JPH07111235A - Method and device for exposure - Google Patents

Abstract

PURPOSE:To enable a pattern transfer to be made with high precision on an object to be exposed without being affected by the change of the absorption coefficient of a resist. CONSTITUTION:An exposure system comprises a reticle stage 1, reducing lens 2, and a wafer stage 3. Built in a wafer chuck 3a of the wafer stage 3a is a light quantity sensor 6 which detects the quantity of light of exposure light 5 passing through a transparent quartz wafer 7 on which a resist 4a is coated in the same condition as the normal wafer 4. Sampling a change with the passage of time of the transmission quantity of light enables the absorption coefficient of the resist 4a to be measured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to exposure technology, and in particular
The present invention relates to a technique effective when applied to an exposure step in a semiconductor manufacturing process that requires highly precise transfer of an extremely fine pattern.

[0002]

2. Description of the Related Art For example, in a semiconductor manufacturing process, a fine circuit pattern is transferred and formed on a semiconductor substrate (wafer) by photolithography. That is, by the exposure light transmitted through the original plate such as a reticle,
After exposing the resist deposited on the wafer to a desired pattern, it is developed, and the resist remaining on the wafer is used as a mask to etch the underlying thin film, etc. Is transferred with high precision.

In such photolithography,
It is known that the physical properties of the resist greatly affect the dimensional accuracy of the transfer pattern. Conventionally, the film quality (refractive index),
Although the film thickness was controlled, the change in absorption coefficient was not controlled at all.

[0004]

However, in the above-mentioned conventional technique for controlling only the film quality and film thickness of the resist, the exposure operation is carried out on the assumption that the absorption coefficient does not change. There was a concern that dimensional defects would occur due to fluctuations in the coefficient.

That is, the transfer pattern on the wafer is
In the recent photolithography process, which has been further miniaturized to 0.5 μm or less, there is a problem that the dimensional fluctuation due to the fluctuation of the absorption coefficient of the resist, which has been allowed so far, becomes manifest as a defect.

An object of the present invention is to provide an exposure technique capable of performing highly accurate pattern transfer on an object to be exposed without being affected by fluctuations in the absorption coefficient of the resist.

Another object of the present invention is to provide an exposure technique capable of accurately measuring the absorption coefficient of a resist in the exposure process.

Another object of the present invention is to provide an exposure technique capable of calculating the optimum exposure amount of the exposure process from the measured absorption coefficient.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0010]

Of the inventions disclosed in the present application, a representative one will be briefly described below.
It is as follows.

That is, the invention according to claim 1 is an exposure method in which the variation of the absorption coefficient of the exposure light in the resist used in the exposure step is monitored and the exposure amount is set or changed according to the variation of the absorption coefficient. .

According to the second aspect of the invention, in the exposure method according to the first aspect, a change in the exposure light transmitted through the resist is measured by using a transparent substrate coated with the resist under the same conditions as the object to be exposed. By doing so, the absorption coefficient is measured.

Further, the invention according to claim 3 is an exposure apparatus including a support table on which an object to be exposed is placed, and an optical system for transferring the pattern of the original plate onto the object to be exposed through exposure light. A light amount sensor is built in the mounting surface of the object to be exposed on the table.

According to a fourth aspect of the invention, in the exposure apparatus according to the third aspect, the light quantity of the exposure light transmitted through the transparent substrate coated with the resist is measured by the light quantity sensor under the same conditions as the object to be exposed. By doing so, the absorption coefficient of the resist is obtained.

Further, the invention according to claim 5 is the exposure apparatus according to claim 3 or 4, which further comprises a control logic for calculating an optimum exposure amount when the object to be exposed is started based on the amount of change in the absorption coefficient. It is a thing.

[0016]

According to the above means, the transparent substrate coated with the resist under the same conditions as the object to be exposed is placed on the support table having the built-in light amount sensor, and the exposure light is applied to the region directly above the light amount sensor on the transparent substrate. Irradiate. Since the amount of light transmitted through the resist changes depending on the irradiation time, the absorption coefficient can be obtained from this. Further, according to the above means, even if the absorption coefficient is changed due to, for example, a change in the resist lot, the amount of change in the absorption coefficient can be measured by measuring the amount of change in the absorption coefficient before the actual exposure work is started. It is possible to calculate the optimum exposure time.

[0017]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of an exposure apparatus which is an embodiment of the present invention, FIG. 2 is a diagram showing an example of its action, and FIGS. FIG. 5 is a flow chart showing an example of the operation of the exposure method and apparatus which is an embodiment of the present invention.

