JPH10294262A - Projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To calculate the reflection rate of a photosensitive substrate and to operate illumination energy which is made incident on a projection lens without providing a reflection face having a known reflectance on a stage. SOLUTION: The first energy of illumination light which is made incident on a projection lens 5 through a reticule R and the second energy of illumination light which is made incident on the projection lens 5 with reflection from the photosensitive substrate W are calculated and a correction device 30 corrects the image-forming characteristic of the projection lens 5. An energy line detector 11 receives energy light reflected by an object positioned within the view of the projection lens 5 and outputs a proportional detection signal. Then, the reflectance of the photosensitive substrate is calculated based on an electric signal I(mW) generated from the reflective energy line detector 11 when the projection lens 5 is made to face the photosensitive substrate W, exposure power P(mW/cm<2> ) which is made incident on the photosensitive substrate W through the reticle R without a pattern and the projection lens 5, the transmissivity TL of the projection lens 5, a chrome reflectance Rrc, a blind area Sb(cm<2> ), a reticle transmission area Sr(cm<2> ), a reticle glass reflectance Rrg and a projection lens reflectance RL, and energy is operated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for projecting and exposing a pattern such as a semiconductor memory or an LCD panel.

[0002]

2. Description of the Related Art In a projection exposure apparatus of this type, for example, an exposure wavelength (for example, g-line) of illumination light from a mercury lamp is used.
Are projected onto a reticle, and a light beam passing through the reticle is imaged on a wafer through a projection lens to project and expose various patterns. Therefore, the reflected light from the wafer may re-enter the projection lens, and the imaging energy (magnification, focus position) of the projection lens may fluctuate depending on the incident energy.

[0003] Japanese Patent Application No. 62-183522 discloses a projection exposure apparatus intended to correct such image forming characteristics. That is, Japanese Patent Application No. 62-183.
In the projection exposure apparatus disclosed in Japanese Patent Application Publication No. 522, the energy incident on the projection lens is measured to calculate the fluctuation of the imaging characteristic, and the air pressure of a predetermined lens chamber in the projection lens is adjusted to adjust the imaging characteristic ( Correction). Therefore, in this projection exposure apparatus, a reflection surface with a known reflectance is provided at two points on the wafer stage, and the amount of reflected light when the projection lens is opposed to each reflection surface is detected. calculating a reflectance R _P of the wafer, and calculates the irradiation energy incident on the projection lens from equation (3) E (mW).

[0004]

[Number 2] wafer reflectance _{R P = R L + {(} I-I L) / (I H -I L)} * (R H -R L) ... (2) However, R _H: the first reflection reflectivity of the surface (known) R _L: reflectance of the second reflecting surface _{(known, R H> R L) I} : detector signal (mW) due to reflection of the wafer I _H: reflected from the first reflecting surface Detector signal (m
W) I _L : detector signal (m due to reflection from the second reflecting surface)
W)

[0005]

Equation 3] irradiation energy E (mW) = P · Sr (1 + R P) ... (3) However, P: exposure power (mW / cm ²⁾ Sr: reticle permeation area (cm ²⁾

[0006]

Incidentally, an exposure apparatus such as an LCD panel seeks an increase in the size of a photosensitive substrate and an increase in a projection exposure area in order to increase the processing capacity. However, in the above-described conventional technique, at least two reflection surfaces having a known reflectance are formed on a photosensitive substrate mounting stage for reflectance measurement, and the stage can move the reflection surface to a projection exposure area. There is a need. Therefore, in the case of a rectangular or square LCD glass substrate, in order to form a known reflection surface outside the photosensitive substrate mounting area, it is necessary to increase the stroke of the substrate mounting stage. growing.

A method is also conceivable in which a reflecting surface is provided in the photosensitive substrate mounting area and measurement is performed in advance before mounting the substrate. In this case, however, a stroke of the Z stage for adjusting both the photosensitive substrate and the reflecting surface to the focal position is considered. However, if <the vertical movement function of the reflection surface is required. Also, the photosensitive substrate is surface-adhered to the stage surface to maintain its flatness, but the reflective surface having an area that satisfies the maximum projection exposure area is within the photosensitive substrate mounting area.
If more than one exists, it is difficult to maintain the flatness because the corresponding portion cannot be sucked. Further, when exposing a transparent photosensitive substrate, it is conceivable that return light from the reflective surface may affect pattern formation.

