the wiring pattern71and line pattern63, the wiring pattern extension part73cconnects the wiring pattern73and line pattern66, and the wiring pattern extension part75cconnects the wiring pattern75and line pattern68. Therefore, a pattern equivalent to the resist pattern60shown inFIG. 15in terms of electrical connection relationship is obtained even in the event of the mask overlay deviation phenomenon in a rightward-slanting direction.

Moreover, because the wiring width LW of the light blocking pattern extension parts81c,83cand85cis set wider than the forming width of the line patterns61to69in view of the overlay tolerance and dimensional accuracy tolerance, the line pattern63and wiring pattern extension part71c, the line pattern66and wiring pattern extension part73c, and the line pattern68and wiring pattern extension part75ccan respectively be connected with reliability even in the event of a overlay deviation in a vertical direction.

FIG. 20illustrates a resist pattern obtained by the pattern forming method according to the second preferred embodiment, where the mask overlay deviation phenomenon in a leftward-slanting direction occurs with an amount of deviation dc3to the left.

As described above, the HT mask6includes the reduced light blocking pattern86, and the light blocking pattern extension parts81c,83cand85c. Accordingly, unnecessary patterns (additionally extending parts of the line patterns61,62,64,65,67and69to the boundary line LB1) not located under the light blocking pattern extension parts81c,83cand85care completely erased during the second exposure process.

Moreover, because the wiring width LW of the light blocking pattern extension parts81c,83cand85cis set wider than the forming width of the line patterns61to69in view of the overlay tolerance and dimensional accuracy tolerance, the line pattern63and wiring pattern71, the line pattern66and wiring pattern73, and the line pattern68and wiring pattern75can respectively be connected with reliability even in the event of a overlay deviation in a vertical direction.

Therefore, in the second preferred embodiment, an exposure mask set including the HT masks1and3for the first exposure and HT masks4and6for the second exposure is used so that a pattern including a grating pattern and standard pattern can be formed on the resist with high accuracy.

Third Preferred Embodiment

Like the first preferred embodiment, the finally obtained grating pattern by the pattern forming method according to the second preferred embodiment is thinner than a resist pattern immediately after the first exposure process, and vertically deteriorated in resist shape. This is possibly the consequence of being subjected to half-tone transmitted light through the second HT mask6used in the second exposure process. As a result, the contrast of a composite optical image of the first mask (during the first exposure process) and the second mask (during the second exposure process) deteriorates, further causing deterioration in line edge roughness (straightness of wiring). Improvements are made to these deteriorations in a third preferred embodiment of this invention.

A general process is performed in the same fashion as the first preferred embodiment illustrated inFIG. 1, except the contents of the first exposure process at step S3and the second exposure process at step S4.

FIG. 21illustrates the plane structure of a triton mask15used in the first exposure process according to the third preferred embodiment.

As shown, the triton mask15for the first exposure process is the same in pattern shape itself as the HT mask1shown inFIG. 5for the first exposure process according to the first and second preferred embodiments. That is, a light blocking pattern41, transmissive pattern42and a light blocking pattern43of the triton mask15have the same shapes as the corresponding patterns of the HT mask1.

The triton mask15, however, differs from the HT mask1in including an HT mask part15a, which is an incomplete light blocking part, and a complete light blocking part15b.

The HT mask part15ais formed as a region where the whole light blocking pattern41is formed, and extends from a boundary line LB3between the light blocking patterns43and41by a shift amount ΔD1to be formed as part of the light blocking pattern43as well.

Meanwhile, the complete light blocking part15bis formed as a region where the whole light blocking pattern43except the portion of the HT mask part15ais formed. That is, the complete light blocking part15bis formed on the whole standard-pattern mask part M2except an adjacent region (boundary adjacent region) to the boundary line LB2between the grating-pattern mask part M1and standard-pattern mask part M2.

Like the HT mask1, the HT mask part15aincludes a transmissive part (which corresponds to the transmissive pattern42) transmitting high intensity light that contributes to exposure, and a light blocking part (which corresponds to the light blocking pattern41) having a transmission factor of about 6% and inverting the phase of light being transmitted. The complete light blocking part15bis a mask part that blocks light completely by covering a light blocking part equivalent to an HT mask further with Cr or the like.

FIG. 22illustrates the plane structure of a triton mask16used in the second exposure process according to the third preferred embodiment.

As shown, the triton mask16for the second exposure process is the same in pattern shape itself as the HT mask4shown inFIG. 12for the second exposure process according to the second preferred embodiment. That is, light blocking patterns51to54and56of the triton mask16have the same shapes as the corresponding patterns of the HT mask4.

