JPS62204527A - mask exposure equipment - Google Patents

Abstract

PURPOSE:To reduce the irregularity of developing size in a mask exposing apparatus by calculating an exposure time with the intensity of light by reflected light from a wafer, operating a shutter and regulating the exposure time. CONSTITUTION:An exposure time tp1 is so controlled as to calculate a photosensitive time Tp1 of an equation (1) by an exposure time calculator 10 by an exposing time set value Tp input from an input unit 13, an emitting intensity Ip to a wafer 8 (to be measured by a photosensor 12) and a reflecting intensity from the wafer 8 (to be measured by a photosensor 11), to transmit it to a shutter controller 4 and to open or close a shutter 9 by the exposing time Tp1. tp1= Tp.(1-L0/Ip0)/(1-Ir1/Ip1). The sensor 2 above a light source 1 measures the decrease in the emitting light intensity due to aging change of the light source 1, and inputs it to the calculator to calculate a correction value tp2 of an equation (2) so that the emitting energy to the wafer becomes constant. tp2=tp1.(Il1/ Ilu)...(2)=Tp.(Il1/Il1)(1-Ir0/Ip0)(1-Ir1/Ip1) It prevents a developing size from varying due to change in the absorbing energy to the wafer 8 and the intensity of the light source. Here, Ip0, Ir0 are emitting intensity and reflecting intensity to wafer in case of reference resist film thickness, and Ip1, Ir1 are intensities thereof when the resist film varies.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection light apparatus, and particularly to a mask exposure apparatus suitable for manufacturing integrated circuits using ultrafine processing technology.

[Conventional technology]

In order to stabilize the exposure illuminance on the wafer, the conventional apparatus is equipped with an illuminance control device to control the light source, as described in Japanese Patent Laid-Open No. 59-161027. However, no mention was made of correction for the fact that the light energy absorbed by a wafer coated with resist varies greatly due to minute variations in the thickness of the resist coated film.

[Problem that the invention seeks to solve]

In the above conventional technology, in order to stabilize the exposure illuminance on the wafer, a sensor that monitors the illuminance is installed in the vicinity of the mask, etc., and the amount of light from the light source is directly captured, compared with a set value, and -cps is determined. It controls the amount of light.

However, even if the amount of light irradiated onto the resist film of the wafer is controlled to be constant, the resist development size is not necessarily constant. This is because even if the resist film thickness changes by about 0.02 μm, the reflectance on the resist surface changes greatly.
This is because the energy actually absorbed inside the resist changes greatly, so the degree of photosensitivity of the resist changes greatly, and the developed size fluctuates.

Therefore, in order to prevent this, it is necessary to keep the value obtained by subtracting the amount of light reflected from the resist surface from the amount of irradiated light, that is, the amount of light actually absorbed by the resist film (photosensitivity), to a constant value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a mask exposure apparatus that can reduce variations in developed dimensions by correcting variations in energy absorption rate within a resist film due to minute variations in resist film thickness.

[Means for solving problems]

The above purpose is to provide a photodetector or a light introduction path to the photodetector in the irradiation optical path of the mask exposure device, measure the reflected light from the wafer coated with resist, and use the value to measure the reflected light from the wafer coated with resist. This is achieved by calculating the change in light absorption rate and correcting the exposure (light irradiation) time to the wafer in accordance with the change.

[Effect]

Apply resist to about 111m on the wafer.

Expose the mask pattern, and use Ueno-
When developed, a pattern similar to the mask pattern is formed in the resist. When using a positive resist, when the exposure time is shorter than the reference value, the developed size of the resist line tends to become thicker, and when the exposure time is lengthened, it tends to become thinner. on the other hand,
Even if the resist coating film thickness changes by about 0.02 μm from the standard value (even if the standard film thickness changes by a certain amount, the resist developed size will change greatly. This is because even a change of about 2% in the resist film thickness , the reflectance at the resist surface increases or decreases by about 10-10, and as a result, the energy actually absorbed into the resist film decreases (or increases), and the exposure time becomes shorter (or longer). It is a reminder that has a similar effect.

