JPS6060503A - Position detector - Google Patents

Abstract

PURPOSE:To detect a mark securely by using an alignment mark having density difference in an addition direction and comparing the mark signal level of an addition result with plural slice levels. CONSTITUTION:The alignment mark having the density difference in the addition direction is a mark in, for example, a cross-pattern shape. This mark is added in an X and an Y direction to obtain two stages of density distributions (B) and (C). Then two slice levels XSL1 and XSL2 are provided corresponding to those two stages of density distributions, and their binary-coded patterns are as showby (D) and (E). Therefore, when the centers of the binary-coded patterns are aligned to each other, the center is the center coordinates of the alignment mark. Thus, the mark is detected easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an apparatus for detecting the position of a pattern on an object to be inspected, and in particular to a device for detecting the position of a pattern on an object to be inspected.
The present invention relates to a device for accurately detecting a pattern position from an image signal obtained by imaging with an imaging means such as a television camera or COD when aligning a pattern (or a reticle).

[Prior art]

Conventionally, when a pattern of a real element is arranged around an alignment mark, it is difficult to distinguish between the mark and the pattern of the real element, and there is a drawback that false detection often occurs.

[Purpose] (The present invention has been proposed in view of the above-mentioned drawbacks. It uses an alignment mark that has a density difference in the direction of addition, and makes a mark by comparing the signal level of the mark resulting from the addition with a plurality of slice levels. The purpose of the present invention is to provide a mark position detection device that detects marks reliably.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

First, we will outline the overall configuration using Figure 1, which depicts the exterior.

Reference numeral 1 denotes a mask having an integrated circuit pattern, and other mask setting marks and fine alignment marks. Reference numeral 2 denotes a mask chuck, which holds the mask 1 and moves the mask 1 within a 1'1' curve and in the rotational direction. 6 is a reduction projection lens, 4 is a wafer provided with a photosensitive layer, and is provided with a fine alignment mark and a final alignment mark . 5 is a wafer stage.

Wafer stay, 15 holds wafer 4 fhj l,
It moves it in the plane and in the rotational direction, and also moves it between the projection position 16 (intra-bone projection) and the television pre-alignment position. 6 is an objective lens of a detection device for television pre-alignment.

Reference numeral 7 indicates an imaging device or solid-state image sensor, and reference numeral 8 indicates a television receiver for viewing images. Reference numeral 9 denotes a binocular Uniso I, which is useful for observing the surface of the wafer 4 through the projection lens 6. 10
is a two-part unit that houses an illumination optical system for converging the mask illumination light emitted from the light source fOa and a detection device for fine alignment.

The wafer stage 5 holds the wafer transported by a general transport means (not shown) in a predetermined position, and first moves the wafer to a position where the second alignment mark is within the field of view of the television pre-alignment objective lens. Move up to. The positional accuracy at this time is due to mechanical prealignment accuracy, and the field of view of the objective lens 6 is approximately 1 to 2 mm in diameter. The alignment mark within this field of view is detected by the image pickup tube 7, and the alignment mark from there is detected with reference to a reference mark for TV pre-alignment (described later) provided in the optical system for TV pre-alignment. The coordinate position of is detected. On the other hand, the detection position for automatic alignment of the projection optical system and the aforementioned TV
Since the position of the pre-alignment reference mark is set in advance, the amount of feed of the wafer stage 5 from the position of these two points and the coordinate position of the television pre-alignment mark to the auto-alignment position is determined.

The position detection accuracy of TV pre-alignment is less than ±5μ, and even if you take into account the error caused by moving the wafer stage from the TV pre-alignment position to the fine alignment position, it is about ±10μ. be.

Therefore, fine alignment only needs to be performed within a range of approximately ±10 μ, which is less than 1/1oo of the field of view of conventional fine alignment, which means that fine alignment 1 can be performed faster than conventional fine alignment.

Figure '32 shows an embodiment of the detection device for television pre-alignment. (-) The lens 6゜ wafer 4, the objective lens 6, the image pickup 7) 7 beams are the same as Figure 'S1'. It is.

On the other hand, 11 is a light source for illumination, and uses a halogen lamp, for example. 12 is a condenser lens. 16A and 13B are a bright field diaphragm and a dark field diaphragm that can be attached and detached interchangeably, and in the figure, a bright field diaphragm i3A is installed in the optical path. A condenser lens 12 images the light source 11 onto a bright field aperture. 1
4 is a relay lens for lighting. 15 is a cemented prism, and the cemented prism 15 has a function of making the optical axis of the illumination system and the optical axis of the light receiving system coaxial, and has an inner reflective surface 15a and a semi-transparent reflective surface 15b.
Shigaian 21. , where light source 11 condenser lens 1
2. Bright or dark field diaphragm 15A and i3B, lj wide open light relay lens 14 cemented prism 15, pair! The lens 6 constitutes an illumination system, and the light beam emitted from the objective lens 6 epi-illuminates the wafer 6.

Next, 16 is a relay lens, 17 is a mirror that bends the light 11'8, and 18 is a glass plate with a base for TV/Bearlint. 1
The pre-alignment mark has the function of providing the origin of the ink mark, so the pre-alignment mark is expressed as the X-coordinate value and the X-coordinate value. Reference numeral 19 denotes an imaging lens, which constitutes a light receiving system together with the above-mentioned cemented lens 15, relay lens 16.trf, 17, glass plate 18, image capturing lens 19, and 11υ image tube 7, and includes an optical path passing through the objective lens 6. is reflected by the inner reflective surface 15a of the cemented prism, reflected by the semi-transparent surface 15b, reflected by the angular inner reflective surface 15a, and then reflected by the relay lens 16.
Head to After the clear alignment mark image on the Ueno)-4 is formed on the glass plate 18 having the fiducial mark,
The image is formed on the imaging surface of the imaging tube 7 together with the reference mark image.

On the other hand, the television pre-alignment mark (conventional example) illustrated in FIG. 6 (FA) is preferably provided in the scribe line of the wafer, but may also be provided at a specific chip pattern position on the wafer. The envelope shape of the mark is a rectangle, and the sides are arranged so as to be substantially parallel and perpendicular to the scanning direction of the image pickup tube. As shown in the figure, a rectangular pattern is made up of a collection of minute par-shaped protrusions tilted at 45° in the scanning direction, and if dark-field illumination is performed so that the illumination light hits the protrusions from a direction perpendicular to them, an extremely clear image can be obtained. Capable of capturing images of pattern shapes. Note that since such a method is for facilitating imaging, it is not always necessary to use this configuration, and li1 may be a pure rectangle. However, the form of the output signal changes.

Returning to FIG. 2, the detection action of the pre-alignment mark will be described, and the electrical processing of the detected video signal will be described later. The luminous flux of illumination light #, 11 is converged by a condenser lens 12 and is applied to a bright field diaphragm 13A or a dark field diaphragm 1.
The opening 1-1 of 313 is illuminated, and the illumination relay lens 14
The Ueno-
Illuminate 4.

The light beam reflected on the surface of the wafer 4 is subjected to an imaging action by the objective lens 6, and enters the cemented prism 15, where it is reflected on the reflecting surface 15a.
Then, it is reflected by a semi-transparent film 5b, reflected by a reflecting surface 15a, and emitted, relayed by a relay lens 16, reflected by a mirror 17, formed into an image on a glass plate 18, and then captured by an imaging lens 19. An image is formed on the image pickup tube 7. Next, night vision!
The state is switched to r state so that the pre-alignment mark image can be clearly seen, and this is imaged to detect the position of the pre-alignment mark image. The wafer stage 5 moves and stops so that the wafer 4 occupies a prescribed position 4' in the projection field of the projection lens B in accordance with the position of the pre-alignment mark detected by electrical processing to be described later. Note that the wafer 4 may be once aligned at a standard position and then deformed so as to be moved into the projection field.

