WO2021135044A1

WO2021135044A1 - Defect inspection apparatus and method

Info

Publication number: WO2021135044A1
Application number: PCT/CN2020/090989
Authority: WO
Inventors: 玉虫秀一; 李琛; 赵宇航; 李铭; 卢意飞; 王鹏飞
Original assignee: 上海集成电路研发中心有限公司; 上海先综检测有限公司
Priority date: 2019-12-30
Filing date: 2020-05-19
Publication date: 2021-07-08
Also published as: JP7340703B2; JP2023508738A; CN111146105A; CN111146105B

Abstract

A defect inspection apparatus and method. The method comprises: measuring position information of an inspected object by using a position measurement module (S1); according to the position information, when the inspected object moves by one pixel of a camera module, generating a timing pulse, and by means of correcting a timing pulse error, delaying the timing pulse by means of a clock and then outputting the timing pulse, wherein the update frequency of the position information is greater than the frequency of the timing pulse (S2); photographing the surface of the inspected object according to the timing pulse delayed by a clock, and outputting an image signal (S3); and inspecting a defect of the inspected object according to the image signal (S4). Therefore, in the solution, by improving the accuracy of a timing pulse, the image resolution is improved, and an accurate trigger pulse can be generated, even when slow output rate position information is used.

Description

Device and method for defect inspection

cross reference

This application claims the priority of the Chinese patent application with the application number 201911388673.8 filed on December 30, 2019. The content of the above application is included here by reference.

Technical field

The present invention relates to the technical field of semiconductor manufacturing, and more specifically, to a defect inspection device and method.

technical background

In semiconductor defect inspection systems, a laser interferometer is usually used to detect the position of the carrier platform on which the inspected object (wafer) is mounted. When imaging the inspected object sample with a time delay integration (TDI) sensor, it is necessary to The fixed displacement of the inspection object generates a trigger pulse (also called a "timing pulse").

Please refer to FIG. 1. FIG. 1 shows a defect inspection device for wafer pattern defect inspection according to Japanese Patent (JP 2003-177101). This device is used to detect the location and image of defects on the wafer surface. As shown in the figure, number 29 in Figure 1 is a timing pulse generating module. The timing pulse generation module generates timing pulses according to the relationship between the output data of the laser interferometer and the position of the target (object to be inspected), that is, the output data is compared with the target position. When the output data position information exceeds the target position, the Send location information at regular intervals.

However, when the timing pulse is generated by the above method, an error of the data output interval of the position measurement circuit will be generated. Even if the fastest position measurement circuit is selected, the error may not meet the system requirements; especially with wafers The moving speed of the bearing platform increases, and timing pulses with sufficient accuracy cannot be generated in the output interval of a normal laser interferometer.

Summary of the invention

The purpose of the present invention is to overcome the above-mentioned defects in the prior art, and provide a wafer defect detection device and a detection method thereof, which is adapted to the moving speed of the carrier platform carrying the wafer, and can be used in the output interval of the normal laser length measuring instrument. Generate timing pulses with sufficient accuracy.

In order to achieve the above objective, the technical solution of the present invention is as follows:

A defect inspection device, which includes:

The master control interface module is used for data input/output; wherein the data includes user information data, inspection result data, and operation flow control data, and the inspection result data includes digital and/or image data;

The carrying platform is used to carry the inspected object and make the inspected object move with the movement of the carrying platform;

An illumination module for illuminating the inspected object mounted on the carrying platform;

A camera module, in cooperation with the illumination module, photographs the surface of the inspected object and outputs an image signal;

A position measuring module, which measures the position information of the inspected object;

The timing pulse generating module receives the position information of the inspected object, and generates a timing pulse when the inspected object moves one pixel of the camera module; and the timing pulse generating module corrects the timing pulse error , Delaying the timing pulse by one clock and outputting it to image the surface of the inspected object, wherein the update frequency of the position information is greater than the timing pulse frequency of the camera module; and

The image processing module detects the defect of the inspected object according to the image signal.

Further, the position measurement module includes a linear image sensing unit.

Further, the timing pulse generating module includes:

The adder adds up the pixel size ΔX of the linear image sensing unit, and outputs the trigger coordinate X _T ;

Differentiator, obtain the speed v according to the position information X _{L of the inspected object;}

A comparator for comparing the _{magnitude relationship between the position information XL} and the output value of the adder to generate a trigger signal Trg;

The arithmetic unit receives the trigger coordinate X _T , the trigger signal Trg, the position information X _L and the speed v, and executes a prescribed calculation (X _T +ΔX-X _L )/v to obtain a clock delay time;

The delay unit sends out a delay pulse delayed by one clock according to the clock delay time;

The falling edge detection unit detects the falling edge of the delayed pulse, and starts the camera module to image the surface of the inspected object; wherein _{the update frequency of the position information XL} is greater than the timing pulse of the linear image sensing unit Frequency, the working frequency of the delay unit is greater than the update frequency of _{the position information XL.}

Further, the _{update frequency of the position information XL} is 10 MHz, the timing pulse frequency of the linear image sensing unit is 3 MHz, and the operating frequency of the delay unit is 300 MHz.

Further, the linear image sensing unit is a time delay integral image sensing unit.

Further, the inspected object is a semiconductor wafer.

Further, the illumination module includes a deep ultraviolet light source, and the method of forming an illumination light path by using the deep ultraviolet light source is a broadband illumination method or a narrowband illumination method with bright lines.

Further, the position measurement module includes a laser length gauge.

A defect inspection method, which includes the following steps:

Step S1: Use the position measurement module to measure the position information of the inspected object;

Step S2: According to the position information, when the inspected object moves one pixel of the camera module, a certain timing pulse is generated; and the timing pulse generation module corrects the timing pulse error to delay the timing pulse by one Output after the clock, wherein the update frequency of the position information is faster than the timing pulse frequency of the camera module;

Step S3: According to the timing pulse delayed by one clock, the surface of the inspected object is photographed, and an image signal is output;

Step S4: Detect the defect of the inspected object according to the image signal.

Further, the step S2 specifically includes the following steps:

Step S21: Add the pixel size ΔX of the linear image sensing unit, and output the trigger coordinate X _T ;

Step S22: It is used _{to compare the magnitude relationship between the position information XL} and the output value of the adder to generate a trigger signal Trg;

Step S23: Receive the trigger coordinate X _T , the trigger signal Trg, the position information XL and the speed v, and perform a prescribed operation (X _T +ΔX-X _L )/v to obtain a clock delay time;

Step S24: Send a delay pulse delayed by one clock according to the clock delay time;

Step S25: Detect the falling edge of the delayed pulse, start the camera module to take a picture of the surface of the inspected object; wherein _{the update frequency of the position information XL} is greater than the timing pulse frequency of the linear image sensing unit, The operating frequency of the delay unit is greater than the update frequency of _{the position information XL.}

It can be seen from the above technical solution that the present invention corrects the timing pulse error by adding a counter circuit, wherein the operating speed of the counter circuit exceeds the output rate of the position measurement circuit and meets the system requirements. That is, the timing pulse generating unit waits for the average interval to be delayed by a predetermined amount of delay time before outputting the pulse.

The invention improves the resolution of the image by improving the accuracy of the timing pulse, and can generate accurate trigger pulses even when using slow output rate position information.

Description of the drawings

Figure 1 shows a schematic diagram of the structure of a defect detection device in the prior art

Figure 2 shows a schematic diagram of the structure of a defect detection device in an embodiment of the present invention

Figure 3 is a schematic diagram of a timing pulse generating module in an embodiment of the present invention

Figure 4 is a schematic diagram illustrating the timing of each pulse in the embodiment of the present invention

Summary of the invention

The specific embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings.

In the following specific embodiments of the present invention, please refer to FIG. 2. FIG. 2 is a schematic structural diagram of a semiconductor wafer defect inspection apparatus 100 of the present invention. The defect inspection device 100 usually includes a general control interface module, a bearing platform, an illumination module, a camera module, an image processing module, a position measurement module, and a timing pulse generation module.

