JPH10261572A - Exposure method and lithography system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure method for obtaining a high resolution even if time from the application of a photosensitive material to exposure scatters. SOLUTION: The image of a specific mark for evaluation is exposed to a plurality of wafers with a different lapse time from the application of a resist to exposure using an exposing device 10 in advance and the shape of a resist pattern that is obtained after development is measured via an alignment sensor 17, thus obtaining the amount of correction of the quantity of exposure for preventing the deterioration of a resolution due to a lapse time from the application of a resist to the exposure. On exposure, the amount of exposure by the exposing device 10 is corrected according to a lapse time from the application of the resist by a resist coater 20 to exposure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method for transferring a mask pattern onto a photosensitive substrate when manufacturing, for example, a semiconductor device, a liquid crystal display device, an image pickup device (CCD) or a thin-film magnetic head. A lithographic system using the method.

[0002]

2. Description of the Related Art Conventionally, when manufacturing semiconductor devices and the like,
A lithography system including a resist coater, an exposure apparatus, a developing apparatus, and the like is used. As the exposure apparatus, a projection exposure apparatus such as a stepper for transferring a reticle pattern as a mask onto a wafer (or a glass plate or the like) coated with a photoresist via a projection optical system, or a reticle pattern directly. A proximity type exposure apparatus or the like for transferring data onto a wafer is used.
In such a lithography system, a resolution (line width control accuracy) for setting a line width of a circuit pattern finally formed on a wafer within a predetermined allowable range with respect to a design value.
is important.

[0003] Among factors affecting such line width control accuracy is the exposure amount (integrated exposure energy) to the photoresist. In general, conventionally, a line and space pattern having a predetermined line width is exposed at various exposure amounts immediately after a photoresist is applied, and the duty ratio of the resist pattern obtained by development immediately after the exposure is determined by, for example, a scanning electron microscope (SEM). ), And the exposure amount when the measurement result reaches a predetermined design value was determined as the appropriate exposure amount for the photoresist.

[0004]

As described above, conventionally, an appropriate exposure amount for a photoresist is set without considering the elapsed time from the application of the photoresist to the exposure and the elapsed time from the exposure to the development. Was. However, recently, pattern rules for LSIs and the like have been further miniaturized, and requirements for line width control accuracy (resolution) have become more stringent. Therefore, for example, when the elapsed time from the application of the photoresist to the exposure or the elapsed time from the exposure to the development is long, if the exposure is performed at a predetermined appropriate exposure amount, it is finally formed on the wafer. The line width of the circuit pattern may not be within the required line width control accuracy.

In particular, recently, in order to increase the resolution, excimer laser light such as a shorter wavelength KrF excimer laser or ArF excimer laser has been used as exposure light. However, the characteristics of the chemically amplified resist, which is mainly used for excimer laser light, tend to change with the passage of time.Therefore, the proper exposure amount depends on the elapsed time from application to exposure and the elapsed time from exposure to development. Therefore, there is a disadvantage that a desired line width control accuracy may not be obtained if the exposure is performed with a predetermined constant exposure amount. It is also conceivable to keep the elapsed time from the application of the photoresist to the exposure constant, but recently, since various devices are manufactured in parallel, there is some variation in the elapsed time. It generally happens.

Conventionally, the shape of the transferred image of the line-and-space pattern is measured with a scanning electron microscope to set an appropriate exposure amount. However, the scanning electron microscope is changed every time the appropriate exposure amount is determined. There is a disadvantage that it is complicated to use and the working time is long. In view of the above, it is a first object of the present invention to provide an exposure method capable of obtaining a high resolution even when the time from application of a photosensitive material to exposure varies. It is a second object of the present invention to provide an exposure method capable of obtaining high resolution even when the time from exposure to development of a photosensitive material to development varies.

Further, the present invention provides a method for evaluating the resolution of a transferred pattern without using a special measuring device such as a scanning electron microscope when using such an exposure method. The purpose is also to do. Another object of the present invention is to provide a lithography system capable of performing such an exposure method.

[0008]

According to a first exposure method of the present invention, after a photosensitive material is applied on a substrate to be processed, the photosensitive material on the substrate is exposed to illumination light having passed through a mask pattern. In the exposure method of transferring the mask pattern to the photosensitive material on the substrate, the method comprises the steps of applying the photosensitive material on the evaluation substrate (W) in advance and exposing the evaluation mark (32). The optimum exposure amount for the photosensitive material is obtained as a function of the elapsed time, and the photosensitive material is applied in accordance with the actual elapsed time from the application of the photosensitive material on the substrate to be processed to the transfer of the mask pattern. Is to correct the exposure amount.

According to the present invention, according to the actual elapsed time from the application of the photosensitive material to the transfer of the mask pattern, the change in the sensitivity characteristics and the like of the photosensitive material is offset. Is corrected. Therefore, a high resolution can be obtained even if the elapsed time varies. In the second exposure method of the present invention, after exposing a photosensitive material on a substrate to be processed with illumination light having passed through a mask pattern, the photosensitive material is developed by applying the mask pattern to the photosensitive material. In the exposure method of transferring, in advance, the optimum exposure amount for the photosensitive material as a function of the elapsed time from the exposure of the evaluation mark to the photosensitive material on the evaluation substrate to the development is performed,
The amount of exposure to the photosensitive material is corrected in accordance with the estimated elapsed time from the exposure of the photosensitive material on the substrate to be processed with the illumination light passing through the mask pattern to the development.

According to the second exposure method, the estimated elapsed time from the exposure of the photosensitive material to the development can be recognized by, for example, a computer for process management. Therefore, by correcting the exposure amount for the photosensitive material so as to cancel the change in the sensitivity characteristic of the photosensitive material according to the estimated elapsed time, a high resolution can be obtained even if the estimated elapsed time varies.

In the above-mentioned first or second exposure method, when the optimum exposure amount for the photosensitive material is determined as a function of the elapsed time until the exposure or the development, the elapsed time is determined by a predetermined elapsed time t. _{When the value} is ₀ , the first relationship between various exposure amounts to the photosensitive material and the imaging characteristics (resolution, etc.) of the transferred image of the evaluation mark is obtained, and the elapsed time is changed stepwise. A second relationship between the elapsed time in the case of the above and the imaging characteristics of the transfer image of the evaluation mark is obtained in advance, and when the photosensitive material on the substrate to be processed is exposed, the actual process is performed. Assuming that the time or the estimated elapsed time is t, the corrected exposure amount for the optimal exposure amount may be obtained from the first relationship based on the imaging characteristics when the elapsed time is t in the second relationship. .

In this case, the evaluation mark is exposed with various exposure amounts during the predetermined elapsed time t ₀ (t ₀ may be, for example, 0), thereby obtaining a relationship between the exposure amount and, for example, the line width (first line). Is required). At this time, the exposure amount when a desired line width is obtained is the optimum exposure amount. Furthermore, by exposing the evaluation mark with a constant exposure amount and varying the elapsed time, the change in the characteristics of the photosensitive material due to the elapsed time can be adjusted at any exposure amount from the optimal exposure amount. Is it equivalent to the case of (the second relation)
Is required. Next, based on the relationship, according to the actual elapsed time or the estimated elapsed time, exposure amount control is performed to cancel a line width change due to a change in the characteristic of the photosensitive material due to the elapsed time. The line width after development becomes an ideal line width.

It is desirable that the evaluation mark (32) is a wedge-shaped mark, and that the imaging characteristics are evaluated based on the length of the transferred image of the wedge-shaped mark. As shown in FIG. 3A, for example, the length of the wedge-shaped mark in the longitudinal direction is sensitively changed depending on the exposure amount or the like. Can be done accurately. Furthermore, since the length of the wedge-shaped mark can be measured with high accuracy by a laser scan type sensor which may be provided as an alignment sensor in the exposure apparatus, a special measuring device such as a scanning electron microscope is used. No need to do.

The lithography system according to the present invention comprises a coating apparatus (20) for coating a photosensitive material on a substrate to be processed, and an exposure apparatus (20) for exposing the photosensitive material on the substrate to illumination light having passed through a mask pattern. 10) and a developing device (23) for developing the photosensitive material exposed by the exposure device,
Based on the result of exposing a predetermined evaluation mark (32) on the evaluation substrate (W) to which the photosensitive material has been applied, the elapsed time from the application of the photosensitive material to the exposure or the exposure A storage device (18a) for storing a relationship of obtaining an optimum exposure amount for the photosensitive material as a function of an elapsed time from exposure of the material to development, and a coating device (20) for storing the photosensitive material on the substrate. The actual elapsed time from application of the material to exposure of the mask pattern by the exposure device (10), or exposure of the mask pattern to the photosensitive material applied on the substrate by the exposure device (10) An exposure amount control system (18) for correcting the exposure amount for the photosensitive material based on the estimated elapsed time from when the image is developed by the developing device (23) and the function stored in the storage device (18a); It includes those were. According to such a lithography system of the present invention, the exposure method of the present invention can be performed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a lithography system of the present embodiment. In FIG. 1, a host computer 1 for process management and a wafer transfer line 2 for transferring a wafer to be processed are provided. Further, along the wafer transfer line 2, a resist coater 20 for applying and pre-baking the photoresist on the wafer, a wafer cassette 21 for storing the wafer after the resist application carried out of the resist coater 20, and a photoresist are applied. Exposure apparatus 10 for exposing a wafer, wafer cassette 22 for storing a wafer carried out of exposure apparatus 10, and PEB (post-exposure bake) as baking before development on an exposed wafer. A developing device 23 for performing development is arranged.

In the exposure apparatus 10, exposure light is emitted from the illumination optical system 11 to the reticle 12 during exposure, and a pattern image of the reticle 12 is projected through the projection optical system 13 under the exposure light. Projection magnification (for example, 1 /
(4, 1/5, etc.) and projected onto each shot area on the wafer W2 coated with the photoresist. Here, an excimer laser beam such as a KrF excimer laser or an ArF excimer laser is used as exposure light, and a chemically amplified resist is used as a photoresist. The exposure light may be an i-ray of a mercury lamp or the like, and the photoresist may be a resist other than a chemically amplified resist.

In the exposure apparatus 10, the wafer W2 is held on a wafer stage 14 via a wafer holder. The wafer stage 14 positions the wafer W2 in a plane perpendicular to the optical axis of the projection optical system 13, and The position (focus position) of the wafer W2 is also adjusted within a predetermined range in the optical axis direction of the projection optical system 13. Further, the projection optical system 1
Off-axis method and laser step alignment method (hereinafter referred to as "LSA method")
Are provided. This LS
When the A-type alignment sensor 17 irradiates the slit-shaped laser beam LB to the vicinity of the test mark on the wafer W2 and drives the wafer stage 14 to relatively move the test mark and the laser beam LB. In addition, the sensor detects the position of the test mark by detecting diffracted light generated from the test mark. Further, a wafer loader system including a slider 15 and a wafer arm 16 sliding along the slider 15 is provided between the wafer stage 14 and the wafer transfer line 2, and the wafer W2 exposed by the exposure apparatus 10 by the wafer loader system is used as a wafer. Returning to the transfer line 2, the unexposed wafer W 1 on the wafer transfer line 2 is set on the wafer stage 14. The reticle 12, the projection optical system 1
3, wafer stage 14, and alignment sensor 17
Is installed in a temperature-controlled chamber (not shown).

An exposure apparatus 10 is provided outside the chamber.
A main control system 18 that controls the operation of the camera W is provided. At the time of normal exposure, the main control system 18 processes a detection signal of the alignment sensor 17 to obtain array coordinates of each shot area on the wafer W2. , The positioning operation of wafer stage 14 is controlled, and exposure is performed on each shot area of wafer W2 in a step-and-repeat manner. At this time, the main control system 18 controls the irradiation time of the exposure light of the illumination optical system 11 (the number of irradiation pulses may be used in the case of pulse light such as an excimer laser) so that the wafer W
The exposure amount for each shot area is controlled to a predetermined exposure amount. In this example, the exposure amount is controlled for each lot of the wafer to be exposed according to the elapsed time from application of the photoresist to the exposure and the estimated elapsed time from the exposure to the development. Data and the like for performing the exposure amount control are stored in a storage device 18a such as a magnetic disk device, and the main control system 1
8 writes and reads data to and from the storage device 18a as needed. In addition, the process control host computer 1 sends the main control system 18 data on the time at which the photoresist is applied to the wafers of each lot to be exposed by the exposure apparatus 10 and the time until development after exposure. Data and the like of elapsed time (estimated elapsed time) in management are supplied. The main control system 18 can calculate the elapsed time from the application of the resist to the exposure from the difference between the time at which the photoresist is applied to each lot and the time at which the exposure is performed. In addition,
The exposure amount may be controlled according to the elapsed time or the estimated elapsed time for each wafer in the lot instead of for each lot.

Next, an example of a method of controlling the exposure amount of the photoresist on the wafer of each lot in the lithography system of the present embodiment to prevent the resolution from deteriorating will be described. Hereinafter, a method of obtaining a high resolution by correcting the exposure amount according to the actual elapsed time from the application of the photoresist to the exposure will be described. First, the elapsed time from the application of the photoresist to the exposure is different.
An unexposed wafer for evaluation (n is an integer of 2 or more) is prepared, and an image of a predetermined evaluation mark is exposed on these wafers using the exposure apparatus 10 of FIG. At this time, the exposure amount for each wafer is the same exposure amount so that the highest resolution can be obtained when the elapsed time is 0, for example. The elapsed time from the application of the resist on the wafer exposed at the i-th (i = 1 to n) to the exposure is defined as t _i .

FIG. 2 shows a wafer W on which an image of an evaluation mark is exposed. In FIG. 2, a large number (for example, 10 to 20) of shot areas 31A arranged vertically and horizontally at a predetermined pitch on the wafer W are shown. , 31B, 31C,... Are sequentially exposed with the image of the evaluation mark. At this time, the focus position of the wafer W is sequentially changed by a predetermined amount every time the process moves to the next shot area. Therefore, the shot area 31 on the wafer 2
Among the images of the evaluation marks exposed to A, 31B, 31C,..., There are images that are exposed in a substantially in-focus state, but other images are intentionally defocused by different amounts. Then, development is performed on the wafer W immediately after the end of the exposure. In this example, a mark in which a plurality of elongated diamond-shaped marks are arranged is used as an evaluation mark. Hereinafter, the resist pattern of the evaluation mark formed by the development is referred to as a “wedge-shaped mark”.

FIG. 3A shows a wedge-shaped mark 32 as an evaluation mark image formed in each shot area of the wafer W after development, and as shown in FIG. The wedge-shaped mark 32 is a mark in which a plurality of elongated diamond-shaped marks are arranged at a predetermined pitch in the short direction. In this case, since the focus positions at the time of exposure are different from each other in each shot area of the wafer W, the wedge-shaped mark exposed near the best focus position is a mark long in the longitudinal direction like the wedge-shaped mark 32. The length of the wedge-shaped mark 32A indicated by a dotted line exposed in a state where the defocus amount is large is short. Thus, by measuring the length (mark length) LM of the wedge-shaped mark 32 in the longitudinal direction, it is possible to determine which mark is closest to the best focus position, that is, the mark exposed at the highest resolution. .

Next, the wafer W after development is set on the wafer stage 14 of the exposure apparatus 10 shown in FIG. 1, and a wedge-shaped mark in each shot area on the wafer W is passed through an LSA type alignment sensor 17. A mark length LM of 32 is measured. Specifically, in a state where the laser beam LB from the alignment sensor 17 is irradiated near the wedge-shaped mark 32 as shown in FIG. When scanning is performed in the longitudinal direction with respect to LB, diffracted light is emitted from wedge-shaped mark 32 in a range where laser beam LB is applied to wedge-shaped mark 32. Wafer stage 14 in the range where this diffracted light is detected
Is the mark length LM. Since the position of the wafer stage 14 is measured by a laser interferometer having a resolution of, for example, about 0.01 μm, the mark length LM of the wedge-shaped mark 32 is
Can be measured with extremely high accuracy.

Therefore, the measured mark length of the wedge-shaped mark 32 in each shot area of the first wafer whose elapsed time is t ₁ is y, and the focus position of the shot area where the mark length y is measured is x. The mark length y is approximated by a quadratic function of the focus position x using the coefficients a ₁ , b ₁ ,..., E ₁ as follows. These coefficients a ₁ , b ₁ ,..., E ₁ can be determined by, for example, the least square method. In this example, a quartic function is used as the approximation function. However, the approximation order may be changed depending on the resist conditions to be measured.

[0024]

Y = a ₁ x ⁴ + b ₁ x ³ + c ₁ x ² + d ₁ x + e ₁ Next, the mark length measured in each shot area for a wafer having an elapsed time from resist coating to exposure of t _2. y is approximated by a quadratic function of the focus position x using the coefficients a ₂ , b ₂ ,..., e ₂ as follows.

[0025]

Y = a ₂ x ⁴ + b ₂ x ³ + c ₂ x ² + d ₂ x + e _{2 By} performing the same operation for the wafers having elapsed times of t ₃ to t _n , the mark is obtained as shown in Table 1. Coefficients a ₃ , b for approximating length y with a quartic function of focus position x
_{3, ..., e 3 ~a n} , b n, ..., e n can be obtained.

[0026]

[Table 1]

Further, in this embodiment, by using an unexposed wafer for evaluation in advance, immediately after the resist coating (that is, in a state where the elapsed time t _i is 0), the _first wafer with a predetermined exposure amount ΔE ₁ is obtained. The evaluation mark image is exposed by sequentially changing the focus position on different shot areas on the wafer, and the mark length of a wedge-shaped mark formed by development immediately after that is measured. At this time, a predetermined line-and-space pattern is also formed in parallel as an evaluation mark, whereby the wedge-shaped mark 32 shown in FIG.
A resist pattern 33 of the line-and-space pattern image shown in (b) is also formed, and the value (P2 / P1) of the ratio (duty ratio) of the line width P2 of each pattern to the pitch P1 of the resist pattern 33 is determined. Measure using a scanning electron microscope.

For example, a broken line 36A in FIG. 4 indicates the relationship between the mark length y (μm) of the wedge-shaped mark measured for the wafer having the exposure amount ΔE ₁ and the focus position x. However, the horizontal axis in FIG. 4 is obtained by converting the focus position x into a defocus amount Δx (μm) from the best focus position. The best focus position is the focus position x where the mark length y is the longest for the wafer.

Next, the exposure amount? En slightly less exposure? En ₂ in the second sheet of the evaluation mark images successively changing the focus position in a different shot areas on the wafer than _1, and the line-and-space pattern Exposure of the image, the mark length of the wedge-shaped mark formed by the development immediately thereafter,
And the duty ratio of the line and space pattern image is measured. For example, a broken line 35A in FIG. 4 indicates the relationship between the mark length y of the wedge-shaped mark and the defocus amount Δx measured on the wafer having the exposure amount ΔE ₂ . Similarly, with respect to the third and subsequent wafers, the mark length y and the defocus amount Δx of the wedge-shaped mark formed by exposing while changing the focus position with the sequentially decreasing exposure amounts ΣE ₃ , ΣE ₄ , and そ れ ぞ れ E _5. The relationship with the line 3 in FIG.
4, 35B and 36B.

Thereafter, these exposure amounts ΔE₁~ ΣE_Fiveof
Which is the optimum exposure amount. In general,
Appropriate exposure amount is specified line and space pattern image
Of the resist pattern obtained by exposing and developing
It is determined by the duty ratio. Then, FIG.
Pattern of line and space pattern image
Exposure when the duty ratio of the image 33 reaches a predetermined value
Is determined as the optimal exposure amount, for example, a polygonal line 34 in FIG.
Exposure when obtained ΔE_ThreeIs the optimal exposure ΣE ₀Tona
You. Also, bend lines 35A and 36A below the bend line 34
Is obtained when the optimum exposure amount ΔE₀Against
Exposure amounts 5% and 10% higher, respectively,
Exposure when the upper polygonal lines 35B and 36B are obtained
The amount is the optimal exposure amount ΣE₀5% and 10% respectively
It is assumed that the exposure amount is smaller by%.

Also, for each of the polygonal lines 36A to 36B in FIG. 4, the mark length y is changed to the focus position x (that is, the defocus amount Δx
(The value obtained by adding the best focus position to the image).

[0032]

Y = ax ⁴ + bx ³ + cx ² + dx + e As a result, the coefficients a to e obtained when the exposure amount is −10% of the optimum exposure amount (polygonal line 36B) are a _{−10 to} e.
_-10 , -5% of the optimal exposure (line 35
In the case where the coefficients a to e obtained in B) are a _{-5 to} e _-5 , the coefficients a to e obtained at the optimum exposure amount (polygonal line 34) are a _{0 to} e ₀ , and + 5% with respect to the optimum exposure amount ( The coefficients a to e obtained in the polygonal line 35A) are a _{5 to} e ₅ , and +1 with respect to the optimum exposure amount.
In the case of 0% (polyline 36A), the coefficients a to e obtained by
When ₁₀ to e _10, these coefficients are associated as shown in Table 2. Note that the exposure time in the leftmost column of Table 2 below is
It can be regarded as an exposure time when the illuminance (pulse energy) of the exposure light is constant, that is, an amount proportional to the exposure amount.

[0033]

[Table 2]

The actual values of the coefficients a to e of (Equation 3) obtained so as to approximate the polygonal lines 36A to 36B of FIG. 4 are as shown in FIGS. 5 (a) to 5 (e). FIG.
The horizontal axis of (e) is the shift amount s of the exposure amount with respect to the optimum exposure amount.
(%), For example, when the shift amount s is -10%, the value approximates the polygonal line 36B in FIG. FIG.
Coefficients a to e represented by (a) to (e) are shift amounts s from the optimal exposure amount in a state where the elapsed time from the application of the photoresist to the exposure is 0 and the resist characteristics are not changed. And the coefficients a to e.

Next, using the evaluation results shown in Tables 1 and 2,
When the elapsed time from resist coating to exposure is t
Degradation of resolution due to temporal change in resist characteristics (line width
Error) and that the resist characteristics have not changed over time.
When the elapsed time is 0,
Of the resolution when exposing with the shift amount of s (%)
A shift amount s of the exposure amount is determined so as to be equal. That
First, the coefficients a to e in FIGS.
A with the subscript of the shift amount s from the appropriate exposure amount_s~ E _sage
And these coefficients a_s~ E_sIs a function f (s) on s
Approximation by k (s) is as follows. In addition, the deviation amount
The sign of s is minus for under exposure and over exposure
Is a plus.

[0036]

Equation 4] _{a = a s = f (s} ), b = b s = g (s), c = c s = h (s), d = d s = j (s), e = e s = k (S) When the coefficients a _{s to} e _s are expressed as a function of the shift amount s as in (Equation 4), the wedge-shaped mark measured when the exposure is performed with the shift amount s (%) from the optimal exposure amount. An approximate expression of (Equation 3) representing the relationship between the length y and the focus position x is as follows.

[0037]

Equation 5] ^{_{y = a s x 4 + b}} s x 3 + c s x 2 + d s x + e s = f (s) x 4 + g (s) x 3 + h (s) x 2 + j (s) x + k (s) more From the evaluation results in Table 1, an approximate function representing the relationship between the mark length y and the focus position x, which is obtained by measuring the mark length of the wedge-shaped mark in the case of the elapsed time t from resist application to exposure, that is, An approximate function that expresses (Equation 1) and (Equation 2) as functions of the elapsed time t is obtained. The approximation function by using the coefficients a _t to e _t expressed as follows. This approximation function can be regarded as a function including information on resolution degradation due to a temporal change in resist characteristics when the exposure time is changed while the exposure amount is constant (optimal exposure amount at elapsed time 0).

[0038]

[6] ^{_{y = a t x 4 + b}} t x 3 + c t x 2 + d t x + e t Then, the approximation function (6) is, how much the shift amount s of the optimum exposure in (5) Is obtained. For this purpose, as an example, (Equation 5) and (Equation 6)
The shift amount s when the value of the following residual error component E, which is the sum of the squares of the differences between the respective coefficients, becomes the smallest may be obtained. For example, if all of the five approximation functions of (Equation 4) are quadratic functions of s, the following equation is a quadratic function, and the shift s when the function takes the minimum value may be obtained. In this case, further the coefficients a _s to e _s respectively for each appropriate weights W _a to _W-e
Is set.

[0039]

(Equation 7)

It is clear from FIGS. 5A to 5E.
As shown in FIG. _s~ E_sIs the amount of change
Various. Therefore, the weight W for each coefficient described above_a,
W_b, W _c, W_d, W_eIs the value of each coefficient a_s~ E_sStrange
It is good to set it according to the state of conversion. Where weight W_a,
W_b, W_c, W_d, W_eMay be commonly set to 1.
Deviation that minimizes the value of the residual error component E in (Equation 7)
When the value of the amount s is determined, the process from the application of the resist to the exposure is performed.
Solution by temporal change of resist characteristics when overtime is t
Degradation of image resolution (line width control error) is caused by the temporal change in resist characteristics.
Exposure to optimal exposure when no change has occurred
Is equivalent to the resolution degradation when the shift amount is s.
Relationship is required. Therefore, the shift amount s of the exposure amount
(%), That is, -s (%) of the appropriate exposure amount
That is, the exposure amount only needs to be corrected.

Next, the optimum exposure time when the exposure apparatus 10 of FIG. 1 performs exposure so as to offset the deviation s (%) from the optimum exposure while keeping the illuminance (pulse energy) of the exposure light constant. A method for determining T will be described. In this case, in the state where the elapsed time from the resist application to the exposure is 0, that is, in the state where the temporal change of the resist characteristics has not occurred, the exposure time for obtaining the optimal exposure amount is T ₀ , and the time from the resist application to the exposure is The exposure time T for correcting the exposure amount by -s (%) of the appropriate exposure amount when the elapsed time is t is as follows.

[0042]

T = 100 · T ₀ / (100 + s) In the storage device 18a of FIG. 1 of this example, (Equation 5) and (Equation 6)
, And a relational expression that determines the exposure time T in (Equation 8). Then, when the host computer 1 supplies the time information of resist application to the wafer of the next exposure target lot to the main control system 18, the main control system 18 performs processing from the exposure time of the lot to the resist application to exposure. Is obtained, and from this elapsed time t,
The shift amount s of the exposure amount that minimizes the residual error component E in (Equation 7) is determined. Then, an exposure time T is determined from (Equation 8) so as to offset the shift amount s, and each shot area on the wafer is exposed at the exposure time T. As a result, even when the characteristics of the photoresist change with the elapse of time after the application, the deterioration of the resolution is prevented, and the deterioration of the line width control accuracy is prevented.

Further, in the present embodiment, similarly to the case where the exposure amount is corrected in accordance with the actual elapsed time t from the application of the resist to the exposure, the estimated elapsed time u from the exposure to the development is also obtained.
The exposure is corrected so as to obtain a high resolution. To this end, after exposing the evaluation mark to a large number of wafers for evaluation in advance while changing the focus position, development is performed by changing the actual elapsed time from exposure to development in various ways. By measuring the mark length of a wedge-shaped mark formed later, the mark length y and the focus position x may be approximated by the following quartic function in accordance with (Equation 6). By the following equation, the coefficient a _u to e _u is a function of the elapsed time u from each exposure to development.

[0044]

Equation 9] ^{_{y = a u x 4 + b}} u x 3 + c u x 2 + d u x + e u Then, when the estimated elapsed time from exposure to development at the time of actual exposure is u is the coefficient a _t in equation (7) to e _t asking each coefficient a _u to e _u a replacement residue of exposure so that the error component E is minimized displacement amount s (%), by correcting the exposure amount so as to cancel the shift amount s I just need.

In the above-described embodiment, the imaging characteristics under various exposure amounts are measured with the elapsed time being 0, but various exposure amounts are measured at various elapsed times. The imaging characteristic under the condition may be measured. Although this method considerably increases the number of measurement data, there is an advantage that the optimum exposure amount can be directly determined as a function of the elapsed time from resist coating to exposure or the elapsed time from exposure to development.

In the above embodiment, the exposure apparatus 1
Although the resolution (line width control accuracy) is improved by controlling the exposure amount of 0, the condition such as the pre-bake temperature at the time of applying the photoresist or the PEB (post-exposure bak) at the time of development is further improved.
e) The conditions such as temperature, development time, and developer concentration are changed according to the elapsed time from resist coating to exposure (estimated elapsed time) and the estimated elapsed time from exposure to development (actual elapsed time). You may do so.

The present invention is not limited to the above-described embodiment. For example, the present invention is applied to a case where a scanning exposure type projection exposure apparatus such as a step-and-scan method is used as an exposure apparatus. It goes without saying that various configurations can be adopted without departing from the gist of the invention.

[0048]

According to the first exposure method of the present invention, the exposure of the photosensitive material is performed according to the actual elapsed time from the application of the photosensitive material on the substrate to be processed to the transfer of the mask pattern. Since the amount is corrected, there is an advantage that high resolution can be obtained even if the time from application of the photosensitive material to exposure varies.

According to the second exposure method of the present invention,
Since the amount of exposure to this photosensitive material is corrected according to the estimated elapsed time from exposure to development of the photosensitive material on the substrate to be processed to development, there is variation in the time from exposure to photosensitive material to development. Even if it occurs, there is an advantage that a high resolution can be obtained. When the optimum exposure amount for the photosensitive material is obtained as a function of the elapsed time, when the elapsed time is a predetermined elapsed time t ₀ , various exposure amounts for the photosensitive material and transfer images of the evaluation mark are evaluated. A first relationship with the imaging characteristics is determined, and a second relationship between the elapsed time when the elapsed time is changed stepwise and the imaging characteristics of the transferred image of the evaluation mark is determined. When the photosensitive material on the substrate to be processed is exposed, the actual elapsed time or the estimated elapsed time is defined as t, and the imaging characteristic at the time when the elapsed time is t in the second relationship is expressed as When the correction exposure amount for the optimum exposure amount is obtained from the first relationship based on the first relationship,
The corrected exposure amount can be accurately obtained with a small amount of measurement data.

The evaluation mark is a wedge-shaped mark. To evaluate the imaging characteristics of the wedge-shaped mark based on the length of the transferred image, a special measuring device such as a scanning electron microscope is required. There is an advantage that the resolution of the transferred pattern can be evaluated using, for example, an alignment sensor provided in the exposure apparatus without using it. Further, according to the lithography system of the present invention, the exposure method of the present invention can be performed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a lithography system according to an example of an embodiment of the present invention.

FIG. 2 is a plan view showing a wafer exposed for evaluation of an imaging characteristic.

3A is an enlarged plan view showing a wedge-shaped mark for evaluating an imaging characteristic, and FIG. 3B is a line and line for evaluating an imaging characteristic.
FIG. 4 is an enlarged plan view showing a resist pattern of a space pattern.

FIG. 4 is a diagram illustrating a relationship between a mark length of a wedge-shaped mark and a focus position (a defocus amount) under a condition that an elapsed time from application of a photoresist to exposure is zero.

FIG. 5 is a graph showing coefficients a to approximation functions corresponding to the measurement results of FIG.
It is a figure showing the value of e.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Host computer 2 Wafer transfer line 10 Exposure device 14 Wafer stage 17 Alignment sensor 18 Main control system 20 Resist coater 23 Developing device

Claims (5)

[Claims] 1. After applying a photosensitive material on a substrate to be processed, the mask material is transferred to the photosensitive material on the substrate by exposing the photosensitive material on the substrate to illumination light that has passed through the mask pattern. In the exposure method, the optimum exposure amount for the photosensitive material is determined in advance as a function of the elapsed time from the application of the photosensitive material on the evaluation substrate to the exposure of the evaluation mark. An exposure method for correcting the exposure amount of the photosensitive material according to an actual elapsed time from the application of the photosensitive material onto the substrate to the transfer of the mask pattern. 2. An exposure method for exposing a photosensitive material on a substrate to be processed with illumination light having passed through a mask pattern and then developing the photosensitive material to transfer the mask pattern to the photosensitive material. The optimum exposure amount for the photosensitive material is determined as a function of the elapsed time from when the evaluation mark is exposed to the photosensitive material on the evaluation substrate to when the development is performed. An exposure method, wherein an exposure amount for the photosensitive material is corrected in accordance with an estimated elapsed time from the exposure of the photosensitive material with the illumination light having passed through the mask pattern to the development. 3. An exposure method according to claim 1, wherein said elapsed time is a predetermined elapsed time t ₀ when obtaining an optimum exposure amount for said photosensitive material as a function of said elapsed time.
In this case, the first relationship between the various exposure amounts of the photosensitive material and the imaging characteristics of the transferred image of the evaluation mark is obtained in advance, and the progress when the elapsed time is changed stepwise is further determined. A second relationship between time and the imaging characteristics of the transfer image of the evaluation mark is obtained, and when the photosensitive material on the substrate to be processed is exposed, the actual elapsed time or the estimated elapsed time An exposure method, wherein a correction exposure amount with respect to an optimum exposure amount is obtained from the first relationship based on an imaging characteristic when the elapsed time is t in the second relationship, where time is t. 4. The exposure method according to claim 1, wherein the evaluation mark is a wedge-shaped mark, and the imaging characteristic is evaluated based on a length of a transfer image of the wedge-shaped mark. An exposure method comprising: 5. An application device for applying a photosensitive material on a substrate to be processed, an exposure device for exposing the photosensitive material on the substrate with illumination light having passed through a mask pattern, and the photosensitive device exposed by the exposure device. A developing device that develops the material, and a lithography system including: a method of applying the photosensitive material based on a result of exposing a predetermined evaluation mark on an evaluation substrate on which the photosensitive material is applied. A storage device that stores the relationship between the elapsed time until exposure, or the optimum exposure amount for the photosensitive material as a function of the elapsed time from exposure to development of the photosensitive material to development. The actual elapsed time from the application of the photosensitive material on the substrate to the exposure of the mask pattern by the exposure device, or the exposure time applied to the substrate by the exposure device An exposure control system that corrects the exposure of the photosensitive material based on an estimated elapsed time from exposure of the mask pattern on the material to development by the developing device and a function stored in the storage device. A lithography system comprising: