JPH06213821A - Foreign-matter inspecting apparatus for semiconductor wafer - Google Patents

Abstract

PURPOSE:To improve the accuracy in foreign-matter inspection by using a threshold value, which is to become the foreign-matter judging reference used in the foreign- matter inspection, as the optimum value for every wafer or every chip in the same wafer. CONSTITUTION:Laser is emitted from an laser emitting device 21 on the specified region of a semiconductor wafer 2 on an X-Y stage 11. The reflected light is detected with a reflected light detector 22. The detector 22 outputs the lightness signal having the value corresponding to the irregularities of the wafer surface based on the reflected light. The lightness signal of one chip is stored in a memory device 31. Then, the signal is compared with the lightness signal associated with the same pattern of the neighboring chip. The difference is computed in an operator 32. The difference is compared with a threshold value T in a comparator 34. It is judged that there is a foreign matter when the difference is larger than the threshold value. The processing for setting the threshold value is performed before the foreign-matter inspection. In this processing, the laser is cast on the specified sampling chip on the wafer. Based on the reflected light, a threshold-value setting and storing device 33 determines the threshold value T suitable for this wafer or the threshold value suitable for every chip.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor manufacturing technique and a technique which is particularly effective when applied to a foreign matter inspection on a semiconductor wafer surface. The present invention relates to a technique useful for a foreign matter inspection by a two-chip comparison method for determining the presence or absence of a foreign matter by using.

[0002]

2. Description of the Related Art In manufacturing a semiconductor device, in order to increase the manufacturing yield, a foreign material inspection on the surface of a wafer that causes a disconnection / short circuit of wiring is carried out after each main manufacturing process. The foreign matter inspection apparatus used for such inspection is known, for example, in "JAP Series 3, Micro Process 89; pages 371 to 376". The foreign substance inspection by this inspection device is generally performed in the following procedure. A semiconductor chip, which is an object to be inspected, is irradiated with a laser for inspecting foreign matter on the entire surface of a specific chip, and the brightness of the reflected light is detected by a reflected light detector (for example, a CCD image pickup device).
Then, the entire surface of the chip adjacent thereto is similarly irradiated with laser to detect the brightness of the reflected light. The signals (brightness signals) representing the brightness of the respective reflected lights reflected from the same pattern of the two chips are compared with each other to obtain the inspection signal representing the difference in the brightness. It is determined whether or not the difference in lightness represented by the inspection signal obtained in this way is lower than a predetermined threshold value.If the threshold value is lower, it is determined that there is no foreign matter, and if it is higher than the threshold value, foreign matter adheres to the wafer. It is determined that The presence or absence of foreign matter can be determined by such a method because the same pattern is formed on two chips to be compared with each other, and the brightness of the reflected light obtained from the same location has substantially the same value. This is because the inspection signal representing the above difference should represent "0" or a value close thereto, if it is not attached.

[0003]

However, the present inventors have clarified that the above-mentioned technique has the following problems. That is, the semiconductor wafer to be inspected has different processing accuracy for each wafer. Further, even between chips formed on the same wafer, the processing accuracy differs depending on the position where they are formed. In this way, when the processing accuracy is different for each wafer, or when the processing accuracy is different for each different chip in the same wafer, even if the same pattern is irradiated with laser light, the brightness of the reflected light will be slightly different. . It is also known that the film quality (for example, the roughness) of the wiring layer formed on the wafer surface is different between the central portion and the outer peripheral portion of the wafer, and in such a case, the brightness of the reflected light also differs. . Therefore, when the conventional foreign matter inspection method is used as it is, there is a possibility that the difference in the brightness of the reflected light due to the difference in the processing accuracy or the film quality is erroneously determined as the foreign matter. For this reason, in the two-chip comparison method, the threshold value for foreign matter determination is set to be larger than this value in consideration of the processing accuracy of the wafer to be inspected and the maximum value of lightness that can occur due to the difference in film quality, and Therefore, the difference in brightness caused by is not mistakenly determined as a foreign substance.

However, if the threshold value is set in accordance with the maximum difference in lightness that can occur due to the difference in the processing accuracy of the underlayer and the difference in film quality as described above, even if the difference in lightness occurs due to minute foreign matter, this is regarded as foreign matter. Since it cannot be determined, the accuracy of foreign matter determination cannot be improved. The present invention has been made in view of such circumstances, a threshold value as a criterion for the presence or absence of foreign matter,
It is a main object of the present invention to provide a foreign matter inspection apparatus that has an optimum value for each wafer to be inspected, or each different chip of the same wafer, and thus enables highly accurate foreign matter inspection.