FIG. 6 is a block diagram showing one embodiment of the television pre-alignment detection circuit. There are various methods for detecting the television pre-alignment mark shown in FIG. 6A, but the embodiment shown in FIG. ) and the Y direction (vertical direction), respectively. The advantages of addition are: - Addition equalizes random noise to S
, /N ratio improves. ■[)°L mounting detection in the X direction and Y direction can be performed independently, making the detection process much simpler. 0
For example, the memory capacity for storing image data is reduced.

Block X surrounded by a broken line in the block diagram of Figure 6
is a block that adds the density of pixels in the X direction, and block Y is a block that adds the density of pixels in the Y direction.

In FIG. 6, 61 is a video amplifier, 62 is an analog-to-digital converter, and 66 is a latch.The video signal sent from the television camera control section is amplified by the video amplifier 61, and then converted to digital by the analog-to-digital converter 62. After being hit once, it is stored in the latch 66. latch 6
The output data of No. 3 is output to addition block X in the X direction and addition block Y in the Y direction. In block Y, 34 is an adder that adds data in the Y direction, 35 is an addition output latch that latches the output data of the adder 64, and 36 is a Y-direction integration memory that stores the data of the addition output latch 65.
67 is an addition input latch that does not latch the output data of the memory 66.

In block X, 68 is an adder that adds data in the X direction, 69 is a latch that latches the output of the adder 68,
Reference numeral 40 denotes an X-direction integration memory that stores the output data of the latch 69.

There is no particular limitation on the number of bits of digital data in this circuit, but for example, the analog-to-digital converter 32
has an 8-bit configuration, and adders 34 and 38 and memories 36 and 40 have a 16-bit configuration.

On the other hand, 41 is a sequence and memory control circuit that controls the timing and sequence of the television pre-alignment detection circuit, as well as read/write and chip selection of the memory 66, and 42 is a memory control circuit that controls the memory 40 in block X. It is a circuit. 46 is a control register for controlling the sequence and memory control circuit 41 by a microprocessor (not shown), and the register's input is connected to the data bus 44 of the microprocessor. The microprocessor also connects the memory 3 via this data bus 44.
6. η1 accessing 40 is n1 capable. 45,4
6, 47 and 48 are the spare inputs, and buffers 45 and 47 are the buffers 11 and 45 where the microprocessor writes data to memory. ．． 11, and buffers 46 and 48 operate when reading data. 49 is a clock circuit; 50.
Reference numeral 51 denotes a memory write address circuit and a memory read address circuit that generate write addresses and read addresses for the X-square calculation memory 36. 52 is an address selector that switches between a read address and a write address of the memory, and 56 is an address buffer when the microprocessor accesses the memory 66.The output of the address selector 52 is selected except when the microprocessor accesses the memory 66. Therefore, the output of the buffer 56 is prohibited. 54 is a memory address circuit that generates the address of the X-direction integration memory 40; 55 is an address selector that switches between the address of the memory address circuit 54 and the address generated when the microcomputer accesses the memory 40. 56 is clock circuit 4
This is a TV synchronization signal generation circuit that generates a TV horizontal synchronization signal, vertical synchronization signal, blanking signal, etc. based on the clock of No. 9. Reference numerals 57 and 58 indicate an X position display register and a Y position display register, respectively, which are connected to the data bus 44 of the microcomputer, and 59 is a marker display circuit, in which the microprocessor indicates the position of the alignment mark detected in the television pre-alignment. By outputting to the position display register 57 and Y position display register 58, the marker display circuit 59 outputs the signal to the TV as a mix signal.
Sent to the video input terminal of the camera control section.

Next, the function and operation of the television pre-alignment detection circuit shown in FIG. 6 will be explained.

The functions of the television pre-alignment detection circuit are: (1) integration of data in the X direction, (2) integration of data in the Y direction, and (2) display of the pre-alignment mark detection position on the TV monitor.

