JP3218547B2 - Projection exposure method and apparatus, and semiconductor element manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, in manufacturing a semiconductor device or a liquid crystal display device by a photolithography process, and projects a reticle pattern onto a substrate coated with a negative type photosensitive material by projection exposure. Exposure method and throw
The present invention relates to a shadow exposure apparatus and a method for manufacturing a semiconductor element .

[0002]

2. Description of the Related Art Conventionally, when a semiconductor device or a liquid crystal display device having a fine pattern such as an LSI is manufactured by a photolithography process, a pattern of a photomask or a reticle (hereinafter, collectively referred to as a “reticle”) is projected. 2. Description of the Related Art A projection exposure apparatus that performs projection exposure on a substrate coated with a photosensitive material via an optical system is used. In such a projection exposure apparatus, various efforts have been made to transfer a pattern to be further miniaturized with high resolution and stably.

One of the techniques for responding to a pattern to be further miniaturized is to shorten the wavelength of exposure light. However, various methods such as a light source for shortening the wavelength and a glass material of a projection optical system which can be used at such a wavelength are used. There is a problem. Another method is to increase the numerical aperture NA of the projection optical system. In this case, it is a big problem for the optical system of the projection exposure apparatus that the increase in the NA causes a decrease in the depth of focus, in addition to the difficulty in designing and manufacturing the projection optical system accompanying the increase in the NA. In addition, a method that devised the shape of the light source,
An annular illumination method, a so-called deformed light source method, or a method devising a pattern configuration of a reticle surface (for example, a phase shift method) has been proposed.

[0004] In this regard, as an approach from the aspect of the imaging characteristics of the projection optical system with respect to a pattern to be further miniaturized, recently, Japanese Patent Laid-Open No. 2-166719 discloses an imaging system in which the amount of spherical aberration of the projection optical system is taken as a parameter. A proposal for a technique to improve performance has been made by the applicant.

[0005]

However, as a result of continuous testing and research by the present inventors, it has been found that the technology disclosed recently may not always be advantageous from the viewpoint of improving optical performance. . Specifically, the prior art is suitable mainly when a positive type photosensitive material (eg, a positive resist) is used, and when a negative type photosensitive material (eg, a negative resist) is used, it does not necessarily greatly contribute to improvement in optical performance. Was revealed.

[0006] When the positive type and the negative type are confirmed, a positive type photosensitive material is one in which a light portion at the time of exposure dissolves during development, and a negative type photosensitive material is one in which a dark portion at the time of exposure dissolves during development. It is. The present invention has been made in view of the above, and has been applied to the case where a negative type photosensitive material is used.
Substantially high depth of focus and high image of the reticle pattern
Projection exposure method capable of transferring at a high resolution, and a projection exposure apparatus that includes a projection optical system having a spherical aberration amount suitable for using a negative type photosensitive material , and can perform such a projection exposure method , And a half using such a projection exposure method.
An object of the present invention is to provide a method for manufacturing a conductor element .

[0007]

According to the present invention , the substrate
When the applied photosensitive material is negative type,
Vertical projection of the projection optics when projecting the
The feature is that spherical aberration is undercorrected. In particular, the
Regarding the vertical spherical aberration of the projection optical system,
Correction of spherical aberration equivalent to 100% of aperture
did.

The amount of spherical aberration corresponding to 100% of the aperture is
Assuming that the half angle of the opening of the projection optical system (4) on the mask pattern (3a) side is θR, it refers to the amount of spherical aberration with respect to the exposure light whose angle with the optical axis of the projection optical system (4) is θR.

[0009]

The principle of the present invention will be described. First, a line-and-space pattern having a duty ratio of 1: 1 is assumed as the mask pattern (3a), and the mask pattern (3a) is assumed.
It is assumed that the ± 3rd-order light from a) is in a spatial frequency region that is not taken into the aperture of the projection optical system (4). Further, only the defocus and the spherical aberration are considered as aberrations of the projection optical system (4), and there are no other asymmetric aberrations (such as coma and astigmatism). Under the above conditions, the image intensity distribution I (x) along the coordinate axis on the substrate (6) is expressed by the following equation.

