JPS6286740A - Semiconductor wafer inspection method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention provides a highly sensitive and highly reliable method for detecting defects (microscopic foreign objects and pattern defects) on semiconductor LSI wafers, especially patterned wafers in intermediate processes of LSI manufacturing. The present invention relates to a semiconductor wafer inspection method suitable for detection at high temperatures.

[Background of the invention]

Conventional foreign particle inspection equipment on wafers uses (1) a combination of one-dimensional high-speed scanning of laser light and low-speed translational movement of the sample;
l) Scanning and detection of the entire surface of the sample is performed using linear scanning based on a combination of high-speed rotation and low-speed translation of the sample. Furthermore, in the conventional technique described in Japanese Patent Application Laid-open No. 57-80546, scanning equivalent to the above (1) is realized by combining electrical scanning of a self-scanning type dimensional photoelectric conversion element array and low-speed movement of the sample. Furthermore, in the conventional technology described in Section 7 Evaluation System of the Latest Semiconductor Factory Automation System Comprehensive Technology Collection, a self-scanning-dimensional photoelectric conversion element array is arranged at the radial position of the sample wafer, and this and the rotational movement of the sample are combined. By combining these, scanning equivalent to the above (11) is realized.

However, in the conventional method described above, since the sample is irradiated with laser light and the scattered light is detected, the pattern is detected at the same time as the foreign object on the wafer on which the pattern has been generated.
This method has the disadvantage that it cannot be applied to patterned wafers.

Inspection of foreign substances on patterned wafers during the intermediate process of LSI manufacturing is essential for improving product yield and reliability. Automation of this work is disclosed in Japanese Patent Application Laid-Open No. 55-149829.
In addition to JP-A-54-101390, 55-941
As shown in a series of published patent publications such as No. 45 and No. 56-30630, detection methods using polarized light have been realized.

This principle will be explained using FIGS. 8 to 14.

As shown in FIG. 8, if only the illumination light 4 is irradiated onto the surface of the wafer 1 at an inclination angle φ, scattered light 5 and scattered light 6 will be generated from the pattern 2 and the foreign matter 3 at the same time.
It is not possible to distinguish and detect the foreign matter 6 and the foreign matter 6. Therefore, an attempt has been made to use polarized laser light as the illumination light 4 to detect only the foreign matter 5.

As shown in FIG. 9, a pattern 2 existing on a wafer 1 is irradiated with S-polarized laser light 4. As shown in FIG. (Here, when the electric vector 10 of the laser beam 4 is parallel to the wafer surface, it is called S-polarized laser illumination.) In general, the surface irregularities of the pattern 2 are microscopically small enough compared to the wavelength of the illumination light, and the optical Since the reflected light 5 also maintains the S polarization component 11. Therefore, if the analyzer 13 that blocks S-polarized light is inserted into the optical path of the reflected light 5, the reflected light 5 is blocked and does not reach the photoelectric conversion element 7. On the other hand, as shown in FIG. 10, the scattered light B from the foreign object 6 includes a P-polarized light component 12 in addition to the S-polarized light component. This is because the surface of the foreign object 3 is rough, and as a result of depolarization, the P-polarized light component 12 is generated.

Therefore, if the P-polarized light component 14 passing through the analyzer 13 is detected by the photoelectric conversion element 7, the foreign object 3 can be detected.

Here, as shown in FIG. 8, when the angle between the longitudinal direction of the pattern 2 and the laser beam 4 is at right angles, the reflected light 5 is completely blocked by the analyzer 13. , if this angle is different from the right angle, the light will not be completely blocked. This discussion is published in Proceedings of the Society of Instrument and Control Engineers, Mo1.17.
m ” t E'232-p 242, 1981. According to this, this angle is ±3 from the right angle.
Since only the reflected light from the pattern force in the range of 0° or less enters the objective lens installed above the wafer, the pattern reflected light 5 in this range is not completely blocked by the analyzer 13, but its intensity is Since the light is small enough to be distinguished from the scattered light from foreign matter of 2 to 5 μm, it poses no practical problem.