In the embodiment of the present invention, as shown in FIG. 2, the master control interface module 9 is used to control the operation of the entire device, that is, for data input/output; wherein, the data includes user information data, inspection result data, and Operation flow control data, and the inspection result data includes digital and/or image data. Specifically, the master control interface module 9 is connected to the display module 10, the input module 11, the storage module 12, and the external network 13; the display device 10 is used to display inspection information, the input device 11 is used to receive user information; the storage module 12 is used to store And manage the inspection result data and operation flow control data; the external network 13 sends/receives the inspection data and operation flow control data to the slave/host computer and other inspection equipment.

In the embodiment of the present invention, the lighting module is used to illuminate the inspected object mounted on the carrying platform. As shown in FIG. 2, the lighting module includes a xenon light source 14, a wavelength filter 15a, a polarization beam splitter (PBS) 15, a λ/4 plate 16, an objective lens 17, and the like.

In a preferred embodiment, the semiconductor wafer defect inspection device 100 is an optical pattern defect inspection device using Deep Ultra Violet (DUV) for the illumination module. The DUV light can choose broadband illumination, such as 200 to 400nm, or narrowband illumination with bright lines. As shown in Figure 2, the light emitted from the xenon light source or mercury xenon light source 14 is limited by the wavelength filter 15a to form A narrow-band illumination DUV light with bright lines.

The use of broadband illumination can reduce the effect of color unevenness caused by the interference of the wafer film; while the use of narrow-band illumination with bright lines can correct the chromatic aberration of the optical system with high precision, and can obtain the effect of improving the resolution.

In this embodiment, the DUV light source is a lamp light source, but in other embodiments of the present invention, a high-brightness laser light source may also be used. For example, a YAG laser (λ=532nm) and a nonlinear optical element can be combined to use 266nm as the second harmonic.

In the embodiment of the present invention, the image signal of the surface of the object to be inspected is collected by the camera module. With the cooperation of the illumination module, the camera module photographs the surface of the object to be inspected and outputs an image signal. It is used to determine whether there are defects on the surface of the inspected object after the manufacturing process is completed. As in the prior art, the camera module may include an objective lens 17, a λ/4 plate 16, a polarization beam splitter 15, an imaging lens 19, a linear image sensing unit 20, and the like.

The optical system of the camera module is described below. As shown in Fig. 2, after being restricted by the wavelength filter 15a, S-polarized light is formed. The S-polarized light is reflected downward in the Polarizing Beam Splitter (PBS) 15 and passes through the λ/4 plate 16 to It becomes circularly polarized light. The objective lens 17 irradiates the wafer 18 (also referred to as the "object to be inspected"), the beam is reflected by the wafer surface, passes through the λ/4 plate 16 again, becomes P-polarized light, and is reflected back to the polarization beam splitter 15 . With the above-mentioned configuration of the optical system, it is possible to prevent the amount of detected light from decreasing sharply.

Next, the imaging lens 19 receives the reflected light, and then transmits it to the linear image sensing unit 20 to form an enlarged optical image of the wafer surface. The enlarged optical image of the wafer surface imaged by the linear image sensing unit 20 is input to the image processing unit 32 as a detection image signal, and defect inspection is performed. In addition, the inspection imaging optical path has another branch, and another reflected light image separated by the imaging lens 19 and the polarization beam splitter 15 is provided to the TV camera unit 21. The TV camera unit 21 is connected to another image processing unit 22, and the image processing unit 22 is used to perform alignment and defect inspection on the detected image signal.

In the embodiment of the present invention, the carrying platform is used to carry the inspected object, and the inspected object is made to move with the movement of the carrying platform. Specifically, the carrier platform includes a wafer chuck 23, a Z carrier platform 30, a θ carrier platform 24, an X level 25, and a Y carrier platform 26 stacked from top to bottom. The inspected object (wafer) 18 is vacuum sucked by the wafer chuck 23 and placed on the wafer chuck 23 to prevent the wafer 18 to be inspected from moving relative to the wafer chuck 23. The wafer chuck 23 is mounted on the stacked Z bearing platform 30, the θ bearing platform 24, the X bearing platform 25, and the Y bearing platform 26. After the wafer is mounted on the wafer chuck 23, it needs to be aligned with the θ-carrying platform 24 so that the aligned chip array arrangement direction is consistent with the scanning direction of the X-carrying platform 25 and fixed during the inspection operation.