I (x) = 1/4 + (2 / π ² ) T (f, f) + (4 / π) ReT (f, 0) cos (2πfx) + (2 / π ² ) T (f , -F) cos (4πfx)

Here, x is a normalized coordinate, f is a normalized spatial frequency, T (f1, f2) is a mutual transmission coefficient, and Re is a real part. (Equation 1) is derived based on partial coherent imaging theory. Details are omitted, but the derivation procedure is, for example, “Method for the calculation
of partially coherent imagery ”, Eric.C.Kintner: A
vol. 17, No. 17, p. 2747 (1978).

The intensity I (bright) of the bright portion of the image intensity distribution of the line-and-space pattern in (Equation 1) is as follows.

I (bright) = I (0) = 1/4 + (2 / π ² ) T (f, f) + (4 / π) ReT (f, 0) + (2 / π ² ) T ( f, -f)

Similarly, the intensity I of the dark part of the image intensity distribution
(Dark) is as follows.

I (dark) = I (1 / (2f)) = 1/4 + (2 / π ² ) T (f, f) − (4 / π) ReT (f, 0) + (2 / π ² ) T (f, -f)

Here, there are dependencies on spherical aberration and defocus due to ReT (f, 0) and T (f, −
f) (T (f, -f) is always a real number), and the others are constants. ReT (f, 0), T
The dependence of (f, -f), I (bright) and I (dark) on spherical aberration and defocus are respectively shown in FIGS.
As shown in FIG.

FIGS. 4A to 4D each show a vertical axis with R
eT (f, 0), T (f, -f), I (bright) and I
(Dark), and the horizontal axis represents the defocus amount. The defocus amount is positive (+) in the direction in which the back focus of the projection optical system (4) becomes longer. Also,
In FIGS. 4A to 4D, the solid line curves show the calculation results on the assumption that the spherical aberration is zero, and the broken line curves show the calculation results on the assumption that the spherical aberration is positive. When the spherical aberration is zero, all evaluation quantities (ReT (f, 0), T (f, -f), I (bright), I
(Dark)) takes a peak value when the defocus amount is zero.

However, assuming a positive spherical aberration as disclosed in Japanese Patent Application Laid-Open No. 2-166719,
4 (a) and 4 (b), ReT (f,
0) and T (f, -f) both shift the peak position to the positive side. Assuming that these shift amounts are Δ1 and Δ2, respectively, it was found by numerical calculation that Δ1 <Δ2. Considering this result together with (Equation 2) and (Equation 3), I
Peak position D1 of (bright) and peak position D2 of I (dark)
Are as shown in FIGS. 4C and 4D, respectively. What is important in this case is that the peak position D1 of I (bright) is
(Dark) relatively positive side from the peak position D2 (substrate (6)
Side).

Consider what this means in actual pattern formation with reference to FIG. FIG. 5 shows a pattern of concavities and convexities formed by developing a positive type (the opposite type of the present invention) photosensitive material applied on the substrate 30. In FIG.
A remaining portion 31 of the AND space pattern and a blank portion 32 are formed. The remaining portion 31 corresponds to a dark portion of the light intensity distribution, and the cutout portion 32 corresponds to a bright portion of the light intensity distribution. Since it is required that the remaining portion 31 does not cause film reduction or maintain a sufficient thickness, the light intensity distribution at the top of the remaining portion 31 is required to be sufficiently dark. That is, the best condition is that the surface 31a of the photosensitive material coincides with the peak position of I (dark).

It is ideal that a sufficient light intensity is obtained in the entire portion to be removed in the cutout portion 32, and the cutout portion 32 is also filled with a photosensitive material at the time of exposure. Therefore, when the thickness of the photosensitive material is t and the refractive index of the photosensitive material is n, the peak position of I (bright) is t / t on the positive defocus side (substrate 30 side) from the surface 31a of the photosensitive material.
(2n) -t / n is the best condition. t
/ (2n) corresponds to the center of the thickness of the photosensitive material, and t / n corresponds to the bottom position, that is, the boundary surface between the substrate 30 and the photosensitive material. It is desirable that the peak position of I (bright) be located below the center of the thickness of the photosensitive material because the photosensitive material itself has absorption and the developing solution is deep in the cutout portion 32 during development. It depends on what you consider to be tired.