Here, the 1v7# angle φ of the polarized laser beam 4 is set to about 1 to 3 degrees. This is for the reason shown below. @1
In the experiment shown in Fig. 1, the intensity V8 (13th
) and the analyzer-passing component intensity Vp of pattern reflected light 5 (
Fig. 14) with objective lens 9 (magnification 40X', N-
A-0,55). Experiment results 12th
As shown in the figure.

This is a plot of the foreign matter/pattern discrimination ratio v8/vp, with the laser inclination angle φ being plotted on the horizontal axis. As shown in the figure, when the inclination angle φ is 5° or less, v8 can be easily distinguished from vp, so stable foreign object detection is possible. Moreover, considering design matters, φ=1 to 3 is optimal.

Here, the reason why two laser light sources 15 are used from the left and right is to enable stable detection of foreign objects that generate scattered light having foreign object properties.

Next, the foreign object inspection method using this detection principle is shown in Figure 15~
This will be explained with reference to FIG.

As shown in FIG. 15, a slit 8 is provided on the sample imaging surface to limit the detection range. As a result, only the scattered light within the projected area 8a of the opening of the slit 8 onto the sample is detected at a time, so that the pattern reflected light P within this area is detected at a time.
Compared to the integrated intensity of the component 14P, the foreign body scattered light P component 14d
If is large enough, the foreign matter 5 can be detected stably. Therefore,
This area 8α is the size of the foreign object to be detected, which is 2 to 3 μm.
), the detection sensitivity will be optimal.

However, as shown in FIG. 16, the smaller the area, the greater the number of scans, and the longer the inspection time. On the other hand, if the opening area 8α is increased, the inspection can be done in a shorter time.
This results in deterioration of detection 1 sensitivity. This situation will be explained using FIGS. 17 and 18.

Figure 17 shows a plan view (α) and a cross-sectional view (h) of the wafer surface.
Show. Is there a slight dent in the nogu turn in pattern 2? , there are places that have angles other than perpendicular to the irradiation direction of the laser beam 4, and a small amount of scattered light pt 14 is emitted from each of these places.
p occurs. On the other hand, from the small foreign matter 3α having a size of about 0.5 to 2 μm and the large foreign matter 34 having a size of 2 μm or more, a P component 14d having a higher intensity than each of the above pattern parts is generated.

FIG. 18 shows the signal output of the photoelectric conversion element 7 when the aperture 8α scans over the sample. In the same figure (α), 2 losses = 14p
and 14d on the sample. Opening 8 on this distribution
When a scans, the output shown in (J) of the same figure is obtained. In this example, since the output from the small foreign object 3α and the edge of pattern 2 are the same, the threshold shown by the broken line must be set at a position higher than this output. As a result, the defect signal is limited to detecting only large foreign objects.

As shown in FIG. 19, there is a test pattern 16 on the wafer.
α and alignment pattern 16-& exist. The test pattern 16α is used to check the completion of the circuit pattern, and the alignment pattern 16b
is a pattern for mask alignment. These are normal circuits.

It is thinner than turn 17 and has a significantly higher pattern step. Some objects have shapes that can be confused with foreign objects, and the foreign object detection limit is determined by these test patterns and alignment patterns. Since these are outside the circuit pattern 17 and their functions are different from the original functions of the LSI, there is no need to perform strict foreign object inspection, but due to their presence, inspection must be performed with the foreign object detection performance degraded. I don't get it. If the sensitivity is increased, the test pattern or alignment pattern will become a five-point signal.

The above situation is similar in the case of pattern defect inspection.

Since the test pattern 16α is made under different conditions than the circuit pattern 17, its shape differs slightly depending on its location. Therefore, defect detection sensitivity is limited by the test pattern 16 that does not need to be inspected.

[Purpose of the invention]

Is the purpose of the present invention a test pattern? It is an object of the present invention to provide a semiconductor wafer 1 inspection method that eliminates false alarms such as alignment patterns and inspects minute foreign objects and pattern defects with high sensitivity.

[Summary of the invention]

The test patterns and alignment patterns are arranged at the same location for each type of wafer (including reticle and photomask). By detecting foreign objects or pattern defects at a level that does not detect circuit patterns, and comparing them with the inspection results of the same type of wafer inspected just before, false alarms due to test patterns and alignment patterns are always at the same location when the wafers are of the same type. Detected.

On the other hand, foreign matter or pattern defects are rarely detected at the same location. Therefore, in the present invention, detections at the same location are excluded from the inspection results as false alarms due to the test pattern or alignment pattern.

As a result, highly sensitive and reliable inspection of foreign matter or pattern defects becomes possible.

Note that before detecting foreign objects, it is necessary to detect the position of the wafer and correct the position.

[Example of light]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7. In addition, we will discuss the case of inspecting foreign objects.
It is also possible to inspect butter for defects in the same way.

FIG. 1 is a configuration diagram of a foreign matter inspection device. The wafer 1 is irradiated with 8-polarized laser light 4, and the reflected light is collected by an objective lens 9 and detected by a photoelectric conversion element 7. Further, an analyzer 13k for blocking the S-polarized component of the reflected light and a slit 8 for limiting the detection range are inserted in the detection optical path.

Wafer 1 is 1X to inspect its entire surface.

X by stage 18 and X stage 21, respectively.

Scan in the Y direction. The X stage 18 is connected to the motor 19.
:l, The X stage 21 is driven by a motor 22.

Here, in order to scan the wafer as shown in FIG. 16, continuous feeding is performed in the X direction and intermittent feeding is performed in the Y direction. X
Since the stage 18 is required to be continuously fed and moved at high speed, a DC motor is normally used as the motor 19. In addition, a position sensor 20 such as a linear scale is required to know the stage coordinates in the X direction. Since the X stage 21 is an intermittent feeder and does not require high-speed movement, a step motor is normally used as the motor 22, and the Y-direction stage coordinates can be determined from the amount of step motor feed. 25 is a stage control circuit which controls the motor 19 and the motor 22 to
The wafer is scanned as shown in FIG. At this time, the motor 23 is driven so that the X-direction scanning and the wafer pattern direction are parallel, and the 9171 rotation direction is adjusted. In this case, the position of the alignment pattern 16b is detected in advance,
The positional deviation in the rotational direction will be measured as described below (b).26j
l: , 26y is! l! These counters each count the output of the position sensor 20 and the amount of intermittent feed in the 1Y direction.

33 is a binarization circuit which binarizes the detection Ii1 signal 35 of the photoelectric conversion element 7 and generates foreign matter 411 No. 37. 2
Value conversion is performed by comparing the detection signal 35 with a threshold value 36, as shown in FIG. Detection signal 35
C and the minute foreign object detection signal 35α are set to levels for binarization.

The foreign object signal processing circuit 34 in FIG. 1 determines whether or not the detected foreign object is a false alarm.
Do not output.

Eliminate false information as follows. When the foreign object signal 37- is received, the coordinate counter 26↓: , 2 (S!/114), which was present on the previously inspected wafer, determines that the detected foreign object is a false alarm and outputs the actual foreign object signal 50. To perform this function, the test pattern and alignment pattern must have the same coordinates each time even if the wafer is replaced, so the wafer must be aligned in the XYθ directions before the start of inspection. Let's do it.

