JP2890413B2 - Exposure apparatus and exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is suitable for performing exposure while positioning an exposure object with very high precision, such as a reduction projection exposure apparatus for manufacturing an integrated circuit. The present invention relates to an exposure apparatus.

2. Description of the Related Art In a conventional exposure apparatus for manufacturing an integrated circuit, a wafer is mounted on a two-dimensional movable stage provided with a servo mechanism, and the stage and an irradiation light beam are relatively moved. The position of the stage by relative movement of the stage is detected by the position detecting means, and the area to be exposed and the irradiation light beam are positioned in a predetermined positional relationship. Then, a method has been adopted in which the servo lock is performed at the positioned position and the exposure is performed after the deviation distance from the positioning target position falls within a predetermined allowable range.

[Problems to be Solved by the Invention] However, in the above-described exposure apparatus, strictly speaking, even if the servo is continuously applied during the exposure time, the stage is X-axis.
Both the Y axis swings. Conventionally, a mercury (Hg) lamp has been generally used as a light source of such an exposure apparatus. However, since the mercury lamp is a continuous light source, the positional relationship between the exposure area and the luminous flux after the start of the exposure. Even if the change exceeds the allowable range, there is a problem that the exposure is continued as it is, and the resolving power of the exposure pattern is significantly reduced.

Here, a conventional exposure method will be described with reference to FIG.
In the figure, (a) is a graph showing a servo state in the x-axis direction, (b) is a graph showing a servo state in the y-axis direction,
FIG. 6 (c) is a graph showing the exposure timing by the shutter. Since (a), (b) and (c) are related to each other, they are shown in a correlated form in FIG. In the figure, the horizontal axis represents time, the vertical axis represents the displacement distance in the x-axis direction, and the vertical axis represents the displacement distance in the y-axis direction.
Zero scale indicates a predetermined positioning target position (exposure position). Incidentally, T ₀ is servo confirmation time, T ₁ is the shutter open time. That is, after the servo check T ₀ hours, (in the figure (c), hatched portion) Open T ₁ times shutter and performs exposure. As shown in FIGS. 6 (a) and (b),
The wobble of the stage in the x and y axis directions during the servo cannot be completely removed, and the exposure is performed in a state where the position of the stage is slightly changed.

In recent years, a pulsed light source such as an excimer laser has been used as a light source of such an exposure apparatus. However, in order to secure a predetermined exposure amount, exposure of a plurality of pulses is usually performed on one exposure region. Therefore, in this case as well, poor stability of the stage stop due to the servo fluctuation of the stage becomes a major obstacle in forming a fine circuit.

The present invention has been made in view of such a point,
It is an object of the present invention to provide an exposure apparatus that can perform exposure in a state where an illumination target and an illumination light beam are positioned with extremely high accuracy.

[Means for Solving the Problems] In order to achieve the above object, the invention according to claim 1 is
A stage for holding the exposure target, an exposure unit for exposing the exposure target with an illumination light beam, and a stage and the illumination light beam for positioning the exposure object and the illumination light beam in a predetermined positional relationship. Moving means for moving the stage and the position of the illumination light beam relative to the stage, wherein the exposure device includes a position detection means for detecting a relative position between the stage and the illumination light beam. First control means for setting a first allowable range, servo-controlling the moving means so that the position information from the position detecting means falls within the first allowable range; and A second allowable range smaller than the first allowable range is set, and the exposing unit is controlled so that exposure is performed when the position information from the position detecting unit is within the second allowable range. Characterized in that a control means.

The invention according to claim 2 is the exposure apparatus according to claim 1, wherein the illumination light beam is a pulsed illumination light beam.

An exposure apparatus according to a third aspect of the present invention includes an exposure unit configured to expose an exposure target with a pattern image formed on a mask;
Position detecting means for detecting a relative positional relationship between the mask and the exposure target; and moving at least one of the mask and the exposure target so that the mask and the exposure target have a predetermined positional relationship. Moving means, and a first allowable range for a relative target position between the mask and the exposure target, so that position information from the position detecting means falls within the first allowable range. A first control unit that servo-controls the moving unit, and a second allowable range that is smaller than the first allowable range with respect to the target position, and the position information from the position detecting unit is the second allowable range. A second control unit for controlling the exposure unit so that the exposure is performed when the exposure time is within the allowable range.

[Operation] In the present invention, when the stage holding the exposure target and the illumination light beam are relatively moved and positioned in a predetermined positional relationship, the servo tracking range is set to be larger than the emission triggerable range. That is, if the servo range itself is set extremely narrow, the servo system will hunt due to mechanical response delay, stage mass, etc.
In this invention, the servo range is the range suitable for the stage to follow the positioning target position at the earliest time. Converges within the servo range.

The stage is slightly swaying within the servo range around the positioning target position even after convergence, but since the stable servo is performed and the displacement distance is small,
The probability that both the X and Y axes fall within a light emission triggerable range (for example, within the minimum resolution of the interferometer) set narrower than the servo range is high. According to the present invention, when both the X and Y axes are within the emission trigger range, the pulse light is emitted, so that exposure can be performed in a highly accurate positioning state. It is possible to substantially completely prevent a reduction in resolution due to shaking and a reduction in overlay accuracy.

Embodiment FIG. 1 is an explanatory view of a step-and-repeat type projection exposure apparatus showing an embodiment of the present invention. An excimer laser is used as a light source as a pulse light source. The feature of this light source is that it can obtain far ultraviolet light (UV) having a short wavelength with pulsed light (emission time is about 10 nsec).

In FIG. 1, a main optical system projects an image of a pattern of a reticle 2 on a wafer 3 by a projection lens 1. Laser light emitted from an excimer laser 14 as an illumination light source enters a lens system including an expander 15 via two mirrors. Expander 15 is a condenser lens
In addition to the optical system 15a, an optical system (such as an optical integrator or a speckle reduction element) for making the light quantity distribution uniform is built in, and the reticle 2 is irradiated with the focused laser beam.

The wafer 3 is mounted and fixed on a stage 4 that moves in the xy directions. A position detecting means is formed by an interferometer comprising a movable mirror 5 attached to the stage 4, a fixed mirror 5a attached to the projection lens 1, a mirror, a half mirror 6 and a detector 7. This interferometer can monitor the stage position with a resolution of about 0.01 μm. The stage 4 comprises a servomotor 8 and a screw 9 in the X-axis direction.
And a servomotor in the Y-axis direction and a screw (not shown) so as to be movable in the x-Y direction, and a moving means using the servomotor is formed.

Reference numeral 10 denotes a control system for the moving means, which includes a digital counter for measuring the position of the interferometer, and first control means 10a for performing servo driving so that the deviation distance with respect to the positioning target falls within a first allowable range. When the deviation distance is within the second allowable range, the CPU includes a second control unit 10b that emits pulse light from a light source via a CPU and a trigger unit described later.

Reference numeral 12 denotes an alignment system which detects an alignment mark formed in advance on the reticle 2 and the wafer 3 and obtains a positional shift amount, such as an optical system for detecting the alignment mark and an electric system for calculating the positional shift. It is included. Reference numeral 11 denotes a system control system (CPU) that gives various instructions to each unit system and checks the operation. Note that 13
Is a trigger unit that causes the excimer laser 14 to emit light in response to commands from the CPU 11 and the alignment system.

In the present invention, instead of a continuous light source such as a mercury lamp, a pulse light source such as an excimer laser is used,
Since the light emission time is as short as about 10 nsec, it is possible to emit pulse light only when positioning is performed with extremely high accuracy. A method of realizing high-precision positioning by utilizing the advantage of the pulsed light and devising the light emission timing of the pulsed light source will be described with reference to FIG. FIG. 2 (a) is a graph showing the servo state in the x-axis direction, and FIG. 2 (b) is a graph showing the servo state in the y-axis direction, all of which are the same as FIGS. 6 (a) and 6 (b). belongs to. FIG. 2 (c) shows servo confirmation based on the conventional method.
After at T ₀ hours, which represents the applying light emission trigger pulse light source at a fixed frequency, during which the x-axis,
Both y-axis and the stage is displaced in the servo range S _0, reduction in resolution, exposure position deviation occurs. In contrast,
FIG. 2 (d) is a diagram showing the timing of the light emission trigger of the pulse light source according to the present invention, in which the light emission trigger is applied only when the position signal is 0 (both at the target position) on both the x and y axes. There is no reduction in resolution and no shift in exposure position.

Next, the flow of exposure control in the present invention will be described with reference to FIG. FIG. 3 shows a flowchart of exposure control for a certain chip. First, step 100
Prior to the exposure, the exposure amount control and the illumination state control are initialized. When the light source is a pulse emission type light source, the amount of light for each pulse varies, so it is difficult to obtain an appropriate amount of exposure unless special exposure amount control (required number of pulses and light amount management for each pulse) is not performed. . Here, initialization of the light amount control unit is performed. Further, when the light source emits light having coherence like an excimer laser, interference fringes are generated on the reticle surface, and sufficient illuminance uniformity cannot be obtained. Therefore, special illumination state control (variable deflection angle of a beam incident on an optical integrator) is required. The initialization of the lighting state control for that purpose is also performed in step 100.

Next, it is monitored whether or not the position of the stage coincides with the exposure position in both the x and y axes with the minimum resolution of the interferometer (step 102).
If they do not match, the process proceeds to step 110. Then, in step 110, the maximum repetition frequency of the laser is set to f,
It waits for Δt = 1 / f time, and then proceeds to step 102 again (that is, when the oscillation is enabled).

Now, in step 104, it is confirmed whether or not the exposure amount control and the illumination state control required for the shot are appropriate.
If so, a light emission trigger is applied in step 106, and if it is not OK, the process proceeds to step 110 described above. In step 108, the first
In the figure, it is determined whether or not the integrated light amount by a light amount integrator (not shown) is a proper exposure amount. If the proper exposure amount is obtained, the exposure of this chip is terminated in step 112, and the stage is moved to the next position. Proceed to exposure of chip. If the exposure amount is less than the proper exposure amount, the process proceeds to step 110, and after waiting for the time Δt, the same operation as described above is repeated from step 102.

As described above, according to the flowchart shown in FIG. 3, it is possible to perform exposure by high-precision positioning while achieving both exposure amount control and illumination state control for reducing interference fringes.

Next, the servo state and the exposure timing will be described in more detail with reference to FIG. FIG. 4 shows a case where the wafer stage is stepped in the x-axis direction.
The vertical axis represents the count value of the interferometer (one count corresponds to 0.01 μm), and the horizontal axis represents time. The signals S _y and S _x indicate the periods in which the count values of the interferometer in the y-axis and x-axis directions are within ± 1 count, respectively, and the signal T _e (the logical product of S _y and S _x ) in both axes A period within ± 1 count, that is, a light emission triggerable period is shown.

In this embodiment, the servo range is set to ± 3 counts for both axes. In this range, the hunting does not occur in the servo system, and the stepped x-axis direction quickly converges to within ± 3 counts and becomes stable. Servo is performed. For this reason, both axes often fall within ± 1 count, that is, the period during which light can be emitted becomes long, and the position coincides with the target position with an accuracy close to the minimum resolution of the interferometer with almost no decrease in throughput. Exposure is possible.

Next, control of the servo and the light emission trigger in this embodiment will be described with reference to the block diagram of FIG. First, the counters 7X and 7Y of the interferometer at the current
And the count values of the target position counters 50X, 50Y are compared by comparators (subtraction) 51X, 51Y, and the difference between the current value and the target value is determined by the stage servo system 53X, 53Y of each axis.
As a deviation signal. This stage servo system 53X,
The servo drive range (± 3 counts) is set in 53Y from the setting units 55X and 55Y. Based on the values from the comparators 51X and 51Y and the set values, the optimum drive signal is determined by the stage servo system.
Output from 53X and 53Y. This drive signal is digital-to-analog converted by the DACs 57X and 57Y, amplified by the servo amplifiers 59X and 59Y, transmitted to the servo motors 8X and 8Y, and controls each of the servo motors 8X and 8Y. Tach generators (TG) 61X, 61Y are directly connected to the servo motors 8X, 8Y, and the speed signals obtained from the rotation speeds of the motors 8X, 8Y are sent to the stage servo systems 53X, 53Y to operate the servo motors. Is controlling.

On the other hand, the above-mentioned deviation signals from the comparators 51X and 51Y correspond to the respective X-Y axes to which the information from the setting unit 63 for setting the trigger range setting value (± 1 count) is input.
The signals are also sent to AND circuits 64X and 64Y, where the triggerable ranges of the X axis and the Y axis are detected. The signal from here is further transmitted to another AND circuit 66. That is, this AND
The output signal of the circuit 66 is Te (logical product of _Sy and _Sx ) in FIG.
When the light emission trigger is applied when Te is “H”, when the difference between the current value and the target value is within ± 1 count (the minimum resolution of the interferometer) for both X and Y axes, Pulsed light is emitted, and exposure in a state where positioning is performed with very high accuracy is achieved. The state of this signal Te is determined in step 102 in FIG.

In the above description, the case where the excimer laser emission trigger is activated when the value of the stage x, y biaxial interferometer matches the target value with the minimum resolution has been described. A trigger can be activated in synchronization with the alignment match signal.

In the above description, the case where the stage is moved is mainly described. In FIG. 1, the position of the stage (not shown) of the reticle 2 is monitored by the interferometer 16 and the position of the reticle 2 is finely aligned. Reticle 2
The present invention can be similarly applied to an apparatus of the type that finely moves the. In this case, the servos of the two stages for holding the wafer and the reticle are respectively performed for the target values, the triggerable range may be set for the difference between the current values of the two stages, or the entire control may be performed for two stages. The difference may be obtained by taking the difference between the stage position signals.

Further, in the embodiment, the projection reduction exposure apparatus using an excimer laser as a light source has been described. However, the present invention is not limited to this, and a plurality of pulsed lights are positioned by positioning an exposure target and a light beam in a predetermined relationship. The same can be applied to any irradiation device. That is, the present invention can be similarly applied to an X-ray exposure apparatus using pulsed soft X-rays such as a plasma X-ray source, and is not limited to the case where a circuit is formed by exposing a photoresist to light. The present invention can also be applied to an apparatus for performing precision processing such as cutting and drilling, and an apparatus for performing laser annealing of a semiconductor.

[Effects of the Invention] As described above, according to the present invention, the range in which the servo tracking is performed quickly is set as the servo range, and the XY axes are allowed to be narrower than the servo range while performing stable servo. Since the light emission trigger is applied when entering (when the target value coincides with the minimum resolution of the position detecting means), exposure can be performed in a state where positioning is performed with extremely high precision. For this reason, it is possible to substantially completely prevent the resolution from deteriorating due to subtle shaking of the stage that holds the exposure target, and to improve the alignment accuracy and the overlay accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing the overall arrangement of an exposure apparatus according to an embodiment of the present invention, FIG. 2 is an explanatory view of an exposure method according to the prior art and the present invention, and FIG. 4 is a flowchart showing an exposure method, FIG. 4 is an explanatory diagram of a servo state in the present invention,
FIG. 5 is a block diagram illustrating control of a servo and a light emission trigger according to the present invention, and FIG. 6 is an explanatory diagram of a conventional exposure method. [Explanation of Signs of Main Parts] 1 Projection lens 2 Reticle 3 Wafer 4 XY stage 10 Moving control system 11 System control system 12 Alignment system 13 Excimer Laser trigger unit 14 ... Excimer laser

Claims (3)

(57) [Claims] An exposing means for exposing an object to be exposed with a pulsed exposure beam from a pulse light source; a moving means for relatively moving the object to be exposed and the exposure beam; An interferometer for detecting a relative positional relationship between the exposure beam and the exposure beam; and setting a first allowable range for positioning with respect to a relative target position between the exposure object and the exposure beam; First control means for servo-controlling the moving means using the position information from the interferometer so that the position information from the first position becomes the first allowable range for the positioning; A second allowable range for exposure smaller than the first allowable range is set, and the exposing unit is configured to perform exposure when the position information from the interferometer is within the second allowable range. Second to control
An exposure apparatus, comprising: control means; 2. An exposure means for illuminating a mask with pulsed light from a pulsed light source and projecting and exposing an image of a pattern formed on the mask to an object to be exposed, and an exposure means for detecting a position of the mask. Position detecting means for detecting a relative positional relationship between the mask and the exposure object using one interferometer and a second interferometer for detecting the position of the exposure object; Moving means for relatively moving the object; setting a first allowable range for positioning with respect to a relative target position between the mask and the exposure object; Relative to the first
A first control unit that servo-controls the moving unit based on an output of the position detection unit so as to be within an allowable range of: A second allowable range for a narrow exposure is set, and the exposure is performed such that the exposure is performed when the relative positional relationship between the mask and the object to be exposed is within the second allowable range. An exposure apparatus, comprising: second control means for controlling the means. 3. The mask and the object to be exposed are positioned using moving means for relatively moving the mask and the object to be exposed, and the mask is illuminated with pulsed light from a pulse light source. An exposure method for projecting and exposing an image of a formed pattern on an object to be exposed, wherein a first position for positioning the mask and the object to be exposed with respect to a relative target position between the mask and the object to be exposed is provided.
A relative positional relationship between the mask and the exposure target is detected using an interferometer; and a relative positional relationship between the mask and the exposure target is determined as the first tolerance. Servo controlling the moving means using the output of the interferometer so as to be within the range; and setting a second allowable range for exposure smaller than the first allowable range for positioning with respect to the target position. An exposure method, wherein a pulse light is emitted from the pulse light source when a relative positional relationship between the mask and the exposure object is within the second allowable range.