As described above, in order to form an ideal photosensitive material profile (cross-sectional shape), I (dark) and I (bright)
It is understood that it is desirable that there is a relative difference between the peak positions in the defocus direction. Further, considering the depth of focus of the projection optical system, the remaining portion 31 is within the depth of focus.
It is required that the top part of the film does not lose its thickness and that the cutout portion 32 is sufficiently removed. Therefore, it can be easily estimated that this increases the depth of focus of the projection optical system. It can also be seen that a state where the spherical aberration of the projection optical system is positive is a desirable state when a positive type photosensitive material is assumed.

The above is a description of the invention disclosed in Japanese Patent Application Laid-Open No. 2-166719 from another angle. At the time when the invention was made, as a photosensitive material, a positive type material such as a positive resist was mainly used, and thus, in fact, sufficient consideration and study on a negative type photosensitive material were not made. . In recent years, in a lithography technique using an excimer laser beam or a lithography technique using an i-line, a negative photosensitive material such as a negative resist is attracting attention.

When a negative photosensitive material is used as in the present invention, in FIG. 5, the remaining portion 31 corresponds to the bright portion of the light intensity distribution and the cutout portion 32 corresponds to the dark portion of the light intensity distribution. It is easy to see that it is desirable to reverse the sign of the ideal difference between the peak position of (bright) and the peak position of I (dark) in the defocus direction as compared with the case of the positive type photosensitive material. That is, the sign of the spherical aberration desired for the projection optical system (4) also becomes negative.

The focus shift Δ1 of ReT (f, 0) in FIG. 4A and the focus shift Δ2 of T (f, −f) in FIG. 4B have a spherical aberration of 100% of the aperture. When positive, 0 <Δ1 <Δ2, and when 100% of the spherical aberration of the aperture is negative, Δ2 <Δ1 <0. Here, there is the essence that the positive and negative of the optimum spherical aberration are divided between the positive type photosensitive material and the negative type photosensitive material. Although the specific optimal amount of spherical aberration varies depending on various conditions such as the pattern size, excessive spherical aberration causes a decrease in the contrast of an optical image. In this case, it is desirable to set ΔS in the following range, where NA is the numerical aperture of the projection optical system and λ is the wavelength of the exposure light. −5λ / (NA ² ) <ΔS <0

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A projection exposure apparatus according to one embodiment of the present invention will be described below with reference to FIG. FIG. 1 shows a projection exposure apparatus of this embodiment. In FIG. 1, illumination light for exposure (exposure light) supplied from an illumination optical device 1 is a condenser lens 2.
After that, the predetermined pattern 3a on the lower surface of the reticle 3 is uniformly illuminated. The pattern 3a on the reticle 3 is reduced and projected on the wafer 6 mounted on the wafer stage 5 by the aberration varying means 17 (described later) and the projection optical system 4. On the wafer 6 of this example, a negative resist is applied. Illumination information such as the wavelength λ of the exposure light in the illumination optical device 1 and the numerical aperture (NA) as an illumination system is supplied to an arithmetic unit 12 composed of a computer via an illumination information input unit 11 and formed on a reticle 3. The information on the projection pattern relating to the line width of the pattern 3a is
The data is supplied to the calculation means 12 via the control unit 3.

Information on the object to be exposed, such as the material of the wafer 6, the type of the negative resist applied to the wafer 6, and the thickness of the resist, is supplied to the arithmetic means 12 through the object information inputting means 14. You. And the aperture value of the projection optical system 4,
That is, information on the numerical aperture (NA) is also supplied to the calculating means 12 via the aperture information input means 15. Based on such various information, the calculating means 12 obtains the optimum amount of spherical aberration of the optical system composed of the aberration varying means 17 and the projection optical system 4, and obtains the desired spherical aberration amount via the aberration varying driving means 16. And a state of appropriate depth of focus according to the line width of the pattern 3a can be obtained.

Incidentally, the projection pattern information input means 13
The calculation means 12 calculates the optimum aperture value of the projection optical system 4 from the information on the fineness of the pattern on the reticle 3 and the information on the illumination conditions from the illumination information input means 11,
The aperture value (numerical aperture) of the projection optical system 4 can be set to the optimal aperture value (optimal numerical aperture) via the aperture control means 18. In this case, based on the optimum aperture value obtained by the calculating means 12 without passing through the aperture information inputting means 15, the calculating means 12 uses the aberration changing means 17 and the aberration changing means 17 and the projection optical system. The spherical aberration amount of the optical system 4 can be set to an optimum value.