An example of wafer alignment is shown in FIG. As shown in the figure, an illumination lamp 29. Half mirror 2728 and TV
Although the image sensor 30 such as a camera may be inserted into the foreign object detection optical system as a completely separate optical system, the optical system becomes more compact if the objective lens 9 of the foreign object detection optical system is shared. The surface of the wafer 1 is illuminated by the illumination lamp 29, and an enlarged image of the wafer pattern by the objective lens 9 is detected by the image sensor 50. The wafer pattern to be detected is the alignment groove 16b or any specific pattern, and as shown in FIG. 4, it is detected at two locations A and B. - As an example, a case where the image sensor 30 is a TV camera and the detection pattern is a guard line corner as a specific pattern will be explained with reference to FIGS. 5 and 6. First, the guard line corner 51 is detected at point A, and the deviation ΔXA + ΔYA from the TV camera internal reference line 51 is determined. Next, the X table 18 is moved and the deviations ΔXB and ΔYB at point B are determined. The amount of movement is an integral multiple of the chip size. After calculating the amount of deviation at two places, depending on the amount of movement Xm and each amount of deviation,
Angle θl (△Y
A-ΔYB)/xm is determined, and the motor 23 is driven so that it becomes zero. Next is △XA.

Motor 19. so that ΔYA (or ΔXB, ΔYB) becomes zero. -E-Drive 22. These position correction calculations are performed by the calculation circuit 70. If the coordinate counters 26X- and 26y are then cleared to zero, the test pattern and alignment pattern can always be detected as having the same coordinates even if the wafer is replaced.

A method for removing a test pattern or alignment pattern as a false alarm will be explained with reference to FIG.

The foreign object memory 38 stores coordinate values of detected foreign objects (including false alarms) on previously inspected wafers. When the foreign object signal 37 is generated, the coordinate counters 262 and 263
A value of 1 is stored in the lunches 41 and 42. At the same time, the contents of the foreign object memory 38 are sequentially read out, and the latches 39, 4
Temporarily set to 0.

The arithmetic circuit 43 calculates the absolute value of the difference between the latch 39 and the latch 41.
, and find the shift in the X-direction coordinates. A coincidence signal is output when this deviation amount is less than or equal to the allowable value εX. Similarly, the arithmetic circuit 44 calculates the absolute value of the difference between the latch 40 and the latch 42, and calculates the shift in the Y-direction coordinate. A comparison circuit 46 compares the amount of deviation in the Y direction with the allowable value εY, and outputs a match signal when the amount of deviation is less than the allowable value εY. Then, an AND gate 47 performs a logical product of the outputs of the comparison circuit 45 and the comparison circuit 46, and an inverter 48 inverts the output of the AND gate 47. If the same coordinate values as the detected foreign object are stored in the foreign object memory for 3 days, the output of the inverter 48 will be 10'.
becomes. When the AND gate 49 takes the logical product of the inverter 48 output and the foreign object signal 67, if there is a foreign object (or a false alarm) with the same coordinates in the previously inspected weno 1, it is assumed that it is a false alarm and the actual foreign object color number 50 is determined. U! You won't be able to do anything.

Here, the foreign object memory 38 stores the foreign object coordinates. If the coordinates to be memorized are those of the first (initial) inspected wafer.

The configuration shown in FIG. 7 is sufficient, but if the wafer inspected immediately before is to be used, it is necessary to prepare another set of foreign object memories.

That is, the foreign object coordinates (26x, 26y outputs) of the wafer under inspection are stored in another set of foreign object memories and compared with the contents of the foreign object memory 38. When inspecting the next wafer, the foreign object memory is replaced and the foreign object coordinates are stored in the foreign object memory 38 and compared with the contents of another set of foreign object memories.

In the above-described method, the determination is made each time a foreign object is detected during the inspection, but the determination can also be made all at once after the inspection is completed. For example, the foreign object coordinates inspected last time are stored in the foreign object memory on the 6th day, and the foreign object coordinates inspected this time are stored in another set of foreign object memories.

By comparing the foreign object coordinates stored in the foreign object memory 58 and another set of foreign object memories for each foreign object after the inspection is completed, the same function as the method described above can be achieved.

