Dark-field inspection using a low-noise sensor

• US 10,462,391 B2
• Filed: 07/14/2016
• Issued: 10/29/2019
• Est. Priority Date: 08/14/2015
• Status: Active Grant

• Current Assignee: KLA-Tencor Corporation
• Original Assignee: KLA-Tencor Corporation
• Inventors: Chuang, Yung-Ho Alex, Brown, David L., Contarato, Devis, Fielden, John, Kavaldjiev, Daniel I., Zhao, Guoheng, Chern, Jehn-Huar, Zheng, Guowu, Pettibone, Donald W., Biellak, Stephen
• Primary Examiner(s): Jo, Taeho
• Application Number:
  US15/210,056
• Publication Number:
  US 20170048467A1
• Time in Patent Office: 1,202 Days
• Field of Search: 250365
• CPC Class Codes: G01N 2021/95676 Masks, reticles, shadow masks
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: H04N 23/56 provided with illuminating means
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/46 by combining or binning pixels
• CPC Class Codes: H04N 25/745 Circuitry for generating timing or clock signals
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components

Abstract

An inspection system and methods in which analog image data values (charges) captured by an image sensor are binned (combined) before or while being transmitted as output signals on the image sensor'"'"'s output sensing nodes (floating diffusions), and in which an ADC is controlled to sequentially generate multiple corresponding digital image data values between each reset of the output sensing nodes. According to an output binning method, the image sensor is driven to sequentially transfer multiple charges onto the output sensing nodes between each reset, and the ADC is controlled to convert the incrementally increasing output signal after each charge is transferred onto the output sensing node. According to a multi-sampling method, multiple charges are vertically or horizontally binned (summed/combined) before being transferred onto the output sensing node, and the ADC samples each corresponding output signal multiple times. The output binning and multi-sampling methods may be combined.

Claims

1. A method of inspecting a sample using an image sensor and an analog-to-digital converter (ADC), the image sensor including multiple pixels disposed in at least one column and an output sensing node, the ADC being configured to convert analog output signals on said output sensing node into corresponding digital image data values, the method comprising:

driving the image sensor such that a plurality of analog image data values are generated in the multiple pixels, each said analog image data value corresponding to a radiation portion directed onto said multiple pixels from a corresponding region of the sample, said driving including systematically transferring said analog image data values along said at least one column from said multiple pixels to said output sensing node while translating said sample relative to said image sensor such that each said analog image data value is shifted from a first said pixel to a second said pixel in said at least one column in coordination with said corresponding region of the sample, whereby said each analog image data value is influenced by said corresponding radiation portion from said corresponding region during a first time period when said each analog image data value is in said first pixel, and said each analog image data value is influenced by said corresponding radiation portion during a second time period when said each analog image data value is in said second pixel, and wherein said systematically transferring is performed such that said output sensing node stores charge values determined by said systematically transferred analog image data values and generates said analog output signals in accordance with said stored charge values, wherein driving the image sensor further includes periodically resetting the output sensing node to an initial charge value according to a reset clock signal; and

controlling the ADC to sequentially convert one or more of said analog output signals generated on said output sensing node into two or more said corresponding digital data values during each cycle of said reset clock signal.

2. The method of claim 1, wherein driving the image sensor further comprises transferring two or more analog image data values to said output sensing node during each cycle of said reset clock signal such that a charge value stored on said output sensing node includes a sum of said two or more of said analog image data values.

3. The method of claim 2,

wherein driving the image sensor further comprises sequentially transferring said two or more analog image data values to said output sensing node such that said output sensing node stores a first said analog image data value during a first time period, and said output sensing node stores a sum of said first analog image data value and a second said analog data image value during a second time period, and

wherein controlling the ADC further comprises generating a first corresponding digital output data value during said first time period, and generating a second corresponding digital output value during said second time period.

4. The method of claim 3, further comprising determining at least one digital image data value by determining a difference between said first and second digital output values.

5. The method of claim 2,

wherein driving the image sensor further comprises driving a shift register using a shift register clock signal such that one of said analog image data values is serially transferred from said shift register to said output sensing node during each cycle of said shift register clock signal, and

wherein periodically resetting the output sensing node to said initial value comprises resetting said output sensing node every two or more cycles of said shift register clock signal.

