JPH0221131B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for controlling the exposure amount of an exposure device used to print a circuit pattern on a mask onto a semiconductor wafer in the manufacturing process of ICs, LSIs, etc. Regarding.

[Prior Art] Normally, a semiconductor exposure apparatus uses a light source even if the intensity of the light source decreases to about half of a predetermined value, so the conventional method has a problem of overexposure or underexposure.

Problems with such conventional devices will be explained in detail using illustrated examples.

FIG. 1 is a block diagram showing an example of a conventional exposure amount control device, in which 1 is a light source, 2 is a mask illuminated by the light source 1, and a circuit pattern is formed thereon.
A wafer 3 is placed near the mask 2, and the circuit pattern on the mask 2 is printed onto its upper surface by light from the light source 1. 4 is a shutter that blocks illumination from a light source; 5 is a light sensor that detects the intensity of light passing through the shutter 4; the light intensity detected by this light sensor 5 is converted into a voltage signal by an amplifier 6; be done. 7 is a V/F converter that converts a voltage signal into a frequency signal; 8 is a total counter that counts the number of pulses from the V/F converter 7; 9 is a value counted by the total counter 8 and an exposure amount setter 10; This is a comparison circuit that compares the set values of , and issues a match signal when these values match. Reference numeral 11 denotes a shutter open/close command device which generates a shutter open command signal in response to an exposure start command, activates the shutter drive circuit 12, starts the opening operation of the shutter 4, and instructs the total counter 8 to start counting. Further, a shutter close command signal is generated based on the coincidence signal from the comparison circuit 9, and the shutter drive circuit 12 is activated.
The closing operation of the shutter 4 is started.

[Problems to be Solved by the Invention] In this example, the exposure amount setting device 10 includes a shutter 4.
In order to correct the overexposure corresponding to the closing operation time, a value obtained by subtracting the value corresponding to the overexposure is stored. For this reason, when the intensity of the light source 1 decreases, an insufficient amount of exposure occurs. This will be explained in more detail.

Figures 2a and b show the shutter operation time charts when the intensity of the light source 1 is a predetermined value and when it is 1/2 of the predetermined value, where the high level is the shutter open state and the low level is the shutter operating time chart. Indicates closed state. As shown in FIG. 2a, when the intensity of the light source 1 is a predetermined value, the shutter 4 starts the opening operation at time t ₀ , the shutter 4 completes the opening operation at time t ₁ , and the shutter opening/closing command 11 starts at time t ₂ .
The shutter close command signal is output from. This is done when the comparator circuit 9 detects that the contents of the exposure amount setter 10 and the counter 8 match. The closing operation of the shutter 4 is completed during a certain period of time _t2 to _t3 . Normally, the opening operation time (t ₁ -t ₀ ) and the closing operation time (t ₃ -t ₂ ) of the shutter 4 are equal. The dash-dotted line shows the intensity change of the light source. For example, when the intensity of light source 1 is a predetermined value,
If the appropriate exposure amount to wafer 3 is "100",
As mentioned above, suppose that the value corresponding to the overexposure amount is, for example, "20", and the digital value corresponding to the value "80" obtained by subtracting it is stored in the exposure amount setter 10. The shutter 4 begins to open at time t ₀ and fully opens at t ₁ . During this time, the V/F converter 7 outputs pulses with a frequency proportional to the input voltage, and the counter 8 counts the pulses. Up to this point, the counter 8 has been set to count "20". During the period _t1 to _t2 , the intensity of the light source is constant, that is, the input voltage of the converter 7 is constant, so the counter 8 counts pulses of a constant frequency, and at time _t2, 20( _t0 to _t1 )+60( _t1 ~t ₂ ) = 80 (t ₂ ), which matches the value "80" stored in the setting device 10, so the comparison circuit 9 sends the match signal to the shutter ON/
Sends to OFF command 11, shutter drive circuit 1
2 is activated, and the shutter 4 starts its closing operation. After this, from t ₂ to _{t 3} , the exposure will be made by the value corresponding to the residual exposure amount "20", and the total exposure amount will be "100".
is achieved and perfectly matches the appropriate exposure amount. However, even if the intensity of the light source drops to 1/2 as shown in Fig. 2b, "80" remains stored in the setting device 10, and the counter 8 starts from time _t0 as before. The detection pulses are continued to be counted, and at time _t4 when the counter 8 counts "80", the comparator circuit 9 outputs a coincidence signal and the shutter 4 starts to close. Here, the shutter closing time t ₅ - t ₄ and the shutter opening time t ₁ - _{t 0} are constant, and the light intensity during this time is 1/2 of the previous value, that is, "10", and 10 (t ₀ - _{t 1} ) + 70 (t ₁ ~ t ₂ ) = 80 (t ₄ )
Between the next time t ₄ and _{t 5} , there is only "10", and the total exposure amount is 80 + 10 = 90, and the appropriate exposure amount "100" is:
There was a problem that there was a shortage of "10", that is, the time period t ₅ to _{t 6} .