During the inspection operation, the X bearing platform 25 can move left and right relative to the paper plane, and when folding back, the Y bearing platform 26 can step in a direction perpendicular to the paper surface. Here, the wafer (singular form of Die and Dice) refers to a bulk semiconductor chip obtained by completing the preparation of the circuit on the surface of the wafer 18 and cutting it into a dice shape.

In the embodiment of the present invention, the platform control computer 27 controls the movement of the θ bearing platform 24, the X bearing platform 25, and the Y bearing platform 26 through control signals. The position measurement module is used to measure the position information of the inspected object. Preferably, the position measurement module may be a laser length gauge. For example, the laser length gauge 28 can measure the position information of the X-carrying platform 25 (ie, the position information of the wafer 18 in the scanning direction of the X-carrying platform 25).

Please refer to FIG. 2 in conjunction with FIG. 3. The timing pulse generating module 200 (also called "timing pulse generating module") generates a linear image based on the position information XL output by the laser length measuring instrument 28 (also called "position measuring circuit"). The start timing signal (also referred to as "timing pulse") of the pixels of the sensing unit 20, that is, the timing pulse is sent to the linear image sensing unit 20, and the image signal is read out.

In this embodiment, only a linearly moving carrier platform (X carrier platform 25) is taken as an example, and the timing pulse generation module 200 is exemplarily described, that is, outputting the inspected object carried on the carrier platform at a specific coordinate interval location information. It should be noted that the case of the X bearing platform 25 can be similarly applied to the Z bearing platform 30, the θ bearing platform 24, and the Y bearing platform 26, which will not be repeated here.

In addition, the platform control computer 27 is connected to the overall control unit 9 via the internal network 33, and downloads wafer layout information, etc., for identifying the inspection position.

The imaging process is explained below. As shown in FIG. 2, every time the X-bearing platform moves a certain distance, it starts to send a timing signal to drive the linear image sensing unit 20. By synchronizing the reading of the linear image sensing unit 20 with the amount of movement of the X stage, two-dimensional images can be sequentially captured. Also, by using a time delay integration (TDI-CCD) image sensor unit as the linear image sensor unit 20, the signal-to-noise (S/N) ratio in high-speed scanning can be improved.

The TDI sensor (Time Delayed and Integration) has a structure in which multiple one-dimensional image sensors are arranged in two dimensions. The output of each one-dimensional image sensor is delayed by a predetermined time, and then superimposed with the image output by the adjacent one-dimensional image sensor captured at the same position of the object to be inspected to increase the amount of detection light.

The auto-focus module includes a detection optical unit 47 and an auto-focus computer 39. The detection optical unit 47 detects the height of a plurality of points near the imaging position, and sends a detection signal to the autofocus computer 39. The autofocus computer 39 calculates the control amount 48 of the Z bearing platform 30 based on the deviation between the detected height and the preset control target, and controls the Z bearing platform 30 to move.

The autofocus computer 39 is connected to the general control interface module 9 through the internal network 33, and switches between operation modes such as an inspection mode and a viewing mode, and transmits and receives an autofocus scheme. In addition, the wafer start signal 40 and the carrier platform return signal 41 are input from the platform control computer 27. In addition, a control signal 43 with high real-time characteristics is sent from the platform control computer 27, for example, an auto-focus ON/OFF signal during the inspection.

Please refer to FIG. 3, which shows a schematic diagram of the configuration of the timing pulse generating module 200 according to this embodiment. The timing pulse generation module 200 receives the position information X _L output from the position measurement circuit 28, and then generates a timing pulse described later and outputs it to the linear image sensing unit 20.

Different from the prior art, in the embodiment of the present invention, the timing pulse generation module 200 includes an adder 210 that adds the pixel size ΔX, etc., and a speed (dX _L /dt=v) _{based on the position information XL.} Differentiator 220, Comparator 230 that compares the magnitude relationship between the position information X _L and the output value of the adder 210, an arithmetic unit 240 that performs a predetermined operation, a delay unit 250 that calculates a delay (Delay), and a delay pulse The falling edge detection unit 260 is the input and output timing pulse.