6. The method of claim 2,

wherein driving the image sensor further comprises simultaneously transferring said two or more analog image data values to said output sensing node such that said output sensing node stores a sum of said two or more analog image data values during a first time period, and

wherein controlling the ADC further comprises generating a first corresponding digital output data value during a first portion of said first time period, and generating a second corresponding digital output value during a second portion of said first time period.

7. The method of claim 6, determining at least one digital image data value by determining an average of said first and second digital output values.

8. A method of inspecting a sample, the method comprising:

directing and focusing radiation onto the sample;

receiving radiation from the sample and directing received radiation to an image sensor, the image sensor comprising at least a first pixel, a second pixel and an output sensing node;

driving the image sensor such that analog image data values captured by the first and second pixels are sequentially transferred to the output sensing node in accordance with at least one first clock signal, said analog image data values being captured while translating said sample relative to said image sensor such that each said analog image data value is shifted from the first pixel to the second said pixel in coordination with a corresponding region of the sample, whereby said each analog image data value is influenced by said corresponding radiation portion from said corresponding region during a first time period when said each analog image data value is in said first pixel, and said each analog image data value is influenced by said corresponding radiation portion during a second time period when said each analog image data value is in said second pixel, and wherein said driving is performed such that the output sensing node is periodically reset in accordance with a reset clock signal, whereby a charge stored on the output sensing node incrementally increases with each sequentially transferred analog image data value; and

generating digital image data values associated with the sample by controlling a converter to digitize an output signal generated by an associated said incrementally increasing charge stored on the output sensing node in accordance with a second clock signal such that at least two digital image data values are generated between each periodic reset of the output sensing node.

9. The method of claim 8, wherein driving the image sensor further comprises transferring two or more analog image data values to said output sensing node during each cycle of said reset clock signal such that said two or more of said analog image data values are stored simultaneously on said output sensing node.

10. The method of claim 9,

wherein driving the image sensor further comprises sequentially transferring first and second analog image data values to said output sensing node such that said output sensing node stores a first charge value generated by said first analog image data value during a first time period, and said output sensing node stores a second charge value equal to a sum of said first analog image data value and said second analog data image value during a second time period, and

wherein generating said digital image data values comprises generating a first digital output value during said first time period by digitizing a first output signal generated in accordance with said first charge value, and generating a second digital output value during said second time period by digitizing a second output signal generated in accordance with said second charge value.

11. The method of claim 10, further comprising determining at least one digital image data value by determining a difference between said first and second digital output values.

12. The method of claim 9,

wherein driving the image sensor further comprises simultaneously transferring said two or more analog image data values to said output sensing node such that said output sensing node stores a corresponding charge value generated by a sum of said two or more analog image data values during a first time period, and

wherein generating said digital image data values comprises generating a first corresponding digital output value by digitizing said corresponding charge value during a first portion of said first time period, and generating a second corresponding digital output value by digitizing said corresponding charge value during a second portion of said first time period.

13. The method of claim 12, determining at least one digital image data value by determining an average of said first and second digital output values.

14. The method of claim 8,

wherein directing and focusing said radiation comprises generating at least one of electromagnetic radiation and charged particles, and

wherein receiving said radiation comprises directing at least one of scattered radiation and reflected radiation received from the sample to the image sensor.

15. The method of claim 8,

wherein the image sensor comprises a plurality of pixels disposed in a line, and

wherein driving the image sensor comprises transferring a plurality of analog image data values respectively captured by the plurality of pixels to the output sensing node such that a total output signal generated by a sum of said plurality of analog image data values is stored on said output sensing node when said converter is controlled to digitize said output signal, whereby an associated digital image data value is generated corresponding to said total output signal.

16. The method of claim 15, further comprising:

comparing said associated digital image data value with a predetermined threshold value; and

transmitting said associated digital image data value to one of a processor and a data storage device only when said associated digital image data value exceeds said threshold value.

