JPH088156A - Exposure method and mask - Google Patents

Abstract

PURPOSE:To prevent the drop of the accuracy in alignment by suppressing the occurrence of dishing by flattening, in a photolithography process for manufacturing a semiconductor element, etc. CONSTITUTION:The distortion of the observed image of a wafer mask is prevented by forming a wafer mark 76X, which has fine sub patterns 74A-74E between the fellow projections 71A-75D arranged at specified intervals, on a wafer W thereby suppressing the occurrence of dishing phenomena on the surface of the flattening film 79 on a wafer mark 76X. Moreover, a reticle for forming the wafer mark 76X has a reticle mark where fine light and dark patterns are arranged between transmission parts or dark parts with specified widths.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method and a mask used in the exposure method, and more particularly to an exposure method having a planarization process in photolithography of semiconductor manufacturing and an exposure method having the planarization process. Regarding the mask.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device, a liquid crystal display device, or the like by a photolithography process, each shot area on a wafer (or glass plate, etc.) on which a reticle (or photomask, etc.) pattern is coated with a photosensitive material. An exposure device is used to expose to. This type of exposure apparatus is a so-called step-and-repeat method in which a wafer stage on which a wafer is placed is stepped and the operation of sequentially exposing the reticle pattern to each shot area on the wafer is repeated. Exposure equipment (steppers, etc.)
Is often used. Further, recently, a so-called step-and-scan projection exposure apparatus has been developed which exposes a reticle pattern in an area wider than the exposure field of a projection optical system by scanning a reticle and a wafer in synchronization. There is.

By the way, since, for example, a semiconductor element is formed by stacking a large number of layers (a large number of layers) of circuit patterns on a wafer, for example, when exposing the circuit patterns of the second and subsequent layers on the wafer, It is necessary to perform accurate alignment between each shot area where a circuit pattern is already formed and the pattern image of the reticle, that is, alignment between the wafer and the reticle. Therefore, a method is generally used in which a wafer mark for alignment is provided on a wafer together with a circuit pattern and the wafer mark is used for aligning a circuit pattern of a subsequent layer.

An alignment sensor used for measuring the position of the wafer mark is an LSA (Laser Step Alignmen) which irradiates the wafer mark on the wafer with laser light and detects the position of the mark by the diffracted / scattered light.
t) method, image processing is performed on a wafer mark illuminated by light with a wide wavelength band width using a halogen lamp as a light source, and F is measured.
The IA (Field Image Alignment) method or the diffraction grating-like wafer mark on the wafer is irradiated with laser light with slightly different frequencies from two directions, and the two diffracted lights generated are caused to interfere with each other, and the phase of the interference light LIA (Laser Interferometric Alignment) to measure the position of wafer mark from
There are some methods. Among them, the LIA method is most effective in detecting the position of a wafer mark on a wafer with a low step or a wafer having a rough surface, and corresponds to a flattening technique described later.

By the way, the shape, the number, or the size of the alignment wafer mark is selected according to the resolution of the projection optical system of the exposure apparatus, the required alignment accuracy, the state of the layer on the wafer, and the like. As for its shape,
Generally, various shapes such as a slit shape, a dot shape, or a lattice shape are used, but conventionally, these wafer marks have relatively large recesses (4 μm width, 6 μm width, etc.) In most cases, is formed only by the concavo-convex pattern that is periodically arranged between the convex portions.

Nowadays, due to high integration and high density found in VLSI and the like, multilayer wiring is inevitable. Among the process technologies necessary for realizing this multilayer wiring structure, the flattening technique for flattening the surface of the film of a predetermined layer is very important. This flattening has become an unavoidable technique not only for realizing multilayer wiring but also in the process of manufacturing an integrated circuit having a multilayer structure. This flattening is usually carried out by a chemical method such as an anodic oxidation method, a resin coating method, a glass flow method, an etch back method, a lift-off method, a bias sputtering method, etc. Thus, the surface of the film formed on the substrate is also subjected to chemical mechanical polishing or the like (chemical mechanical polishing).

[0007]

However, when the metal film underlying the film to be planarized has a concave pattern of 2 μm or more in the planarization process by the chemical mechanical polishing, the film in that portion is present. A dish-shaped recess is generated on the surface,
A phenomenon called so-called dishing occurs.
Therefore, when a relatively large concave portion (4 μm width, 6 μm width, etc.) is formed like a conventional wafer mark, and these are formed only by a concavo-convex pattern that is periodically arranged,
A similar phenomenon occurs on the surface of the film formed thereon.
The situation is shown in FIG.

FIG. 8A shows a state in which an oxide film 92 is formed on a substrate 93 such as a wafer, a recess 90a is formed by etching, and a metal coating 91 is formed by aluminum sputtering or the like. After that, the state after performing the above-mentioned chemical mechanical polishing is shown in FIG. In FIG. 8B, when the width of the recess 90a is 2 μm or more, the recess 90a
Dishing D1 occurs on the top. Also, as shown in FIG. 9A, a pattern in which a plurality of concave portions 90b are periodically arranged is formed on the substrate 93, and the metal coating 91 is deposited on this pattern, the same is true. Although dishing occurs in the above case, when chemical mechanical polishing is performed in this case, large dishing D2 occurs on the array of the recesses 90b as shown in FIG. 9B. Therefore, when the wafer mark M having a line-and-space pattern in which the convex portions 90c are periodically arranged as shown in FIG. 9C is used, a large dishing D3 occurs on the wafer mark M. For this reason, there is a problem in that the observed image of the wafer mark is distorted when it is detected by the alignment system, and the alignment accuracy is deteriorated.

In view of the above point, the present invention does not cause dishing on the alignment mark (wafer mark) even when a flattening process such as a wiring process is performed on the alignment mark. It is an object to provide an exposure method. Further, the present invention aims to provide a mask that can be used in such an exposure method.

[0010]

In the exposure method according to the present invention, a first step (step 10) of forming a positioning mark (76X) made of an uneven pattern on a substrate (W).
1 to 105), a second step (step 106) of forming a coating (79) on the alignment mark (76X) of the substrate and other regions, and the coating (79) is planarized. A third step (107) and a fourth step (steps 108 to 11) of applying a photosensitive material on the film (79) planarized by the third step and exposing a mask pattern.
0) and the alignment mark (76X) formed in the first step (steps 101 to 105) of the exposure method, the convex portion (75A to 75A) having a predetermined width or more.
D) (hereinafter “the convex portion of the main pattern (75A to 75A
D) ”) is formed between the concavo-convex patterns (74A to 74E) (hereinafter, also referred to as“ sub-patterns (74A to 74E) ”) having a pitch smaller than the predetermined width.

Further, the mark (76) for aligning the position is used.
The effect of the present invention is particularly large when the interval between the convex portions (75A to 75D) of X) having a predetermined width or more is 2 μm or more. Furthermore, in the mask according to the present invention, in the mask (R) in which the original pattern of the alignment mark (76X) is formed together with the transfer pattern, the original pattern of the alignment mark (76X) has a predetermined width. Between the plurality of light portions or dark portions (66A, 66B) described above, the light / dark patterns (67A, 67) having a pitch smaller than the predetermined width.
B) is formed.

[0012]

According to the exposure method of the present invention, since the sub-patterns (74A to 74E) are formed in the regions which are conventionally recesses, the space between the recesses on the substrate W is made extremely small. Generation of dishing on the alignment mark (76X) due to the flattening is suppressed. Therefore, mark distortion does not occur and alignment is performed with high accuracy. Further, in the exposure method of the present invention, the convex portion (75A) of the main pattern of the alignment mark (76X) is
~ 75D) the interval between them is equal to or higher than the resolution of the alignment sensor, and the protrusions (7A to 74E) of the sub-patterns (74A to 74E) are
8) The intervals between the recesses (77) and between the recesses (77) can be set to be equal to or smaller than the resolution of the alignment sensor. Therefore, the main pattern and the sub pattern (7
4A to 74E) are used as the light and dark patterns, respectively, and the alignment can be performed by the conventional alignment sensor.

If the distance between the convex portions (75A to 75D) of the alignment mark (76X) having the predetermined width or more is set to 2 μm or more, dishing is likely to occur between the convex portions. Therefore, the sub pattern (74A to 74A
By providing E), the occurrence of dishing is suppressed. It can also be used with alignment sensors that have poor resolution.

Further, according to the mask (R) of the present invention, the alignment mark (76X) exposed and transferred onto the substrate (W) by using the mask (R) is a convex portion having a predetermined width or more of the main pattern. (75A to 75D), a sub-pattern (74A to 74A) made of unevenness having a pitch equal to or less than the predetermined width.
74E) is formed. Therefore, as described above, the dishing on the alignment mark (76X) is suppressed, and therefore, the alignment is executed with high accuracy without causing the mark distortion.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a schematic configuration of a projection exposure apparatus suitable for applying the exposure method of the present embodiment.
Illumination light IL generated from the ultra-high pressure mercury lamp 1 at
Is reflected by the elliptical mirror 2 and once condensed at its second focal point, and then collimator lens, interference filter, optical integrator (fly eye lens) and aperture stop (σ
The light enters the illumination optical system 3 including a diaphragm). Although not shown, the fly-eye lens is arranged in the in-plane direction perpendicular to the optical axis AX so that the reticle-side focal plane of the fly-eye lens substantially coincides with the Fourier transform plane (pupil conjugate plane) of the reticle pattern.

A shutter (for example, a four-blade rotary shutter) 37 for closing and opening the optical path of the illumination light IL by a motor 38 is arranged near the second focal point of the elliptic mirror 2. As the illumination light for exposure, laser light such as an excimer laser (KrF excimer laser, ArF excimer laser) or a harmonic wave of a metal vapor laser or a YAG laser is used in addition to the bright line of the ultra-high pressure mercury lamp 1 or the like. It doesn't matter.

In FIG. 3, illumination light (i-line or the like) in a wavelength range in which the photoresist layer emitted from the illumination optical system 3 is exposed to light.
Most of the IL is reflected by the beam splitter 4, and then passes through the first relay lens 5, the variable field stop (reticle blind) 6 and the second relay lens 7 to reach the mirror 8. Then, the illumination light IL reflected by the mirror 8 in a substantially vertically downward direction illuminates the pattern area PA of the reticle R with substantially uniform illuminance via the main condenser lens 9. The arrangement surface of the reticle blind 6 and the pattern formation surface of the reticle R are in a conjugate relationship (image formation relationship), and the drive system 3
By opening and closing a plurality of movable blades constituting the reticle blind 6 by 6 to change the size and shape of the opening, the illumination field of the reticle R can be arbitrarily set.

Here, in FIG. 3, the Z axis is taken parallel to the optical axis AX of the illumination optical system that intersects the reticle R, and its Z
The X axis is parallel to the plane of FIG. 3 and the Y axis is perpendicular to the plane of FIG. 3 in the plane perpendicular to the axis. FIG. 5C shows the reticle R of this embodiment. In the reticle R of this FIG.
Reticle marks 64X and 64Y serving as alignment marks are respectively provided in the light-shielding band 62 which is adjacent to approximately the center of two orthogonal sides of the pattern area 61 surrounded by the light-shielding band 62.
Are formed. By projecting the images of these reticle marks onto the photoresist layer of the wafer W and developing them, the images of the reticle marks are formed on the wafer W as the wafer marks of the concavo-convex pattern.
Further, the reticle marks 64X and 64Y may be commonly used as alignment marks when aligning each shot area of the wafer W with the reticle R. The two reticle marks 64X and 64Y have the same configuration (however, the directions are different), and are formed by a light-shielding film such as chromium in the transparent windows 63X and 63Y provided in the light-shielding band 62 of the reticle R, respectively. Further, on the reticle R, alignment marks 65A and 65B, which are two cross-shaped light-shielding marks, are formed in the vicinity of the outer periphery of the reticle R so as to face each other. These two alignment marks 65A and 65B
Is used for alignment of the reticle R (positioning with respect to the optical axis AX).

The reticle mark of the reticle R will be described in more detail with reference to FIGS. 5 (c) and 5 (d). As shown in FIG. 5C, the reticle mark is composed of a reticle mark 64X for detecting the position in the X direction and a reticle mark 64Y for detecting the position in the Y direction. Each of the sub-marks is composed of five sub-marks arranged in the transparent portion. The Y-direction reticle mark 64Y is obtained by rotating the X-direction reticle mark 64X by 90 °.

FIG. 5 (d) shows a part of the structure of the reticle mark 64X for the X direction. In FIG. 5 (d),
The reticle mark 64X is configured by arranging sub-marks 67A, 67B, ... Of substantially the same width as the transmissive portion between the transmissive portions 66A, 66B ,.
Each of the sub-marks 67A, 67B, ... Arranges five sets of slit-shaped light-shielding films 68 and slit-shaped transmission portions 69 at a predetermined pitch in the X direction.

The sub-marks 67A, 67B, ... Are formed at intervals of a predetermined width or more. This interval is determined in consideration of the resolution of the alignment sensor, but when exposed and transferred onto the wafer W, the sub patterns of the wafer marks formed on the wafer W by the sub marks 67A, 67B ,. Is 2 in this embodiment.
It is desirable that the thickness be at least μm. The sub mark 67
The shape of A, 67B, ... Is not limited to the shape of FIG. Further, the reticle marks 64X and 64Y may be marks in which the bright portion and the dark portion are reversed.

Now, the sub marks 67A and 6A shown in FIG.
The pitch interval between the light-shielding film 68 and the transmissive portion 69 in 7B, ..., When the sub-mark is transferred onto the wafer W,
The image of the sub mark is set to have a size less than the resolution of the alignment sensor. Incidentally, the sub mark 67A in the reticle mark 64X in this embodiment,
67B, ... Are regular patterns, but may be irregular patterns. However, the interval between the bright parts or the interval between the dark parts of the irregular pattern is
When transferred onto the wafer, the internal structure of the sub-pattern (partial pattern) of the wafer mark formed by the sub-mark may be set to a fineness equal to or lower than the resolution of the alignment sensor used for its detection. desirable. The reticle marks 64X and 64Y can be formed by a known optical pattern generator or electron beam drawing device.

Now, returning to FIG. 3, the description will be continued. The reticle R is driven by the motor 12 so as to have an optical axis A of the projection optical system 13.
A reticle stage RS that can be finely moved in the X direction (which coincides with the optical axis of the illumination optical system) (Z direction), and can be two-dimensionally moved and finely rotated in a horizontal plane perpendicular to the optical axis AX.
It is placed on top. A movable mirror 11m that reflects the laser beam from the laser light wave interferometer length measuring device (laser interferometer) 11 is fixed to the end of the reticle stage RS, and the two-dimensional position of the reticle stage RS is determined by the laser interferometer 11. , Is constantly detected with a resolution of, for example, about 0.01 μm. Above the reticle R, reticle alignment systems (RA systems) 10A and 10B are arranged.
The systems 10A and 10B include two cross-shaped alignment marks 65A and 65B formed near the outer periphery of the reticle R.
Is to detect. By finely moving the reticle stage RS based on the measurement signals from the RA systems 10A and 10B, the reticle R is positioned so that the center point of the pattern area 61 coincides with the optical axis AX of the projection optical system 13.

The illumination light IL which has passed through the pattern area 61 of the reticle R enters the projection optical system 13 which is telecentric on both sides, and is projected by the projection optical system 13 to a projected image of the circuit pattern of the reticle R which is reduced to ⅕. However, a photoresist layer is formed on the surface, and the surface is projected (imaged) so as to be superposed on one shot area on the wafer W held so that the surface substantially coincides with the best imaging plane of the projection optical system 13. It

The wafer W is vacuum-sucked by a finely rotatable wafer holder (not shown), and is held on the wafer stage WS via this wafer holder. The wafer stage WS is configured to be two-dimensionally movable in a step-and-repeat manner by a motor 16,
When the transfer exposure of the reticle R onto one shot area is completed, the wafer stage WS is stepped to the next shot position. A movable mirror 15 that reflects the laser beam from the laser interferometer 15 is provided at the end of the wafer stage WS.
m is fixed, and the two-dimensional coordinates of the wafer stage WS are constantly detected by the laser interferometer 15 with a resolution of about 0.01 μm, for example. The laser interferometer 15 is
The coordinates of the wafer stage WS in the X and Y directions are measured, and the stage coordinate system (stationary coordinate system) of the wafer stage WS is determined by the coordinates in the X and Y directions.
(X, Y) is defined. That is, the coordinate value of the wafer stage WS measured by the laser interferometer 15 is the coordinate value on the stage coordinate system (X, Y).

On the wafer stage WS, a reference member (glass substrate) 14 having a reference mark used when measuring a baseline amount (a distance between the reference point of the alignment sensor and the exposure center) is attached to the wafer W. The height of the exposed surface is approximately the same as that of the exposed surface. Further, in FIG. 3, an image formation characteristic correction unit 19 capable of adjusting the image formation characteristic of the projection optical system 13 is also provided. The imaging characteristic correction unit 19 in the present embodiment independently drives some of the lens elements forming the projection optical system 13, in particular, each of the plurality of lens elements close to the reticle R by using a piezoelectric element such as a piezo element. By performing (moving or tilting in a direction parallel to the optical axis AX), the imaging characteristics of the projection optical system 13, for example, the projection magnification and distortion are corrected.

Next, an off-axis type image processing type alignment sensor (hereinafter referred to as "Field Image Alignment system (FIA system)") is provided on the side of the projection optical system 13.
Is provided. In this embodiment, the position of the wafer mark is detected by this FIA system. In this FIA system,
The light generated by the halogen lamp 20 is passed through the condenser lens 21 and the optical fiber 22 to the interference filter 23.
Then, the light in the photosensitive wavelength region and infrared wavelength region of the photoresist layer is cut off here. The light transmitted through the interference filter 23 is incident on the both-side telecentric objective lens 27 via the lens system 24, the beam splitter 25, the mirror 26, and the field stop BR. The light emitted from the objective lens 27 is reflected by a prism (or mirror) 28 fixed around the lower part of the lens barrel of the projection optical system 13 so as not to block the illumination visual field of the projection optical system 13, and the wafer W is almost vertical. To irradiate.

The light from the objective lens 27 is applied to a partial area including the wafer mark on the wafer W, and the light reflected from the area is the prism 28, the objective lens 27, the field stop BR, the mirror 26, and the beam splitter 25. And is guided to the index plate 30 via the lens system 29. Here, the index plate 30 is arranged in a plane conjugate with the wafer W with respect to the objective lens 27 and the lens system 29, and the image of the wafer mark on the wafer W is formed in the transparent window of the index plate 30. Further, the index plate 30 is formed with two linear marks extending in the Y direction at predetermined intervals in the transparent window as index marks. The light that has passed through the index plate 30 is guided to an image pickup device (CCD camera or the like) 34 via a first relay lens system 31, a mirror 32 and a second relay lens system 33, and a wafer is provided on the light receiving surface of the image pickup device 34. An image of the mark and an image of the index mark are formed. The image pickup signal SV from the image pickup device 34 is supplied to the main control system 18, where the position (coordinate value) of the wafer mark in the X direction is calculated. Although not shown in FIG. 3, the FI having the above configuration is used.
In addition to the A system (X-axis FIA system), another set of FIA systems (Y-axis FIA system) for detecting the position of the wafer mark in the Y direction is provided.

Next, TT is provided on the upper side of the projection optical system 13.
An L (through the lens) type alignment sensor 17 is also arranged, and the position detection light from the alignment sensor 17 is transmitted through the mirrors M1 and M2 to the projection optical system 1.
It is led to 3. The light for detecting the position is the projection optical system 1
The wafer W on the wafer W is irradiated with the reflected light from the wafer W via the projection optical system 13, the mirror M2, and the mirror M1, and the alignment sensor 17
Is returned to. The alignment sensor 17 obtains the position of the wafer mark on the wafer W from the signal obtained by photoelectrically converting the returned reflected light.

FIG. 4 shows the detailed structure of the TTL alignment sensor 17 in FIG. 3. In FIG. 4, the alignment sensor 17 of this example is a two-beam interference alignment system (hereinafter referred to as “LIA system”). ) And a laser step alignment type alignment system (hereinafter referred to as “LSA system”), and the optical members thereof are maximally shared. Although briefly described here, a more specific configuration is disclosed in Japanese Patent Laid-Open No. 2-272305.

In FIG. 4, a laser beam emitted from a light source (He-Ne laser light source, etc.) 40 is split by a beam splitter 41, and the laser beam reflected here is passed through a shutter 42 to a first beam shaping optical system. (LI
A optical system) 45. On the other hand, the laser beam transmitted through the beam splitter 41 enters the second beam shaping optical system (LSA optical system) 46 via the shutter 43 and the mirror 44. Therefore, the shutters 42 and 43
Can be used by switching between the LIA system and the LSA system by appropriately driving.

The LIA optical system 45 includes two sets of acousto-optic modulators, etc., and emits two laser beams having a predetermined frequency difference Δf substantially symmetrically with respect to the optical axis.
Further, the two laser beams emitted from the LIA optical system 45 reach the beam splitter 49 via the mirror 47 and the beam splitter 48, and the two laser beams transmitted therethrough are a lens system (inverse Fourier transform lens). 5
The light enters the reference diffraction grating 55, which is fixed on the apparatus, from two different directions at a predetermined crossing angle, and forms an image (crossing) through the mirror 3 and the mirror 54. The photoelectric detector 56 receives the interference light of the diffracted lights that are transmitted through the reference diffraction grating 55 and generated in substantially the same direction, and outputs a sinusoidal photoelectric signal SR corresponding to the intensity of the diffracted light to the main control system 18 (FIG. 3))
It is output to the A arithmetic unit 58.

On the other hand, the two laser beams reflected by the beam splitter 49 intersect once at the opening of the field stop 51 by the objective lens 50, and then the mirror M2 (see FIG. 3).
The inside mirror M1 is incident on the projection optical system 13 via a mirror (not shown). Further, the two laser beams incident on the projection optical system 13 become substantially symmetrical with respect to the optical axis AX on the pupil plane of the projection optical system 13 and once converged in a spot shape. The parallel luminous fluxes are inclined with respect to the direction (Y direction) with respect to each other with the optical axis AX in between, and become parallel luminous fluxes, which are incident on the wafer mark from two different directions at a predetermined crossing angle. A one-dimensional interference fringe that moves at a speed corresponding to the frequency difference Δf is formed on the wafer mark, and the ± first-order diffracted light (interference light) generated in the same direction from the mark, here, in the optical axis direction, is projected onto the projection optical system. 13. The photoelectric detector 52 receives the light through the objective lens 50 and the like, and the photoelectric detector 52 receives the sine-wave photoelectric signal S corresponding to the cycle of the change in contrast of the interference fringes.
Dw is output to the LIA operation unit 58. The LIA calculation unit 58 calculates the position shift amount of the wafer mark from the phase difference on the waveforms of the two photoelectric signals SR and SDw, and uses the position signal PDs from the laser interferometer 15 to determine the position shift amount. The coordinate position of the wafer stage WS when it becomes zero is obtained.

The LSA optical system 46 includes a beam expander, a cylindrical lens, etc., and the laser beam emitted from the LSA optical system 46 enters the objective lens 50 via the beam splitters 48 and 49. Further, the laser beam emitted from the objective lens 50 once converges into a slit shape at the opening of the field stop 51, and then enters the projection optical system 13 via the mirror M2. The laser beam incident on the projection optical system 13 passes through almost the center of its pupil plane, then extends in the X direction within the image field of the projection optical system 13 and is directed to the optical axis AX as an elongated strip-shaped spot light on the wafer. Projected onto W.

When the spot light and the wafer mark (diffraction grating mark) on the wafer W are moved relative to each other in the Y direction, the light generated from the wafer mark passes through the projection optical system 13, the objective lens 50 and the like and is a photoelectric detector. The light is received at 52. The photoelectric detector 52 has ± 1st order of the light from the wafer mark.
Only the third-order diffracted light is photoelectrically converted, and the photoelectric signal SDi corresponding to the light intensity obtained by photoelectrically converting in this manner is used as the main control system 18
It is output to the LSA calculation unit 57 in the inside. The LSA arithmetic unit 57 has a position signal PDs from the laser interferometer 15.
Also, the LSA calculation unit 57 samples the photoelectric signal SDi in synchronization with the up / down pulse generated for each unit movement amount of the wafer stage WS. Furthermore, LS
The A calculation unit 57 converts each sampling value into a digital value and stores it in the memory in the order of addresses, and then calculates the position of the wafer mark in the Y direction by a predetermined calculation process.
Further, the position of the LIA type wafer mark for the X-axis and L
An X-axis alignment sensor for detecting the position of the SA type wafer mark is also provided separately.

Next, an example of the exposure operation in this embodiment will be described with reference to the flowchart of FIG. First,
In step 101 of FIG. 1, a photoresist is applied on the wafer W by a coater (not shown) and baking is performed if necessary, and in step 102, the wafer W is placed on the wafer stage WS of the projection exposure apparatus of FIG. Then, the reticle R shown in FIG. 5C is loaded on the reticle stage RS shown in FIG. Then in step 103,
The circuit pattern and the reticle marks 64X and 64Y in the pattern area 61 on the reticle R of FIG. 5C are reduced to 1/5 in the photoresist layer applied on the wafer W via the projection exposure system 13. And then projected. This allows
As shown in FIG. 5A, the shot area S on the wafer W is
A circuit pattern image is projected in A, and its shot area S
An image 70X of the reticle mark 64X and an image 70Y of the reticle mark 64Y are projected in the vicinity of A. For example, the image 70X of the reticle mark 64X is the image of sub-marks 71A, 71B, ..., 71E arrayed in the X direction at a predetermined pitch, as shown in FIG. 5B. The images 70X and 70Y of these reticle marks become wafer marks formed of an uneven pattern after processing such as development.

The wafer W onto which the circuit pattern on the reticle R and the images of the reticle marks 64X and 64Y are transferred is developed in step 104, and then subjected to etching processing in step 105 using the resist pattern as a mask after baking processing. After that, it is washed again if necessary. The development processing apparatus used in step 104 includes a spray method in which a predetermined cleaning solution and a developing solution are sprayed in a spray or shower form, or a dip method in which a predetermined cleaning solution and a developing solution are immersed in the developing solution or the cleaning solution for a certain period of time for development. The wafer W is developed and washed by any one of these methods. Further, the etching is performed by a wet method or a dry method, but today, the etching is often performed by the dry method, and for this dry etching, for example, a plasma etching apparatus is used.

In step 105, the completion of etching is detected by a spectroscopic analysis method, a laser beam interferometry method utilizing optical reflection, an ellipsometer method, a grating light diffraction method, or the like, and the completion of the etching is confirmed, and then the wafer W is transferred if necessary. To wash. In this way, the resist layer and the unnecessary oxide film portion or metal film portion are removed.
Required circuit and wafer mark 76X as shown in (b)
Are unevenly formed in the film 73 on the film (lower circuit pattern layer) 72 on the wafer W. This wafer mark 7
6X is a projection optical system PL for the X-axis reticle mark 64X.
Is formed from the image transferred onto the wafer W in accordance with the reduction magnification of.

FIG. 2 shows a wafer mark 76X formed on the wafer W by transferring the wafer mark formed in this embodiment, that is, the reticle mark 64X. Note that FIG. 2 also shows a flattening layer made of an insulating film (or a metal film) which will be described later, and is also used when explaining the flattening step. FIG. 2A shows a wafer mark 76X for the X axis,
FIG. 2B is a sectional view as seen from the Y direction, and FIG. 2B is a plan view of the wafer mark 76X.

The wafer mark 76X is shown in FIG.
As shown in (b), a film 73 formed on the film 72 on the wafer W is formed together with the circuit as described above, and the film 73 is formed as convex portions 73a and 73b at both ends, and a plurality of convex portions are provided therebetween. The portions 75A to 75D are formed at intervals of a predetermined width or more, and sub-patterns 74A to 74E made of a fine concavo-convex pattern including a convex portion 78 and a concave portion 77 are formed between the convex portions. Here, the width P1 of each sub-pattern and the width P2 of each convex portion are formed with a predetermined length (in this example, P1 and P2 are each about 6 μm). Further, the width P3 of the convex portion 78 or the concave portion 77 of the sub pattern is formed to have a predetermined length, but in this example, the width P3 is set to about 0.67 μm.
However, the width P3 is not limited as long as it is a width that is detected and processed as a dark portion of the alignment sensor used. In addition, the distance between the convex portions of the mark 76X (that is,
The width P1 of the sub-pattern is set to about 6 μm in this example, but this width is not particularly limited as long as it is equal to or larger than the resolution of the alignment sensor used. However,
If possible, the distance P1 is preferably 2 μm or more.
Since the sub-patterns 74A to 74E of the alignment sensor formed as described above cannot be resolved by the FIA type mark sensor, the convex portion 75 of the wafer mark 76X is formed.
Processing can be performed as a light-dark pattern in which A to 75D are bright portions and sub-patterns 74A to 74E are dark portions. The wafer mark 76Y is also formed similarly to the wafer mark 76X.

As described above, the surface of the wafer W on which the predetermined circuits and the wafer marks 76X and 76Y are formed is then flattened in steps 106 and 107 to form an upper layer circuit. This planarization is performed by the above-described method, but in this example, first, in step 106, an insulating film (or a metal film) such as silicon oxide (SiO ₂ ) on the wafer W, hereinafter referred to as a “planarizing film”. ) 79 is coated. At this stage, as shown in FIG. 2A, minute irregularities are seen on the surface 79a of the flattening film 79. Next, in step 107, the surface 79a of the flattening film 79 is chemically mechanically polished. This chemical mechanical polishing is performed by a method of mechanically polishing the surface of the flattening film 79 while adding a predetermined chemical or water if necessary.

FIG. 2A shows the wafer W flattened by the above method, particularly the flattening film 7 on the wafer mark 76X.
The state of the surface 80 of 9 is shown. The surface 80 of the flattening film 79 forms a smooth surface without being recessed on the wafer mark 76X. This is the convex portion 75 of the wafer mark 76X.
This is because by filling the space between A to 75D with the fine sub-patterns 74A to 74E, the recesses of 2 μm or more are eliminated, and as described above, the flatness of the flattening film 79 on the wafer mark 76X is maintained. .

In step 108, the photoresist is coated again on the wafer W whose surface is flattened by the above steps. Here, for example, a photoresist coating apparatus (coater) such as a spin coat method that rotates the wafer W and forms a photoresist thin film on the wafer W by centrifugal force is used. In step 109, the wafer W coated with the photoresist is set again on the wafer stage of the above-described projection exposure apparatus or another projection exposure apparatus suitable for the exposure method of this embodiment or a general pattern forming apparatus. .

By the way, for example, the flattening film 79 is a transparent insulating film such as silicon oxide, and the wafer mark 76 is formed.
If X and 76Y are metal, even if the flattening film 79 is formed on the entire surface of the wafer W including the wafer marks 76X and 76Y, the wafer marks 76X and 76Y are detected by the FIA-based alignment sensor which is an image processing system. it can. However, if the flattening film 79 is made of metal, the wafer marks 76X and 76Y are not detected. Therefore, in that case, a portion which is not flattened may be provided on the wafer W, and another wafer mark may be formed there. If the detection is possible in this way, the alignment of the wafer W set on the wafer stage WS is performed as described above using the FIA system alignment sensor.

The wafer marks of the LSA type or LIA type also have the LSA type or LIA type, respectively.
With the alignment sensor of the system, like the FIA system,
The wafer mark can be detected and aligned. Here again, in step 110, another reticle is used to form a new circuit pattern and, if necessary, a new wafer mark. At this time, there is no dish-shaped recess due to the above-mentioned dishing phenomenon at the formation position of the new wafer mark, and the surface 80 of the flattening film 79 on the wafer W is
A stable wafer mark without mark distortion is formed.

FIG. 6 shows F used in the exposure method of the present invention.
FIG. 6A shows another embodiment of the IA-based X-axis wafer mark, and FIG. 6A shows a wafer mark in which fine sub-patterns are line-and-space patterns arranged in the non-measurement direction. Are formed by the line marks 81A, 81B, and 81C, each of which has a convex portion 83 and a concave portion 82 having a predetermined width or less. Here, line marks 81A, 81B, 81C
In the drawing, the concave portions 82 and the convex portions 83 are formed at a predetermined pitch in the Y direction. FIG. 6B is a wafer mark in which a fine sub-pattern is formed into a two-dimensional grid pattern, and a line mark 84 having a fine grid-shaped concavo-convex pattern, respectively.
It is formed by A, 84B and 84C. Here, the line marks 84A, 84B, and 84C are formed with an interval equal to or larger than a predetermined width, as in FIG. Also, FIG. 6 (c)
Indicates a wafer mark in which a fine sub-pattern is formed in a random dot shape, and is formed by line marks 85A, 85B, 85C each having a random dot-shaped convex portion. Here, the line marks 85A, 85B, and 85C are formed at intervals of a predetermined width or more, as in FIGS.
The alignment mark having such a fine sub-pattern can be used not only in the FIA system but also in other alignment sensor systems such as the LSA system and the LIA system.

FIG. 7 shows a wafer mark for LSA,
A fine sub-pattern 87 composed of a slit-shaped concavo-convex pattern parallel to the X-axis, a Y-axis pattern 86A composed of a plurality of combinations of convex portions 88, and a sub-pattern composed of a concavo-convex pattern parallel to the fine Y-axis. 89 and a pattern 86B for the X-axis, which is formed by a plurality of combinations with 89. The wafer mark used in the exposure method of the present invention can be similarly applied to wafer marks of other shapes.

Further, the present invention can be applied not only to a stepper type exposure apparatus, but also to a step-and-scan type exposure apparatus in which a reticle and a wafer are relatively scanned to perform exposure. As described above, the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0049]

According to the exposure method of the present invention, dishing does not occur on the alignment mark even if the flattening process is performed. Therefore, the distortion of the detection light of the alignment mark at the time of alignment can be suppressed, and the alignment accuracy is improved. Further, there is no need to change the mechanism on the side of the device for exposing and transferring, and therefore it is simple.

Further, when the interval between the convex portions of the alignment mark is set to 2 μm or more, the alignment mark can be detected by the conventional alignment sensor of ordinary resolution. Further, when the interval is 2 μm or more, dishing is particularly likely to occur, but the present invention can suppress the occurrence of dishing. Further, according to the mask of the present invention, the alignment mark exposed and transferred onto the substrate by using the mask can suppress dishing on the alignment mark in the flattening process step, and therefore, the mark distortion can be prevented. High-precision alignment can be achieved without causing

[Brief description of drawings]

FIG. 1 is a flowchart showing an exposure operation of an embodiment of the present invention.

2A is a cross-sectional view of a wafer mark used in the embodiment, and FIG. 2B is a plan view of the wafer mark.

FIG. 3 is a configuration diagram showing a projection exposure apparatus suitable for carrying out the exposure method of the embodiment.

FIG. 4 is a configuration diagram showing an LSA type and LIA type alignment sensor used in the projection exposure apparatus of FIG. 3;

5A is a plan view showing an image of a circuit pattern and a reticle mark exposed on a wafer, and FIG.
Part (a) is an enlarged plan view, (c) is a plan view showing the pattern arrangement of the reticle of the embodiment, (d) is an enlarged plan view showing part of the reticle mark in FIG. 5 (c). is there.

FIG. 6 is a diagram showing another example of a FIA type wafer mark, FIG. 6A is an enlarged plan view showing a wafer mark in which a fine sub-pattern is a line-and-space pattern in a non-measurement direction; FIG. 6B is an enlarged plan view showing a wafer mark in which a fine sub-pattern has a two-dimensional lattice shape, and FIG. 7C is an enlarged plan view showing a wafer mark in which a fine sub-pattern has a random dot shape.

FIG. 7 is an enlarged plan view showing an example of an LSA wafer mark.

FIG. 8 is an explanatory diagram of occurrence of conventional dishing.

FIG. 9 is a diagram showing a state in which dishing occurs on a conventional wafer mark.

[Explanation of symbols]

 1 Light Source 3 Illumination Optical System 9 Main Condenser Lens R Reticle 13 Projection Optical System W Wafer WS Wafer Stage 15 Laser Interferometer 18 Main Control System 67A, 67B Reticle Mark Sub-Mark 64X, 64Y Reticle Mark 76X X-Wafer Mark 73a, 75A to 75D, 73b Wafer mark projections 74A to 74E Wafer mark sub-pattern 79 Flattening film

Claims (3)

[Claims] 1. A first step of forming an alignment mark made of a concavo-convex pattern on a substrate; a second step of forming a film on the alignment mark and other regions of the substrate; A third step of flattening the coating;
A fourth step of applying a photosensitive material onto the film planarized by the step of exposing a mask pattern; and the alignment mark formed in the first step,
An exposure method, wherein an uneven pattern having a pitch smaller than the predetermined width is formed between convex portions having a predetermined width or more. 2. The exposure method according to claim 1, wherein an interval between the projections having the predetermined width or more of the alignment mark is 2 μm or more. 3. A mask in which an original pattern of marks for alignment is formed together with a transfer pattern, wherein the original pattern of marks for alignment is between a plurality of bright portions or dark portions having a predetermined width or more, A mask, wherein a light-dark pattern having a pitch smaller than the predetermined width is formed.