JP5084432B2 - Exposure method, exposure apparatus, and device manufacturing method - Google Patents

Description

  The present invention relates to an exposure method for exposing and transferring an original pattern onto the substrate while scanning the substrate. In particular, the present invention relates to a step-and-scan exposure method and exposure apparatus for transferring a mask pattern onto a substrate by moving the mask and the substrate in synchronization with a projection optical system.

In general, various exposure apparatuses are used when manufacturing a semiconductor element, a liquid crystal display element, or the like in a photolithography process.
Currently, a pattern image of an original photomask or reticle (hereinafter collectively referred to as “reticle”) is transferred onto a substrate such as a wafer or a glass plate whose surface is coated with a photosensitive material such as a photoresist via a projection optical system. A projection exposure apparatus for transferring the image onto the screen is used.
In recent years, as this projection exposure apparatus, a step-and-repeat type static reduction projection exposure apparatus (so-called stepper) has become mainstream.
In this stepper, a substrate is placed on a two-dimensionally movable substrate stage, and the substrate is stepped (stepped) by the substrate stage to sequentially expose a reticle pattern image on each shot area on the substrate. It is a static reduction projection exposure apparatus that repeats operation.

Recently, for example, a step-and-scan projection exposure apparatus (so-called scanner) proposed in Japanese Patent Application Laid-Open No. 7-176468 (Patent Document 1), which is an improvement on a stationary exposure apparatus such as a stepper. Has also been used relatively frequently.
Compared with a stepper, this scanner can expose a large field with a smaller optical system, can easily manufacture a projection optical system, and can be expected to have a high throughput due to a reduction in the number of shots due to the large field exposure.
Further, the relative effect of scanning the reticle and wafer with respect to the projection optical system has an averaging effect, and there is an advantage that an improvement in distortion and depth of focus can be expected.

For example, JP-A-4-281665 (Patent Document 2) and JP-A-6-283403 (Patent Document 3) propose a conventional example in which a substrate is exposed using this scanning projection exposure apparatus (scanner). ing.
Using multiple detection points provided in front of the exposure field in the scanning direction as sample points, all focus position values at the sample points are measured in advance before exposure, and the autofocus and autoleveling mechanisms are controlled during exposure. To do.
In parallel with this, a so-called look-ahead control method has been implemented in which the inclination in the non-scanning direction is obtained from the measurement value of the focus position at each sample point of the measurement point, and leveling control in the non-scanning direction is performed.
Japanese Patent Laid-Open No. 7-176468 JP-A-4-281665 JP-A-6-283403

Since the projection exposure apparatus is mainly used as a mass production machine for semiconductor elements and the like, it is inevitably required to improve the throughput, that is, the throughput, that is, how many wafers can be exposed within a certain time. Is done.
In the case of a step-and-scan type projection exposure apparatus (scanner), when a large field is exposed, as described above, the number of shots exposed in the wafer is reduced, so that an improvement in throughput is expected.
However, since exposure is performed during constant speed movement by synchronous scanning of the reticle and wafer, an acceleration / deceleration area is required before and after the constant speed movement area.
For this reason, when exposing a shot having a size equivalent to the shot size of the stationary exposure apparatus (stepper), the scanning projection exposure apparatus (scanner) has a lower throughput than the stationary exposure apparatus (stepper). There is a case.

The flow of processing in a stationary exposure apparatus (stepper) and a scanning projection exposure apparatus (scanner), which are projection exposure apparatuses, is as follows.
First, a wafer loading process for loading a wafer onto a wafer table using a wafer loader is performed.
Next, a search alignment process is performed in which the position of the wafer is roughly detected by the search alignment mechanism.
Specifically, this search alignment process is performed, for example, based on the outer shape of the wafer or by detecting a search alignment mark on the wafer.
Next, a fine alignment process for accurately determining the position of each shot area on the wafer is performed.
In this fine alignment process, an AGA (Advanced Global Alignment) method is generally used.
In this method, a plurality of sample shots in a wafer are selected, and the positions of alignment marks (wafer marks) attached to the sample shots are sequentially measured.
Furthermore, based on the measurement result and the shot array design value, statistical calculation such as so-called least square method is performed to obtain all shot array data on the wafer, and the coordinate position of each shot area is relatively high with high throughput. The accuracy can be obtained.
Next, the respective shot areas on the wafer are sequentially positioned at the exposure position based on the coordinate position of each shot area obtained by the AGA method or the like and the baseline amount measured in advance, and the reticle is moved through the projection optical system. An exposure process for transferring the pattern image onto the wafer is performed.
Next, a wafer loading process is performed in which the wafer on the wafer table subjected to the exposure process is loaded using a wafer loader.
This wafer loading process is performed simultaneously with the first wafer loading process of the wafer to be exposed.
That is, a wafer exchange process is constituted by the first wafer loading process and the final wafer loading process.

Thus, in the conventional projection exposure apparatus, four operations are repeatedly performed using one wafer stage, such as wafer exchange → search alignment → fine alignment → exposure → wafer exchange.
Further, the throughput WPH [pieces / hour] of the projection exposure apparatus is expressed by the following equation (1) when the wafer exchange time is T1, the search alignment time is T2, the fine alignment time is T3, and the exposure time is T4. It can be expressed as
WPH = 3600 / (T1 + T2 + T3 + T4) (1)
The operations from T1 to T4 are repeatedly executed sequentially (sequentially) in the order of T1, T2, T3, T4, T1, and so on.
For this reason, if each element from T1 to T4 is speeded up, the denominator becomes small and the throughput WPH can be improved.
However, the above-described T1 (wafer exchange time) and T2 (search alignment time) are relatively small since only one operation is performed on one wafer.
In the case of T3 (fine alignment time), the throughput can be improved by reducing the number of shot samplings when using the AGA method described above and shortening the measurement time of a single shot.
However, since the alignment accuracy is deteriorated, T3 cannot be easily shortened.
T4 (exposure time) includes a wafer exposure time and a stepping time between shots.
For example, in the case of a scanning projection exposure apparatus such as the step-and-scan method, it is necessary to increase the relative scanning speed of the reticle and wafer by the amount that shortens the wafer exposure time, but the synchronization accuracy deteriorates. The scanning speed cannot be increased easily.

In a scanning projection exposure apparatus (scanner), the exposure order for each shot area on the wafer W is (a) acceleration / deceleration time during scanning, (b) settling time, (c) exposure time, and (d) to adjacent shots. It is determined by the parameters (a) to (d) such as the stepping time.
However, when pre-reading control is performed in the above-described conventional example of Japanese Patent Laid-Open No. 4-281665 (Patent Document 2), it is necessary to set the following state in order to stabilize the focus accuracy.
That is, when the detection point provided on the near side in the scanning direction reaches the exposure area, the vibration of the wafer W is stopped, and (a) the acceleration / deceleration time during scanning needs to end.
Here, (b) settling time indicates the time from the position at which the exposure slit finishes (a) acceleration / deceleration during scanning until the exposure slit reaches the exposure area, and the scanning speed during this period is constant.
At this time, the vibration of the wafer W is reduced regardless of the detection point position (first measurement point in the shot) provided on the front side in the scanning direction within the exposure region.
Therefore, (a) the distance from the acceleration / deceleration end position during scanning to the exposure area is driven at a constant speed. (B) If the speed is the same, (b) the settling time is always the same.
However, in a process such as a rough process in which there is a margin in focus accuracy, productivity is emphasized even if focus accuracy is somewhat sacrificed rather than focus accuracy.
Accordingly, an object of the present invention is to provide an exposure method, an exposure apparatus, and a device manufacturing method that optimize the focus measurement position from the allowable focus value of the substrate in the exposure process and improve the throughput.

An exposure method of the present invention for solving the above-described problems is an exposure method in which a slit-like light through an original is irradiated on the substrate, and the pattern of the original is exposed to the substrate while being scanned and transferred. The step of measuring the surface position of the substrate at a plurality of focus measurement positions inside the exposure area of the substrate where the pattern is exposed, and the information on the surface position of the substrate measured in the step, A step of controlling at least one of a height and a tilt of the substrate, and in the step of measuring the surface position, the surface position of the substrate is measured after the acceleration of the substrate during scanning is completed, and the substrate After the acceleration of the substrate during scanning and the acceleration of the substrate during scanning is completed based on the allowable focus value of the substrate that is allowed when exposing End of the exposure area at the position bets like light is irradiated to change the time to reach.

  According to the present invention, the focus measurement position is optimized from the allowable focus value of the substrate in the exposure process, and the throughput is improved.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

With reference to the schematic block diagram of FIG. 1, the exposure apparatus 100 of the Example of this invention is demonstrated.
The exposure apparatus 100 according to the present embodiment includes a light source 110, an illumination optical system 120, a reticle stage 135 that holds a reticle 130 that is an original, and a projection optical system 140.
Furthermore, a wafer stage 155 that holds a wafer 150 as a substrate, a detection system 160, and a control unit 170 are included.
The exposure apparatus 100 according to the present embodiment is a projection exposure apparatus that exposes a circuit pattern formed on a reticle 130 onto a wafer 150 by a step-and-scan method called a scanner.
The exposure apparatus 100 of this embodiment is suitable for a lithography process of submicron or quarter micron or less.
Light emitted from a light source 110 such as an excimer laser illuminates a pattern formed on the reticle 130 through an illumination optical system 120 that is formed into an exposure light beam having a predetermined shape optimum for exposure.
The pattern of the reticle 130 includes an IC circuit pattern to be exposed, and light emitted from the pattern passes through the projection optical system 140 to form an image in the vicinity of the surface of the wafer 150 corresponding to the imaging surface.
The reticle 130 is mounted on a reticle stage 135 that is configured to be movable in a plane perpendicular to the optical axis of the projection optical system 140 and in the optical axis direction.
The wafer 150 is placed on a wafer stage 155 that is configured to be movable in the direction perpendicular to the optical axis of the projection optical system 140 and in the optical axis direction and to be capable of tilt correction.

The shot area of the reticle 130 is exposed by relatively scanning the reticle stage 135 and the wafer stage 155 at the speed of the ratio of the exposure magnification.
After the one-shot exposure is completed, the wafer stage 155 moves stepwise to the next shot, scanning exposure is performed in the opposite direction to the previous shot, and the next shot is exposed.
By repeating this, shot exposure is performed on the entire area of the wafer 150.
During scanning exposure within one shot, surface position information on the surface of the wafer 150 is acquired by a detection system 160 that measures focus and tilt.
Further, the amount of deviation from the exposure image plane is calculated, the wafer stage 155 is driven in the focus (height) and tilt (tilt) directions, and the operation of adjusting the shape in the height direction of the wafer 150 approximately in units of exposure slits. Has been done.
The detection system 160 uses an optical height measurement system.
A method is adopted in which a light beam is incident on the surface of the wafer 150 at a large angle (low incident angle), and an image shift of reflected light from the wafer 150 is detected by a position detection element such as a CCD camera.
A light beam is incident on a plurality of points to be measured on the wafer 150, each light beam is guided to an individual sensor, and a tilt of a surface to be exposed is calculated from height measurement information at different positions.

Next, an exposure method according to an embodiment of the present invention will be described with reference to FIGS.
In the exposure method according to the embodiment of the present invention, the wafer 150 is exposed using the exposure apparatus 100 that transfers the pattern of the reticle 130 as the original to the wafer 150 while scanning the wafer 150 as the substrate.
In the first step, the surface position of the wafer 150 is measured at a plurality of focus measurement positions (1) to (8) inside the exposure areas 500, 510, and 520 of the wafer 150 where the pattern of the reticle 130 is exposed.
Further, the surface position of the wafer 150 is measured at a plurality of focus measurement positions outside the exposure areas 500, 510, and 520 of the wafer 150 where the pattern of the reticle 130 is exposed.
Next, at least one of the height and inclination of the wafer 150 is controlled based on the information on the surface position of the wafer 150 measured in the previous step.
Further, the focus measurement positions (1) to (8) are changed based on the allowable focus value of the wafer 150 that is allowed when the wafer 150 is exposed.

