JP2959496B2 - OPC mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a photomask for a projection exposure apparatus, and more particularly to a photomask used for forming a fine pattern in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art At present, in a manufacturing process of a semiconductor device, an optical lithography technique is mainly used to form a pattern on a semiconductor substrate. In optical lithography,
A pattern of a photomask (an exposure original plate on which a pattern composed of a transparent area and a light-shielding area is formed. When the reduction ratio is not 1: 1, the pattern is particularly called a reticle, but each is called a photomask). Is transferred onto a semiconductor substrate coated with a photosensitive resin, and a predetermined pattern of the photosensitive resin is formed by development. This pattern of the photosensitive resin serves as a mask in the next step of lithography, such as etching or impurity introduction (ion implantation) (the photosensitive resin is also called a resist in the sense that it resists etching).

The conventional photolithography technology has mainly responded to the development of an exposure apparatus, particularly to the miniaturization of a semiconductor element by increasing the NA of a projection lens system. Here, the NA (numerical aperture) corresponds to how much light the lens can collect, and the larger the value, the more light that can be collected, and the higher the NA, the better the lens performance. Become. Further, as is well known in general as Rayleigh's equation, there is an R between the limit resolution R (the size of the fine pattern at the limit of resolution) and the NA.
= K ₁ × λ / NA (where K ₁ is a constant that depends on the process such as the performance of the photosensitive resin). As the NA is increased, the limit resolution becomes finer.

[0004] However, although the resolution is improved by increasing the NA of the exposure apparatus, the depth of focus (the range in which the deviation of the focal position can be tolerated) is reduced, and it becomes difficult to further miniaturize the focal depth. Was. Again, the actual physical explanation is omitted, but the depth of focus DOF and NA
It is known that the relationship DOF = K ₂ × λ / NA ² (where K ₂ is a process-dependent constant) holds between the _two . That is, as the NA is increased, the depth of focus becomes narrower, and a slight shift of the focal position cannot be tolerated.

Accordingly, various super-resolution techniques have been studied. In general, the super-resolution technique is a technique for improving the light intensity distribution on the imaging plane by controlling the transmittance and phase of light on the pupil plane of the illumination optical system, the photomask, and the projection lens system.

[0006] Among various super-resolution techniques, improvement in resolution characteristics by optimizing an illumination optical system, that is, a so-called modified illumination method is highly feasible and has attracted particular attention in recent years.

In addition, studies on a phase shift mask, which is a super-resolution technique based on an improvement on the photomask side, have been actively conducted. As a phase shift mask, the phase of light passing through a transparent region in a periodic pattern called a Shibuya-Levenson system is alternately set to 1.
An 80-degree change scheme was first proposed. However, in this method, it is necessary to make all the phases of adjacent transparent regions different. For this reason, it has been very difficult to design a mask for a complicated semiconductor element pattern. There is also a problem that the method cannot be applied to an isolated pattern. Therefore, after that, auxiliary pattern, rim,
Alternatively, other methods such as a halftone method have been proposed. In these various phase shift masks, the phases of light in adjacent transparent portions on the mask are shifted by 180 degrees from each other, and the light intensity in the light-shielded region is further reduced by interference of light having phases different by 180 degrees, thereby reducing image contrast. Has improved.

In addition to the above-described super-resolution technique, attention has been paid to optical proximity effect correction for improving the two-dimensional shape of a photosensitive resin pattern. This is because, although the limit of the optical lithography is extended by the super-resolution method, near this limit, a problem that the performance of the semiconductor element is deteriorated due to the deformation of the pattern shape due to the proximity effect has occurred. Here, the proximity effect is a phenomenon in which the shape of a transferred photosensitive resin pattern is deformed under the influence of another pattern existing around the pattern.

As a means for correcting this proximity effect in optical lithography, it is effective to increase the NA to improve the resolving power. However, this has a problem in the depth of focus as described above. Therefore, a method of correcting a mask pattern so as to obtain a target pattern has been proposed.
This is the optical proximity correction (Optical Proximity Collection: Optical Proximit)
y effect Correction). A mask for that purpose is called OPC.

In general, optical proximity effects are classified into 1) a dimensional difference between a line-and-space pattern and an isolated pattern, 2) shrinkage of a line pattern in the long side direction, and 3) rounding of a pattern corner. Here, 2) an OPC mask for correcting shrinkage of a line pattern will be described.