The triton mask16, however, differs from the HT mask4in including an HT mask part16a, which is an incomplete light blocking part, and a complete light blocking part16b.

The HT mask part16ais formed as a region where the whole light blocking patterns51to54are formed, and extends from a boundary line LB4between the reduced light blocking pattern56and the light blocking pattern extension parts53c,54cby a shift amount ΔD2to be formed as part of the reduced light blocking pattern56as well.

Meanwhile, the complete light blocking part16b is formed as a region where the whole reduced light blocking pattern56except the portion of the HT mask part16ais formed. That is, the complete light blocking part16bis formed on the whole grating-pattern mask part M1except an adjacent region to the boundary line LB2.

FIG. 23illustrates the plane structure of a resist pattern obtained by the pattern forming method according to the third preferred embodiment, schematically depicting observed results by an electron microscope.

As shown, it has been confirmed that the grating pattern100of 65 nm L/S and standard pattern101were subjected to patterning with high accuracy, and the line pattern12and wiring pattern23, and the line pattern14and pad pattern24were respectively connected excellently. It was therefore shown that the resist pattern obtained by the pattern forming method according to the third preferred embodiment has an excellent pattern shape without becoming thinner in dimension, or deteriorated in shape or in straightness like the resist patterns obtained by the methods according to the first and second preferred embodiments.

The effects of the third preferred embodiment are described with reference toFIG. 23. A region EX1(region on the right side of the boundary line LB4by the shift amount ΔD2or more inFIG. 23) equivalent to the most part of the line patterns11to14is subjected to the first exposure process with the HT mask part15a, and the second exposure process with the complete light blocking part16b. Accordingly, no part of the region EX1is subjected to light transmission during the second exposure process. This prevents the line patterns11to14in the region EX1from being subjected to half-tone transmitted light, and allows the line patterns11to14to be obtained with high accuracy.

A region EX2(region on the left side of the boundary line LB3by the shift amount ΔD1or more inFIG. 23) equivalent to the most part of the patterns21to24is subjected to the first exposure process with the complete light blocking part15b, and the second exposure process with the HT mask part16a. Accordingly, no part of the region EX2is subjected to light transmission during the first exposure process. This prevents the patterns21to24in the region EX2from being subjected to half-tone transmitted light, and allows the patterns21to24to be obtained with high accuracy.

A region EX3equivalent to a connection region between the grating pattern100in the region EX1and the standard pattern101in the region EX2is subjected to the first exposure process with the HT mask part15a, and the second exposure process with the HT mask part16a. Accordingly, the region EX3is subjected to two light transmissions through the light blocking parts. The effects of the region EX3will be described later.

The first and second exposure processes may be performed in other ways than those described above. A first mode is the pattern forming method described above that includes the first exposure process with the triton mask15shown inFIG. 21and the second exposure process with the triton mask16shown inFIG. 22.

In a second mode, the first exposure process is performed with the triton mask15shown inFIG. 21, in the same fashion as the first mode.

FIG. 24illustrates a triton mask used in the second exposure process in the second mode according to the third preferred embodiment. As shown, a triton mask18for the second exposure process is the same in pattern shape itself as the HT mask4shown inFIG. 12for the second exposure process according to the second preferred embodiment, like the first mode.

The triton mask18, however, differs from the HT mask4in including an HT mask part18a, which is an incomplete light blocking part, and a complete light blocking part18b.

The complete light blocking part18bis formed as a region where the whole reduced light blocking pattern56is formed, and extends from the boundary line LB4between the reduced light blocking pattern56and the light blocking pattern extension parts53c,54cby a shift amount ΔD4to be formed as parts of the light blocking patterns53and54as well. That is, the complete light blocking part18bis formed as a light blocking pattern of the whole grating-pattern mask part M1and an adjacent region to the boundary line LB2.

Meanwhile, the HT mask part18ais formed as a region where the entire light blocking patterns51to54except the portion of the complete light blocking part18bis formed.

The result is that the region EX3shown inFIG. 23is subjected to the first exposure process with the HT mask part15a, and the second exposure process with the complete light blocking part18b. Accordingly, like the region EX1, no part of the region EX3is subjected to light transmission during the second exposure process. It is desired that the shift amount ΔD4should be set a little wider than (the shift amount ΔD1+the predetermined amount C) in order to prevent two light transmissions through the region EX3with reliability.

FIG. 25illustrates a triton mask used in the first exposure process in a third mode according to the third preferred embodiment. As shown, a triton mask17for the first exposure process is the same in pattern shape itself as the HT mask1shown inFIG. 5for the first exposure process according to the first and second preferred embodiments, in the same fashion as the first and second modes.

The triton mask17, however, differs from the HT mask1in including an HT mask part17a, which is an incomplete light blocking part, and a complete light blocking part17b.

The complete light blocking part17bis formed as a region where the whole light blocking pattern43is formed, and extends from the boundary line LB3between the light blocking patterns41and43by a shift amount ΔD3to be formed as part of the light blocking pattern41as well. That is, the complete light blocking part17bis formed as a light blocking pattern of the entire standard-pattern mask part M2and an adjacent region to the boundary line LB2.

Meanwhile, the HT mask part17ais formed as a region where the entire light blocking pattern41except the portion of the complete light blocking part17bis formed.

In the third mode, the second exposure process is performed with the triton mask16shown inFIG. 22, in the same fashion as the first mode.

The result is that the region EX3shown inFIG. 23is subjected to the first exposure process with the complete light blocking part17b, and the second exposure process with the complete light blocking part16b. Accordingly, like the region EX2, no part of the region EX3is subjected to light transmission during the first exposure process. It is desired that the shift amount ΔD3should be set a little wider than (the shift amount ΔD2+the predetermined amount C) in order to prevent two light transmissions through the region EX3with reliability.

(Forming Accuracy of Connection Region)

FIGS. 26 to 28illustrate optical simulation results of connection regions (which correspond to the region EX3shown inFIG. 23) of the respective resist patterns obtained by the pattern forming methods in the first to third modes according to the third preferred embodiment.

As shown, in a simulation result ofFIG. 26(first mode), a connection portion76corresponding to the wiring pattern extension parts23cand24cdoes not taper off in wiring width, but has a stable shape to almost the same degree as the forming width of the line patterns in a grating-pattern forming region A11. However, in simulation results ofFIGS. 27 and 28(second and third modes), connection portions77and78corresponding to the wiring pattern extension parts23cand24ctaper off, and have unstable shapes.

It is confirmed from the above simulation results that, as for the connection region (which corresponds to the region EX3shown inFIG. 23) between the grating pattern100and standard pattern101, the first mode is most suitable where an HT mask part is used both in the first and second exposure processes, namely, where an HT mask part is used in an adjacent region to the boundary line LB2both in the first and second exposure processes. This is due to the fact that optical image contrast is enhanced for fine patterns in the connection region by using an HT mask both in the first and second exposure processes.

As for the regions EX1and EX2that are subjected to substantially the same first and second exposure processes in the first to third modes, there is no difference between these two regions. Although the complete light blocking parts are effective when having a smaller transmission factor than the light blocking part having a transmission factor of about 6%, it is desired that the complete light blocking parts should block light completely (transmission factor of 0%).

FIG. 29illustrates a triton mask used in the first exposure process in a fourth mode according to the third preferred embodiment. As shown, a triton mask19for the first exposure process includes an HT mask part19a, which is an incomplete light blocking part, and a complete light blocking part19b. The relationship between the parts19aand19bis the same as that between the HT mask part15aand complete light blocking part15bof the triton mask15used in the first mode.

The triton mask19differs from the triton mask15in that the light blocking pattern41on the HT mask part19ais increased in thickness by about 6 nm in total on its both sides to about 71 nm in an adjacent region to the boundary line LB3. That is, the triton mask19differs from the triton mask15in additionally providing light blocking pattern extension parts41deach of which extends from one side of the light blocking pattern41toward the transmissive pattern42by about 3 nm. The remaining structure is the same as the triton mask15, so the description thereof is omitted.

In the fourth mode, the second exposure process is performed with the triton mask16shown inFIG. 22, in the same fashion as the first mode.

In this manner, in the pattern forming method of the fourth mode according to the third preferred embodiment, the first and second exposure processes are performed with the triton masks19and16, respectively. Therefore, the same effects as the first mode are obtained.

Further in the fourth mode, connection to the standard pattern101can be established with stability by partially increasing the forming width of the light blocking pattern41near the connection region to the standard pattern101.

Therefore, in the third preferred embodiment, an exposure mask set including the HT masks15,17and19for the first exposure and HT masks16and18for the second exposure is used so that a pattern including a grating pattern and standard pattern can be formed on the resist with high accuracy.

Application to First Embodiment

The first to fourth modes described above may be applied to the first preferred embodiment. In such cases, no part of the region EX1equivalent to the most part of the line patterns11to14is subjected to light transmission during the second exposure process. This prevents the line patterns11to14in the region EX1from being subjected to half-tone transmitted light, and allows the line patterns11to14to be obtained with high accuracy.

In addition, no part of the region EX2equivalent to the most part of the patterns21to24is subjected to light transmission during the first exposure process. This prevents the patterns21to24in the region EX2from being subjected to half-tone transmitted light, and allows the patterns21to24to be obtained with high accuracy.

In the first preferred embodiment, the first mode where an HT mask part is used for the connection region (which corresponds to the connection region A3shown inFIG. 2) both in the first and second exposure processes should be applied again to increase the possibility of enhancing optical image contrast, as in the second preferred embodiment.

Fourth Preferred Embodiment

FIG. 30illustrates a flow chart for an exposure method to be performed on a plurality of wafers according to a fourth preferred embodiment of this invention. A general process is performed in the same fashion as the first preferred embodiment illustrated inFIG. 1, except that this method is performed on a plurality of wafers (predetermined substrate of each wafer) and that the steps S3and S4are performed as shown inFIG. 30.

For convenience of explanation, the first exposure process with the HT mask1and the second exposure process with the HT mask4will be described as an example in the fourth preferred embodiment.

Turning toFIG. 30, at step S11, the first exposure process with the HT mask1is performed on (a predetermined substrate of) a first wafer to be exposed. Then, at step S12, the HT mask1is exchanged for the HT mask4, and the second exposure process with the HT mask4is performed on the first wafer to be exposed.

Processing then continues with step S13where the presence or absence of unexposed wafers is checked, and then moves on to step S14when they exist (YES), or is completed when they do not (NO).

At step S14, the first wafer is replaced by a new wafer to be exposed. That is, one of the unexposed wafers is mounted on an exposure device as a second wafer to be exposed.

Then, at step S15, the second exposure process is performed on (a predetermined substrate of) the second wafer to be exposed by successively using the HT mask4that was used in step S12and has not been exchanged. Then, at step S16, the HT mask4is exchanged for the HT mask1, and the first exposure process with the HT mask1is performed on the second wafer to be exposed.

Processing then continues with step S17where the presence or absence of unexposed wafers is checked, and then moves on to step S18when they exist (YES), or is completed when they do not (NO).

At step S18, the second wafer is replaced by a new wafer to be exposed. That is, one of the unexposed wafers is mounted on the exposure device as a third wafer to be exposed.

Processing then returns to step S11where the first exposure process is performed on (a predetermined substrate of) the third wafer to be exposed by successively using the HT mask1that was used in step S16and has not been exchanged. Then, at step S12, the HT mask1is exchanged for the HT mask4, and the second exposure process with the HT mask4is performed on the third wafer to be exposed.

Steps S11to S18are repeated thereafter until the absence of unexposed wafers has been confirmed at step S13or step S17.

In this manner, in the exposure method according to the fourth preferred embodiment, either one of the first and second exposure processes is performed successively on two successively exposed wafers. This requires only one exchange of masks for two-exposure processes (first and second exposure processes), resulting in a reduction in processing time required for mask exchange, which further results in a reduction in overall processing time of the pattern forming method for a plurality of wafers.

Each of the first and second exposure processes may in some instances include a plurality of exposure steps by a plurality of masks. When the second exposure process is done by first to third partial exposure steps (not in particular order), for example, step S12should be performed by first, second and third partial exposure steps in this order, and step S15should be performed by third, second and first partial exposure steps in this order. This results in a reduction in processing time required for mask exchanges between the partial exposure steps by the time required for a mask exchange at the third partial exposure step.

<Application to Semiconductor Device Manufacturing Method>

The pattern forming methods (including the case where the exposure method according to the fourth preferred embodiment is incorporated) described in the first to third preferred embodiments may be applied to semiconductor device manufacturing methods.

That is, semiconductor device manufacturing methods to which the pattern forming methods according to this invention are applied would include a first step of applying a resist to a semiconductor substrate surface or an object to be patterned inside the semiconductor substrate, a second step of subjecting the resist to patterning with one of the pattern forming methods according to the first to third preferred embodiments, and a third step of subjecting the object to be patterned to patterning with the patterned resist as a mask.

The result is that a pattern including a grating pattern and a standard pattern that are formed continuously with each other through a connection pattern can be formed on the object to be patterned with high accuracy.

In the first to third preferred embodiments, the resist subject to the first and second exposure processes is made of a positive type resist material to obtain the convex grating pattern and standard pattern.

Alternatively, a chemically amplified negative type resist may be used to obtain the same effects as the first to third preferred embodiments in forming a trench-type wiring pattern.

FIG. 31illustrates the structure of another illumination system stop used in the second exposure process. As shown, an illumination system stop48includes four circular openings49. The use of this illumination system stop48allows for four-lens illumination.

In this manner, four-lens illumination may be used instead of the ⅔ annular illumination (seeFIG. 6) as illumination for the second exposure process described in the first to fourth preferred embodiments.