Although the optical alignment explained in FIGS. 3 to 6 is not necessarily necessary, wafer outline reference alignment as rough alignment is at least necessary.

4. By aligning the wafer outline reference before inspection and increasing the allowable values εX and ξY shown in FIG. 7, the same function as optical alignment can be achieved.

It is clear that even in the case of wafer pattern defect inspection, the above effects can be obtained simply by changing the illumination system detector and the detection signal processing circuit.

As described above, foreign object detection accuracy can be improved by treating □ that existed at the same coordinates as the previously inspected wafer as a test pattern or alignment pattern and not outputting it as a foreign object signal. .

〔Effect of the invention〕

According to the present invention, even if there is a shape similar to a defect (foreign object or pattern defect), such as a test pattern or an alignment pattern, it is possible to detect minute particles in a circuit pattern without erroneously detecting them as defects. It is possible to detect only certain defects with high sensitivity and stability.

Note that the present invention is not limited to wafers, but can also be applied to the inspection of other products such as photomasks and reticles.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a foreign matter inspection device to which an embodiment of the present invention is applied, FIG. 2 is an explanatory diagram of detection signal processing, FIG. 3 is a configuration diagram of a wafer positioning device, and FIG. 4 is a plan view of a wafer. 5 and 6 are partially enlarged views of the wafer shown in FIG. 4, FIG. 7 is a detailed configuration diagram of the foreign object signal processing circuit, FIG. 8 is an explanatory diagram of reflected light and scattered light, and FIG. 9 is a pattern 10 is an explanatory diagram of scattered light from a foreign object. FIG. 11 is an explanatory diagram of a laser beam irradiation method. FIG. 12 is a graph showing experimental results of pattern/foreign object discrimination performance. 14 are explanatory diagrams of V8 and Vl shown in FIG. 12, respectively, FIG. 15 is an overview of the main parts of the inspection device, and FIG. 16 is an explanatory diagram of scanning,
Figures 7(a) and 117IN(b) are a partial enlarged plan view and cross-sectional view of the wafer, respectively. Figure 18(α) is a unidirectional distribution diagram of patterns and foreign particles on the wafer. Figure 18(6) is a diagram of the detection. Waveform diagrams of signals and defect signals, and FIG. 19 are detailed plan views of Ueno 1. 1: Wafer, 2: Pattern, 3: Foreign matter, 4: Illumination light 15
: Reflected light, 6: Scattered light, 7: Photoelectric conversion element, 8 Nislit, 9: Objective lens, j3: Analyzer, 16: Test pattern, 17: Circuit pattern, 18: X stage, 19:
X motor, 20: Position sensor, 21: Y stage, 22: Y motor, 23: θ motor, 29: Illumination lamp, 30: Image sensor, 33: Binarization circuit 13
4: Foreign object signal processing circuit, 38 two-coordinate memory, 39.42
:Latch, 43, 44: Arithmetic circuit, 45, 46: Comparison circuit. Representative Patent Attorney Katsuo Ogawa - Etaka 1 Figure - 1shi 0' 5°, 10° Fig. 15 Fig. 17 Fig. 18 - - [.

Claims (1)

[Claims] 1. The defect signal generation position of the previously inspected wafer is memorized, and the defect signal generation position of the wafer inspected this time is compared with the memorized defect signal generation position to determine whether the defect signal generation position is the same. A semiconductor wafer inspection method characterized by removing a signal generated from a position as a false alarm. 2. The semiconductor wafer inspection method according to claim 1, characterized in that each time a defect signal is generated, the generation position is compared with a stored defect signal generation position. 3. The defect signal generation position obtained from the previous inspection is stored in the first storage means, and the defect signal generation position obtained from the current inspection is stored in the second storage means.
2. The semiconductor wafer inspection method according to claim 1, wherein the contents of the second storage means are compared with the contents of the first storage means after the inspection is completed.