JPS63108719A - Exposure apparatus - Google Patents

Abstract

PURPOSE:To perform highly precise positioning when a wafer disposed on a wafer table movable in two dimensions is exposed with another pattern overlaid on the pattern of the wafer, by utilizing a pulsed light source capable of emitting light for an extremely short time and triggering it in synchronization with a positional signal or an alignment signal of one axis of the two dimensions. CONSTITUTION:When an excimer laser having such a short duration of light emission as 10 ns is used as a pulse light source, it causes no deterioration in resolving power even if a stage is moved during an exposure process. Taking this advantage, the excimer laser is strongly servo controlled in the direction of the axis (x) by a control system 10, whereby the light is quickly converged and does not deviate from the servo range S0. It is servo controlled rather weakly in the direction of the axis (y) so that it is converged but fluctuates. If the laser 14 is triggered by a trigger unit 13 at a time t1-t4 in which the stage passes the target value (position 0), exposure can be performed with a desirable positional precision. More particularly, a wide servo range S1 is set with respect to the axis (y) and pulse exposure is started from the point of time at which the stage enters into the servo range S1 and passes the the target value for the first time. Accordingly, exposure can be carried out without deterioration of resolving power due to vibration during exposure or without servo deviation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor exposure apparatus, and particularly to an exposure method using a novel combination of light source control and alignment.

(Prior Art) In a conventional semiconductor exposure apparatus (not shown), a length measuring device such as a laser interferometer is used to measure a reticle (mask) held on a two-dimensionally movable stage each equipped with a servo mechanism. After detecting the position of the wafer (including The method used was to carry out exposure after the light was no longer available. In this case, a mercury (Hg) lamp is generally used as the light source of the semiconductor exposure apparatus.

[Problem that the invention seeks to solve]

As mentioned above, in conventional exposure equipment that uses a mercury lamp as a light source, since the mercury lamp is a continuous light source,
During the exposure time, it is necessary to keep servoing the wafer stage on both the x and y axes. Further, it was necessary to open the shutter for exposure after confirming that the servo was applied to both the y-axis and the y-axis. For this reason, the time it takes for the stage to settle down inevitably causes a drop in throughput.

Moreover, even if the wafer stage was servo-locked as described above, strictly speaking, it was shaking in both the X and Y axes in the servo area.

For example, an explanatory diagram of the exposure method in this case is shown in FIG.

In the figure, FIG. 3(a) is a graph representing the servo state in the X-axis direction, FIG. 3(b) is a graph representing the servo state in the y-axis direction, and FIG. 3(C) is the timing of exposure by the shutter. However, since both (a), lb), and (C) are related to each other, they are shown in a correlated format as a group in Figure 3. In the figures, the horizontal axis is time, and the vertical axis is (a) the position distance in the X-axis direction, (b) the position distance in the ) indicates the shutter timing status.

Note that To is the servo confirmation time, and T is the shutter open time. In other words, check the servo T. After going for an hour,
Exposure is performed by opening the shutter for 71 hours. Therefore, it takes too much time to servo both the
) and (b), it could not be completely removed, and problems remained in meeting the goal of miniaturization of lithography technology.

In addition to the above, if the servo status is lost during exposure,
There is a risk that the image will be blurred, and due to the mechanical
The servo system for aligning both axes was also complicated.

To summarize the above-mentioned matters, problems with conventional exposure apparatuses include loss of time until the stage stops and a decrease in resolution due to poor stage stop stability caused by servo fluctuations of the stage. Note that it has been reported at academic conferences that resolution is reduced due to vibration during exposure.

The present invention has been made to solve the above problems, uses a pulsed light source as a light source, and aims to provide an exposure apparatus and an exposure method suitable for the pulsed light source.

(Means for Solving the Problems) The exposure apparatus according to the present invention is an exposure apparatus that uses an extremely short-time pulsed light source, such as an excimer laser, and is placed on a two-dimensionally movable wafer stage. When exposing another pattern over a pre-formed wafer pattern, the technical point is to make the light source emit light in synchronization with the two-dimensional at least one-axis position signal or alignment signal. It is something to do.

[Effect]

In this invention, first, an excimer laser, for example, is used as the pulsed light source, so the light emission time is extremely short and is not affected by image blurring at all. Further, by utilizing this, in the stage control method, the servo of the x-y stage is strongly applied on one side and the other side is applied weakly, so that the positioning accuracy and time for one side of the stage are improved. Since the light emission is triggered by a position signal regarding the other axis, highly accurate positioning (superposition) in both the x and y directions is possible. Hereinafter, the present invention will be explained by examples.

[Embodiments of the invention]

FIG. 1 shows a step-and-step process showing an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a repeat-type projection exposure apparatus. An excimer laser is used as a pulsed light source. A feature of this light source is that it can provide far ultraviolet light (U) with a short wavelength using pulsed light (emission time is approximately IC (nsec)).

In FIG. 1, the main optical system projects an image of a pattern on a reticle 2 onto a wafer 3 using a projection lens 1. Laser light emitted from an excimer laser 14 serving as an illumination light source enters a lens system composed of an expander 15 via two mirrors. In addition to the condensing lens 15a, the expander 15 incorporates an optical system (such as an optical integrator or a speckle reduction element) that makes the light intensity distribution uniform, and the reticle 2 is irradiated with a condensed laser beam. The above excimer laser 14. expander 15
etc. form the illumination means. Also, wafer 3
is mounted and fixed on a stage 4 that moves in the XX direction. An interferometer composed of a movable mirror 5 attached to the stage 4, a fixed mirror 5a attached to the projection lens 1, a mirror and a half mirror 6, and a detector 7 forms a position detection means. This interferometer can monitor the stage position with an accuracy of about 0.01 μm.

The stage 4 is moved in the X direction by a servo motor 8 and a screw 9, forming a moving means using the servo motor 8. Note that illustration of an X-direction moving mechanism for moving in a direction perpendicular to the X-direction is omitted. , 10 is a control system for this moving means, which includes a digital counter for measuring the position of the interferometer and a power supply control system for the motor 8.

Reference numeral 12 denotes an alignment system, which detects alignment marks previously formed on the reticle 2 and wafer 3 and calculates the amount of positional deviation thereof, and includes an optical system for detecting alignment marks and an electrical system for calculating positional deviation. etc. are included. Reference numeral 11 denotes a system control system (CPU) which gives various commands to each unit system and checks its operation. In addition,
Reference numeral 13 is a trigger unit that causes the excimer laser 14 to emit light according to CPU and alignment system commands.

In an exposure apparatus having the above mechanism and functions, if an excimer laser is used as a pulsed light source instead of a continuous light source such as the conventional mercury lamp, the light emission time is as short as about 10 ns. , even if the stage 4 moves during exposure, there is no reduction in resolution due to this movement.

Therefore, by applying the above advantages, we changed the stage control method, for example, applying a strong servo to the I will apply it loosely.

The situation is shown in the explanatory diagram of FIG. In FIGS. 2(a) and (b), the horizontal axis shows the positioning time by the servo, and the horizontal axis in FIG. 2(C) shows the timing of the trigger 13,
This time corresponds to the time shown in FIGS. 2(a) and 2(b).

In addition, the vertical axis in FIG. 2(a) indicates the deviation distance in the X-axis direction,
So shown in the figure is the servo range, and the 0 position is the reference value (exposure value l) of the position to be detected. The vertical axis in FIG. 2(b) indicates the deviation distance in the X-axis direction, and the vertical axis in FIG. 2(C) indicates the amount corresponding to the intensity of the pulsed light of the excimer laser.

As shown in Figure 2, if the servo is applied strongly in the X-axis direction as shown in Figure 2 (a),
It converges rapidly and does not deviate from the servo range S0. On the other hand, the servo is weak in the X-axis direction, so the
) Even if the state is almost converged as shown in Figure 2 (C), there will be some fluctuation, but the time it takes to cross the target value (0 position), for example 1. ．． 1. ．． By triggering the excimer laser 13 at the time position of 1° and t4, exposure with good positional accuracy can be performed. Specifically, the servo range S1 is widened with respect to the y-axis, and pulse exposure is started when the stage enters the range S1 and crosses the target value for the first time. In this way, exposure can be performed without any problems in resolution due to vibrations during exposure or any risk of servo misalignment. In particular, in the case of the step-and-repeat method, one row of shots on the wafer is exposed in the X direction, and then the stage is moved in the X direction by one row. It is best to keep the direction servo weak (when stepping in the X direction).

In the above embodiment, the excimer laser is triggered in synchronization with the position on the loosening side, such as the y-axis, that is, the case where the trigger is applied at a temporal position where the interferometer value of y@ crosses the target value. It goes without saying that the same effect can be obtained by applying a trigger in synchronization with an alignment matching signal of an alignment system.

In this case, for example, the servo lock is strongly applied to the y-axis of the wafer stage 4, and the servo-lock is weakened to the X-axis, and the marks on the reticle 2 and the marks on the wafer 3 are The excimer laser is triggered at the moment when both marks are in a predetermined positional relationship while monitoring the positional deviation of the marks.

In addition, the excimer stepper currently being considered has 1
It is expected that more than a few pulses will be required for exposing a shot (one projected area on a wafer). The number of pulses has a correlation with the power of one pulse of the excimer laser. As shown in FIG. 2(b), the positional deviation of the stage 4 in the direction in which the servo lock is weakly applied generally converges to the target value with damped vibration.

Therefore, if the excimer laser is triggered at the moment when the position detected by the interferometer (or alignment system) of stage 4 matches the target value, the overall exposure time may become longer depending on the characteristics of the damped vibration. be. Therefore, in order to solve this problem, a two-stage exposure method is adopted.

This method will be explained based on FIG. 4. FIG. 4 corresponds to FIGS. 2(b) and (C), and the horizontal axis represents time, and the vertical axis in FIG. 4(a) represents the amount of positional deviation of the stage 4 in the y-axis direction. The vertical axis in FIG. 4(b) represents the light intensity (level) of the excimer laser pulse. As in the case of FIG. 2, the servo lock area Sl is determined, and the excimer laser is triggered at times t+, t2+ ts, and t4. At this time, an optical attenuator (not shown) or the like is used to set the energy per pulse of the excimer laser that irradiates the reticle to approximately the maximum. Then, after a certain period of time tc has elapsed from time t, the servo lock area for the stage drive motor in the y-axis direction is narrowed from Sl to 32. In other words, tighten the servo.

This area S2 is determined by the line width and overlay accuracy of the pattern to be exposed. For example, when exposing a pattern with a width of 0.8 μm, if the overlay accuracy is about 1/10 of the line width, the area S2 is 0.08 μm, that is, ±0.04 μm with respect to the target value. If the resolution of the interferometer is 0.01 μm, the change in the count value of the digital counter will be within ±4 counts. Therefore, after switching to area S2, while the amount of change with respect to the target value of the digital counter is within ±4 counts, at time t in FIG.
, ~t6, and t7~11%, the excimer laser pulse emission is performed continuously at a high repetition frequency. Between time 6 and t7, the pulse emission is interrupted because the count has changed by ±4 or more. And in this example,
The level of the pulsed light was made to gradually decrease from time t to time t6. This means that since the light intensity of each pulse of the excimer laser is uneven, a corrective exposure is added when the exposure is nearing its end in order to obtain an appropriate amount of exposure on the wafer. Of course, at time t, ~t.

Excimer laser pulses may be applied at maximum power between Incidentally, time t9 in FIG. 4 is the point in time when stage 4 steps for the next shot. Furthermore, the level adjustment for each pulse of the excimer laser can be performed using the laser light source itself.

Further, the present invention can be similarly implemented in an apparatus that performs exposure using pulsed energy. For example, plasma
An X-ray exposure apparatus that uses pulsed soft X-rays such as a radiation source can also be used in the same manner. In addition, in Fig. 1, reticle 2
Even in a device that monitors the position of a stage (not shown) with an interferometer 16 and moves the reticle 2 slightly during fine alignment between the wafer 3 and the reticle 2, the position of the stage (not shown) is monitored by the interferometer 16.
The excimer laser can be triggered based on position information from one axis of the .

〔Effect of the invention〕

As described above, according to the present invention, the x-y
By applying the servo on one side of the axis servo motor strongly and the other side weakly, the accuracy and time of positioning on one side of the stage are improved. Furthermore, since the trigger is activated by the other position signal, it can be expected that accuracy close to the minimum resolution of the interferometer can be obtained even in overlapping multiple exposures.

In addition, due to the pulse nature of pulsed light such as excimer laser,
It is completely unaffected by image blur. Furthermore, by adopting an alignment method that allows alignment signals to be obtained even during exposure, it is possible to prevent deterioration in resolution not only from vibrations from outside the exposure apparatus but also from internal vibrations.

Furthermore, mechanically, since this system uses a single-axis servo, the electrical and control systems can be simplified accordingly.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the entire exposure apparatus showing an embodiment of the present invention, FIG. 2 is an explanatory diagram of the position of the stage and the timing of triggering the excimer laser in the exposure method of the present invention, and FIG. 3 is a conventional diagram. FIG. 4 is an explanatory diagram of the exposure timing of an exposure apparatus using a mercury lamp as a light source, and FIG. 4 is an explanatory diagram of the stage position and the trigger timing of the excimer laser. In the figure, 1 is a projection lens, 2 is a reticle, 3 is a wafer, 4 is an x-y stage for the wafer, 11 is a system control system, 12 is an alignment system, 13 is an excimer laser trigger unit, 14 is an excimer laser, and 16 is a This is a reticle interferometer and reticle control system.

Claims (4)

[Claims] (1) A pulse generation type energy irradiation means, and a mask is irradiated with the pulse energy obtained by the energy irradiation means, and a two-dimensional mask pattern formed on the mask is
An exposure apparatus that positions and exposes at a predetermined position on a sensitive substrate, comprising a drive unit that moves the mask and the sensitive substrate relatively two-dimensionally in two directions orthogonal to each other independently with respect to the two directions. a position detecting means capable of independently detecting the two-dimensional relative position of the mask and the sensitive substrate in the two directions; An exposure apparatus comprising: a control means for controlling energy generation. (2) The position detecting means is two length measuring devices that output positional information in each of the two directions, and when the positional information from one of the length measuring devices almost matches predetermined target positional information. 2. An exposure apparatus according to claim 1, wherein said control means outputs a pulse generation command to said energy irradiation means. (3) The position detecting means in one direction is a length measuring device that detects the relative position, and the detecting means in the other direction directly detects the pattern formed in advance on the sensitive substrate and the mask pattern. An alignment detection system that detects and determines positional deviation, and the control means outputs a pulse generation command to the energy irradiation means based on the positional deviation information from the alignment detection system. Exposure apparatus according to item 1. (4) The exposure apparatus according to claim 1, wherein the pulse generation type energy irradiation means is an excimer laser.