17. A system for inspecting a sample, the system comprising:

an illumination source;

an imaging device comprising an image sensor including a plurality of pixels disposed in at least one column and at least one output sensing node;

optics configured to direct light from the illumination source to the sample, and to direct light from the sample to the imaging apparatus;

at least one Analog-to-Digital Converter (ADC) configured to generate digital image data values by digitizing corresponding output signals generated on said at least one output sensing node;

at least one Digital Signal Processor (DSP) configured to receive and evaluate said digital image data values;

a stage configured to facilitate translation of the sample relative to the optics; and

a digital control device configured to generate clock, reset and control signals utilized to drive the image sensor, the ADC and the DSP in coordination with translation of said sample by said stage such that;

a plurality of analog image data values are generated in the multiple pixels, each said analog image data value corresponding to a radiation portion directed from a corresponding region of the sample, wherein each said analog image data value is shifted from a first said pixel to a second said pixel in said at least one column in coordination with translation of said corresponding region of the sample, whereby said each analog image data value is influenced by said corresponding radiation portion from said corresponding region during a first time period when said each analog image data value is in said first pixel, and said each analog image data value is influenced by said corresponding radiation portion during a second time period when said each analog image data value is in said second pixel;

said analog image data values are systematically transferred from said multiple pixels to said output sensing node in accordance with at least one first clock signal;

said output sensing node stores charge values determined by said systematically transferred analog image data values and generates said analog output signals in accordance with said stored charge values;

said output sensing node is periodically reset to an initial value according to a reset clock signal; and

the ADC generates at least two digital image data values between each periodic reset of the output sensing node.

18. The system of claim 17, wherein the digital control device is configured such that a number of said digital image data values generated between each periodic reset of the output sensing node is determined by stored mode control data.

19. The system of claim 18,

wherein said at least one Digital Signal Processor (DSP) is configured to compare each of said digital image data values against predetermined condition value, and to generate one or more feedback signals in accordance with at least one said comparison, and

wherein said digital control device is configured such that said stored mode control data is determined by said one or more feedback signals, whereby said number of said digital image data values generated between each periodic reset of the output sensing node is adjustable by way of said comparison between said digital image data values and said predetermined condition value.

20. A system for inspecting a sample, the system comprising:

an illumination source;

an imaging device comprising an image sensor including a plurality of pixels and at least one output sensing node;

optics configured to direct light from the illumination source to the sample, and to direct light from the sample to the imaging apparatus;

at least one Analog-to-Digital Converter (ADC) configured to generate digital image data values by digitizing corresponding output signals generated on said at least one output sensing node;

at least one Digital Signal Processor (DSP) configured to receive and evaluate said digital image data values;

a digital control device configured to generate clock, reset and control signals utilized to drive the image sensor, the ADC and the DSP such that;

a plurality of analog image data values are generated in the multiple pixels, each said analog image data value corresponding to a radiation portion directed onto said multiple pixels from a corresponding region of the sample;

said analog image data values are systematically transferred from said multiple pixels to said output sensing node in accordance with at least one first clock signal;

said output sensing node generates said analog output signals in accordance with one or more of said plurality of analog image data values;

said output sensing node is periodically reset to an initial value according to a reset clock signal; and

the ADC generates at least two digital image data values between each periodic reset of the output sensing node,

wherein the DSP is configured to measure an amplitude of background signals by evaluating the output signals accumulated at said at least one output node for a plurality of pixels read out in between reset operations; and

wherein the digital control logic is configured to vary the reset clock signal, based on feedback signals received from the DSP, to change the number of said digital image data values generated between each periodic reset of the output sensing node.

21. A system for inspecting a sample, the system comprising:

an illumination source;

an imaging device comprising an image sensor including a plurality of pixels and at least one output sensing node;

optics configured to direct light from the illumination source to the sample, and to direct light from the sample to the imaging apparatus;

at least one Analog-to-Digital Converter (ADC) configured to generate digital image data values by digitizing corresponding output signals generated on said at least one output sensing node;

at least one Digital Signal Processor (DSP) configured to receive and evaluate said digital image data values;

a digital control device configured to generate clock, reset and control signals utilized to drive the image sensor, the ADC and the DSP such that;

a plurality of analog image data values are generated in the multiple pixels, each said analog image data value corresponding to a radiation portion directed onto said multiple pixels from a corresponding region of the sample;

said analog image data values are systematically transferred from said multiple pixels to said output sensing node in accordance with at least one first clock signal;

said output sensing node generates said analog output signals in accordance with one or more of said plurality of analog image data values;

said output sensing node is periodically reset to an initial value according to a reset clock signal; and

the ADC generates at least two digital image data values between each periodic reset of the output sensing node,

wherein the DSP is configured to count the occurrences of signals of interest above said background signals within a plurality of pixels read out in between reset operations; and

wherein the digital control logic is configured to vary the reset clock signal, based on said count received from the DSP, to change the number of said digital image data values generated between each periodic reset of the output sensing node.