Therefore, by detecting the reflected light from the wafer using a light detection means and using the detected value to control the exposure time in accordance with changes in the resist film, a pattern with suitable developed dimensions can be obtained.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Light emitted from a light source 1 is reflected by a reflecting mirror 2, converged by a condenser lens 5, and becomes parallel light.

This light is a mask (reticle) with a circuit pattern drawn on it.
6, and the image of the mask 6 is projected onto the wafer 8 by a projection lens 7. The irradiation (exposure) time to the wafer 8 is adjusted by controlling the closing time of the shutter 9 by the shutter control device 4.

Here, II! The general relationship between photoperiod and absorption rate will be explained. If the absorption rate of the wafer is 80 when a resist with a standard film thickness is applied, the standard exposure time in that case is 1. Then, the exposure time correction value when the resist film thickness changes from the reference value and the wafer absorption rate changes to AI is 1 /
, is expressed by the following formula.

11,=1.・ (At/Ao n -1...
・・・・・・・・・・0n Also, wafer absorption rate A1e A
o can be calculated by measuring the irradiation intensity Ipo, Ipt+ to the wafer and the intensity ItOsL1 of reflected light from the wafer using an optical sensor provided in the optical path of the mask exposure device, and is expressed by a linear equation.

Ao = (11-o/Ite) ”・-”・
12) AI = (1-1-s/Ipt) ・
... Group ... (3) Here, 'PO# Ir (1
are the irradiation intensity and reflection intensity s Ipt to the wafer when the resist film thickness is the standard, and Ll are the respective intensities when the resist film changes.

Using the exposure time tPI calculated by equation (1), /! By using light, fluctuations in developed dimensions can be prevented.

In FIG. 1, *light time tP1 is the exposure time setting value TP input from the input device 13, the irradiation intensity Ip to the wafer 8 (measured by the light sensor 12), and the reflection intensity 1 from the wafer 8. ．． (measured with optical sensor/su 11) using g
The exposure time tel is calculated by the light time calculation 610 and transmitted to the shutter control device 4, which controls the shutter 9 to open and close at this exposure time tel.

tPl is expressed by the following equation from equation α).

tpt = rp ・(l Lo /Ipo)/ (l
Lt/bx ) −(4) Here a 1roy
Lpo+Lrt*Ipt is the same value as used in equations (2) and (3).

In FIG. 1, an optical sensor 3 is provided above a light source 1. This sensor measures a decrease in the emission intensity of the light source 1 due to changes over time. Even if the exposure time to the wafer 8 (controlled by the opening/closing time of the shutter 9) is constant, if the luminous intensity of the light source decreases.

Since the irradiation energy to the wafer 8 is reduced and the exposure time is shortened, it is necessary to correct the irradiation energy to the wafer 8 so that it is constant.

The initial emission intensity of light source 1 is calculated as t1. When the luminescence intensity after the change over time is hl, the correction value tP2 of the quaternary time is expressed by the following equation.

1,, = 1. Bi (ItI/It u)
−・” −(5)=Tp・(Iz I/Ltx) (
1-Iro/Ipo) (1-I-1/IPI
)......(6) This calculation is performed by manually inputting the light emission intensity measurement value of the light source 1 by the optical sensor 3 into the exposure time calculator. This has the effect of improving the manufacturing yield of integrated circuits since it is possible to prevent variations in developed dimensions due to variations in absorbed energy and variations in light emission intensity of the light source.

The exposure time calculation described above is performed by the 1g light time calculator 10, and its internal configuration is the same as that of a conventional computer as shown in FIG.
It consists of l0I and input/output interface l10102. The input values are light source intensity 1 reflected light intensity, and exposure time setting value.

The first output shift is the exposure time.

FIG. 2 shows another embodiment of the invention. Is the optical sensor different from Figure 1? Points 14, 15, 16, and 17 are impressive. According to this embodiment, the intensity of the irradiated and reflected light at the bottom and top of the mask and the top of the condenser lens is measured, so an appropriate sensor is selected depending on the type of wafer and the mask. and used alone or as 4i number li
It is also possible to use the average value of the outputs of d. According to this embodiment, there is an effect that fluctuations in absorption to the wafer can be measured with f# density.

FIG. 3 shows another embodiment of the invention. The difference from FIG. 2 is that the optical sensors 12, 15, and 17 are removed.

In the case of this embodiment, the fact that the irradiation intensity to the wafer is proportional to the emission intensity of light (ill) is utilized.

Then, the irradiation intensity 'PO+ to the wafer in equation (6) is
Let Lpl be the value obtained by multiplying the fixed value of the light emission intensity of the light source by the correction coefficient. In other words, V, Ipoe Ipt is expressed by the following equation.

Ipo=kp ・Iro・・・・・・(7)I
p1=Kp-Izt...
...(8) Here, * Izo is the light emitted from the wafer coated with the standard resist film thickness (lil emission intensity,
Izt is the light emission intensity of the light source 1 when exposing a film coated with a resist of an arbitrary thickness. In this embodiment, the intensity of reflected light from the wafer is measured using at least one of the optical sensors 11, 14, and 16. Measurement accuracy can be improved by measuring using a plurality of sensors and using the average value.

The exposure time t1 in this embodiment is expressed by the following equation.

tp3=Tp ・(Iz I/Iz+) (I It
o / kpat o ) A I -ir t/ kpI
41) (9) Here, is a correction coefficient.

The truth IIl! A1511 has the effect of lowering the a of the optical sensor and lowering the cost.

FIG. 4 shows another embodiment of the invention. The difference from FIG. 3 is that the developed dimension of the resist in the wafer development process 19 is measured by a developed dimension measuring device 20, and the value is input into the exposure time calculator 10 to correct the exposure time. be.

If the correction coefficient at this time is , then the corrected exposure time tP4 is expressed by the following equation. Reference numeral 18 indicates parts of the optical system of the exposure apparatus.

t, 4=J t,...
(10) hq = 1 + a (Xz Xs)
--(11) Here, xt Ni-resist development dimension Xs Ni-resist development dimension setting value α: Correction coefficient. α takes different values depending on the type of resist.

According to this embodiment, it is possible to compensate for minute fluctuations in the developing process conditions, so that the manufacturing yield can be improved.

Another embodiment of the present invention is shown in the gs diagram. The difference from FIG. 1 is that the optical sensor 11 is not installed in the optical path, but is placed outside, and the light in the optical path is guided to the optical sensor 11 by a light guide 21. According to this embodiment, the light guide device 21 can be made smaller.

This has the effect of not creating a shadow on the mask projection image.

〔Effect of the invention〕

According to the present invention, it is possible to compensate for variations in the energy absorption rate in the V cyst film due to minute variations in the resist film thickness on the wafer, so it is possible to provide a mask exposure apparatus that can reduce variations in resist development dimensions. effective.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the basic configuration of the present invention;
2 to 5 are diagrams showing other embodiments of the present invention, and FIG. 6 is a diagram showing another embodiment of the present invention.
The figure shows the internal configuration of the exposure time calculator. DESCRIPTION OF SYMBOLS 1... Light source, 4... Shutter control device, 6... Mask, 7... Projection lens, 8... Wafer, 9...
Kuyatsuta.

Claims (1)

[Scope of Claims] 1. In a mask exposure apparatus that performs mask exposure by converging a light beam from a light source for mask irradiation and irradiating the mask, and projecting the mask image onto a wafer by an optical system, A shutter that controls the irradiation time to the mask,
1. A mask exposure apparatus comprising: a light detection means for detecting reflected light from a wafer; the exposure time is calculated using the light intensity of the reflected light; and the exposure time is adjusted by operating the shutter. 2. Claim 1 provides that when calculating the exposure time, in addition to the light intensity of the reflected light, the developed dimension of the resist in the wafer development process is measured to correct the exposure time. Features of mask exposure equipment. 3. A mask exposure apparatus according to claim 1, characterized in that the mask exposure apparatus is constituted by a projection light apparatus. 4. The mask exposure apparatus according to claim 1, wherein the optical system for projecting the mask image onto the wafer includes a reduction projection lens. 5. The mask exposure apparatus according to claim 1, wherein the light detection means is constituted by a light sensor. 6. The mask exposure apparatus according to claim 1, wherein the light detecting means is configured to guide at least a part of the light in the irradiation optical path to an optical sensor using a light guide for measurement.