Of these, the integration of data in the X direction and the integration of data in the Y direction are performed by the hardware of the television pre-alignment detection circuit, and the added data is stored in the memory. Data addition [11] is performed in units of one frame of the television signal, and as described later, the addition may be completed with one frame, or multiple frames may be added as necessary. Good too.

In either case, during addition, the data and address buses of memory 36, 40 are electrically isolated from the data path 44 and address path of the microprocessor, and the addresses of memory 66 are connected to the address selector. 52, the address of the memory 40 is connected to the address of the address circuit 54, and addition is executed under the control of the read/write signal and step select signal generated by hardware from the sequence and memory control circuit 41 and the memory control circuit 42. be done.

When the addition of a predetermined number of frames is completed, the sequence and memory control circuit 41 connects the interconnected signal line I.
An end of addition signal is generated on NT.

After the addition completion signal is generated, the microprocessor accesses the memory 36 and the memory 40 and detects the television pre-alignment mark position from the addition data.

When the microprocessor accesses the memory 66°40, the memory address, read/write signal, step select signal, etc. are naturally controlled by the microcomputer.
Performed by 1alI. Also, data in the memory 66 is stored in the buffer 46, and data in the memory 40 is stored in the buffer 48.
via the data bus 44 and read by the microprocessor.

By the way, addition in the X direction in block X in FIG.
Before explaining addition in the Y direction in block Y, a pixel division method will be described with reference to FIG. FIG. 7 shows the pixels of a television screen divided into N parts in the X direction and M parts in the Y direction. Pixel IVi indicates the pixel in the first row and the lhth pixel in the evening. The number of divisions M in the Y direction usually matches the number of horizontal scanning lines, so in order to divide into pixels, -
It is sufficient to perform sampling N times in the analog-to-digital converter (62 in FIG. 6) within the horizontal synchronizing signal section.

Therefore, addition in the X direction is Sx BiDATA (pH) + DATA (PI3) +-・
・±DATA (PIN), SX22 DATA (P2+)
+DATA (P22) -1-...-1-DATA (Pz
N), SXM 2 DATA (PMI) 10 DATA (P
M2)+...+DATA (pM, ), addition in the Y direction is Sy+2 DATA(P++) +DATA(P2+)+
...-1-DATA (PMI), SY2-DAT
A (PI3) +DATA (P22)+... +D
ATA(PM2), SYN=DATA(PIN)+
DATA(PzN)+・・・・・・+DATA(PMN
), Hail to you.

When the addition is finished, is the product in the X direction? , '11 memory 40
The data of SXI + Sx2...Sl[M is stored in the memory 66, and the data of Sy++Sy2... is stored in the Y direction subtraction memory 66.
SyN data car is stored.

Mark the TV pre-alignment mark shown in Figure 6)
The temperature distribution when the concentration is added in the direction and the Y direction is as shown in FIGS. 6(B) and 6(C). Figure 6 (B) is
The Y direction (two pairs of distributions) of the concentration when added in the Y direction.

FIG. 6(C) shows the distribution of dark vines in the X direction when added in the Y direction. Therefore, for example, Fig. 6 (
When an appropriate slice level XSL is set in CL and binarization is performed with additive density, Fig. 6 (11 as shown in DJ) becomes a binarization pattern of M R - M L, and the center MX of the pattern is It is calculated by (MR-ML)/2.

Similarly in the Y direction, the center MY of the pattern is aligned, and these values become the center coordinates of the pre-alignment mark. As for the set value of the slice level, the microprocessor accesses the contents of the addition memory (36, 4 [1), determines its maximum value (peak value), and sets a value of, for example, 30% of the peak value as the slice level. Determined by By the way, the pre-alignment shown in Figure 3 (A)
Areas 1, 2, and 3.4 around the mark are provided with turns of the actual element, and are not necessarily shown in Fig. 6 (Bl, (
It is not always possible to obtain a concentration distribution with a good S/N ratio as shown in C).

Further, due to the mechanical pre-alignment accuracy of the wafer transport system, etc., the alignment mark is not necessarily captured within the field of view of the television image pickup tube. Therefore, the binarization pattern may not be one ζ2 as shown in the sixth diagram, but a large number of binarization turns may appear, which may cause erroneous detection of the mark position.

The present invention detects an alignment mark having a density difference in the addition direction using a plurality of slice levels. An example of the alignment mark of the present invention is a mark in the shape of a cross pattern shown in FIG.

Adding the density in the Y direction results in the density distribution shown in FIGS. 4(B) and 4(C). As can be seen from the figure, the characteristic of the density distribution in Fig. 4 (Bl, (C)) is that the added density of the marks is in two stages. If two slice levels, e.g. If they match, these become the center coordinates of the alignment mark.

A more detailed explanation will be given using the flowchart of FIG. 8 (however, only the integration in the Y direction). When an addition start command is issued by the microprocessor in step 801, addition in the X and X directions is started as described above. The microprocessor waits at step 802 for the completion of addition, and when the addition of the fixed number of frames of )9T is completed, the process proceeds to step 803. In step 803, the microprocessor searches for the maximum and minimum values of the image density data stored in the addition memory. When the maximum value and minimum value are found, next in step 804 the slice level X5LI,
Set up X5RI. The slice level X5LI is set to a value of, for example, 70% of the difference between the maximum value and the minimum value (referred to as the peak value) of the image density data. Next, in step 805, the slice level X5LI is compared with the memory contents, and the XLI
, put in XRI. Similarly, in step 806, slice level
Get the XR2.

As described above, the binarization pattern shown in FIG. 4(D) and (E), that is, the coordinates XLI, XRJ, XL
2. XR2 can be determined. At step 808 (XR2
-XL2)/2 is calculated and compared to see whether it is equal to If the marks are significantly different, it is determined that the mark is not an alignment mark, and the process proceeds to step 810. If you proceed to step 810, for example, change the slice level setting value and re-measure, or ll!
It is assumed that there is no alignment pattern within the 11th plane, and the process proceeds to search for an alignment pattern.

Incidentally, FIG. 5(A) shows an alignment mark according to another embodiment of the present invention, and shows the alignment mark in the X direction.

When the density is added in the Y direction, the density distribution shown in FIG. 5(FB) and (C) is obtained. Even in this case, marks can be detected reliably by setting at least two slice levels and following the procedure described above.

〔effect〕

As described above, the present invention has the advantage of being able to prevent erroneous detection of alignment marks and detecting marks with high detection rate and high accuracy.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an alignment device according to an embodiment of the present invention, and FIG. 2 is a perspective view of an optical system of a television pre-alignment detection device. FIG. 6 is a plan view of a TV alignment mark according to a conventional example and the integrated internal image density data distribution with respect to the coordinate direction, FIG. 4 is a diagram according to an embodiment of the present invention, and FIG. This is according to the example. 6th
FIG. 7 shows an example of pixel division of a television screen, and FIG. 8 explains the operation of a position detection device according to an embodiment of the present invention. FIG. 61・Video amplifier 62・AD converter 33.35, 37.59・Latch 34, 38 1der 36.40・・Memory 41・Sequence/memory control circuit 42・Memory control circuit 46・Control register 44・・Data bus 45 to 48.53...Buffer 49 - Tarock circuit 50...Memory write address circuit 51...Memory read address circuit 52.55...Address selector 54...Memory address circuit 56 -TV synchronization signal generation circuit 57...X Position display register 58...Y position display register 59...Marker display circuit Y direction Fig. 7 Fig. 8

Claims (1)

[Scope of Claims] Imaging means for imaging an object having a position detection mark of a predetermined shape; addition means for adding 1+;;i image density data obtained by the imaging means in a predetermined coordinate direction; Comparing the magnitude relationship between the non-uniform integrated image density data distribution in a direction perpendicular to the coordinate direction obtained by the adding means obtained by the position detection mark having a predetermined shape and a plurality of predetermined set level values. and means for detecting the position of the Mij position detection mark based on a plurality of comparison results.