The exposure apparatus of this embodiment comprises a reticle stage unit 1, a reduction lens unit 2 and a wafer stage unit 3.

In the reticle stage portion 1, for example, a reticle 1a in which a desired transfer pattern is formed on one main surface of a transparent glass substrate by a light-shielding material such as a metal thin film.
Is placed.

The wafer stage section 3 can be moved horizontally, for example, in a plane perpendicular to the optical axis of the reduction lens section 2.
The Y table and the rotational displacement of the reduction lens unit 2 around the optical axis are configured by combining a rotational table and the like,
The wafer 4 on which the resist 4a is applied or the quartz wafer 7 on which the resist 4a is applied under the same conditions as the wafer 4 is attached to the uppermost wafer chuck 3a.
With the surface to be adhered facing upward, it can be detachably mounted by a method such as vacuum suction.

The reduction lens unit 2 is composed of a combination of lens groups (not shown). The exposure light is emitted from a light source (not shown) arranged above the reticle stage unit 1 and transmitted through the reticle 1a to a desired transfer pattern. 5 is reduced to a desired magnification and projected on the resist 4a of the wafer 4 to be exposed.

In this case, in the wafer stage unit 3,
The light amount sensor 6 is built in the wafer chuck portion 3a on which the wafer 4 is placed, and the light amount of the exposure light 5 which is irradiated onto the wafer 4 through the reduction lens portion 2 and which passes through the wafer 4 is measured. Then, it can be output to an external control logic or the like (not shown).

In the case of this embodiment, the wafer chuck unit 3
A transparent quartz wafer 7 coated with a resist 4a under the same conditions as the wafer 4 is placed on a and irradiated with exposure light 5, and at this time, a change with time of the light amount detected by the light amount sensor 6 is measured. Thus, the operation of measuring the transmittance of the exposure light 5 in the resist 4a, that is, the absorption coefficient is performed.

An example of the operation of the exposure method and apparatus of this embodiment will be described below.

As illustrated in the flow chart of FIG. 3, first, the conditions for starting the work are set (step 1
0), the actual wafer 4 is set on the wafer chuck portion 3a, and the exposure operation is executed (step 20).

The condition setting for the start of step 10 is shown in FIG.
, A transparent quartz wafer 7 having a resist 4a applied under the same conditions as the wafer 4 is placed on the wafer chuck 3a, and the region immediately above the light amount sensor 6 is exposed. Irradiate with light 5 to expose (step 11),
After collecting the transmitted light amount data of the resist 4a (quartz wafer 7) at regular intervals (step 12), the acquired data is curve-approximated to store the data as an absorption coefficient characteristic and determine the optimum exposure amount (step). 1
3).

Then, it is determined whether or not there is a resist characteristic variation factor such as a lot change of the resist 4a deposited on the wafer 4 (step 30). Continue the exposure work.

On the other hand, when the resist characteristic variation factor occurs, the exposure condition changing process is performed (step 4).
0), return to the normal exposure operation of step 20.

The exposure condition changing process is, for example, as shown in FIG. 5, a transparent quartz wafer 7 deposited under the same conditions as the case where the resist 4a after the lot change is the wafer 4.
With the wafer mounted on the wafer chuck 3a, the region immediately above the light amount sensor 6 is exposed (step 41), and the transmitted light amount data of the resist 4a (quartz wafer 7) is sampled at regular intervals (step 42). ), The obtained data is approximated to a curve to calculate the absorption coefficient of the resist 4a (step 4).
3).

Then, the obtained absorption coefficient characteristic is compared with the data at the time of condition setting for the start of the previous step 10,
For example, the optimum exposure time (usually, the illuminance of the light source is constant, so the exposure time determines the exposure amount) is set so that the exposure amount is increased or decreased according to the variation amount of the absorption coefficient ( Step 45).

Based on the exposure time thus determined, the normal exposure operation of the wafer 4 in step 20 is started.

FIG. 2 shows the relationship between the absorption coefficient of the resist 4a and the exposure energy (exposure amount). When the resist 4a exceeds a certain exposure energy E1, the absorption coefficient becomes a constant value for the energy higher than that. However, if the energy is lower than E1, variations will occur from lot to lot.

In the area E of the exposure energy used in the current resist process, the exposure time cannot be increased to a certain extent or more in consideration of economical conditions such as throughput, and E <E1. This variation is reflected in the dimensional accuracy of the process.