As shown in FIGS. 2 and 3, a plurality of measurement points K1 to K5 have a surface shape in the front area 510 and the rear area 520 with respect to the exposure area 500 that is the position of the exposure slit. Has been placed.
Then, before the exposure slit during scanning exposure reaches the exposure area 500, it is possible to simultaneously measure the focus and tilt information of the wafer 150, in particular, the tilt information in the scanning direction.
2 and 3 are schematic views showing an example of the arrangement of the measurement points K1 to K5 with respect to the exposure region 500. FIG. 2 shows a case where five measurement points K1 to K5 are arranged, and FIG. The case where the measurement points K1 to K3 of the points are arranged is shown.
The three measurement points and the five measurement points are not limited to the three points and the five points, respectively, and may be any number as long as the number is three or more. It is preferable that the three or more measurement points are not arranged on a straight line.
In other words, when three points are selected from three or more measurement points, it is preferable that the three points form a triangle when viewed from the vertical direction of the wafer.
As shown in FIG. 2, the five measurement points K1 to K5 are projected onto the exposure area 500 in the previous area 510, and before the exposure area 500 is reached, the measurement immediately before exposure is performed with high accuracy. Focus and tilt information can be acquired and exposure position correction driving can be performed.
Similarly, five measurement points K1 to K5 are similarly projected on the subsequent area 520 so as to correspond to the scanning exposure in the reverse direction.
Further, in order to confirm the focus and tilt of the wafer 150 during the exposure, the same number of five confirmation measurement points CK1 to CK5 are located in the exposure region 500 at substantially the same positions as the front region 510 and the rear region 520. Place.
That is, it is possible to confirm the correction driving amount of the wafer 150 based on the measurement values in the front area 510 and the rear area 520 with respect to the exposure area 500 by the confirmation measurement points CK1 to CK5.

As shown in FIG. 4, the settling time is uniquely determined for the exposure process conditions A, B, and C from the relationship between the settling time obtained by experiment and the allowable value of the focus of the substrate in the exposure process.
In the exposure process condition A, since focus accuracy is required, it is necessary to increase the settling time.
In addition, since the tolerance of focus accuracy is large under the exposure process condition C, the settling time can be shortened to improve productivity.

FIG. 5 shows the focus measurement positions (1) to (8) in the same exposure region 500 as the exposure regions in the exposure process conditions A, B, and C in FIG.
The arrangement of the focus measurement positions (1) to (8) in the exposure area 500 is calculated and set so as to be an optimum arrangement for improving the focus accuracy.
Further, the focus measurement position is also optimized in accordance with the size of the exposure area 500.
The focus measurement position is 8 points (1) to (8) under the A process condition that requires high focus accuracy, and 7 points (1) to (7) under the exposure process condition B where it is desired to achieve both focus accuracy and productivity. It has become.
In the exposure process condition C, which requires higher productivity than the focus accuracy, there are 6 points (1) to (6).

The details of FIG. 5 will be described with reference to FIG.
Here, the present embodiment will be described assuming that the detection point position before the scanning direction and the physical distance between the exposure slits are 12 mm and the scanning speed is 500 mm / s.
A boundary line where the first focus measurement position (1) is not arranged in a certain area from the end 500a of the exposure area 500 based on the relationship between the allowable focus value and the settling time depending on the exposure process conditions A, B, and C. 500b is set.
Further, the first focus measurement position (1) and the second focus measurement position (2) are set after the boundary line 500b.
Here, focus measurement positions after the third focus measurement position (3) are not shown.
Here, the settling time is the time from the position where the exposure slit finishes acceleration / deceleration during scanning to the end 500a of the exposure region 500.
The boundary line 500b indicates the detection point position before the scanning direction when acceleration / deceleration during scanning is completed.

In the case of the exposure process condition A that requires high focus accuracy, a settling time of 24 ms is acquired from the focus tolerance shown in FIG.
Settling time: 24 ms, speed: 500 mm / s Scanning distance: 24 ms × 500 mm / s = 12 mm.
Since the physical distance between the detection point position in front of the scanning direction and the exposure slit is 12 mm, the boundary line 500b is set at the end 500a of the exposure region 500: 0 mm.
On the condition that the first focus measurement position (1) is not set in the boundary line 500b, the focus measurement position (1)... Optimal for improving the focus accuracy is set in the exposure region 500.
In the present embodiment, the first focus measurement position (1) is set on the boundary line 500b.
In this case, since there are eight focus measurement positions (1) to (8) and measurement is performed from the end portion 500a of the exposure region 500, focus accuracy is improved, but throughput is slow.

In the case of the exposure process condition B, the settling time: 22 ms is acquired from the focus allowable value shown in FIG. 4 from the balance of focus accuracy and productivity.
Settling time: 22 ms, speed: 500 mm / s Scanning distance: 22 ms × 500 mm / s = 11 mm.
Since the physical distance between the detection point position in front of the scanning direction and the exposure slit is 12 mm, the boundary line 500b is set at the end portion 500a of the exposure region 500: 1 mm.
On the condition that the first focus measurement position (1) is not set in the boundary line 500b, the focus measurement position (1)... Optimal for improving the focus accuracy is set in the exposure region 500.
In the present embodiment, the first focus measurement position (1) is set 2.0 mm inside the end portion 500a of the exposure area 500 .
In this case , the focus measurement positions (1) to (7) are 7 points, and measurement is performed from 2 mm inside the end portion 500a of the exposure area 500. Therefore , the focus accuracy is degraded from the exposure process condition A, but the productivity is improved.

In the case of the exposure process condition C, since productivity is given priority over focus accuracy, a settling time of 20 ms is acquired from the focus tolerance shown in FIG.
Settling time: 20 ms scanning speed: 500 mm / s Scanning distance: 20 ms × 500 mm / s = 10 mm.
Since the physical distance between the detection point position before the scanning direction and the exposure slit is 12 mm, the boundary line 500b is set at the end 500b of the exposure region 500: 2 mm.
On the condition that the first focus measurement position (1) is not set in the boundary line 500b, a focus measurement position optimal for improving the focus accuracy is set in the exposure region 500.
In this embodiment, the measurement position (1) of the first focus is set 3.0 mm inside the end portion 500a of the exposure area 500 .
In this case , the focus measurement positions (1) to (6) are 6 points, and measurement is performed from the inside of the end portion 500a of the exposure region 500 by 3 mm.
Therefore, the focus measurement is not performed between 3 mm from the end portion 500a of the exposure region 500, and the exposure is performed based on the near focus reference, and the focus accuracy is most deteriorated in the exposure process conditions A, B, and C. However, productivity is greatly improved.

With reference to FIGS. 6 and 7, the process of changing the focus measurement position according to the focus allowable value of the process condition in the present embodiment will be described.
First, an allowable focus value in the exposure process of the wafer 150 as a substrate is checked. (Step S1)
Next, a settling time emphasizing focus accuracy is acquired from the focus allowable value in the exposure process. (Step S2)
Next, a settling time that achieves both focus accuracy and productivity is acquired from the focus tolerance in the exposure process. (Step S3)
Next, the settling time with an emphasis on productivity is acquired from the focus allowable value in the exposure process. (Step S4)
Next, the boundary line 500b is set from the acquired settling time. (Step S5)
Next, focus measurement positions (1), (2)... Taking into account the boundary line 500b are set. (Step S6)
Finally, the boundary line 500b is reset at the first focus measurement position (1). (Step S7)

Next, an embodiment of a device manufacturing method using the above-described exposure apparatus will be described with reference to FIGS.
FIG. 8 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, a semiconductor chip manufacturing method will be described as an example.
The method comprises the steps of exposing a wafer using an exposure apparatus and developing the wafer, and specifically comprises the following steps.
In step 1 (circuit design), a semiconductor device circuit is designed.
In step 2 (mask production), a mask is produced based on the designed circuit pattern.
In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon.
Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer using the mask and the wafer by the above-described exposure apparatus using the lithography technique.
Step 5 (assembly) is referred to as a post-process, and is a process for forming a semiconductor chip using the wafer produced in step 4, and an assembly process such as an assembly process (dicing, bonding), a packaging process (chip encapsulation), or the like. including.
In step 6 (inspection), the semiconductor device manufactured in step 5 undergoes inspections such as an operation confirmation test and a durability test.
Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 9 is a detailed flowchart of the wafer process in Step 4.
In step 11 (oxidation), the surface of the wafer is oxidized.
In step 12 (CVD), an insulating film is formed on the surface of the wafer.
In step 13 (electrode formation), an electrode is formed on the wafer.
In step 14 (ion implantation), ions are implanted into the wafer.
In step 15 (resist process), a photosensitive agent is applied to the wafer.
Step 16 (exposure) uses the exposure apparatus to expose a circuit pattern on the mask onto the wafer.
In step 17 (development), the exposed wafer is developed.
In step 18 (etching), portions other than the developed resist image are removed.
In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed.
By repeatedly performing these steps, multiple circuit patterns are formed on the wafer.

It is a schematic block diagram of the exposure apparatus of the Example of this invention. It is the schematic at the time of arrange | positioning five measurement points with respect to the exposure area | region of a present Example. It is the schematic at the time of arrange | positioning three measurement points with respect to the exposure area | region of a present Example. It is a relationship figure of the focus allowable value of the process calculated | required by experiment in a present Example, and settling time. It is the schematic which shows the focus measurement positions (1)-(8) in the exposure area | region in exposure process conditions A, B, and C. FIG. FIG. 6 is a schematic diagram showing detailed focus measurement positions and boundary lines under the exposure process conditions A, B, and C shown in FIG. 5. It is a flowchart figure which shows the process of calculating | requiring a focus allowable value and settling time, and setting a focus measurement position from the process conditions at the time of exposure in a present Example. It is a flowchart for demonstrating manufacture of the device using an exposure apparatus. It is a detailed flowchart of the wafer process of step 4 of the flowchart shown in FIG.

Explanation of symbols

100: exposure apparatus 110: light source 120: illumination optical system 130: reticle 140: projection optical system 150: wafer 160: detection system 170: control unit

Claims (4)

In an exposure method of irradiating a substrate with slit-shaped light through an original and exposing and transferring the pattern of the original to the substrate while scanning the substrate, the inside of the exposure area of the substrate to which the pattern is exposed Measuring the surface position of the substrate at a plurality of focus measurement positions in
Controlling at least one of the height and inclination of the substrate based on the information on the surface position of the substrate measured in the step, and
In the step of measuring the surface position, the surface position of the substrate is measured after the acceleration of the substrate during scanning is completed,
Based on the allowable focus value of the substrate that is allowed when the substrate is exposed, the focus measurement position and the position where the slit-shaped light is irradiated after the acceleration of the substrate during scanning is completed. An exposure method characterized in that the time until the end of the exposure area reaches is changed . The distance between the edge of the exposure area of the substrate and the focus measurement position is increased and the time is shortened when the substrate is changed to a substrate having a large focus tolerance. The exposure method as described. Exposure apparatus characterized by exposing the substrate using an exposure method according to claim 1 or 2. A step of exposing a substrate using an exposure apparatus according to claim 3,
And a step of developing the substrate.

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