JPS6214825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for exposing a pattern on a wafer or a photomask, and particularly to a control apparatus thereof.

In recent years, in semiconductor element, especially IC manufacturing,
There is a demand for finer circuit patterns, and one
Highly accurate exposure control has also been desired for devices that print patterns having line widths of μm or less, so-called exposure devices.

Generally, it is desirable that an exposure device that exposes a circuit pattern image onto a wafer or a photomask always applies a constant amount of exposure to a photosensitive material (photoresist) coated on the wafer. An outline of such an exposure apparatus is shown in FIG.

In FIG. 1, light from a light source for exposure, such as a mercury lamp 1, is focused by a condenser lens 2, and then passes through a condenser lens 5 and a projection lens 8 via a rotary plate 3, which serves as a shutter. , wafer 9
(A photomask may also be used.) (The same applies to exposure apparatuses of other types.) The rotary plate 3 is divided into four parts, for example, and has light-shielding parts and transparent parts alternately provided, and is rotated by a rotational drive mechanism, for example, a pulse motor 4.
Works as a rotary shutter. A glass substrate 7 (reticle or photomask) having a circuit pattern is placed between the condenser lens 5 and the projection lens 8 , and the pattern of the glass substrate 7 is imaged onto the wafer 9 . The photodetector 6 is a photoelectric conversion element that measures the light intensity of a light source, measures the light that has passed through the shutter, and its output is used for exposure control. In such devices, the opening and closing time of the shutter is mechanically long, ranging from several m sec. to several m sec.
It extends to 10m sec. Further, FIG. 2 shows changes in light intensity (value detected by the detector 6 or value measured on the wafer 9) accompanying the exposure operation. In FIG. 2, the horizontal axis represents exposure time and the vertical axis represents light intensity, and trapezoidal broken lines A and B represent differences due to deterioration of the light source lamp. If the lamp is new and the light intensity is high, the line will look like broken line A, and if the lamp has deteriorated and the light intensity is low, the line will look like broken line B. Note that the light intensities at the top of the trapezoid, that is, when the shutter is fully open, are L _N and L _O . Thus, the trapezoidal light intensity characteristic is based on the opening/closing operation time of the shutter.
This occurs due to the time it takes for the rotary plate 3 to rotate 1/4 as shown in FIG. Rotating plate 3
The time it takes for the rotary plate 3 to rotate 1/4 of a turn and completely transmit light from the state where the light shielding part blocks the light (shutter opening time) is expressed as the time ta-to in Figure 2. be. Note that the time when the rotary plate 3 starts rotating is defined as to. Then, after the time ta-to has elapsed, the light completely passes through the rotary plate 3 (hereinafter referred to as fully opening the shutter), so that the light intensity becomes stable at L _N or L _O . Then, after a predetermined exposure time, that is, from time tb or time td, the rotary plate 3 further rotates by 1/4, and the light is blocked by the light blocking section. The time when the light is completely blocked is the time
tc or te. Furthermore, due to the structure of the shutter, the opening operation time and the closing operation time are almost equal, so
Time tc-tb and time te-td are both equal and time
It is also almost equal to ta-to.

As shown in this light intensity characteristic, in such a device, the exposure time is usually changed depending on the brightness of the lamp in order to keep the exposure amount constant. Therefore,
Conventional exposure control will be explained with reference to FIG. In FIG. 3, the photoelectric output of the photoelectric detector 6 is amplified by an amplifier 11 and then input to an integrator comprising a resistor 12, a capacitor 14, and an amplifier 13. The output of the integrator is a value proportional to the exposure amount, a so-called light amount integral value. The output of this integrator is
The comparator 15 compares it with a predetermined target value (reference voltage) E _S .