[0005]

The typical ones of the inventions disclosed in the present application will be outlined below. That is, the semiconductor wafer foreign matter inspection apparatus of the present invention, a light source for irradiating a predetermined area of the semiconductor wafer mounted on the sample table with a light source, and a value corresponding to the unevenness of the wafer surface by detecting the reflected light. Reflected light detection means for outputting an inspection signal, foreign matter determination means for determining the presence or absence of foreign matter on the wafer according to whether the value represented by the inspection signal is larger than a predetermined threshold, and a specific area of the wafer And a threshold value deciding means for deciding the threshold value based on the inspection signal obtained in step 1.

[0006]

The threshold value of the inspection signal relating to the brightness of the reflected light, which is used to determine the presence or absence of foreign matter, is appropriately determined according to the processing accuracy of the chip to be inspected, that is, the processing accuracy of the wafer, the variation in film quality that occurs during manufacturing, etc. Therefore, the foreign matter on the wafer can be accurately determined.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory diagram showing an outline of a foreign substance inspection apparatus 1 for performing a foreign substance inspection by two-chip comparison of the present embodiment. As shown in this figure, the foreign matter inspection apparatus 1 includes a drive system 10 for moving a sample stage (XY stage).
And an optical system 20 centering on the laser irradiation device and a signal processing system 30 for detecting the laser reflected light and processing the detection result.

Of these, the drive system 10 includes an XY stage (sample stage) 11 for performing high-speed scanning of the mounted inspection object (wafer) 2 in the X direction and step movement in the Y direction.
It comprises a drive unit 12 for executing this stage movement, and an XY stage control unit 13 for outputting a control signal for step movement to the drive unit 12. By the action of the drive system 10, for example, after irradiation of a specific chip at the laser irradiation position A of the stage 11 / irradiation of the specific chip / measurement of the reflected light is performed, movement in the X direction is performed,
Another chip in the vicinity of this is moved to the irradiation position A, and the irradiation of a light beam on this / measurement of the reflected light is performed. Such irradiation of light rays / measurement of reflected light is sequentially performed for all chips on the wafer.

The optical system 20 irradiates a chip at the laser irradiation position A on the XY stage 11 with a laser beam for irradiating a foreign substance, and a laser irradiation device 21 for detecting a foreign substance. A reflected light detector (for example, a CCD) 22 that outputs an electric signal (brightness signal) having a value corresponding to the reflected light detector 22
An objective lens 23 for focusing on a detection unit (not shown), and a mirror 24 interposed between the objective lens 23 and the reflected light detector 22 for sending reflected light for focusing to an automatic focusing device (not shown). It will be equipped.

Further, the signal processing system 30 is capable of collectively storing the brightness signals of one chip sent from the reflected light detector 22, and a memory 31 for storing the brightness signal of the previous detection stored in this memory. A calculator 32 that calculates the difference between the brightness signal of one chip and the brightness signal of the adjacent chip detected this time, a threshold value that stores the threshold value data obtained by the "threshold value setting storage process" described below performed before the inspection. A comparison that compares the signal representing the difference obtained by the setting storage device 33 and the calculator 32 with the threshold signal sent from the threshold setting storage device 33 to determine the size of the foreign matter or the presence / absence thereof. It is equipped with a container 34. Of these, the comparator 34
The inspection result output device 40 (display control device 41 and display device (CRT) 42) is connected to the output device 40.
Is based on the foreign matter determination signal from the comparator 34 and the XY stage position data sent from the XY stage controller 13 described above, and the foreign matter is attached to any position on the wafer. The size is determined, and the size is displayed and displayed on the CRT 42 to inform the operator.

Next, the procedure of "threshold setting storage processing" for each wafer by the threshold setting storage device 1 will be described.
FIG. 2 is a plan view showing a selection pattern of the sampling chips C _{1 to} C ₆ for setting a threshold value specific to the wafer 2. The sampling tip with C ₁ -C ₆ "threshold setting storage process" is performed before the particle inspection run. By performing this process, it is possible to set a threshold value in which the difference in the brightness of the reflected light caused by the processing accuracy of the underlayer of the wafer 2 and the density of the film quality of the wafer surface is added in advance.

The determination of this threshold value is performed by the following procedure.
That is, when the sampling chips C _{1 to} C ₆ are selected from the wafer 2 to be inspected by the threshold value setting storage device 33 (chips indicated by diagonal lines in the drawing), a signal indicating the position of the chip is a threshold value setting storage device. 33 to the XY stage controller 13. Upon receipt of this signal, the XY stage control device 13 sends a control signal to the drive device 12 so that the selected one sampling chip (for example, C ₁ ) is at the laser irradiation position, and the XY stage 11 moves. Make a move. After that, the chip C ₁ is irradiated with a laser, and the reflected light is detected by the reflected light detector (CCD) 22 as a signal representing the brightness (brightness signal), and the value is stored in the storage unit 31. .

When the detection of the brightness signal for the entire surface of the sampling chip C ₁ and its storage are completed, a signal indicating the end of storage is sent to the XY stage control device 13 via the setting storage device 33. Receiving this, the XY stage control device 33 outputs a control signal to the drive device 12 so that the chip (for example, the adjacent chip C ₁₁ ) to be compared with the chip C ₁ comes to the laser irradiation position A. . When the chip C ₁₁ to be compared by this series of controls reaches the irradiation position of the XY stage, the brightness signal of the reflected light for the entire surface of the chip C ₁₁ is detected / stored by the same procedure as described above.

The brightness signal of the sampling chip C ₁ and the brightness signal of the chip C ₁₁ to be compared with the sampling chip C ₁ are both sent to the arithmetic unit 32, in which the two brightness signals are compared. It should be noted that the comparison of the brightness signals is performed with respect to the brightness signal of the reflected light with respect to the same pattern. Then, when the two lightness signals are compared with respect to the entire surface of the chip, the difference between them is averaged to obtain the difference L _{1 of the} chip C ₁ . In such a two-chip comparison method, if the reflection conditions of both chips C ₁ and C ₁₁ are exactly the same over the entire surface, the two lightness signals are canceled and the difference L ₁ thereof is “0”. become. However, in the actual inspection, a difference in the bases of the two chips C ₁ and C ₁₁ due to the position of the chips or a difference in brightness due to the nonuniformity of the formed film quality within the wafer appears. Hereinafter, similarly, for all the sampled chips (C _{2 to} C ₆ ), the difference (L _{2 to} L ₆ ) of the brightness signal with the adjacent chip is calculated, and the values are sequentially calculated.
It is stored in the threshold setting storage device 33.

The threshold setting storage device 33 substitutes the differences L ₁ , L ₂ , L _3, ..., L _n obtained for each of these chips into, for example, the following equation to calculate the threshold values peculiar to the wafer. Set / store as reference value TB. TB = (L ₁ + L ₂ + L ₃ ... + L _n ) / n where n represents the sampling number (n = 6 in the example of FIG. 2). In the above calculation formula for calculating the reference value T, it is assumed that no foreign matter is attached to the sampling chip itself, but in case the foreign matter is attached to the sampling chip, a significantly large difference L is generated. When it occurs, an arithmetic process such as excluding it from the arithmetic may be performed.

When actually inspecting a foreign substance on a wafer, a value obtained by adding a constant margin ΔT to the reference value TB thus obtained is used as the threshold value T for the determination. In the above description, the difference in the brightness signal of one sampling chip was obtained by comparing with the chip adjacent thereto. However, the differences of the brightness signal are calculated by comparing the sampling chips with each other, and the difference is calculated based on the difference. Alternatively, the threshold may be determined.

According to the above method, since the threshold value T is determined for each semiconductor wafer (see FIG. 3), conventionally, the wafer having the largest difference (lot No. 3 in FIG. 3) among the lots at the time of manufacturing is selected. It becomes possible to improve the accuracy of inspection by substituting the optimum value for each wafer for the threshold value TMAX1 of.

Next, a procedure for setting / storing an optimum threshold value for each chip by the threshold value setting storage device 33 will be described. The brightness signal for the entire surface of a predetermined sampling chip (for example, C ₁ ) is stored by the same procedure as the setting / storing of the threshold value for each wafer described above, and then the brightness signal for the entire surface of the chip C ₁₁ adjacent thereto is stored. When stored in the container 31,
The brightness of reflected light for the same pattern is sequentially compared by the calculator 32, and the difference L ₁ calculated for the entire surface of one chip is averaged. Threshold setting storage device 3
3 is a threshold value T _{1 which} is obtained by adding a predetermined margin to the difference L ₁ and uses this value as the XY stage control device 13
It is stored in association with the position data of the chip C ₁ sent from the device.

Chips stored in this way (C _{1 to} C ₆ )
The thresholds (T _{1 to} T ₆ ) for each are used in the foreign matter determination as follows. For example, when the chip C _{31 of} FIG. 2 and the chip C ₃₂ adjacent thereto are compared to determine the foreign matter,
The difference between the brightness signals obtained from these chips is calculated, and the sampling chip (for example, C ₃ ) closest to the chip is obtained.
The threshold value T ₃ is compared with the threshold value T ₃ . In the two-chip comparison method, when the lightness signals are compared, the lightness signal on the side to which the foreign matter adheres remains, so it is determined which of the two chips the foreign matter occurs.
It can be determined only by comparing two chips. According to the above method, the threshold value T for each chip in the semiconductor wafer
(See FIG. 4), the threshold value T of the chip (wafer No. 2 in FIG. 4) having the largest difference in the wafer in the past is determined.
The accuracy of the foreign matter inspection can be improved by replacing the value matched with MAX2 with the threshold value of the sampling chip closest to each chip to be inspected for foreign matter.