Also, at this time, when determining the value ``20'' by subtracting ``20'' from the predetermined value of the light source, the calculation is complicated, and it must be recalculated and stored as the intensity of the light source decreases. It was extremely troublesome to have to do it again. Furthermore, the throughput of the exposure apparatus was inevitably reduced.

The present invention was made in view of the above circumstances, and its purpose is to use a shutter to control the exposure of a wafer through a mask with high precision even when the intensity of the light source decreases, and to reduce the amount of exposure. An object of the present invention is to provide an exposure amount control method that can always make the exposure amount match a set amount.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides that when exposing a wafer through a mask, the exposure amount is faster by a correction amount than when the exposure amount matches a preset setting amount. In the exposure amount control method for starting the closing operation of the shutter, a sensor is provided to detect light passing through the shutter, and a digital value corresponding to the output of the sensor is used from the start of the shutter opening operation to the shutter closing operation. The correction amount is determined based on the added digital value, which is added only for a predetermined time corresponding to the operation delay.

[Embodiments] The present invention will be described in detail below based on the embodiments shown in FIG. The explanation will be omitted. In the first embodiment shown in FIG. 3, 13 is a light amount correction timer;
is a light amount correction counter, 15 is a two-input AND gate, and the correction timer 13 starts operating when the V/F converter starts operating, and outputs an output for a time period t ₂ to t ₃ corresponding to the closing time of the shutter 4. Occur. The correction timer 13 is connected to one input terminal of the AND gate 15. Further, the output of the V/F converter 7 is applied to the other input terminal of the AND gate 15. Therefore, the correction counter 14 counts the number of pulses corresponding to the closing time _t2 to _t3 of the shutter 4. 16 is an adder that adds the count values of the total counter 8 and the correction counter 14;
The added value of the adder 16 and the value set in the exposure amount setter 10 are compared by the comparator circuit 9.
Note that in this embodiment, the setting value of the exposure amount setting device 10 is different from the example shown in FIG.
is set.

When the light source has _a predetermined intensity as shown in _FIG .
is counted and applied to adder 16. Therefore, when the value counted by the counter 8 from the shutter operation start time _t0 reaches "80", the output of the adder 16 becomes "100", and the value set in the setting device 10 is "100".
, and this time becomes t ₂ . This time _t2 is a time when the actual exposure amount is "80" and is "20" less than the set amount "100". The shutter 4 starts the closing operation from this time _t2 , and stops the closing operation at _t3 . this
The light amount during the period t ₂ to _{t 3} is 20, the same as during the shutter open time, and 80 (t ₀ to _{t 2} ) + 20 (t ₂ to t ₃ ) = 100, and the total exposure amount is the set appropriate exposure amount. Match.

Further, when the predetermined intensity of the light source becomes 1/2 as shown in FIG. 4b, the correction counter 14 counts "10" and applies it to the adder 16 as described above. When counter 8 counts "90", 10+90 as in the previous example
= 100, the comparator circuit 9 sends out a match signal,
As in the previous example, the remaining exposure amount "10" is exposed during the shutter closing time _t5 to _t6 , and the process ends.

FIG. 5 shows a second embodiment of the invention.

Similar to the embodiment shown in FIG. 3, the correction timer 13 outputs an output to the AND gate 15 for a period corresponding to the closing time of the shutter 4, which actually corresponds to the opening time, from the start of operation of the V/F converter 7. During this time, the AND gate 15 outputs a pulse signal corresponding to the intensity of the light from the light source 1 that is incident on the optical sensor 5. The number of pulse signals is counted by the correction counter 14, and this count value is input to the exposure amount setting device 10. A value corresponding to the appropriate exposure amount, for example 100, is set in the exposure amount setter 10, but this set number is equal to the count value of the correction counter 14, for example "10".
will be subtracted. Therefore, in the comparator circuit 9,
The subtracted set value "90" and the count value "90" of the total counter 8 are compared. The following is the same as the first embodiment shown in FIG. 3, so the explanation will be omitted.

Next, a third embodiment of the present invention using a microcomputer will be described with reference to FIG. The difference from the first embodiment shown in FIG. Random as
The access memory RAM1 is used, and the oscillator OSC and RAM2 are used as the correction timer 13. In order to have the same functions as the embodiment shown in FIG. 3, the main routine shown in FIG. 7a and the interrupt routine shown in FIG. 7b are provided. Exposure control usually operates on the main side, and when an interrupt occurs, the main routine is temporarily suspended, the interrupt routine is jumped to, and the interrupt processing is determined and processed. When this is completed, the exposure amount control is completed while repeating the operation of returning to the main routine again. In FIG. 6, the output of the V/F converter and the output of OSC13 are used for interrupts.

Next, FIGS. 7a and 7b will be explained. When entering the main routine, first clear the RAM1 that counts the output pulses of the V/F converter 7 (step 1-1), then open the shutter 4 (step 1-2), and the V/F converter 7 will operate. (Step 1-3). V/F converter 7
The operation is detected by interrupt processing (steps 2-1 and 2) by the output of the V/F converter 7, and RAM1=
This is done by making it no longer 0. When the V/F converter 7 starts operating, a value corresponding to the closing time of the shutter 4 is set in RAM2 (step 1-4).
Create a loop until RAM2=0 (steps 1-5). RAM2 is incremented by the interrupt processing by the output pulse of OSC13 (step 2-
3, 4, 5). “0” after RAM2 is set
Until then, the number of output pulses of the V/F converter 7 according to the exposure amount is also controlled by interrupt processing.
It is counted in RAM1. When RAM2 is detected as ``0'', the value of RAM1 is doubled (steps (1-6)). This function is equivalent to adding the value of the correction counter 14 and the value of the total counter 8.

After that, in the interrupt routine, RAM2 is set to V/F.
It is incremented according to the output of converter 7. In the main routine, input the exposure setting value,
When compared with RAM1, if the values are the same, a match signal for closing shutter 4 is output to shutter drive circuit 12 (steps 1-7, 8, and 9). The following operations are similar to those of the previous embodiment, so the explanation will be omitted.

[Effects of the Invention] As explained above, according to the present invention, it is possible to always accurately determine the amount of correction commensurate with the shutter operation delay regardless of changes in the light source intensity, etc., so that the wafer can be exposed through the mask. In this case, in the exposure amount control method, the shutter close operation is started earlier by the correction amount than when the exposure amount matches a preset setting amount, so that the exposure amount can always be controlled with high precision.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an example of a conventional exposure amount control device, FIGS. 2a and 2b are diagrams showing a shutter operation time chart of the example in FIG. 1, and FIG. 4a and 4b are diagrams showing a time chart of shutter operation in the embodiment of FIG. 3; FIG. 5 is a block diagram showing a second embodiment of the present invention; FIG. 6 7 is a block diagram showing a third embodiment of the present invention, FIGS. 7a and 7b show an operation routine of the embodiment of FIG. 6, FIG. 7a is a diagram showing a main routine, and FIG. 7b is a diagram showing a main routine. FIG. 3 is a diagram showing an interrupt routine. In the figure, 1 is a light source, 2 is a mask, 3 is a wafer, and 4
is a shutter, 5 is a light sensor, 6 is an amplifier, 7 is a V/F converter, 8 is a total counter, 9 is a comparison circuit, 10 is an exposure amount setting device, 11 is a shutter opening/closing command device, 12 is a shutter drive circuit, 13 14 is a correction timer, 14 is a correction counter, and 15 is an AND gate.

Claims (1)

[Claims] 1. When exposing a wafer through a mask, in an exposure amount control method in which the shutter starts closing operation by a correction amount earlier than when the exposure amount matches a preset setting amount, the light passing through the shutter is A sensor for detecting the shutter is provided, and a digital value corresponding to the output of the sensor is added for a predetermined period of time commensurate with the delay in closing the shutter from the start of the opening operation of the shutter, and based on this added digital value, the An exposure amount control method, characterized in that a correction amount is determined.