On the other hand, the flip-flop circuit 16 is set at the start of the exposure operation, and the flip-flop circuit 16 is set at the start of the exposure operation.
7, the motor etc. are driven to open the shutter. After the shutter is opened, when the integrated value of the amount of light reaches the reference voltage E _S as described above, the output of the comparator 15 is inverted and the flip-flop circuit 16 is reset. By this reset, the drive circuit 17
then rotate the motor etc. further and close the shutter. In this way, the shutter is controlled so that the integrated value of the amount of light remains constant even if the brightness of the lamp changes. Here, the exposure amount at that time is shown in the graph of FIG. In the graph of FIG. 4, the horizontal axis is the same time axis as in FIG. 2, and the vertical axis is the exposure amount, that is, the integrated light amount value. As shown in FIG. 2, the period from exposure start time to to time ta is the shutter opening operation time, and the exposure amount gradually increases. time
The period from ta to time tb or time td is the shutter fully open period. As shown in FIG. 2, the exposure amounts A and B indicate when the light intensity of the light source is high and when it is low. Then, the exposure amount A or B is the target value E
When _S is reached, the shutter begins to close. However, the exposure will also occur during the time tc-tb or te-td until the shutter is completely closed, and as a result, the total exposure amount will be E _O or E _O ',
Exceeds the predetermined target value E _S (E _O -E _S or E
_O ′−E _S ).

If the light intensity of the light source is always constant, the excess amount can be predicted and the total exposure amount can be determined, but in reality, the brightness of the light source changes significantly as the lamp deteriorates.
Therefore, as shown in FIG. 4, even though the time tc-tb and the time te-td are the same, the excess amount changes.
This excess change (E _o -E _o ') can be ignored if the light intensity of the light source is small and the exposure time is sufficiently long. However, if the light intensity of the light source increases and the exposure amount during the shutter closing time becomes a larger proportion of the total exposure amount, the total exposure amount due to the excess change (E _O -E _O ') The fluctuation of is an important issue. Generally, when controlling the exposure amount, it is necessary that the total exposure amount fluctuates by a few percent or less, but in the case described above, with conventional equipment, there is no consideration given to excess amounts, so it is difficult to control the amount of exposure over a long period of time. However, it had the disadvantage that a stable exposure amount could not be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the conventional drawbacks and provide an exposure apparatus that controls the total exposure amount to be constant regardless of the light intensity of the light source.

Examples of the present invention will be described below. Figure 5 shows
This is the first embodiment of the present invention, and circuit blocks, elements, etc. that have the same functions as those shown in FIG. 3 are given the same numbers.

The photoelectric signal from the photodetector 6 is amplified by an amplifier 11 and then sent to a voltage frequency converter (hereinafter referred to as VFC).
30, it is converted into a pulse signal with a frequency proportional to the light intensity. If the number of pulses of this pulse signal is counted, the counted value will be a value proportional to the exposure amount. The counter 31 (hereinafter referred to as UC31) outputs an added count value SU of the number of pulses of the pulse signal. The amplifier 11, VFC 30, and UC 31 constitute the photometric circuit of the present invention.

On the other hand, the photoelectric signal from the amplifier 11 is analog
A digital signal corresponding to the photometered light intensity input to the digital converter (hereinafter referred to as ADC) 37
Output SL. Arithmetic circuit 38 (hereinafter referred to as CUL38)
) is based on its digital signal SL,
Predetermined arithmetic processing, in fact, multiplication of a value corresponding to the shutter closing operation time by the value of signal SL, and storage operation are performed, and the digital signal of the calculation result is generated.
SX is output to the comparator 39. With this ADC37
The CUL 38 constitutes the detection means of the present invention. The comparator 39 can set the target value E _S (digital signal) from the outside, and can also set the CUL3 from the target value E _S
The value obtained by subtracting the digital signal SX of 8 is held (stored) as a reference value. Furthermore, the comparator 39 is UC31
The count value SU and the reference value are compared, and when the count value SU and the reference value match, a match signal (shutter close signal) is output to the flip-flop circuit 16. This starts the shutter closing operation. In addition, in this embodiment, CUL38 is functionally
The CUL 38 and the comparator 39 will be explained separately, but in reality, the functions of the CUL 38 and the comparator 39 are realized by a program of a digital computer such as a microcomputer. Although not shown, a position detector such as a disk sensor is provided to detect the rotational position of the shutter (rotary plate 3 shown in FIG. at the time of completion)
Inform CUL38.

Next, the operation of this embodiment will be explained using the flowchart shown in FIG. UC before starting the exposure operation.
31 is cleared, and a target value E _S proportional to the target exposure amount is set in the comparator 39. [Step 100] At the same time as the shutter opening operation starts, the UC
31 counts the number of pulses output by the VFC 30. On the other hand, the ADC 37 outputs a digital signal S _L proportional to the light intensity. When the shutter is fully opened, that is, when the opening operation is completed [Step 10
1], the signal S _L (light intensity) at that time is multiplied by a digital signal proportional to the closing operation time (time tc - tb [or te - td] in Fig. 2) measured in advance. Then, a signal SX corresponding to the amount of light exposed during the closing operation period (E _O - E _S [or E _O ' - E _S ] in Fig. 4) is output immediately after time ta (when fully open). The comparator 39 inputs this signal SX, subtracts the value of the signal SX from the set target value, and holds it as a reference value. [Step 102] After that, exposure is performed with the shutter fully open, and the UC31
continues counting. Then, when the value of the count signal SU of UC31 reaches the reference value, [Step 10
3] The comparator 39 outputs a coincidence signal, and the shutter closing operation is started as described above. [Step 104] In this embodiment, the exposure amount only during the shutter closing operation time is determined based on the shutter closing operation time (tc-tb or te-td) measured in advance and the light intensity when the shutter is fully open. Signal according to (excess exposure amount)
I started looking for SX digitally. However, exposure control similar to this is also possible in an analog manner. To do this, for example, the circuit shown in FIG. 3 must be equipped with an arithmetic circuit that multiplies the voltage corresponding to the shutter closing operation time by the output voltage of the amplifier 11 when the shutter is fully open, and holds the multiplied value. , and a differential amplifier that applies a reference value obtained by subtracting the multiplied value from the target value E _S to the comparator 15.

Next, a second embodiment of the present invention will be described based on the flowchart of FIG. Exposure control in this embodiment is assumed to be realized by one digital calculator including the functions of the CUL 38 and comparator 39 shown in FIG.

Clearing UC31 prior to the shutter opening operation in step 110 is exactly the same as the operation shown in FIG. And step 111
If it is determined in step 112 that the value of the count signal SU matches the reference value, a match signal is output in step 112 to start the shutter closing operation, and the exposure up to the start of the shutter closing operation is amount
Read E ₁ (count signal SU). When the shutter is completely closed, the exposure amount E ₂ (count signal SU) up to the time when the shutter closing operation is completed is read in step 113. And next step 11
In step 4, the difference E' between the exposure amounts E ₂ and E ₁ (the exposure amount only during the closing operation period) is calculated and stored. When it is determined in step 115 that the next exposure operation is to be performed, the process proceeds to step 116, where the stored difference E' is subtracted from the set target value E _S to obtain a new reference value. (Update of reference value) Steps 110 to 115 are then repeated in the same manner, but the reference value compared with the count signal SU in step 111 is the reference value determined in step 116.

As described above, according to this embodiment, even if a gradual change such as a drift occurs in the shutter closing operation time, the exposure amount (excess exposure amount) measured only during the shutter closing operation period is always measured during the previous exposure operation. ),
Since the exposure control in the subsequent exposure operation is corrected, accuracy is further improved.

Furthermore, when the closing operation time and the opening operation time of the shutter are almost equal, the shutter opening operation period (ta-to in Fig. 2) is the same as that of the preceding exposure operation.
It is also possible to memorize the exposure amount during a subsequent exposure operation and update the reference value with the stored exposure amount during a subsequent exposure operation.

Next, a third embodiment of the present invention will be described based on the flowchart of FIG. In step 120, for example, in order to obtain an appropriate exposure amount for a wafer other than the wafer that should be originally exposed, a trial printing is performed, and the excess exposure amount (exposure amount during the shutter closing operation period) at that time is calculated. ' is determined in the same manner as steps 112, 113, and 114 in FIG. 7, for example. Next, in step 121, a reference value is obtained by subtracting the excess exposure amount E' from the target value E _S , and this reference value is set (stored) for subsequent exposure operations. The original exposure operation starts from step 122, and after opening the shutter, step 1 starts.
When it is determined in step 23 that the reference value and the value of the count signal SU match, a match signal is output in the next step 124, and the shutter closing operation is started.
Then, when it is determined in step 125 that the next exposure operation is to be performed, the same operation is repeated again from step 122.

In the case of this embodiment as well, if the closing operation time and the opening operation time of the shutter are equal, the exposure amount during the shutter opening operation period during trial printing can be measured as the excess exposure amount E'.

In each of the embodiments of the present invention, the shutter is a rotary shutter rotated by a motor, but the shutter may be moved reciprocally by a solenoid, and furthermore, the shutter itself may be moved other than rotatably.
A sliding type shutter that moves in a straight line may also be used.

As explained above, according to the present invention, a value corresponding to the overexposure amount that is exposed only during the shutter closing operation period is always introduced as a correction value for the target value corresponding to the appropriate exposure amount. The target total exposure amount, that is, the appropriate exposure amount can always be obtained, and the influence of lamp deterioration is eliminated, making it possible to perform extremely high-precision exposure control.

In particular, even when the opening operation time and the closing operation time of the shutter are different, accurate exposure control can be performed.

Additionally, if the overexposure amount is measured during the preceding exposure operation and then corrected using the measured overexposure amount during the subsequent exposure operation, a gradual drift will occur in the shutter closing operation time. Highly accurate exposure control can be achieved without being affected by this.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a wafer or photomask exposure apparatus, Fig. 2 is a diagram showing the characteristics of exposure intensity by a light source, Fig. 3 is a circuit block diagram for conventional exposure control, and Fig. 4 is a diagram of a conventional exposure control system. FIG. 5 is a circuit block diagram showing the first embodiment of the present invention, FIG. 6 is a flowchart explaining the operation of the first embodiment of the present invention, and FIG. 7 is a diagram showing the operation of the first embodiment of the present invention. FIG. 8 is a flowchart diagram explaining the operation according to the second embodiment of the invention, and FIG. 8 is a flowchart diagram explaining the operation according to the third embodiment of the invention. Explanation of symbols of main parts, 3... Shutter, 1
1, 13, 30, 31...photometric circuit, 15, 1
6, 17, 39... control means, 37, 38... detection means.

Claims (1)

[Scope of Claims] 1. A shutter that switches between a state in which the wafer or photomask is irradiated with light from a light source and a state in which it is not irradiated; and an amount of exposure to the wafer or photomask from the start of the opening operation of the shutter; a photometric circuit that outputs a photometric value according to; a control means that starts a closing operation of the shutter when the photometric value has a predetermined relationship with a target value that corresponds to a desired amount of exposure to the wafer or photomask; The exposure apparatus has a detection means for measuring an excess exposure amount from the start of the closing operation of the shutter to the completion of the closing operation, and detecting a correction value corresponding to the excess exposure amount. . A wafer or photomask exposure apparatus, wherein the control means operates the shutter so as to correct the excess exposure amount by introducing the correction value. 2. The detection means includes a circuit for detecting the intensity of light passing through the shutter after the opening operation of the shutter is completed, and based on the value of the light intensity and the value of the closing operation time of the shutter, 2. The apparatus according to claim 1, further comprising an arithmetic circuit that predicts and calculates the excess exposure amount. 3. A shutter that switches the state of irradiating the wafer or photomask with light from the light source and the state of not irradiating it; from the start of the opening operation of the shutter, a photometric value corresponding to the amount of exposure to the wafer or photomask is calculated. an exposure apparatus comprising: a photometric circuit for output; and a control means for starting a closing operation of the shutter when the photometric value has a predetermined relationship with a target value corresponding to a desired amount of exposure to the wafer or photomask; In the preceding exposure operation,
The control means includes a detection means for detecting and storing a correction value corresponding to the excess exposure amount from the start of the shutter closing operation to the completion of the shutter closing operation, and the control means detects and stores a correction value corresponding to the excess exposure amount from the start of the shutter closing operation to the completion of the shutter closing operation. A wafer or photomask exposure apparatus, characterized in that the shutter is operated so as to correct the excess exposure amount by introducing a correction value determined by the shutter.