An object of the present invention is to provide a projection exposure apparatus capable of calculating the reflectance of a photosensitive substrate and calculating the irradiation energy incident on a projection lens without providing a reflecting surface having a known reflectance on a stage. To provide.

[0009]

The present invention will be described with reference to the drawings of an embodiment. In FIG. 1, an illumination apparatus 1 for illuminating a reticle R and illumination light transmitted through the reticle R are used. A projection lens 5 for projecting and exposing a pattern on the reticle R onto a photosensitive substrate, a correction device 30 for correcting the imaging characteristics of the projection lens 5, and a field of view of the projection lens 5 at a position substantially conjugate with the pupil of the projection lens 5. A reflected energy ray detector 11 which receives an energy ray reflected by an object located inside and generates an electric signal corresponding to the amount of the energy ray.
And calculating the first energy of the illumination light incident on the projection lens 5 via the reticle R and at least the second energy of the illumination light incident on the projection lens 5 by reflection from the photosensitive substrate W. The correction device 30W0 corrects the imaging characteristics of the projection lens 5 based on the calculation result.
The present invention is applied to a projection exposure apparatus having a control circuit 31 for controlling. The above-mentioned object is to provide an electric signal I generated from the reflected energy ray detector 11 when the projection lens 5 is opposed to the photosensitive substrate W, a reticle without a pattern, and illumination light incident on the photosensitive substrate via the projection lens. Incident energy P per unit area, transmittance _TL of projection lens 5, chrome reflectance _RRC , blind area Sb, reticle transmission area S
r, reticle glass reflectance Rrg, projection lens reflectance _RL
It is accomplished by calculating the second energy based on the reflectance R _P of the photosensitive substrate W, which is calculated based on. The invention of claim 2 is

R _P = (I / P) · (1 / ( _TL · Sr)) − (1 / _TL ² ) · (Rrc ((Sb / Sr) −1) + Rrg + R (4) R _P : Reflectivity of photosensitive substrate I: Electric signal generated from reflected energy ray detector 11 when projection lens 5 faces photosensitive substrate W P: Incident on photosensitive substrate via reticle without pattern and projection lens incident energy T _L per unit area: the projection lens transmittance Rrc: chrome reflectance Sb: blind area Sr: reticle permeation area Rrg: reticle glass reflectance R _L: the reflectance of the photosensitive substrate W on the basis of the projection lens reflectance It is to be calculated.
According to a third aspect of the present invention, the control circuit 31 determines whether or not the ratio of the illumination light transmitted through the reticle R is equal to or more than a predetermined value, and projects the sum of the first and second energies when the ratio is equal to or more than the predetermined value. The irradiation energy to the lens 5 is corrected, and if less than a predetermined value, the first energy is corrected as the irradiation energy to the projection lens 5. Thus, even if the reticle chrome reflectance is set to a fixed value without being changed for each reticle, it is possible to accurately control the influence of the irradiation energy on the projection lens on the imaging characteristics.

Although the drawings of the embodiments are used in the section of the means for solving the above problems, the present invention is not limited to the embodiments. ,

[0011]

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

Exposure light from the mercury discharge lamp 1 is condensed by the elliptical mirror 2, passes through a shutter 3 for controlling the amount of exposure, and is made uniform in illuminance by an optical integrator (not shown).
The reticle R is illuminated via a main condenser lens (not shown). Illumination field stop (so-called reticle blind)
Reference numeral 4 shields a pattern portion on the reticle R that should not be exposed in an arbitrary shape. If the light emission intensity of the discharge lamp 1 is almost constant, the opening time of the shutter 3
By controlling at 2, it is possible to always obtain a constant exposure amount.

The reticle R has an X direction, a Y direction, and θ
It is held on a reticle stage (not shown) that slightly moves in the rotation direction. The light transmitted through the reticle R is image-formed and projected on the wafer W by the projection lens 5. The initial position of the reticle R is set by finely moving the reticle stage based on a mark detection signal from a reticle alignment system (not shown) that photoelectrically detects an alignment mark around the reticle R.

Exposure light transmitted through the exposure pattern portion of the reticle R enters the projection lens 5, and a projection image of the pattern is formed on a wafer W as a photosensitive substrate. The wafer W is mounted on a Z stage 6, and the Z stage 6 is provided on an XY stage 7 so as to be vertically movable (in the optical axis direction of the projection lens 5). The XY stage 7 is two-dimensionally moved by a drive unit such as a motor in parallel with the projection image plane of the projection lens 5. A moving mirror 8 (the other moving mirror is not shown) for vertically reflecting a laser beam LB from a laser interferometer (not shown) for detecting a two-dimensional position of the XY stage 7 is fixed to the Z stage 6. I have. Reference marks are provided on the Z stage 6 to serve as references for various types of alignment.

The pressure regulator 30 is provided to control the imaging characteristics (magnification, focal position) of the projection lens 5 itself by a very small amount. For this reason, the pressure controller 30 receives from the main control system 31 a pressure control value that can momentarily correct the fluctuation of the imaging characteristic due to the transmission of the exposure light from the projection lens 5, and responds to the input. The pressure of a predetermined air space (air chamber) in the inside is adjusted.

The main control system 31 supplies an open signal to a shutter control system 32 for controlling the opening / closing operation of the shutter 3 and the exposure time, and determines whether the shutter 3 is open or closed within a unit time (for example, 5 seconds). Is input to the shutter control system 32. Main control system 31
Is a pressure for estimating a magnification change amount and a focus change amount due to the incidence of exposure light of the projection lens 5 based on a shutter opening / closing signal in consideration of environmental information (atmospheric pressure value, temperature value), and correcting the change amount. Calculate the value.

Light reflected from the wafer W and light reflected from the upper surface of the projection lens 5 are guided to a photoelectric detector 11 by a mirror 10. Here, the mirror 10 is disposed near a position substantially conjugate with the pupil of the projection lens 5. As the mirror 10, simple glass, a light source-side surface coated with anti-reflection coating, the projection lens side as plain glass, and the projection lens side as a half mirror can be used. It is desirable that the light receiving surface of the photoelectric detector 11 has an accurate conjugate relationship with the pupil of the projection lens 5.

A procedure for calculating the energy incident on the projection lens by the projection exposure apparatus thus configured and correcting the imaging characteristics of the projection lens will be described. When the reflection from the photosensitive substrate W is not considered, the energy E applied to the projection lens 5 is given by the following equation (5).

[0019]

[Equation 5] Irradiation energy E (mW) = P · Sr (5) where P: exposure power (mW / cm ² ) and on a substrate stage that has passed through a transparent reticle glass and the projection optical system 14. Exposure power measured Sr: Reticle transmission area (cm ² )

However, since the reflected energy from the photosensitive substrate is actually received, the irradiation energy E (mW) is represented by the following equation (6).

[Equation 6] Irradiation energy E (mW) = P · Sr (1 + R _P ) (6) where R _P : Reflectivity of photosensitive substrate

On the other hand, the detection signal I (mW) received and output by the reflected energy detector 11 is represented by the following equation (7).

Equation 7] Detection signals I (mW) = P _{[(1 / T L) · {} (Rrc (Sb-Sr) + Rrg · Sr + R L · Sr)} + T L · R P · Sr ] ... (7) however, T _L : lens transmittance Rrc: reflectance of chrome coated on the reticle Rrg: reflectance of the reticle glass R _L : reflectance of the lens of the projection lens Sb: blind area (cm ² )

In the equation (7), P (1 / T _L ) is the exposure power applied to the reticle R because the exposure power P is an exposure pattern after passing through the reticle R and the projection lens 5. Exposure power calculated back. Here, the exposure power will be described as PA. PA *
Rrc (Sb-Sr) is the energy at which the illumination light emitted from the light source to the reticle R is reflected from the chrome portion (pattern portion) of the reticle R and enters the detector 11. PA * R
rg · Sr is the energy at which the illumination light emitted from the light source to the reticle R is reflected from the glass portion (non-pattern portion) of the reticle R and enters the detector 11. PA * _RL *
Sr indicates that the light reflected from the upper surface of the projection lens 5 is a reticle R
Is the energy that enters the detector 11 via P * T
_L · R _P · Sr is a reticle R that is reflected from the light source through the reticle R and the projection lens 5 and incident on the wafer W and reflected.
Is the energy that passes through and enters the detector 11.

[0023] can reflectance R _P of the photosensitive substrate W is based on the detection signal I of the detector 11 is calculated by the following equation (8).

(8) Wafer reflectivity R _P = (I / P) · (1 / ( _TL · Sr)) − (1 / _TL ² ) · (Rrc ((Sb / Sr) −1) + Rrg + _RL ) (8)

Therefore, in the present invention, the wafer reflectivity R _{P is} calculated by the equation (8) without using two known reflecting surfaces.
Is calculated in advance, the data of equation (8) is stored in the main control system 31 in advance. That is, the exposure power P,
Transmission T _L of the projection lens 5, chrome reflectance Rrc, blind area Sb, reticle transmission area Sr, reticle glass reflectance Rrg, lens reflectance R _L is stored in the main control system 31.

Next, how to store such data will be described. The exposure power P is as described in the expression (5), and is stored in a preparation period before performing pattern exposure. The blind opening area Sb is registered when reticle data is created.

The reticle transmission area Sr (cm ² ) is originally registered and stored in order to calculate the equation (5). That is, in the stage of creating reticle data for exposure, illumination light having a known exposure power PK is regulated by a predetermined blind opening, and the light passing therethrough is transmitted through the reticle R and the projection lens 5 to the energy placed on the stage 15. By receiving light with a detector (not shown in FIG. 1) and obtaining a detection signal IK, it can be calculated by the following equation (9).

Reticle transmission area Sr = α · IK / PK (9) where α: constant

The lens transmission T _L of the projection lens 5, the reflectance R _L may be pre-stored as the design value data. Alternatively, it may be stored as data measured after manufacturing the exposure apparatus. The reflectance Rrg of the glass surface of the reticle can be stored as substantially constant regardless of the reticle.

The reflectance Rrc of chrome (pattern) of the reticle differs for each reticle depending on the reflection coat or the like.
Then, it can be stored in advance as follows. [1] The reflectance data of the reticle maker is stored. [2] Reflectance Rst on photosensitive substrate adsorption surface on stage 6
Is measured in advance, and when measuring the reticle transmission area Sr, the detection signal I (mW) of the detector 11 based on the energy reflected from the adsorption surface of the photosensitive substrate is obtained, and R _P is calculated by the above equation (8).
Is substituted for Rst to calculate the chromium surface emissivity Rrc.

[3] A chrome pattern surface is formed at a designated position on the reticle surface, and a reflectance measuring device is provided in advance in the projection exposure apparatus, and the reflectance Rrc is measured and stored before exposure processing.

FIG. 2 shows an example of this type of reflectance measuring apparatus. In FIG. 2, an optical cable 7 for guiding and illuminating the illumination light of the discharge lamp 1 onto the reticle is provided near the reticle stage.
One light projecting surface is arranged, and a reflectance sensor 72 for receiving the light reflected from the reticle chrome 73 is arranged. The light receiving signal Is of the reflectance sensor 72
Is input to the main control system 31 to calculate the chrome reflectance Rrc by the following equation (11).

Chromium surface reflectance Rrc = [1 / {P · (1 / _TL )}] · Is (10) where P: exposure power T _L described above: transmittance of projection lens Is: reflectance Detection signal of sensor 72 (mW)

[4] Depending on the permissible accuracy of magnification / focus due to energy error due to reflection of the photosensitive substrate,
The reflectance Rrc of the reticle Cr (chromium) may be calculated as a fixed value.

Incidentally, the measurement error of the reflectance of the photosensitive substrate due to the individual difference of the reflectance Rrc of the reticle Cr largely depends on the blind area Sb, especially when the reticle transmission area Sr is small (when the reticle transmittance is large). The effect is greater. On the other hand, if the reticle permeation area Sr is small because the energy stored in the projection lens 5 becomes small, also decreases the influence of the reflectance R _P itself photosensitive substrate. That is, if the energy incident on the projection lens 5 due to the reflected light from the photosensitive substrate decreases, the change in the imaging characteristics due to the reflected light can be ignored. Then, after setting the reflectance Rrc of the reticle Cr to a fixed value, the reticle transmittance (reticle transmission area Sr / blind area Sb)
The threshold provided, the reflectance R _P of the photosensitive substrate when reticle transmittance at or above the threshold also performs the energy calculation in consideration, the algorithm does not perform the energy calculation according to the case of less than the threshold value Can also be adopted.

This will be further described with reference to FIG. A straight line A represents a magnification / focus error with respect to a reticle transmittance when light reflected from the photosensitive substrate is not taken into account in energy calculation at an arbitrary blind opening area and an arbitrary reflectance of the photosensitive substrate. That is, it indicates that the magnification / focus error increases as the amount of light transmitted through the reticle increases. A straight line B represents the maximum value of the magnification / focus error with respect to the reticle transmittance when the reflectance from the photosensitive substrate is added to the energy calculation with the reflectance Rrc of the reticle Cr being a fixed value. In other words, this indicates that the magnification / focus error decreases as the amount of light transmitted through the reticle increases. The procedure example of limiting the scope of using the reticle transmittance represented by Th in Figure 3 the energy calculated reflectance R _P of the photosensitive substrate as a threshold shown in Fig.

In step S1 of FIG. 4, the reticle transmittance is calculated by reading the reticle transmission area Sr and the blind opening area Sb measured and stored in advance, and the magnitude relationship between the transmittance and the threshold value Th is compared. . If the transmittance is equal to or greater than the threshold Th, in step S2, the reticle reflectance R _P is calculated based on the above equation (8), and in step S3, the irradiation energy is calculated by E = P · Sr (1 + R _P ). I do. If it is less than the threshold value Th is a reticle reflectance R _P will not use the energy calculating operation in step S4, and calculates the irradiation energy at E = P · Sr. Then, in step S5, step S3
Alternatively, pressure control calculation is performed in consideration of the irradiation energy calculated in step 4.

In the above description, the imaging characteristic of the projection lens is adjusted by adjusting the pressure in the lens chamber.
The movement of the lens itself may be performed, or the movement of the lens and the pressure adjustment may be used in combination.

[0036]

【The invention's effect】

(1) As described in detail above, according to the present invention, the reflectance of the reticle chrome, which has not been used conventionally, is stored in advance to calculate the reflectance of the photosensitive substrate and perform the energy calculation. Therefore, it is possible to solve the disadvantage of the conventional example in which the substrate reflectance is obtained from the reflectance at two points on the substrate stage. (2) According to the third aspect of the present invention, the influence of the reflected light of the photosensitive substrate on the image forming characteristics of the projection lens is considered in accordance with the magnitude of the reticle transmittance. Since the energy applied to the projection lens is calculated taking into account the reflected energy, even if a fixed value is used without setting the reflectivity of the reticle chrome for each reticle, the effect on the imaging characteristics due to the irradiation energy can be reduced. The influence can be controlled accurately.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining a reticle chrome reflectance measuring device.

FIG. 3 is a graph showing the relationship between reticle transmittance and magnification / focus error.

FIG. 4 is a flowchart for determining whether or not to use reflected light from a substrate for energy calculation in accordance with the magnitude of the reticle transmittance and performing pressure control;

[Explanation of symbols]

 5 Projection lens 6 Z stage 7 XY stage 11 Detector 30 Pressure regulator 31 Main control system

Claims (3)

[Claims] An illumination device for illuminating a reticle; a projection lens for projecting and exposing a pattern on the reticle onto the photosensitive substrate with illumination light transmitted through the reticle; and a correction for correcting an imaging characteristic of the projection lens. A device for detecting a reflected energy ray which receives an energy ray reflected by an object located in a field of view of the projection lens at a position substantially conjugate with a pupil of the projection lens and generates an electric signal according to the amount of the reflected energy ray; A first energy of illumination light incident on the projection lens via a reticle and at least a second energy of illumination light incident on the projection lens by reflection from the photosensitive substrate, A control circuit that controls the correction device so as to correct the imaging characteristics of the projection lens based on the calculation result. The control circuit is configured to control an electric signal generated from the reflected energy ray detector when the projection lens is opposed to the photosensitive substrate, a reticle having no pattern, and a unit area of illumination light incident on the photosensitive substrate via the projection lens. Based on the incident energy per unit, the transmittance of the projection lens, the chrome reflectance, the blind area, the reticle transmission area, the reticle glass reflectance, and the reflectance of the photosensitive substrate calculated based on the lens reflectance. A projection exposure apparatus for calculating energy. 2. The projection exposure apparatus according to claim 1, wherein: R _P = (I / P) · (1 / ( _TL · Sr)) − (1 / _TL ² ) · (Rrc ( (Sb / Sr) -1) + Rrg + R L) ... (1) However, R _P: photosensitive substrate reflectivity P: incident energy T _L per unit area incident on the photosensitive substrate: a projection lens transmittance Rrc: chrome reflectance Sb : blind area Sr: reticle permeation area Rrg: reticle glass reflectance R _L: projection exposure apparatus and calculates the reflectivity of the photosensitive substrate based on the projection lens reflectance. 3. The projection exposure apparatus according to claim 1, wherein the control circuit determines whether a ratio of the illumination light transmitted through the reticle is equal to or greater than a predetermined value. The sum of the first and second energies is defined as the irradiation energy to the projection lens.
A projection exposure apparatus, wherein the correction is performed by using the energy of the projection lens as irradiation energy to the projection lens.