The aberration varying means 17 of this embodiment is composed of a light-transmissive parallel flat plate whose thickness can be freely changed in and out of the direction perpendicular to the optical axis of the projection optical system 4. The amount of spherical aberration of the projection optical system 4 can be controlled by using a phenomenon in which a positive spherical aberration is generated when a spherical wave passes through a parallel plane plate. Then, the spherical aberration of the projection optical system 4 is corrected to be under, and the spherical aberration can be adjusted to the positive side by inserting a parallel plane plate into the condensed or divergent light beam. By changing the distance, the spherical aberration of the projection optical system 4 can be arbitrarily controlled.

A specific example of the aberration varying means 17 is shown in FIG.
2A shows two parallel flat glasses 19 and 20 having different thicknesses, and the amount of spherical aberration can be changed by alternately inserting the parallel flat glasses 19 and 20 into the optical path. Another example of the aberration varying unit 17 is the two wedge prisms 21 and 22 shown in FIG. 2B. The thickness of the face plate can be changed.
Also, as shown in FIG. 2C, a mechanism in which a transparent fluid 25 is filled between two parallel flat glass plates 23 and 24 is used as the aberration changing unit 17, and two parallel flat glass plates 23 and 24 are used. The desired amount of spherical aberration can also be imparted by changing the interval Δd of 24.

Next, an example of the characteristic of the vertical spherical aberration of the optical system combining the projection optical system 4 and the aberration varying means 17 of FIG. 1 will be described. In this embodiment, since a negative resist is applied on the wafer 6, the amount of spherical aberration corresponding to 100% of the aperture is set to be insufficiently corrected, that is, set to be negative. FIG.
Assuming that the half angle of the opening on the reticle 3 side with respect to the projection optical system 4 is θR, the spherical aberration amount of the exposure light whose inclination angle with respect to the optical axis of the projection optical system 4 is θR is equivalent to 100% of the aperture. It is. Accordingly, an example of the spherical aberration characteristic of the optical system including the projection optical system 4 and the aberration varying unit 17 of the present example is the curve 26A or 26B shown in FIG.
By increasing the thickness of the plane-parallel plate as the aberration varying means 17, the spherical aberration can be changed from the curve 26A to the curve 26B.

As described above, when the amount of vertical spherical aberration corresponding to 100% of the aperture becomes negative, the focus position of the bright portion of the exposure light on the wafer 6 is projected onto the focus position of the dark portion of the exposure light. It becomes closer to the direction of the optical system 4. Therefore, after development, the projection optical system 4
In contrast, when a negative resist in which a dark part becomes a concave part and a light part becomes a convex part is used, the profile (cross-sectional shape) of the resist on the wafer 6 corresponding to the pattern image of the reticle 3 becomes good, and the pattern of the reticle 3 becomes Can be transferred with a substantially deeper depth of focus and higher resolution.

In the above embodiment, the projection optical system 4
Is preferably telecentric on the reticle 3 side as well, and the aberration varying means 17 is preferably arranged on the reticle 3 side of the projection optical system 4. This is because when a parallel plane plate is inserted into the part where the light beam is telecentric, only the spherical aberration changes, and other aberrations (coma aberration, astigmatism, etc.)
Is not affected. Further, in the reduction projection exposure apparatus, since the space between the projection optical system 4 and the wafer 6 is generally telecentric, it is also conceivable to insert the aberration varying means 17 on the wafer 6 side of the projection optical system 4. However, this arrangement has limitations such as a short working distance.

