JPS63100724A - Alignment process - Google Patents

Abstract

PURPOSE:To correct any positional errors in case of an exposure by a method wherein, when a chip on a wafer is exposed by step.repeating process, alignment is advanced from on a chip near the middle point in the spiral direction to the peripheral part. CONSTITUTION:The alignment is advanced from on a chip near the middle point 1a in the arrow direction spirally to the peripheral part. Resultantly, any distortion in the radial directions can be recognized by a calculator if there is any distortion of alignment marks in the radial directions since a signal 12 (mark position) becomes asymmetrical while alignment light 10 is scanning alignment marks 11. Through these procedures, the relative positions of a mask and a wafer can be shifted to correct any positional errors due to mark distortion in case of an exposure so that the alignment precision may be promoted all over the wafer surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a method for aligning a pattern in an exposure apparatus, an inspection apparatus, or the like. (Prior Art) When each chip (2) on a wafer (1) is exposed by a step-and-repeat method, the alignment or exposure is conventionally performed at the top left of the figure, for example, as shown by the arrow in FIG. The chips (2) in the same row are sequentially aligned with the mask and then exposed to light.The numbers in the figure indicate the order in which alignment and exposure are performed.

To perform alignment, as shown in Figure 3, a slit-shaped alignment light (lO) is applied to each chip (2).
The alignment mark (11) formed along with the alignment mark (11) is relatively scanned, and the alignment light (lO)
1) Detect the signal (12) when scanning above, and perform alignment with the mask using this signal (12) and the scanning position.

By the way, this alignment mark (11) is shown in Figure 4 (
If there is distortion in the radial direction as shown in a), the waveform of the signal (12) will not be symmetrical, but will have a distorted waveform as shown in FIG. 4(b).

Note that the strain in the radial direction is at the center point (1a) of the wafer (1).
Since they are often the same on the same circumference, as shown in Figure 4 (a), points equidistant from the center (la) to the que often have the same shape symmetrically about the center point. , FIG. 4(a) schematically represents a cross section of the wafer (1) in the diametrical direction, and a photoresist layer (PR) is coated on the marks (11) and the circuit pattern (not shown). .

In FIG. 4(b), the horizontal axis represents the scanning position and the vertical axis represents the level of the photoelectric signal, but since the mark (11) is distorted in the radial direction, the center of gravity of the waveforms (12a) (12b) X 2 * X 4 is shifted by ΔA, ΔB from the original mark position XI,
In order to detect the position based on the signal of b), mark (
The alignment error varies greatly depending on the position of 11) on the wafer (1).

(Problem to be Solved by the Invention) By the way, when aligning each chip (2) on a wafer (1) using the step-and-repeat method, as shown in FIG. Then, the distortion in the radial direction of the alignment mark (11) is
This cannot be known until the alignment of the entire surface of the sea urchin is completed, and therefore it is impossible to correct the error due to the distortion during alignment.

The present invention has been made in order to solve the above-mentioned problems of the conventional method, and it is an object of the present invention to provide an alignment method that can perform exposure while correcting errors caused by radial distortion of alignment marks.

(Means for Solving the Problems) In order to achieve the above object, in the present invention, when exposing chips (local areas) on a wafer in a step-and-repeat method, starting with the chips at the center of the wafer,
We adopted a method of proceeding with alignment in a spiral direction toward the outer periphery.

(Function) As a result, by detecting the alignment marks of several chips around the center of the sea urchin eight, it is possible to know the distortion in the radial direction of the marks, and the resulting positional error during exposure can be corrected. .

(Embodiment of the Invention) FIG. 1 is a plan view showing the alignment order of each chip on a wafer according to an embodiment of the present invention, in which (1) indicates the wafer, (2) indicates the chip, and the arrow indicates the alignment. direction,
The numbers on the Q stamp are the order of alignment.

As shown in the figure, the alignment starts from the chip r I J near the center (la) of the wafer (1) and proceeds in a spiral manner toward the outer periphery.

As a result, as shown in Fig. 4, if there is radial distortion in the alignment mark, the signal (12) becomes asymmetrical, so that several chips rl, r2 near the center (la)
．． r3. r4. By detecting the alignment marks, the radial distortion can be generally recognized in any direction on the wafer using a computer.

Therefore, during exposure, it is possible to shift the relative positions of the mask and the square so as to correct positional errors due to mark distortion. Moreover, such radial distortion is caused by the wafer (
1) becomes larger toward the outer periphery.

Therefore, if alignment and exposure are performed sequentially from the wafer center (la) toward the outer periphery, the alignment mark (
11) The amount and tendency of mark distortion can be learned from when the distortion is small, and the learning amount increases toward the outer periphery, making it possible to accurately correct errors caused by mark distortion before exposing each chip.

In the above embodiment, alignment measurement was performed for all the chips (2), but if particularly high precision alignment is not required, alignment measurement is performed on several chips located on approximately concentric circles. For chips for which measurement is not performed based on the results, a method may be adopted in which the alignment position is determined by calculation and then exposed.

For example, r I J r 2 J , r in Figure 1
3 J r 4 J and “17 J r20. r
21'J r24. r25J r28J 129.
r32. It is also possible to select a chip, measure the alignment of the chip, detect mark distortion in the radial direction, and correct the error.

Now, FIG. 5 is a block diagram when the method according to the embodiment of the present invention is applied to a step-and-repeat type projection exposure apparatus.

The reticle R on which the circuit pattern is formed is attached to the projection lens (
20). A projected image of the reticle R is projected onto the wafer (1). Wafer (1
) is a wafer stage (21
) is placed on top. The stage (21) is the motor (22)
The coordinate position is determined by a laser interferometer (23
) is detected sequentially.

An alignment system is provided between the projection lens (20) and the reticle R to detect marks on the wafer (1). This alignment system includes a laser light source (24),
It consists of a beam splitter (25), an objective lens (26), and a mirror (27), and a third beam is placed on the wafer (1).
A light transmitting system for forming a sheet-like spot light (10) as shown in the figure, and a mirror (27) for receiving optical information from a mark (11) via a projection lens (20).
), objective lens (26), beam splitter (25),
It includes a light receiving system composed of a relay lens (2B), a spatial filter (29), and a photoelectric element (30).

Furthermore, this alignment system has a unit value detected by an interferometer (23). l! In response to the pulse signal for each II amount,
It includes a waveform processing circuit (32) that digitally samples the photoelectric signal from the photoelectric element (30).

This waveform processing circuit (32) includes a ^/D converter, a memory, etc., and stores the waveform of the diffracted light from the mark (11). The mark position detection circuit (34) inputs the waveform information from the waveform processing circuit (32) and determines the center position (spot light (lO)) of the mark (11) from the characteristics of the waveform.
Stage (21) when and mark (11) match
(coordinate position) is detected by calculation. Computer (3
8) inputs information on the current position of the stage (21) from the interferometer (23) based on the detected position,
The motor (22) is controlled to send the stage (21) to a predetermined position.

This makes it possible to perform overlapping exposure of the desired chip (2) on the wafer (1) and the projected image of the reticle R.

The above configuration is known from Japanese Patent Application Laid-open No. 130742/1982, and the new configuration required to implement the method of the present invention is to input waveform information from the waveform processing circuit (32) and mark A waveform distortion detection circuit (36) is provided which detects waveform distortion, calculates the estimated shift amount of the mark position from the distortion, and sends the result to the computer (38).

A computer (38) is a chip (2) on a wafer (1).
has map data that is aligned in the order shown in Figure 1, and each time the alignment of the chip is completed, the shift amount obtained by the waveform distortion detection circuit (36) is inputted and stored sequentially in correspondence with the map data. I will do it.

Then, as shown in Fig. 1, the four chips r1 near the center
．． r2jr3. r4. alignment (and exposure)
When this is completed, the shift amount and direction of the mark at the position of chip "5" are estimated by taking into account the mark shift information collected in the alignment of the previous four chips, and the alignment error (shift amount) is calculated. The position of the stage (21) is corrected and the chip "5" is exposed.

The above steps are repeated in the same manner for each chip on the wafer (1).

Therefore, as the number of aligned chips increases, the ability to estimate the shift amount and shift direction of the mark increases accordingly.

There are several methods for detecting waveform distortion.
For example, since the light intensity in the scanning direction of the alignment spot light (10) has a Gaussian distribution, there is a method to find the correlation between the mark waveform and the theoretical Gaussian waveform, and the slope of the rising and falling parts of the mark waveform. A method that uses the difference in quantity as distortion,
Binarizes the mark waveform at many different slice levels,
A method of determining each center point on the binarized waveform corresponding to each slice level and calculating distortion from the shift of each center point, or the shift between the center of gravity (center of area) of the mark waveform and the peak position of the waveform. A method that uses distortion as the distortion can be adopted. Of course, it goes without saying that waveform distortion (mark distortion) can be recognized by other methods.

(Effects of the Invention) As explained above, according to the present invention, the chips on the wafer are aligned in a spiral manner from the center of the wafer toward the outer circumference, so that the following excellent effects can be achieved. Ta.

■ Radial distortion of alignment marks can be detected,
It has become possible to correct positional errors during exposure due to this distortion.

■ Distortion becomes larger toward the outer periphery of the chip, and the amount of computer learning increases, making it possible to recognize local chip mark distortion and improving alignment accuracy across the entire surface of the chip.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an alignment method according to an embodiment of the present invention, FIG. 2 is a plan view showing a conventional alignment method, FIG. 3 is an explanatory diagram showing how alignment marks are detected and signal waveforms, and FIG. FIG. 5 is an explanatory diagram showing the state of mark distortion and signal waveforms, and FIG. 5 is a block diagram showing a schematic configuration of a projection exposure apparatus to which the method of the present invention is applied. (1)...Wafer, (2)...Chip, (10)
...Spot light, (11) ...Mark, (20)-
・・Projection lens, (21) ・・Stage, (22)・
...Motor, (23)...Laser interferometer, (24)...
・・Laser light source, (30) ・・Photoelectric element, (32)・
... Waveform processing circuit, (34) ... Mark position detection circuit, (38) ... Computer, R ... Reticle.

Claims (1)

[Claims] In an alignment method using an apparatus that exposes each of a plurality of local regions arranged in a matrix on a wafer in a step-and-repeat method, an alignment mark attached to each of the local regions to be exposed is provided. An alignment method characterized in that the order of detection is selected in a spiral manner from a specific local area at the center of the wafer toward the outer periphery.