Dark-field inspection using a low-noise sensor

Patent metadata

Field	Value
Publication number	US-10462391-B2
Application number	US-201615210056-A
Country	US
Kind code	B2
Filing date	Jul 14, 2016
Priority date	Aug 14, 2015
Publication date	Oct 29, 2019
Grant date	Oct 29, 2019

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.

First claim

The invention claimed is:

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. T

Assignees

• Kla Tencor Corp

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

Classifications

• H04N23/56 Primary

  provided with illuminating means · CPC title

• H04N25/46

  by combining or binning pixels · CPC title

• H04N25/00 Primary

  Circuitry of solid-state image sensors [SSIS]; Control thereof · CPC title

• H04N25/77

  Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components · CPC title

• G01N21/9501

  Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20) · CPC title