However, the most desirable spherical aberration characteristic of the optical system in which the projection optical system 4 and the aberration varying means 17 are actually combined is as shown by a curve 27 in FIG. Is positive, then 10
The absolute value becomes negative and gradually increases up to the split position R10. Further, since excessive spherical aberration causes a decrease in the contrast of an optical image, when the amount of vertical spherical aberration of 100% of the aperture is ΔS, the numerical aperture of the projection optical system 4 is NA, and the wavelength of the exposure light is λ. , ΔS are desirably set within the following ranges. −5λ / (NA ² ) <ΔS <0

In order to control the amount of spherical aberration with a characteristic as shown in FIG. 3B, a predetermined lens group among a plurality of lens groups constituting the projection optical system 4 is moved in the optical axis direction. It may be. In this case, the projection optical system 4 does not generate other asymmetric aberrations (coma aberration, astigmatism, etc.).
May be changed only by combining the movements of a plurality of lens groups constituting the above. It should be noted that the present invention is not limited to the above-described embodiments, but can take various configurations without departing from the gist of the present invention.

[0032]

According to the present invention, a photosensitive material coated on a substrate is provided.
When the material is negative type, the pattern is
Corrects vertical spherical aberration of the projection optics when projecting upwards
Due to the shortage, the focus position of the bright part of the exposure light approaches the projection optical system side with respect to the focus position of the dark part. Therefore, when a negative type photosensitive material is used in which a bright part is a convex part and a dark part is a concave part with respect to the projection optical system by development, the profile of the photosensitive material becomes good, and a sufficient depth of focus can be secured. There is an advantage that the resolution is improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus according to one embodiment of the present invention.

2A is a side view showing an example of the aberration varying unit 17 of FIG. 1, FIG. 2B is a side view showing another example of the aberration varying unit 17, and FIG. It is a side view which shows the example of.

3A is an aberration diagram illustrating an example of vertical spherical aberration of the embodiment of FIG. 1, and FIG. 3B is an aberration diagram illustrating another example of vertical spherical aberration of the embodiment.

FIG. 4 is a characteristic diagram showing various changes in optical amounts when the amount of defocus is changed in the description of the principle of the present invention.

FIG. 5 is an enlarged sectional view showing an example of a profile of a photosensitive material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Illumination optical device 2 Condenser lens 3 Reticle 4 Projection optical system 6 Wafer 12 Operation means 16 Aberration variable drive means 17 Aberration variable means

Continuation of the front page (72) Inventor Masaomi Kameyama 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (56) References JP-A-2-278811 (JP, A) JP-A-2-234411 (JP) , A) JP-A-64-61716 (JP, A) JP-A-3-11720 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 521 G03F 7/207

Claims (8)

(57) [Claims] 1. A projection exposure apparatus comprising: an illumination optical system for illuminating a mask on which a pattern is formed with exposure light; and a projection optical system for projecting the pattern onto a substrate coated with a photosensitive material. A projection exposure apparatus, wherein when the applied photosensitive material is of a negative type, vertical spherical aberration of the projection optical system when projecting the pattern onto the substrate is insufficiently corrected. 2. The projection exposure apparatus according to claim 1, wherein an amount of spherical aberration corresponding to 100% of the aperture in the projection optical system is insufficiently corrected for vertical spherical aberration of the projection optical system. 3. An apparatus according to claim 2, further comprising an aberration changing unit that changes an amount of vertical spherical aberration of said projection optical system.
The projection exposure apparatus according to claim 1. 4. When the wavelength of the exposure light is λ, the numerical aperture of the projection optical system is NA, and the amount of spherical aberration corresponding to the 100% aperture is ΔS, the following condition is satisfied. 3. The projection exposure apparatus according to claim 2, wherein: One 5λ / (NA ² ) <△ S <0 5. A projection exposure method in which a mask on which a pattern is formed is illuminated with exposure light and the pattern is projected onto a substrate coated with a photosensitive material via a projection optical system, the method comprising: A projection exposure method, wherein when the material is of a negative type, correction of longitudinal spherical aberration of the projection optical system when projecting the pattern onto the substrate is insufficient. 6. The projection exposure method according to claim 5, wherein the amount of spherical aberration corresponding to 100% of the aperture is insufficiently corrected for the vertical spherical aberration of the projection optical system. 7. When the wavelength of the exposure light is λ, the numerical aperture of the projection optical system is NA, and the amount of spherical aberration corresponding to the 100% aperture is ΔS, the following condition is satisfied. The projection exposure method according to claim 6, wherein: One 5λ / (NA ² ) <△ S <0 8. A method for manufacturing a semiconductor device, comprising using the projection exposure method according to claim 5. Description: