JP2002299219A - Charged beam exposure method and charged beam exposure apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charged beam exposing method which can achieve high resolution high accuracy pattern transfer exposure. SOLUTION: Geometric blur of a projection optical system is measured or estimated for each subfield and the largest geometric blur is selected. When it does not satisfy a management criterion, each section of an aligner is modified. When it satisfies the management criterion, exposure is performed while regulating the geometric blurs of all subfields dynamically to coincide with the management criterion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a charged beam exposure method and a charged beam exposure apparatus mainly used in a lithography process for manufacturing a semiconductor integrated circuit. In particular, high-resolution and high-resolution
The present invention relates to a method capable of realizing high-precision pattern transfer exposure. Note that the charged beam mentioned here includes an electron beam and an ion beam.

[0002]

2. Description of the Related Art The prior art will be described below by taking transfer exposure using an electron beam as an example. Electron beam exposure has high accuracy but low throughput,
Various technical developments have been made to solve the disadvantages.

[0003] At present, a figure part batch exposure system called cell projection, character projection or block exposure has been put to practical use. In the figure partial batch exposure method, a repetitive small circuit pattern (about 5 μm square on a wafer) is repeatedly transferred using a reticle on which a plurality of types of similar small patterns are formed, with one small pattern as one unit. Perform exposure. However, even in this method, in order to perform drawing by the variable shaping method for a pattern distribution having no repeatability, the electron beam is adjusted based on a point beam as an optical system. That is, the optical system is adjusted so that the geometric blur of the point beam is minimized. Here, the geometric blur refers to a blur of a beam edge due to an optical system's resolution limit and aberration, which does not include the Coulomb effect.

On the other hand, as an electron beam transfer exposure system aiming at a much higher throughput than the graphic partial batch exposure system, a reticle provided with a circuit pattern of an entire semiconductor chip is prepared, and an electron beam is applied to a certain area of the reticle. And an electron beam reduction transfer exposure apparatus that reduces and transfers an image of a pattern in the irradiation range by a projection lens.

[0005] In this type of apparatus, the entire area of the reticle is usually exposed by irradiating an electron beam collectively. But,
If it is attempted to transfer the entire pattern at once, the pattern cannot be transferred accurately. Also, it is difficult to manufacture a reticle serving as an original.

Therefore, a system which has been studied energetically recently does not expose one die (chips on a wafer) or a plurality of dies at once, but has a large field of view as an optical system, but has a small pattern. This is a method in which transfer exposure is performed by dividing each area (hereinafter, referred to as a division transfer method). In this method, a small area (subfield)
Each time, the exposure is performed while correcting aberrations such as the focal point of the image of the small area formed on the surface to be exposed and the field distortion. Then, these small areas are connected by deflection or stage movement on the surface to be exposed. This makes it possible to perform exposure with high resolution and high accuracy over an optically wide area as compared with batch transfer of the entire die. In this case, since the beam at the time of transfer exposure is not a point beam but a surface beam, optical adjustment in the point beam state cannot be performed.

In the case of exposure to a charged particle beam such as an electron beam, if the beam current for forming an image increases, there is a problem that the repulsion of charges of the charged particles in the beam changes the properties of the image. . The properties of the subfield image also change depending on the pattern distribution state of the subfield transferred at one time. However, most of these property changes can be corrected by the optical correction function of the exposure apparatus. In particular, in the case of the variable shaping exposure method,
The optimum focus correction amount can be predicted from the area of the shaped beam and the device parameters (acceleration voltage, current density, beam opening angle, length of the optical system, etc.).

[0008]

The blur depending on the reticle pattern or the like as described above can be corrected by adjusting the parameters of the apparatus. However, these corrections are based on the fact that the geometric blur of the optical system is constant. It is assumed. However, actually, even if the setting of the optical system of the apparatus is constant, the geometric blur varies depending on the environment and specification conditions of the apparatus. The blur amount also changes depending on the beam deflection amount. Therefore, merely adjusting the parameters of the apparatus is not sufficient, and the pattern transfer accuracy is reduced. Furthermore, by changing the blur depending on the beam exposure position (deflection position),
Also at the pattern connecting portion, a defect of the connecting portion occurs.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a charged beam exposure method and a charged beam exposure apparatus capable of realizing high-resolution and high-accuracy pattern transfer exposure. I do.

[0010]

In order to solve the above-mentioned problems, a charged beam exposure method of the present invention comprises forming a pattern to be transferred onto a sensitive substrate on an original, and forming the pattern in a small area ( Each of the sub-fields) is sequentially illuminated with a charged beam, and the charged beam that has passed through the sub-field is sequentially projected and imaged on the sensitive substrate via a projection optical system, and the image of each sub-field is projected on the sensitive substrate. A method of transferring the entire pattern by joining together; measuring or estimating the geometric blur of the projection optical system for each subfield, and obtaining the largest one of the obtained geometric blurs of each subfield. When the maximum geometric blur does not satisfy the management criterion, the respective parts of the exposure apparatus are corrected. When the maximum geometric blur satisfies the management criterion, each subfield is corrected. It said projection optical system is adjusted dynamically so that the geometric blurring becomes the same as the management criteria, characterized by exposing while adding it to the amount of blurring correction depends on the mask pattern.

Regardless of whether the condition of the apparatus is good or bad, the geometric blur at the time of exposure is always the same. By doing so, the continuity of the exposure state is maintained, and the reproducibility of the device manufacturing process is improved.

In the charged beam exposure method, the geometric blur is equal to a maximum blur amount in a deflection area of the projection optical system and is equal to or less than a blur amount necessary to realize accuracy of a pattern to be exposed. Is preferred.

A charged beam exposure apparatus according to the present invention comprises: a stage on which an original plate having a pattern to be transferred onto a sensitive substrate is mounted; and a step in which the pattern is successively charged by a charged beam for each partial area (subfield). An illumination optical system for illuminating,
A projection optical system for sequentially projecting and forming an image of the charged beam passing through the sub-field on the sensitive substrate; and a stage for mounting the sensitive substrate, wherein an image of each sub-field is formed on the sensitive substrate. An apparatus for transferring the entire pattern by joining together, wherein exposure is performed while dynamically adjusting the projection optical system so that the geometric blur of all subfields is the same.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. First, an outline of an electron beam projection exposure technique of a division transfer system will be described with reference to the drawings.

FIG. 2 is a diagram showing an outline of an image forming relationship and a control system in the entire optical system of the electron beam projection exposure apparatus of the division transfer system. The electron gun 1 arranged at the uppermost stream of the optical system emits an electron beam downward. Electron gun 1
Are provided with two stages of condenser lenses 2 and 3, and the electron beam passes through these condenser lenses 2 and 3.
Converged and crossover to blanking aperture 7
Image CO.

A rectangular opening 4 is provided below the second-stage condenser lens 3. The rectangular aperture (illumination beam shaping aperture) 4 allows only an illumination beam that illuminates one subfield (a pattern small area to be one unit of exposure) of the reticle (mask, original) 10 to pass. The image of the opening 4 is formed on the reticle 10 by the lens 9.

Below the beam shaping aperture 4, a blanking deflector 5 is arranged. The deflector 5 deflects the illumination beam as needed to hit the non-opening portion of the blanking opening 7 so that the beam does not hit the reticle 10. Below the blanking aperture 7, an illumination beam deflector 8
Is arranged. The deflector 8 sequentially scans the illumination beam mainly in the horizontal direction (X direction) in FIG. 2 to scan each subfield (small pattern area, unit exposure area) of the reticle 10 within the visual field of the illumination optical system. Perform lighting. An illumination lens 9 is disposed below the deflector 8. Lighting lens 9
Image the beam shaping aperture 4 on the reticle 10.
The illumination beam is formed on the reticle 10 into a square having a size of slightly more than 1 mm square.

The reticle 10 actually extends in a plane perpendicular to the optical axis (XY plane) and has many subfields. On the reticle 10, a pattern (chip pattern) forming one semiconductor device chip as a whole is formed. Needless to say, a pattern forming one semiconductor device chip may be divided and arranged on a plurality of reticles. At the time of beam blur measurement, a reticle 10 having a reference pattern for measurement is used.

The reticle 10 is mounted on a movable reticle stage 11, and by moving the reticle 10 in a direction perpendicular to the optical axis (XY directions), the reticle 10 spreads over a wider area than the field of view of the illumination optical system. Each subfield can be illuminated. On the reticle stage 11,
A position detector 12 using a laser interferometer is provided, so that the position of the reticle stage 11 can be accurately grasped in real time.

Below the reticle 10, projection lenses 15 and 19 and a deflector 16 are provided. Reticle 1
The electron beam passing through one subfield of 0 is imaged at a predetermined position on a wafer (sensitive substrate) 23 by the projection lenses 15 and 19 and the deflector 16. Projection lens 1
Detailed operations of the deflectors 5 and 19 and the deflector 16 (image position adjusting deflector) will be described later with reference to FIG. At the same position as the projection lenses 15 and 19, a dynamic focus coil for focus adjustment (see FIG. 3) is also arranged. An appropriate resist is applied on the wafer 23, the resist is given an electron beam dose, and the pattern on the reticle is reduced and transferred onto the wafer 23.

A crossover CO is formed at a point at which the reticle 10 and the wafer 23 are internally divided at a reduction ratio, and a contrast opening 18 is provided at the crossover position. The opening 18 blocks the electron beam scattered by the non-pattern portion of the reticle 10 from reaching the wafer 23.

Above the wafer 23, the backscattered electron detector 22
Is arranged. The backscattered electron detector 22 detects the amount of electrons reflected on a surface to be exposed of the wafer 23 or a mark on the stage. For example, the mark on the wafer 23 is scanned with a beam that has passed through the mark pattern on the reticle 10,
By detecting reflected electrons from the mark at that time,
The relative positional relationship between reticles 10 and 23 can be known.

The wafer 23 can be moved in the X and Y directions via an electrostatic chuck (not shown).
4. By synchronously scanning the reticle stage 11 and the wafer stage 24 in directions opposite to each other, each part in the chip pattern extending beyond the field of view of the projection optical system can be sequentially exposed. Note that the wafer stage 24 is also provided with a position detector 25 similar to the reticle stage 11 described above. The wafer stage 24 is also provided with a knife-edge-shaped reference mark for beam blur measurement (see FIG. 4). Below the knife-edge reference mark, an electronic detector (not shown) (FIG. 4)
105) is arranged.

Each of the lenses 2, 3, 9, 15, and 19 and each of the deflectors 5, 8, and 16 are provided with a coil power controller 2
a, 3a, 9a, 15a, 19a and 5a, 8a, 16
This is controlled by the controller 31 via the line a. Further, the reticle stage 11 and the wafer stage 2
4 is also controlled by the controller 31 via the stage controllers 11a and 24a. Stage position detector 1
2 and 25 send signals to the controller 31 via interfaces 12a and 25a including an amplifier and an A / D converter. The backscattered electron detector 22 also sends a signal to the controller 31 via the same interface 22a.

The controller 31 grasps the control error of the stage position, and corrects the error by the image position adjusting deflector 16. Thus, the reduced image of the subfield on the reticle 10 is accurately transferred to the target position on the wafer 23.
Then, the subfield images are joined on the wafer 23, and the entire chip pattern on the reticle is transferred onto the wafer. The controller 31 also performs dynamic adjustment of blur of each subfield described later with reference to FIG.

Next, a detailed example of a projection optical system used for the electron beam projection exposure of the division transfer system will be described with reference to FIG. FIG. 3 is a cross-sectional view schematically showing a device arrangement of a projection optical system used for the electron beam projection exposure of the division transfer system. FIG. 3 shows a main part of the projection optical system shown in FIG.

At the top of the figure, a reticle 10 is shown. The reticle 10 receives an electron beam illumination from an illumination optical system having a deflector 5 and the like from above the figure. The acceleration voltage of the electron beam is, for example, 100 kV. Reticle 10
Below this, the first-stage projection lens 15, the contrast aperture 18, the second-stage projection lens 19, and the wafer 23 are arranged in this order along the optical axis (dashed line at the center). The deflector 1 is provided above the projection lens 15 and below the projection lens 19.
6 is shown.

A dynamic focus coil 65 is arranged inside the first stage projection lens 15. A dynamic focus coil 66 is also arranged inside the second-stage projection lens 19. The focus adjustment in the two dynamic focus coils 65 and 66 can be performed while minimizing the rotation and the change in magnification of the beam by flowing opposite currents to both coils.

The reticle 10 is provided with a plurality of sub-fields (small pattern areas, unit exposure areas) 42 and struts (reinforcement beams) 45. Here, reference numeral 42-1 is assigned to the subfield located on the leftmost side of the figure.
The sub-field 42 to be exposed is selected by deflecting the illumination beam by the deflector 5. Reticle is 2μm thick
Is a so-called scattering stencil mask having a pattern opening. The illumination beam is formed into a square having a dimension of slightly more than 1 mm square in reticle size conversion. It should be noted that the figure is drawn in a simplified manner, and actually, more than several thousand subfields are formed on one reticle.

The image of the subfield on the reticle is transferred onto the wafer 23 to form a plurality of subfields (transferred small areas) 52. Here, reference numeral 52-1 is assigned to the subfield located on the rightmost side of the figure.

The electron beam EB passing through the subfield 42-1 is converted into a predetermined area 52 on the wafer 23 by the action of the two-stage projection lenses 15, 19 and the image position adjusting deflector 16.
The projection is reduced to -1. The electron beam is reticle 1
Between the 0 and the wafer 23, the light is deflected twice from the direction parallel to the optical axis to the direction crossing the optical axis and vice versa by the action of the two-stage projection lens.

The transfer position of the subfield image on the wafer 23 is determined by the deflector 16 provided in the optical path between the reticle 10 and the wafer 23 so that each pattern small area 42
Are adjusted so that the transfer target small regions 52 corresponding to. That is, by merely converging the electron beam that has passed through the pattern small area 42 on the reticle onto the wafer 23 by the first projection lens 15 and the second projection lens 19, not only the pattern small area 42 of the reticle 10 but also the strut 4
Even the fifth-level image is transferred at a predetermined reduction rate, and non-exposed areas corresponding to non-pattern areas such as struts 45 are generated between the small areas 52 to be transferred. To prevent this, the transfer position of the pattern image is shifted by an amount corresponding to the width of the non-pattern area. Note that 1 in the X direction and 1 in the Y direction.
One position adjusting deflector is provided.

As described above, the beam is largely deflected while transferring one pattern. When the beam is largely deflected, the optical condition changes greatly, and the geometric blur of the beam changes. Further, the geometric blur of the beam also changes depending on the use conditions of the exposure apparatus. Therefore, when performing the above-described transfer exposure, the focus position of the beam is shifted by the two dynamic focus coils 65 and 66, and the amount of beam blur is actively adjusted.

Next, a beam blur measuring system of the charged beam exposure apparatus according to the embodiment of the present invention will be described. FIG.
FIG. 2 is a side sectional view and a block diagram schematically showing a beam blur measurement system of the exposure apparatus. At the top of this exposure device,
A reticle (see FIG. 2) having an illumination beam source and a measurement pattern (not shown) is arranged. At a certain position on the wafer stage at the same height as the wafer, a rectangular opening having a knife-edge-shaped reference mark 101 is arranged. The electron beam formed through the measurement pattern is irradiated as a rectangular beam EB (transfer image of a reticle) on a rectangular opening having a knife-edge-shaped reference mark 101. An electronic detector (sensor) 105 is arranged below the knife-edge-shaped reference mark 101.

When the rectangular beam EB is scanned in the direction of the arrow (right side in the figure), electrons hitting the non-opening portion (knife edge plate 100) of the knife-edge-shaped reference mark 101 are absorbed by the knife edge plate and the opening portion 102 Are detected by the electron detector 105.

The beam current corresponding to the electron e1 detected by the electron detector 105 is amplified by a preamplifier 106 and then converted into a change rate with respect to time by a differentiating circuit 107.
The output waveform is output to the oscilloscope 108 or the like.
Then, beam blur is measured from the output waveform, and based on this, beam adjustment (calibration of various correction values such as focus, astigmatism, magnification, rotation, etc.) and evaluation of imaging performance are performed. In addition, as this kind of beam blur measurement method, for example, Japanese Patent Application Laid-Open No.
00-12620 and the like.

Next, a beam blur control system of the charged beam exposure apparatus according to the embodiment of the present invention will be described. FIG.
1 is a block diagram showing a beam blur control system of a charged beam exposure apparatus according to an embodiment of the present invention. 5 shows a beam blur measurement system 109 shown in FIG. 4, a controller 31 of the exposure apparatus shown in FIG. 2, an input unit 121 for inputting management reference data and the like to the controller 31, a dynamic focus coil 65 shown in FIG. 66 is shown. The controller 31 calculates a storage unit 123 that stores the management reference data input from the input unit 121, a comparison unit 125 that compares the blur amount with the management reference data, and an adjustment amount of the dynamic focus coils 65 and 66. Arithmetic unit 1
26, a storage unit 127 that stores the calculated adjustment amount as table data, and a command unit 128 that controls the dynamic focus coils 65 and 66 while referring to the table data.

Next, a charged beam exposure method using the above-described exposure apparatus will be described. FIG. 1 is a flowchart showing a charged beam exposure method according to the embodiment of the present invention. In FIG. 1, first, when adjusting the apparatus after mounting the reticle, the beam blur measurement system 109 shown in FIG. 4 is used to measure the geometric blur of the beam at each deflection position by the knife edge method for each subfield. (Step 1). In addition,
At the time of this measurement, for example, a subfield in which only a 30 μm square pattern is formed can be used. At the time of this measurement, the beam current is kept to a minimum in order to prevent measurement of blur due to factors other than geometric blur. Specifically, at the time of exposure, 100
The current of about μA is adjusted to about 10 μA on the reticle at the time of adjustment.

Next, the comparison unit 125 in FIG. 5 selects the largest one of the obtained geometrical blurs of the respective subfields and compares it with the management standard (step 2).

If the maximum geometric blur does not satisfy the management criterion (a value equal to or less than the blur amount necessary to realize the accuracy of the pattern to be exposed) (step 3), the target pattern size cannot be exposed. Therefore, readjustment of each part of the exposure apparatus (for example, readjustment of optical axis, astigmatism, focus, etc.) is performed (step 4). Then, the geometric blur amount is measured again (step 1). As management criteria, for example, 60 nm
In the case of exposing a pattern having a size of, the maximum geometric blur should be 50 nm or less.

On the other hand, if the maximum geometric blur satisfies the management criterion (step 3), the calculation unit 12 in FIG.
In step 6, the dynamic focus coil adjustment amount is calculated (step 10).

At this time, the blur adjustment amount at each deflection position is stored as a blur amount offset value (table data) corresponding to the deflection position in the storage unit 1 in the controller 31 of the exposure apparatus.
27 (see FIG. 5) (step 11). The adjustment and storage of the blur amount is preferably performed about once a month on the entire reticle surface, and the spot sampling confirmation of the gate layer portion on the reticle surface is preferably performed every day.

At the time of exposure, the value is used as an offset amount to adjust the blur, and another correction amount (obtained by calculating the blur correction amount depending on the mask pattern) is added (step 12). This makes it possible to equalize the amount of blur at each deflection position, thereby facilitating the handling of other correction amounts. Thereafter, exposure is performed while dynamically adjusting the blur amount (step 13).

According to the above-described charged beam exposure method, the blur is equal at each deflection position, so that the connecting portion of the pattern in each subfield or the like is constant over the entire exposure area, and the beam can be easily controlled. Uniform exposure becomes possible. In addition, the error in the joint shape can be suppressed to approximately 1/10 of the line width.

The charged beam exposure method and the like according to the embodiment of the present invention have been described with reference to FIGS. 1 to 5, but the present invention is not limited to this. Can be added. For example, the present invention can cope with a change in the amount of blur due to a change in the height of the reference surface when the stage is driven, and an apparent change in geometric blur due to a reproducible change at the time of chucking the mask and wafer.

[0046]

As is apparent from the above description, according to the present invention, in the so-called divided transfer type charged beam exposure, by changing the image forming conditions, the difference in the pattern distribution and the mask Shape defects such as astigmatism of a transferred image due to a manufacturing error at the time of manufacturing can be efficiently corrected, and as a result, pattern transfer exposure with high resolution and high accuracy can be realized.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a charged beam exposure method according to an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of an image forming relationship and a control system in the entire optical system of the electron beam projection exposure apparatus of the division transfer system.

FIG. 3 is a cross-sectional view showing a device arrangement of a projection optical system used for electron beam projection exposure in a division transfer system.

FIG. 4 is a side sectional view and a block diagram schematically showing a beam blur measurement system of the exposure apparatus.

FIG. 5 is a block diagram showing a beam blur control system of the charged beam exposure apparatus according to the embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 1 electron gun 2, 3 condenser lens 4 illumination beam shaping aperture 5 blanking deflector 7 blanking aperture 8 illumination beam deflector 9 condenser lens 10 reticle (mask) 11 reticle stage 12 reticle stage position detector 15 first projection lens 16 Image position adjusting deflector 18 Contrast aperture 19 Second projection lens 22 Backscattered electron detector 23 Wafer 24 Wafer stage 25 Wafer stage position detector 31 Controller 41 Small membrane area 42 Subfield 43 Skirt 44 Electrical stripe 45 Strut 49 Mechanical stripe 50 Chip 52 Subfield 59 Stripe 65, 66 Dynamic focus coil

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/30 541E F term (Reference) 2H097 AA03 CA16 GB00 LA10 5C033 DE02 DE07 MM03 5C034 BB02 BB08 5F056 BA06 BB09 CB09 CB28 CB29 CB32 CC09

Claims (4)

[Claims] 1. A pattern to be transferred onto a sensitive substrate is formed on an original plate, and the pattern is sequentially illuminated with a charged beam for each partial area (subfield), and the charged beam passing through the subfield is illuminated. A method of sequentially projecting and forming an image on the sensitive substrate via a projection optical system, and transferring the entire pattern by connecting images of respective subfields on the sensitive substrate;
The geometric blur of the projection optical system is measured or estimated for each subfield, and the largest one among the obtained geometric blurs of each subfield is selected, and the maximum geometric blur does not satisfy the management criterion. If the maximum geometric blur satisfies the management criterion, the projection optical system is dynamically adjusted so that the geometric blur of each subfield is the same as the management criterion. A charged beam exposure method, wherein exposure is performed while adjusting. 2. The method according to claim 1, wherein the geometric blur is equal to a maximum blur amount in a deflection area of the projection optical system, and is equal to or less than a blur amount necessary to realize accuracy of a pattern to be exposed. Item 1. A charged beam exposure method according to Item 1. 3. The charged beam exposure method according to claim 2, wherein a blur amount dependent on a pattern of a subfield to be exposed is corrected. 4. A stage on which an original plate on which a pattern to be transferred onto a sensitive substrate is formed is mounted; an illumination optical system for sequentially illuminating the pattern with a charged beam for each partial area (subfield); A projection optical system for sequentially projecting and forming an image of the charged beam passing through the sub-field on the sensitive substrate; and a stage for mounting the sensitive substrate, wherein an image of each sub-field is formed on the sensitive substrate. An apparatus for transferring the entire pattern by joining together;
A charged beam exposure apparatus, wherein exposure is performed while dynamically adjusting the projection optical system so that all subfields have the same geometric blur.