Therefore, as described above, in the present embodiment, the change in the absorption coefficient of the resist 4a when the exposure energy of the same condition is applied is sampled as data, and the process condition is determined when the condition for starting the process is determined. By comparing with the absorption coefficient of the resist, the actual product wafer 4
The optimum exposure time at the time of start of construction is calculated and reflected in the actual exposure conditions on the wafer 4.

As described above, according to the exposure method and apparatus of this embodiment, the exposure time is changed so as to cancel the dimensional variation of the transfer pattern due to the variation of the absorption coefficient of the resist 4a deposited on the wafer 4. Highly accurate pattern transfer can be performed on the wafer 4 without being affected by variations in the absorption coefficient.

Further, since the absorption coefficient is measured by using the light quantity sensor 6 provided on the wafer chuck 3a of the wafer stage 3 of the exposure apparatus, for example, a so-called off-line inspection which uses a separate inspection-dedicated apparatus is performed. There is no fear of such a complicated operation or increase in the time required for the inspection, and the quartz wafer 7 on which the target resist 4a is deposited is mixed with the normal wafer 4 and allowed to flow in the exposure step, whereby the variation of the absorption coefficient in-line. It becomes possible to monitor and correct exposure conditions based on it, and to realize efficient operation of the exposure apparatus.

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the embodiments and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, the object to be exposed is not limited to the wafer but can be widely applied to those requiring precise pattern transfer by photolithography.

[0040]

The effects obtained by the typical ones of the inventions disclosed in the present application will be briefly described as follows.
It is as follows.

That is, according to the exposure method of the present invention, highly precise pattern transfer can be performed on an object to be exposed, without being affected by fluctuations in the absorption coefficient of the resist.
The effect is obtained. Further, there is an effect that the absorption coefficient of the resist in the exposure process can be accurately measured. Further, there is an effect that the optimum exposure amount of the exposure process can be calculated from the measured absorption coefficient.

Further, according to the exposure apparatus of the present invention, it is possible to obtain a highly accurate pattern transfer to the object to be exposed without being affected by the fluctuation of the absorption coefficient of the resist. Further, there is an effect that the absorption coefficient of the resist in the exposure process can be accurately measured. Further, there is an effect that the optimum exposure amount of the exposure process can be calculated from the measured absorption coefficient.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the configuration of an exposure apparatus that is an embodiment of the present invention.

FIG. 2 is a diagram showing an example of the operation.

FIG. 3 is a flow chart showing an example of the operation of the exposure method and apparatus which is an embodiment of the present invention.

FIG. 4 is a flow chart showing an example of the operation of the exposure method and apparatus which is an embodiment of the present invention.

FIG. 5 is a flow chart showing an example of the operation of the exposure method and apparatus which is an embodiment of the present invention.

[Explanation of symbols]

 1 reticle stage part 1a reticle (original plate) 2 reduction lens part (optical system) 3 wafer stage part 3a wafer chuck part (support base) 4 wafer (exposed object) 4a resist 5 exposure light 6 light intensity sensor 7 quartz wafer (exposed object) object)

Front Page Continuation (72) Keizo Kuroiwa 5-20-1 Kamimizuhoncho, Kodaira-shi, Tokyo Within the Semiconductor Business Division, Hitachi, Ltd. (72) Kohei Sekiguchi 5-20, Kamimizuhoncho, Kodaira-shi, Tokyo No. 1 Stock Company Hitachi Ltd. Semiconductor Division

Claims (5)

[Claims] 1. An exposure method comprising: monitoring a variation of an absorption coefficient of exposure light in a resist used in an exposure step, and setting or changing an exposure amount for an object to be exposed according to the variation of the absorption coefficient. . 2. The absorption coefficient is measured by using a transparent substrate coated with the resist under the same conditions as those of the object to be exposed and measuring a change in the exposure light transmitted through the transparent substrate. The exposure method according to claim 1, which is characterized in that: 3. An exposure apparatus comprising: a support table on which an object to be exposed is placed; and an optical system for transferring a pattern of an original plate onto the object to be exposed by using exposure light as a medium. An exposure apparatus having a built-in light amount sensor on a surface on which an exposed object is placed. 4. The absorption coefficient of the resist is obtained by measuring the light quantity of the exposure light transmitted through the transparent substrate coated with the resist under the same conditions as the object to be exposed by the light quantity sensor. The exposure apparatus according to claim 3. 5. The exposure apparatus according to claim 3, further comprising a control logic for calculating an optimum exposure amount when the object to be exposed is under construction, based on the amount of change in the absorption coefficient.