JPH04318913A - Exposure method and manufacture of semiconductor device using that method - Google Patents

Abstract

PURPOSE:To provide an exposure method which can print a pattern excellent in contrast on a photosensitive layer. CONSTITUTION:By changing the relative position in the direction of the optical axis of a photosensitive layer 4 to the image face of a projecting optical system 3, in the condition that any place of the photosensitive layer 4 is focused on this image face, and projecting the image of a circuit pattern in each position and laying them on top of each other, a circuit pattern is printed on the photosensitive layer 4.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION This invention relates to an exposure method and a method for manufacturing semiconductor devices using the method, and more particularly, the present invention relates to an exposure method and a method for manufacturing semiconductor devices using the method. This invention relates to the improvement of so-called projection exposure technology that exposes images.

0002

Conventionally, when manufacturing semiconductor devices, an image of a circuit pattern on a reticle is projected onto a wafer using a reduction projection lens system, and a resist on the wafer is exposed with the circuit pattern image. , a reduced circuit pattern was printed on the resist, and the resist was developed.

This type of projection exposure is normally carried out by fixing the relative positions of the image plane of the projection lens system and the wafer with respect to the optical axis direction of the projection lens system. However, in recent years, in order to improve the resolution, the numerical aperture (NA) of the projection lens system has been increased.
As the depth of focus of the projection lens system increases, the depth of focus of the projection lens system becomes extremely shallow, which compensates for the curvature of field of the projection lens system and the unevenness of the wafer surface to clearly project a circuit pattern image over the entire exposed area. is becoming difficult.

Therefore, in recent years, when projecting a circuit pattern image of a reticle onto a wafer using a reduction projection lens system,
A method has been proposed in which multiple relative positions of the wafer to the circuit pattern image are set by moving the wafer up and down in the optical axis direction of the projection lens system, and the circuit pattern image is projected at each position for multiple exposure. It was done. According to this method, the depth of focus of the projection lens system is apparently increased, so that the above-mentioned problem is solved to some extent.

[0005]

[Problems to be Solved by the Invention] However, in this exposure method, the amount of vertical movement of the wafer is large compared to the thickness of the resist on the wafer, and the circuit pattern image is not focused on the resist. The proportion of exposure to light is low. Therefore, the contrast of the circuit pattern printed on the resist is not very good.

Furthermore, this exposure method has limitations on the reticle patterns that can be used. In other words, when projecting an image of a hole pattern, the pattern printed on the resist
The contrast is not very good, but when projecting a line-and-space pattern image, if the wafer resist is greatly defocused, false resolution will occur and the intensity distribution will be reversed. The pattern image is projected onto the resist. Therefore, a pattern image of a normal intensity distribution during focusing and a pattern image of an inverted intensity distribution during defocusing are projected onto the resist, resulting in extremely poor contrast and line and space
The page may not be printed.

[0007]

Means for Solving the Problems In the exposure method of the present invention, a plurality of relative positions of the substrate to be exposed with respect to the image plane of the projection optical system are set in the optical axis direction of the projection optical system, and a predetermined pattern is set at each position. In the method of exposing the exposed substrate by projecting an image of the image onto the exposed substrate, by aligning the image plane with a plurality of positions in the optical axis direction of the photosensitive layer of the exposed substrate, and exposing the exposed substrate. Solve the above issues.

In the first embodiment of the manufacturing method of the present invention, a plurality of relative positions of the wafer to the image plane of the projection optical system are set in the optical axis direction of the projection optical system, and a circuit pattern is formed at each position.
In the method of manufacturing a semiconductor device by projecting an image onto the wafer to expose the wafer and then developing the wafer, the resist film of the wafer is exposed at a plurality of positions in the optical axis direction. The above problem is solved by aligning the image planes and performing exposure.

Furthermore, a second form of the manufacturing method of the present invention is as follows:
A plurality of relative positions of the wafer to the image plane of the projection optical system were set in the optical axis direction of the projection optical system, and a circuit pattern image was projected onto the wafer at each position to expose the wafer. After that, in the method of developing the wafer and manufacturing a semiconductor device, the image plane is exposed to light by aligning the image plane with a plurality of positions in the optical axis direction of a layer including a resist film and a transparent film of the wafer. Solve problems.

In a preferred embodiment of the present invention, the plurality of positions in the optical axis direction of the photosensitive layer, the plurality of positions in the optical axis direction of the resist film, and the plurality of positions in the optical axis direction of the layer include the photosensitive layer, the resist film , including first and second positions in order from the upper surface side of the layer, and multiple exposure is performed by sequentially projecting the pattern image on the first and second positions.

In another aspect of the present invention, the pattern image is simultaneously projected onto the first and second positions.

In the exposure method and manufacturing method of the first aspect of the present invention, at least one of a plurality of positions in the optical axis direction of the resist film is set within the resist film, and the resist film at the at least one position is The distance from the top surface is d
There is a preferred form that satisfies the following condition: 0<d≦t0/n0, where the thickness and refractive index of the resist film are t0 and n0, respectively.

[0013] In the manufacturing method of the second embodiment of the present invention,
At least one of a plurality of positions in the optical axis direction of the layer is set in the layer, the distance of the at least one position from the upper surface of the layer is d, the thickness and refractive index of the resist film are t0, n0, respectively. The thickness and refractive index of the transparent film are respectively tS,
When nS, there is a preferable form that satisfies the following condition: 0<d≦t0/n0+tS/nS.

Furthermore, in the present invention, there are various methods for setting a plurality of relative positions of the wafer (substrate to be exposed) with respect to the image plane of the projection optical system. For example, (1) wafer
(2) move at least a portion of the projection optical system in the optical axis direction; (3) move the reticle (projection target original plate) provided with a pattern in the optical axis direction of the projection optical system. (4) Provide an optical path length changing member such as an air lens or prism in the projection optical system to sequentially change the optical path length. (5)
Sequentially changing the wavelength of the light used to project the pattern (6
(7) A plurality of reticles with the same pattern are arranged close to each other along the optical axis direction of the projection optical system, and the pattern of each reticle is projected using light of different wavelengths at the same time. - project images at the same time.

[0015] Further, to project a pattern, light emitted from ultra-high pressure mercury, a laser, an X-ray source, etc. is irradiated onto a reticle provided with a pattern, and a fine pattern is formed on the reticle. This is done by transmitting or reflecting the light and directing it to the pupil of the projection optical system. The projection optical system used may be one composed of a lens assembly, one composed of a mirror assembly, or one composed of a lens and a mirror.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram showing changes over time in optical properties of a resist film 4 on a substrate 5 when exposed through a line-and-space pattern.

The intensity distribution of the pattern image is shown at the top of FIG. 1, and this pattern image is projected onto the resist 4. As shown by the arrow in FIG. 1, the resist 4 on which the pattern image is projected and exposed first absorbs light energy in a portion near its upper surface 40, and a photochemical reaction occurs in this portion, forming the resist 4. The photosensitive material is decomposed, and so-called bleaching occurs in which light energy absorption by the resist 4 is reduced. If the exposure is continued, the light energy reaches the center of the resist 4 and the vicinity of the lower surface 50 of the resist in sequence, so that bleaching occurs in this order. Incidentally, the bleached portion of the resist 4 becomes almost transparent to the light forming the pattern image.

The present invention focuses on such a resist bleaching process, and the wafer is
When setting multiple relative positions, each position is determined according to the progress of bleaching of the resist, and while focusing the pattern image on the top surface of the resist and other parts,
Exposure is performed on the upper surface of the resist and then on the other parts. This increases the rate at which the pattern image is exposed to light while being focused on the resist, thereby improving the contrast of the pattern printed on the resist.

FIG. 2 shows an example of a projection exposure apparatus for manufacturing semiconductor devices to which the exposure method of the present invention is applied.

In FIG. 2, reference numeral 1 denotes illumination light consisting of g-line, i-line, KrF excimer laser light, etc., and the illumination system 10
provides illumination light 1. Illumination system 10 illuminates reticle 2 with illumination light 1 with uniform illuminance.

The light that illuminates the reticle 2 and passes through the light-transmitting part of the circuit pattern (including the line-and-space pattern) of the reticle 2 enters the pupil of the reduction projection lens system 3 (the light exit side is telecentric). The light enters and exits through the projection lens system 3. At this time, the projection lens system 3 uses this light to form a circuit pattern image on its image plane.

A wafer having a resist 5 coated on a substrate 4 is placed on a wafer stage 6. As shown in FIG. The wafer stage 6 includes an XY stage 9 movable along a plane perpendicular to the optical axis of the projection lens system 3, a plurality of piezoelectric elements 7 attached to the XY stage 9, and a plurality of piezoelectric elements 7. The wafer is held by the Z stage 8. Furthermore, by applying a pulse voltage to each piezoelectric element 7, the Z stage 8 can be moved a desired distance in the optical axis direction of the projection lens system 3.

Therefore, in this apparatus, the wafer is placed on the wafer stage 6, and the XY stage 9 is moved so that the exposed area of the wafer is aligned with the reticle 2. The stage 9 is positioned, the Z stage 8 is moved to focus the exposed area of the wafer on the image plane of the projection lens system, and the circuit pattern image of the reticle 2 is placed on the exposed area of the wafer. Project and expose. After the exposure, the wafer is taken out from the wafer stage 6 and subjected to various steps such as development using a developing device (not shown) and etching using an etching device (not shown), thereby manufacturing semiconductor devices.

An example of performing the exposure method of the present invention using the apparatus shown in FIG. 2 will be described with reference to FIGS. 3(A), (B), and (C).

In this embodiment, by raising the Z stage 8 in FIG. B) The center of the resist 4 and (C) the lower surface of the resist 4 are sequentially positioned, and a pattern is printed on the resist 4 by performing projection exposure using a circuit pattern image at each position. Here, exposure is performed with the top surface of the resist 4 aligned with the image plane, the vicinity of the top surface of the resist 4 is bleached and turned almost transparent, and then the center of the resist 4 is aligned with the image plane. After bleaching progresses near the center of the resist 4 to make it almost transparent up to this part, the resist 4 is finally exposed with the lower surface of the resist 4 aligned with the image plane. . The amount of exposure to the resist 4 is determined based on the sensitivity of the resist 4. Also, the total exposure amount E required to print the pattern is (A), (B), (C)
The distribution method for each projection exposure will be determined at the appropriate time. For example, in each projection exposure of (A), (B), and (C), E/
For example, 3 each will be distributed. As a result of such exposure by superimposing intermittent projection exposure, a very clear pattern can be printed on the register 4.

In this embodiment, a plurality of relative positions of the resist 4 with respect to the circuit pattern image are set, and the pattern is printed by superimposing projection exposure at each position.
The apparent depth of focus of the projection lens system 3 is increased. Moreover, here, as the bleaching of resist 4 progresses, the image plane is matched only to the top, inside, and bottom surfaces of resist 4, and printing is completed without setting the image plane anywhere other than resist 4. Therefore, the contrast of the pattern printed on this resist is also high.

In this embodiment, the position of the image plane with respect to the wafer is intermittently changed from the upper surface to the lower surface of the resist 4, but it may be changed continuously. Also, when changing the image plane position continuously, even if you move it linearly,
It may be moved non-linearly. Also, when changing the image plane position intermittently, the amount of movement of the image plane position, the number of movements,
For example, the vertical movement of the wafer is controlled by considering the residence time at each position as a main parameter. Furthermore, when changing the image plane position intermittently, the illumination system 1
It is possible to adopt a mode in which the image plane position is changed with the shutter open for the illumination light 1 of 0, or a mode in which opening and closing of the shutter for the illumination light 1 of the illumination system 10 and changes in the image plane position are synchronized. On the other hand, when changing the image plane position continuously, it is possible to change the image plane position while the shutter is open, or to synchronize the opening and closing of the shutter with changes in the image plane position.

Furthermore, in this embodiment, the image plane position is set to the resist 4.
Although the wafer is moved so as to change from the upper surface to the lower surface (the upper surface of the substrate 5), the wafer is not limited to such a form in which the amount of movement of the wafer and the thickness of the resist 4 are made the same. In other words, the exposure is completed with the image plane aligned with a certain plane within the resist 4 before reaching the lower surface of the resist 4, or with the image plane aligned below the lower surface of the resist 4. The wafer may be moved so that the exposure is completed at . Therefore, for example, (
It is also possible to complete printing of the pattern with only steps A) and (B). Furthermore, it is not necessary to align the image plane position with the upper surface of the resist 4;
The image plane position may be changed from the upper surface to the lower surface of the resist 4 at a plurality of different positions in the film thickness direction, preferably at a plurality of positions within the resist 4. and,
It is highly effective if the exposure is completed in such a way that the image plane does not coincide with any location other than the resist 4.

The relative movement amount and movement characteristics of the image plane of the projection lens system 3 with respect to the resist 4 are determined by the bleed of the resist 4.
It is changed depending on the switching characteristics, the surface structure (pattern structure) and reflectance of the substrate 5, the intensity of the illumination light 1, etc. Incidentally, as parameters indicating the characteristics of resist 4, A, B, C
One example is a parameter. Among these, the A parameter represents the bleaching characteristic, the B parameter represents the basal absorption that does not change over time, and the C parameter
represents the sensitivity.

In our study, in this embodiment, considering the case where the substrate 5 has a surface that reflects the illumination light 1 and the resist 4 becomes completely transparent to the illumination light 1 by bleaching, the resist The optimum value of the maximum relative movement amount d of the image plane from the upper surface 40 of the resist 4 to the resist 4 is d=t0 / when the thickness and refractive index of the resist 4 are t0 and n0, respectively.
It turns out that it is given by n0. It has also been found that, in reality, the optimum value deviates slightly from this value of d due to the influence of basal absorption represented by the B parameter.

Further, when the structure of the wafer is such that a SiO2 film 11 transparent to the illumination light 1 is formed on the substrate 5 and a resist 4 is formed on the SiO2 film 11 as shown in FIG. Considering the case where the substrate 5 has a surface that reflects the illumination light 1 and the resist 4 becomes completely transparent to the illumination light 1 by bleaching, the layer consisting of the resist 4 and the film 11 from the top surface of the resist 4 The optimum value of the relative maximum movement amount d of the image plane relative to
is given by Therefore, when printing a pattern on the wafer shown in FIG. 4, the pattern is printed on the wafer shown in FIG.
There are times when it is necessary to perform exposure control that is different from that used when printing images. Also, in the case of the wafer shown in FIG. 4, the optimum value actually deviates slightly from this value of d due to the influence of basic absorption represented by the B parameter.

Therefore, if the amount of relative movement of the image plane from the top surface of the resist is kept below the value obtained by dividing the thickness of the resist on the substrate or the light-transmitting layer such as SiO2 by their refractive index, the contrast of the resist will be reduced. You can print good patterns.

That is, taking the wafers shown in FIGS. 3 and 4 as an example, the thickness and refractive index of the resist are set to t0 and n0, respectively.
When, the distance d of the set image plane position in the resist film from the top surface of the resist satisfies 0<d≦t0/n0, and the thickness and refractive index of the resist are respectively t0, n0,
When the thickness and refractive index of the SiO2 film are tS and nS, respectively, the distance d from the top surface of the resist to the image plane position set in the layer containing the resist and the light-transmitting layer made of the SiO2 film is:
It is preferable to satisfy 0<d≦t0/n0+tS/nS.

In the above embodiment, the position of the image plane with respect to the wafer was changed by driving the Z stage 8 to move the wafer up and down, but the relative position of the image plane of the projection lens system 3 and the resist 4 There are other ways to change the. For example, (1) the image plane position can be adjusted by driving a reticle stage (not shown) to move the reticle 2 in the optical axis direction of the projection lens system 3, or (2) using an air lens or prism in the projection lens system 3. The optical path length changing member of the mechanism is provided, and by changing the optical path length with this member, the image plane position can be adjusted, (3)
Adjusting the image plane position by changing the wavelength of the illumination light 1 from the illumination system 10; (4) adjusting the image plane position by moving at least some lenses of the projection lens system 3 in the optical axis direction; (5) projecting a pattern using light of different wavelengths simultaneously; (6) arranging a plurality of reticles with the same pattern close to each other along the optical axis direction of the projection optical system; The pattern images of each reticle are projected simultaneously. The air lens of method (2) seals the space between a pair of lenses in the lens assembly constituting the projection lens system 3, and changes the pressure in this space. Further, in the prism mechanism of method (2), a pair of prisms are arranged close to each other so that their slopes face each other and are moved relative to each other. When method (3) is applied to a projection exposure apparatus that uses i-line or g-line as illumination light 1, a rotatable interference filter or the like is provided in illumination system 10 to adjust the wavelength of illumination light 1. It's good to adjust. In addition, when applied to a projection exposure apparatus that uses laser light from an excimer laser as the illumination light 1, a diffraction grating, an etalon, etc. in the laser resonator are rotatably supported, and the illumination light is It is best to adjust the wavelength of light 1. Furthermore, methods (5) and (6) are both methods that are applied when circuit pattern images are simultaneously projected at different image plane positions.

In the present invention, a pattern image is projected by irradiating light emitted from ultra-high pressure mercury, a laser, an X-ray source, etc. onto a patterned original plate. This is done by transmitting or reflecting the light according to the pattern on the original plate and directing it to the pupil of the projection optical system. This projection optical system is not limited to one composed of a lens assembly like the projection lens system 3 of the above embodiment. In other words, a mirror assembly or a lens and mirror may be used.

Furthermore, as described above, the present invention also includes a form in which circuit pattern images are simultaneously projected at different image plane positions; setting a plurality of relative positions in the optical axis direction of the projection optical system;
When exposing a substrate by projecting an image of a predetermined pattern onto the substrate at each position, multiple positions in the optical axis direction of the photosensitive layer of the substrate or in the optical axis direction of the layer consisting of the photosensitive layer and the transparent layer of the substrate are used. Exposure may be performed by aligning the image plane at a plurality of positions.

[0037]

[Effects of the Invention] As described above, according to the present invention, the ratio of exposing the photosensitive layer with a focused pattern image can be increased compared to the conventional method, and a clear pattern can be printed on the photosensitive layer. becomes possible. Therefore, by applying this exposure method to the manufacture of semiconductor devices, it becomes possible to manufacture high quality semiconductor devices.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing changes over time in optical properties of a resist when a resist film on a substrate is exposed to light.

FIG. 2 is a diagram showing an example of a projection exposure apparatus for manufacturing semiconductor devices to which the exposure method of the present invention is applied.

3 is an explanatory diagram showing an example of printing a pattern by the exposure method of the present invention using the apparatus shown in FIG.
) is a diagram showing how projection exposure is performed with the image plane and the top surface of the resist aligned; (B) is a diagram showing how projection exposure is performed with the image plane and the center of the resist aligned; (C) is a diagram showing how projection exposure is performed with the image plane and the lower surface of the resist aligned.

FIG. 4 is a diagram showing another example of the structure of the wafer.

[Explanation of symbols]

2 Reticle 3 Projection lens system 4 Resist 5 Wafer substrate 11　SiO2 40 Top surface of resist 50 Bottom surface of resist

Claims (23)

[Claims] 1. A plurality of relative positions of the exposed substrate with respect to the image plane of the projection optical system are set in the optical axis direction of the projection optical system, and an image of a predetermined pattern is projected onto the exposed substrate at each position. An exposure method characterized in that the image plane is aligned with a plurality of positions in the optical axis direction of a photosensitive layer of the exposed substrate to expose the exposed substrate. 2. The plurality of positions in the optical axis direction of the photosensitive layer include first and second positions in order from the upper surface side of the photosensitive layer, and the predetermined pattern image is placed in the first and second positions in order. 2. The exposure method according to claim 1, wherein the projections are performed sequentially. 3. At least one of a plurality of positions in the optical axis direction of the photosensitive layer is set within the photosensitive layer, and the distance of the at least one position from the upper surface of the photosensitive layer is d, and the thickness of the photosensitive layer is When the refractive index is t0 and n0, respectively, 0<
The exposure method according to claim 1 or 2, characterized in that the following condition is satisfied: d≦t0 /n0. 4. The exposure method according to claim 1, wherein the exposure is performed without projecting the predetermined pattern image while aligning the lower surface of the photosensitive layer with the image plane. 5. The exposure method according to claim 1, wherein the exposure is performed without projecting the predetermined pattern image while aligning the upper surface of the photosensitive layer with the image plane. 6. The exposure method according to claim 2, wherein the first position is an upper surface of the photosensitive layer. 7. The exposure method according to claim 2, wherein the first and second positions are within the photosensitive layer. 8. A plurality of relative positions of the wafer with respect to the image plane of the projection optical system are set in the optical axis direction of the projection optical system, and a circuit pattern image is projected onto the wafer at each position. After exposing a wafer, the wafer is developed to produce a semiconductor device, in which the image plane is aligned with a plurality of positions in the optical axis direction of the resist film of the wafer, and the exposure is performed. A method for manufacturing semiconductor devices. 9. The plurality of positions in the optical axis direction of the resist film include first and second positions in order from the upper surface side of the resist film, and the circuit pattern image is formed in the order of the first and second positions. 9. The method of manufacturing a semiconductor device according to claim 8, wherein the projections are performed sequentially. 10. At least one of a plurality of positions in the optical axis direction of the resist film is set within the resist film, and a distance of the at least one position from the upper surface of the resist film is d, and a thickness of the resist film is set. The refractive index is t0,
10. The method of manufacturing a semiconductor device according to claim 8, characterized in that when n0, the following condition is satisfied: 0<d≦t0/n0. 11. The method of manufacturing a semiconductor device according to claim 8, wherein the exposure is performed without projecting the circuit pattern image with the lower surface of the resist film aligned with the image plane. 12. The method of manufacturing a semiconductor device according to claim 8, wherein the exposure is performed without projecting the circuit pattern image while aligning the upper surface of the resist film with the image plane. 13. The method of manufacturing a semiconductor device according to claim 9, wherein the first position is an upper surface of the resist film. 14. The method of manufacturing a semiconductor device according to claim 9, wherein the first and second positions are within the resist film. 15. The wafer on the image plane of the projection optical system.
A plurality of relative positions are set in the optical axis direction of the projection optical system, and a circuit pattern image is projected onto the wafer at each position to expose the wafer, and then the wafer is developed; 1. A method of manufacturing a semiconductor device, wherein exposure is performed by aligning the image plane with a plurality of positions in the optical axis direction of a layer including a resist film and a transparent film of the wafer. 16. The plurality of positions in the optical axis direction of the layer include first and second positions in order from the upper surface side of the layer, and the circuit pattern image is sequentially projected at the first and second positions. 16. The method of manufacturing a semiconductor device according to claim 15. 17. At least one of a plurality of positions in the optical axis direction of the layer is set within the layer, the distance of the at least one position from the upper surface of the layer is d, and the thickness and refractive index of the resist film are 17. The semiconductor device according to claim 15, characterized in that when t0 and n0 respectively, and the thickness and refractive index of the transparent film are tS and nS, respectively, the following condition is satisfied: 0<d≦t0/n0+tS/nS Production method. 18. The method of manufacturing a semiconductor device according to claim 15, wherein the exposure is performed without projecting the circuit pattern image while aligning the lower surface of the layer with the image plane. 19. The method of manufacturing a semiconductor device according to claim 15, wherein the exposure is performed without projecting the circuit pattern image with the upper surface of the layer aligned with the image plane. 20. The method of manufacturing a semiconductor device according to claim 16, wherein the first location is a top surface of the layer. 21. The method of manufacturing a semiconductor device according to claim 16, wherein the first and second locations are within the layer. 22. The method of manufacturing a semiconductor device according to claim 21, wherein the first and second positions are within the resist film. 23. The method of manufacturing a semiconductor device according to claim 22, wherein the transparent film contains SiO2.