FIG. 5 shows a comparison of one pattern portion between a normal photomask and an OPC mask. FIG.
FIG. 3 is a plan view showing a mask pattern of a normal photomask. The pattern shown in FIG. 5A is a pattern in which two line patterns 12 and 12 face each other. In such a pattern, when the exposure amount is adjusted to the line width of the line pattern 12, the leading end of the line pattern 12 is formed. And the dimensions of the transfer pattern due to the line pattern 12 shrink.

FIGS. 3B, 3C, 3D and 3E.
Is a plan view showing various OPC masks. FIG.
Is simply a line pattern 12 called a mask by eye.
(C) is a correction for adding a partial square pattern 12a called a hat (or a hammer head) to the corner of the tip of the line pattern 12, and (d) is a correction for changing This is a correction for adding a fine projection 12b called a sheriff to the tip of the line pattern 12. FIG. 5E shows a method of lowering the light intensity by using the translucent film 5 (for example, see Japanese Patent Application Laid-Open No. 7-5675).
etc). That is, in the case of FIG.
On both sides of the position where the end portions of the two face each other, a translucent film 5 made of extremely thin chromium having a film thickness of about 10 nm is provided, and the translucency is reduced by about 40% using the translucent film 5 so as to correct the transmittance.

In the masks shown in FIGS. 5 (b) to 5 (e), a portion of the light where the light intensity becomes too high is partially cut, the transferred pattern is made thicker, and a pattern made of a photosensitive resin close to the design is formed. You can do it.

[0014]

However, the conventional OPC mask has the following problems. Especially,
Although the OPC mask having the sheriff or the hat shown in FIGS. 5C and 5D has a high correction effect by the sheriff or the hat, it is difficult to put it into practical use in performing the mask fabrication and inspection.

That is, in an OPC mask to which a complicated fine pattern is added as shown in FIGS. 5C and 5D, the data amount becomes large at the stage of designing the mask pattern. Also,
The additional pattern of the sheriff or the hat is designed with a finer grid size (minimum step on CAD) than the design of the semiconductor element, and therefore, there has been a problem of increasing the writing time in mask writing.

An electron beam lithography apparatus is usually used for mask writing. The diameter of an electron beam at the time of writing is the address size (minimum step of writing data, five times the design grid for a normal five-fold mask). Is determined by That is,
In order to draw a mask including an additional pattern having a fine address size in this manner, the electron beam diameter must be reduced to a normal one.
/ 2, and the writing time has been quadrupled (when the beam diameter is reduced to 1/2, four exposures have to be performed to expose the area that was conventionally exposed by one exposure.) ).

Further, since the additional pattern of the sherif or hat has a size close to the limit of electron beam drawing even in terms of resolution, it cannot be formed according to design data. In general, the dimensions of the protruding sheriff and the fine line auxiliary pattern shown in the above example tend to be thin. Therefore, if a mask can be manufactured according to design data, an OPC mask that can obtain an effect has not been sufficiently obtained.

In addition, a batting error (misalignment of a field joint) of a drawing apparatus has been a more serious problem in the OPC mask. The electron beam lithography apparatus electromagnetically deflects the electron beam and moves it to draw a pattern. The swing width is several mm, and the range that can be drawn only by the electromagnetic deflection is called a field. Then, in order to draw the entire mask, after drawing in this field, the mask stage is moved to continue drawing in the next field. At this time, a pattern displacement occurs between adjacent fields. This shift between the fields is called a batting error particularly in mask drawing. For example, even in a continuous line pattern, there has been a problem that a shift occurs at a field joint portion or a line width becomes abnormal.

In particular, the O shown in FIGS. 5 (c) and 5 (d)
In the PC mask, when the fine additional pattern is located at a joint portion of the field, the pattern shape is more significantly deformed. Further, since the dimensional accuracy of the additional pattern is low, there is a problem that the additional pattern is detected as a defect in the inspection process.

In a mask of a semiconductor element having a large number of repetitive patterns, such as a DRAM, a so-called die-to-die method for comparing two points on the mask can be performed to some extent, so that the test can be performed even if the additional pattern is deformed. is there. However, in the case of logic devices, only the so-called die database inspection, which compares the mask and design data, can be performed.Therefore, any deformation of the additional pattern is detected as a defect, and the number is extremely large. There is a problem that it is difficult to distinguish the defect from the defect to be performed.

In the correction method using the translucent film shown in FIG. 5E, the number of steps for forming the translucent film 5 is increased, and the number of defects in this step is problematic. Usually, like the translucent film 5 and the light-shielding film, the film is formed by a sputtering method. However, there is a problem of adhesion of dust by the sputtering method itself and generation of pinholes due to extremely thin film thickness. There was a problem.

Further, the conventional OPC mask improves the shape when there is no shift in the focal position. However, when the focus position changes, there is a problem that the shape is more seriously deteriorated than the normal mask. This is because the contrast of the transferred image is reduced by the fine pattern or the translucent film.
Therefore, there was no effect of improving the focus characteristics as in the phase shift mask shown in FIGS. 5 (c) and 5 (d).

An object of the present invention is to provide a method for stably obtaining a photosensitive resin pattern having a predetermined size in place of a conventional OPC mask.
It is to provide a PC mask.

[0024]

In order to achieve the above object, an OPC mask according to the present invention is an OPC mask having a light-shielding pattern on a transparent substrate, wherein the light-shielding pattern is formed on a photosensitive resin by transparent illumination. A half-tone portion for transferring a pattern having a predetermined shape, wherein the half-tone portion is provided in a transparent region near the light-shielding pattern and has a phase of transmitted light in a range of 10 to 90 °. Is changed.

The halftone portion is formed of a step portion provided in a transparent region near the light-shielding pattern.

The halftone portion is formed of a transparent film provided in a transparent region near the light shielding pattern.

[0027]

[Function] For example, the phase is inverted (phase difference = 180 degrees)
It is well known that a steep dark portion is formed by light interference, but the phase difference is slightly different (phase difference = 10 to 90).
Degree) Due to interference between light beams, a dark portion that cannot be transferred to the photosensitive resin can be formed. The phase difference is appropriately selected according to the exposure conditions.

In the present invention, the shape of the photosensitive resin pattern to be transferred is improved by using the effect of forming a dark portion in the phase change portion. Further, in the interference due to the phase difference other than 180 degrees, the light intensity changes asymmetrically due to the +/- change of the focal position. Therefore, the focus characteristic can be adjusted by using this asymmetry.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1A is a plan view showing Embodiment 1 of the present invention, and FIG.
FIG. 4 is a cross-sectional view taken along a line A. In the first embodiment shown in the figure, as the exposure apparatus, a reduction ratio of 1/5 (mask pattern size: pattern size on the imaging surface = 5: 1), NA = 0.6, 50% annular illumination (maximum σ = 0) , 7), i-line (wavelength λ = 365 nm)
Is used.

In FIG. 1, the pattern dimensions are all shown on the semiconductor substrate, and are set to be five times larger on the actual mask.

In the photomask according to the first embodiment of the present invention shown in the drawing, one pattern portion of a plurality of patterns formed on the transparent substrate 1 has two line patterns 12 having a line width of 0.3 μm. They are arranged so as to face each other at intervals of 0.3 μm. The line pattern 12 is formed of the same light-shielding film 2 of chromium (film thickness: 80 nm) and chromium oxide (film thickness: 20 nm) as in a normal photomask.

[0033] Further, in the present invention, to form a step portion 3 on the substrate 1 by etching the substrate 1 of the distal end portion 12 ₁ of the line pattern 12 at depth 65 nm. Here, the step 3
The light-shielding film 2 forming the line pattern 12 is not provided on the upper side, and the line pattern 12 is formed linearly starting from the facing edges 3a, 3a of the stepped portion 3 as starting points. The refractive index n for the i-line of the quartz substrate 1 is 1.4.
7, a phase difference of 30 degrees occurs due to the step 3 provided on the substrate 1.

Next, the effect of the photomask according to the first embodiment of the present invention will be described. FIG. 2 is a diagram showing the focus position dependency of the space dimension between line patterns. Here, the focus position = 0 μm is when the focus surface is located on the photosensitive resin surface, and the focus is “+” when the focus surface moves upward and “−” when the focus surface moves downward. And As is evident from the simulation of the photosensitive resin pattern, the present photomask prevents the end portion of the line pattern from shrinking, and a pattern close to the design size is obtained in a wide focus range.