As described above, the foreign matter inspection apparatus according to the present embodiment detects the brightness of the reflected light of the laser beam applied to one chip on the wafer and irradiates the same pattern on the other chip. Detecting the brightness of the reflected light of the laser beam, comparing these detection results with each other, in comparing the difference with a predetermined threshold to determine whether foreign matter is attached on the wafer, the threshold is Since the brightness of a particular sampling chip of the wafer is compared in advance and the determination is made based on the comparison result, the processing accuracy of the undercoating that occurs for each wafer and the difference in brightness of reflected light due to the difference in film quality Accurate foreign matter inspection can be performed without being affected. In addition, since the threshold value is set for each sampling chip within the same wafer, it is possible to perform accurate foreign substance inspection without being affected by the processing accuracy that may occur for each chip and the difference in brightness of reflected light due to the difference in film quality. Become.

Although the invention made by the present inventor has been specifically described based on the embodiments, the invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say. For example, in the present embodiment, an example of performing a foreign matter inspection by a so-called two-chip comparison method in which two chips are compared in performing the foreign matter inspection is shown, but another inspection method using an optical system, for example, polarization is performed on the wafer surface. The present invention can also be applied to a method of irradiating the surface of the sheet with light and detecting irregularities on the surface thereof. In addition, in the present embodiment, when comparing two chips, an example in which adjacent chips are compared with each other has been shown. However, the brightness difference of the reflected light is calculated by comparing with a chip distant from the chip, and a threshold value is obtained. May be set. In this case, the threshold value obtained by the interpolation calculation may be used for the foreign matter determination of the chips located in the middle of them. Further, in this embodiment, at the time of calculating the threshold value, the brightness differences obtained by comparing the entire surfaces of the two chips are averaged, the values obtained for each sampling chip are further averaged, and the wafer-specific threshold value is based on this value. However, the threshold value may be calculated on the basis of the brightness differences obtained by the above comparison stored for all the sampling chips, the values are collectively averaged. Further, in calculating the average value, the weight of averaging may be changed according to the position of the chip. Further, in the present embodiment, when setting the threshold value, the brightness difference of the reflected light was detected over the entire surface of the sampling chip, but the brightness difference at a specific portion of the chip was detected, and the threshold value was determined based on this result. May be. Further, in the above-mentioned embodiment, the apparatus for determining the presence / absence of foreign matter on the wafer surface by using the laser beam has been described, but it can be applied to an inspection apparatus using other radiation rays. In the above description, the case where the invention made by the present inventor is mainly applied to the foreign matter inspection on the surface of a semiconductor wafer which is the field of application which is the background has been described, but the present invention is not limited thereto and the optical system It can be generally used for foreign matter inspection using.

[0022]

According to the present invention, since the threshold value used for foreign matter determination is set to the optimum value for each wafer or the optimum value for each chip, it is possible to accurately determine the presence or absence of foreign matter adhering to the wafer surface. Well done.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an outline of a foreign matter inspection apparatus 1 for performing a foreign matter inspection by two-chip comparison of the present embodiment.

FIG. 2 is a plan view showing a selection pattern of sampling chips C _{1 to} C ₆ for setting a threshold value specific to a wafer.

FIG. 3 is a graph showing a value of a threshold value T set for each wafer.

FIG. 4 is a graph showing a value of a threshold T set for each chip.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Foreign substance inspection device 2 Wafer (inspection target) 10 Drive system 11 XY stage (sample stage) 13 XY stage control device 20 Optical system 21 Laser irradiation device for foreign substance inspection (irradiation device) 22 Reflected light detector (CCD) ) 30 signal processing system 31 memory device 32 arithmetic unit 33 threshold value setting memory device 34 comparator C _{1 to} C ₆ sampling chip

Claims (3)

[Claims] 1. A irradiating means for irradiating a predetermined area of a semiconductor wafer mounted on a sample stage with a light beam, and a reflected light detection for detecting the reflected light and outputting an inspection signal having a value according to the unevenness of the wafer surface. In a foreign matter inspection apparatus having a means and a foreign matter determination means for determining the presence or absence of a foreign matter on the wafer according to whether or not the value represented by the inspection signal is larger than a predetermined threshold value, it is obtained in a specific region of the wafer. A foreign matter inspection device for a semiconductor wafer, comprising: a threshold value determining means for determining the threshold value based on the inspection signal. 2. The inspection signal is a signal representing the difference between the brightness signals of two reflected lights obtained by irradiating the same pattern of two different chips on the same semiconductor wafer with a light beam. The foreign matter inspection apparatus for a semiconductor wafer according to claim 1. 3. The threshold value determining means determines a different threshold value for each semiconductor chip.
A semiconductor wafer foreign matter inspection apparatus according to item 1.