Multiple column per channel CCD sensor architecture for inspection and metrology
First Claim
1. A multiple-column-per-channel charge-coupled-device (CCD) image sensor comprising:
- a pixel array including a plurality of pixels arranged in a plurality of columns and a plurality of pixel rows, the pixel array being configured to generate image charges and to sequentially transfer each said image charge between associated pixels disposed in a corresponding said column in response to a plurality of pixel control signals, whereby a set of image charges disposed in a first said pixel row is simultaneously transferred to an adjacent second said pixel row during each cycle of said plurality of pixel control signals;
a readout circuit comprising;
a plurality of buffer cells disposed to simultaneously receive image charges from an edge pixel row in response to one or more buffer control signals such that each buffer cell receives a corresponding image charge from an associated pixel of said edge pixel row upon assertion of said one or more buffer control signals;
a plurality of transfer gates disposed in said plurality of columns and arranged in a plurality of transfer gate rows including a first transfer gate row disposed to receive a corresponding image charge from an associated said buffer cell, each of said plurality of transfer gates being operably controlled by and associated transfer clock signal;
a summing gate coupled to a last transfer gate row; and
an output circuit coupled to the summing gate,wherein said plurality of transfer gates are configured and coupled such that asserting a first transfer clock signal during a first time periodcauses a first image charge to be transferred from a first said buffer cell to a first transfer gate, and causes a second image charge to be transferred from a second said transfer gate to a third said transfer gate,wherein said first buffer cell and said first transfer gate are disposed in a first said column, and said second transfer gate and said third transfer gate are disposed in a second said column, andwherein the summing gate is configured to receive the second image charge from the second column during a second time period subsequent to the first time period in accordance with a summing gate control signal, and the summing gate is further configured to receive the first image charge from the first column during a third time period subsequent to the second time period in accordance with the summing gate control signal andwherein a clock rate of the summing gate control signal is at least two times faster than a line clock rate of the plurality of pixel control signals.
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Abstract
A multiple-column-per-channel image CCD sensor utilizes a multiple-column-per-channel readout circuit including connected transfer gates that alternately transfer pixel data (charges) from a group of adjacent pixel columns to a shared output circuit at high speed with low noise. Charges transferred along the adjacent pixel columns at a line clock rate are alternately passed by the transfer gates to a summing gate that is operated at multiple times the line clock rate to pass the image charges to the shared output circuit. A symmetrical fork-shaped diffusion is utilized in one embodiment to merge the image charges from the group of related pixel columns. A method of driving the multiple-column-per-channel CCD sensor with line clock synchronization is also described. A method of inspecting a sample using the multiple-column-per-channel CCD sensor is also described.
270 Citations
21 Claims
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1. A multiple-column-per-channel charge-coupled-device (CCD) image sensor comprising:
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a pixel array including a plurality of pixels arranged in a plurality of columns and a plurality of pixel rows, the pixel array being configured to generate image charges and to sequentially transfer each said image charge between associated pixels disposed in a corresponding said column in response to a plurality of pixel control signals, whereby a set of image charges disposed in a first said pixel row is simultaneously transferred to an adjacent second said pixel row during each cycle of said plurality of pixel control signals; a readout circuit comprising; a plurality of buffer cells disposed to simultaneously receive image charges from an edge pixel row in response to one or more buffer control signals such that each buffer cell receives a corresponding image charge from an associated pixel of said edge pixel row upon assertion of said one or more buffer control signals; a plurality of transfer gates disposed in said plurality of columns and arranged in a plurality of transfer gate rows including a first transfer gate row disposed to receive a corresponding image charge from an associated said buffer cell, each of said plurality of transfer gates being operably controlled by and associated transfer clock signal; a summing gate coupled to a last transfer gate row; and an output circuit coupled to the summing gate, wherein said plurality of transfer gates are configured and coupled such that asserting a first transfer clock signal during a first time periodcauses a first image charge to be transferred from a first said buffer cell to a first transfer gate, and causes a second image charge to be transferred from a second said transfer gate to a third said transfer gate, wherein said first buffer cell and said first transfer gate are disposed in a first said column, and said second transfer gate and said third transfer gate are disposed in a second said column, and wherein the summing gate is configured to receive the second image charge from the second column during a second time period subsequent to the first time period in accordance with a summing gate control signal, and the summing gate is further configured to receive the first image charge from the first column during a third time period subsequent to the second time period in accordance with the summing gate control signal and wherein a clock rate of the summing gate control signal is at least two times faster than a line clock rate of the plurality of pixel control signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of inspecting a sample, the method comprising:
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directing and focusing radiation onto the sample while moving the sample relative to a source of said radiation; directing received radiation from the sample to an image sensor, the image sensor comprising a multiple-column-per-channel charge-coupled-device (CCD) including an array of pixels arranged in a plurality of rows and a plurality of associated groupsof adjacent columns, each said associated group including at least a first column a second column and a third column; driving the image sensor with line clock signals that are synchronized to said moving of the sample relative to the radiation source, the line clock signals causing first and second charges to be respectively transferred along the first, second and third columns from one said row of pixels to an adjacent said row of pixels; driving a row of buffer cells of the image sensor with a buffer clock signal, the buffer clock signal causing said first and second charges to be respectively transferred from an edge pixel row of pixels in the first, second and third columns of each associated group of columns to first, second and third buffer cells of the row of buffer cells; simultaneously driving with a first transfer clock signal during a first time period a first transfer gate, a third transfer gate and a fifth transfer gate, said first transfer gate being disposed in a first row of said transfer gates and disposed in the first column, the third transfer gate being disposed in a third row of said transfer gates and disposed in the second column, and the fifth transfer gate being disposed in a second row of said transfer gates and disposed in the third column, simultaneously driving with a second transfer clock signal during a second time period a seventh transfer gate, an eighth transfer gate and a ninth transfer gate, said seventh transfer gate being disposed in the first row of said transfer gates and disposed in the second column, the eighth transfer gate being disposed in said second row of said transfer gates and disposed in the first column, and the ninth transfer gate being disposed in the third row of said transfer gates and disposed in the third column, simultaneously driving with a third transfer clock signal during a third time period a fourth transfer gate, a second transfer gate and a sixth transfer gate, said fourth transfer gate being disposed in the first row of said transfer gates and disposed in the third column, the second transfer gate being disposed in said second row of said transfer gates and disposed in the second column, and the sixth transfer gate being disposed in the third row of said transfer gates and disposed in the first column, utilizing an output circuit and an analog-to-digital converter (ADC) circuit to sequentially convert image charges transferred along the first, second and third columns to digital numbers, wherein utilizing the ADC circuit includes driving the ADC circuit with a clock frequency greater than at least three times a frequency of the line clock signals. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21)
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Specification