If the phase difference is further increased, the light-shielding effect is also enhanced. However, with a normal pattern layout, the shrinkage can be sufficiently prevented with a phase difference of about 30 degrees as in the embodiment of the present invention. On the other hand, if the phase difference is 90 degrees or more, the light intensity is too low, and the adjacent patterns cannot be separated. Further, +/- of the phase difference affects the inclination of the focus characteristic,
Depending on the phase difference of +/-, the focus characteristic may be inclined more than a normal mask. In the embodiment of the present invention, it is better to etch the end of the line pattern. Conversely, if a transparent film is applied to generate a + phase difference,
The focus characteristic is inclined more than a normal mask.

In mask production, the light-shielding pattern is usually the same as that of a photomask and can be easily produced. In addition, the second drawing using the superposition is added to the step portion production, but the dimension of the step portion is sufficiently large, so that the step portion can be formed stably. On the other hand, in the mask inspection, a step portion having a phase difference of about 30 degrees is not detected at all by the mask inspection apparatus, so that the light shielding pattern can be inspected with the same accuracy as the conventional mask. Note that a defect at a step portion having a phase difference of 30 degrees has almost no effect on the transfer result, and therefore does not require inspection.

The i-line exposure has been described above. However, there is no limitation on the exposure wavelength. Similarly, a KrF excimer laser beam or other wavelengths such as X-rays can be used to reduce the light intensity due to a slight phase difference. The pattern of the conductive resin can be changed.

(Embodiment 2) FIG. 3 is a plan view showing Embodiment 2 of the present invention. FIG. 3A shows a step portion 3 which causes a phase change, and a step portion _{1 1} of a line pattern 12.
It is provided between and protrudes from both sides. FIG.
(B) shows the stepped portion 3 as the tip 12 of the line pattern 12.
And provided so bite into ₁ side, FIG. 3 (c), is provided by disposing a step portion 3 on both sides of the front end portion 12 ₁ of the line pattern 12, FIG. 3 (d), FIG. 3 (c ) Are provided so as to protrude forward.

(Embodiment 3) FIG. 4 is a diagram showing Embodiment 3 of the present invention. In the third embodiment shown in FIGS. 4A and 4B, instead of forming the step portion 3 on the transparent substrate 1, a pattern of the transparent film 4 is partially formed on both sides of the light shielding film 2 to reduce the phase difference. Is causing it. The transparent film 4 is made of SOG (spin
If an on-glass (spun coat) method is used, it can be formed relatively easily. Further, the third embodiment has an advantage that a desired resist plane shape can be further obtained by giving a slight light absorption using, for example, a dye-containing SOG and controlling the transmittance in accordance with the phase difference. doing.

[0040]

As described above, according to the present invention, a mask pattern is partially formed into a halftone portion by utilizing a difference in exposure amount (difference in light intensity distribution) between the halftone phase shift mask and the mask. Thus, the image is transferred to a target pattern shape. Therefore, it is not necessary to use a complicated pattern shape as in the conventional OPC, and the fabrication and inspection of the mask are facilitated. Also, the dimensional change due to the change of the focal position is smaller than that of the conventional mask, and it has the effects of improving the dimensional accuracy and expanding the depth of focus.

[Brief description of the drawings]

FIG. 1A is a plan view showing a photomask according to a first embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA of FIG. 1A.

FIG. 2 is a diagram showing a simulation result (a relationship between a space dimension and a focal position) of a photosensitive resin pattern obtained by the present invention and a conventional photomask.

FIG. 3 is a plan view showing a photomask according to a second embodiment of the present invention.

FIG. 4 is a plan view showing a photomask according to Embodiment 3 of the present invention.

FIG. 5 is a plan view showing a conventional OPC mask.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light shielding film 3 Step part 4 Transparent film 5 Translucent film 12 Line pattern

Claims (3)

(57) [Claims] An OP having a light-shielding pattern on a transparent substrate
A C mask, the light-shielding pattern is for transferring a pattern having a predetermined shape on the photosensitive resin by a transparent lighting, has a halftone part, the halftone part, the transparent areas of the light shielding pattern near An OPC mask, which is provided and changes the phase of transmitted light within a range of 10 to 90 °. 2. The OPC mask according to claim 1, wherein the halftone portion is formed of a step portion provided in a transparent region near a light shielding pattern. 3. The OPC mask according to claim 1, wherein the halftone portion is formed of a transparent film provided in a transparent region near a light shielding pattern.