Here, the position information update frequency X _L (10MHz = 100nsec) is greater than the linear image timing pulse frequency (3MHz = about 333nsec) sensing unit 20. In addition, the delay unit 250 operates at 300 MHz (about 3 nsec).

That is to say, the timing pulse generation module corrects the timing pulse error, delays the timing pulse by one clock, and then outputs it, so as to image the surface of the inspected object.

The adder 210, the comparator 230, and the arithmetic unit 240 will be described in detail below.

The output X _T of the adder is the trigger coordinate of the pixel. It is compared at the moment when _{the position information X L} _{is read. When X T} <X _L , a timing pulse (also called "traditional timing pulse") is generated. It is sent to the linear image sensing unit 20 for reading the image signal.

In the embodiment of the present invention, the adder 210 outputs a new signal based on the pixel size (pixel size, ΔX) of the linear image sensing unit 20, the previous output X _{T of the} adder 210, and the trigger signal Trg output by the comparator 230. The trigger coordinates.

In the embodiment of the present invention, the comparator 230 is used to compare the magnitude relationship between the _{output value X T of the} adder 210 and the position information X _L _{in real time, and when X L is} greater than X _T (X _T <X _L ) , Output the trigger signal Trg. The arithmetic unit 240 receives the trigger coordinate X _T , the position information X _L and the velocity v as inputs based on the value of ΔX held in advance, and performs an operation of (X _T +ΔX-X _L )/v according to the trigger signal Trg.

Example 1

Please refer to FIG. 4, which is a schematic diagram illustrating the timing of each pulse according to this embodiment. In this embodiment, the update frequency of the _{location information XL is 10 MHz.} Therefore, _{the acquisition time of the position information XL} may be equal intervals of 100 nanoseconds. The bearing platform (such as the X bearing platform in this embodiment) can be set to move one pixel at an interval of about 333 nanoseconds.

Under ideal circumstances, the timing pulse output time should be issued when one pixel is moved. This is shown in FIG. 4 as the original timing pulse output time.

Since in the prior art, the output time of the comparator is used as the timing pulse, an error M will occur between the original timing pulses. This error M is equivalent to causing a blur of 1/3 pixel. The goal in this embodiment is to reduce the blur to about 1/10 to 1/100 pixels.

Therefore, in this embodiment, the conventional timing pulse needs to be delayed by one clock. For this purpose, a delay pulse is required, and the delay pulse may be generated by the delay unit 250.

In order to obtain the output time of the delayed pulse, firstly, a prescribed operation (X _T +ΔX-X _L )/v can be performed by the arithmetic unit 240 to obtain a clock delay time. Next, the delay unit 250 also delays the error M by (X _T +ΔX-X _L )/v. In this way, the pulse width of the delayed pulse is calculated.

Then, the falling detection path 260 detects the falling edge of the delay pulse, and outputs the timing pulse of this embodiment. In this way, the prior art timing pulse can be used after being delayed by one clock.

According to the embodiment of the present invention, the operating frequency of the delay unit 250 is 300MHz, _{the update frequency of the output position information XL} of the position measuring circuit 28 is 10MHz, and the delay unit 250 operates at 300MHz (approximately 3nsec). The error is delayed by one clock to be corrected, that is, while waiting for the time obtained by subtracting the time delay (error M) from the average interval

After (X _T +ΔX-X _L )/v, a timing pulse is output.

The defect inspection method is briefly described below. In the embodiment of the present invention, it may specifically include the following steps:

Step S2: According to the position information, when the inspected object moves one pixel of the camera module, a certain timing pulse is generated; and the timing pulse generation module corrects the timing pulse error to delay the timing pulse by one Output after the clock;

Step S2 of the defect inspection method may specifically include the following steps:

Step S23: Receive the trigger coordinate X _T , the trigger signal Trg, the position information X _L and the speed v, and perform a prescribed operation (X _T +ΔX-X _L )/v to obtain a clock delay time;

The above descriptions are only the preferred embodiments of the present invention, and the described embodiments are not used to limit the scope of patent protection of the present invention. Therefore, any equivalent structural changes made using the contents of the description and drawings of the present invention should be included in the same reasoning. Within the protection scope of the appended claims of the present invention.

Claims

A defect inspection device, characterized in that it comprises:

The master control interface module is used for data input/output; wherein the data includes user information data, inspection result data, and operation flow control data, and the inspection result data includes digital and/or image data;

The carrying platform is used to carry the inspected object and make the inspected object move with the movement of the carrying platform;

An illumination module for illuminating the inspected object mounted on the carrying platform;

A camera module, in cooperation with the illumination module, photographs the surface of the inspected object and outputs an image signal;

A position measuring module, which measures the position information of the inspected object;

The timing pulse generating module receives the position information of the inspected object, and generates a timing pulse when the inspected object moves one pixel of the camera module; and the timing pulse generating module corrects the timing pulse error , Delaying the timing pulse by one clock and outputting it to image the surface of the inspected object, wherein the update frequency of the position information is greater than the timing pulse frequency of the camera module; and

The image processing module detects the defect of the inspected object according to the image signal.
The defect inspection device according to claim 1, wherein the position measurement module comprises a linear image sensing unit.
The defect inspection device according to claim 2, wherein the timing pulse generating module comprises:

The adder adds up the pixel size ΔX of the linear image sensing unit, and outputs the trigger coordinate X T ;

Differentiator, obtain the speed v according to the position information X L of the inspected object;

A comparator for comparing the magnitude relationship between the position information XL and the output value of the adder to generate a trigger signal Trg;

The arithmetic unit receives the trigger coordinate X T , the trigger signal Trg, the position information X L and the speed v, and executes a prescribed calculation (X T +ΔX-X L )/v to obtain a clock delay time;

The delay unit sends out a delay pulse delayed by one clock according to the clock delay time;

The falling edge detection unit detects the falling edge of the delayed pulse, and starts the camera module to image the surface of the inspected object; wherein the update frequency of the position information XL is greater than the timing pulse of the linear image sensing unit Frequency, the working frequency of the delay unit is greater than the update frequency of the position information XL.
The defect inspection device according to claim 2, wherein the linear image sensing unit is a time delay integral image sensing unit.
The defect inspection apparatus according to claim 1, wherein the inspected object is a semiconductor wafer.
The defect inspection device according to claim 1, wherein the illumination module comprises a deep ultraviolet light source, and the method of forming the illumination light path by using the deep ultraviolet light source is a broadband illumination method or a narrowband illumination method with bright lines.
The defect inspection device according to claim 1, wherein the position measurement module comprises a laser length gauge.
A method for defect inspection, which is characterized in that it comprises the following steps:

Step S1: Use the position measurement module to measure the position information of the inspected object;

Step S2: According to the position information, when the inspected object moves one pixel of the camera module, a certain timing pulse is generated; and the timing pulse generation module corrects the timing pulse error to delay the timing pulse by one Output after the clock, wherein the update frequency of the position information is greater than the timing pulse frequency of the camera module;

Step S3: According to the timing pulse delayed by one clock, the surface of the inspected object is photographed, and an image signal is output;

Step S4: Detect the defect of the inspected object according to the image signal.
The defect inspection method according to claim 8, wherein the step S2 specifically includes the following steps:

Step S21: Add the pixel size ΔX of the linear image sensing unit, and output the trigger coordinate X T ;

Step S22: comparing the magnitude relationship between the position information XL and the output value of the adder to generate a trigger signal Trg;

Step S23: Receive the trigger coordinate X T , the trigger signal Trg, the position information X L and the speed v, and perform a prescribed operation (X T +ΔX-X L )/v to obtain a clock delay time;

Step S24: Send a delay pulse delayed by one clock according to the clock delay time;

Step S25: Detect the falling edge of the delayed pulse, start the camera module to take a picture of the surface of the inspected object; wherein the update frequency of the position information XL is greater than the timing pulse frequency of the linear image sensing unit, The operating frequency of the delay unit is greater than the update frequency of the position information XL.