Reticle defect inspection apparatus and reticle defect inspection method

• US 8,355,044 B2
• Filed: 04/29/2009
• Issued: 01/15/2013
• Est. Priority Date: 05/16/2008
• Status: Active Grant

• Current Assignee: NuFlare Technology, Inc. (Toshiba Corporation)
• Original Assignee: NuFlare Technology, Inc. (Toshiba Corporation)
• Inventors: Tsuchiya, Hideo, Watanabe, Toshiyuki
• Primary Examiner(s): STRANGE, AARON N
• Application Number:
  US12/432,182
• Publication Number:
  US 20090284591A1
• Time in Patent Office: 1,357 Days
• Field of Search: 382/141, 382/144, 348/92, 348/125, 348/126, 348/129
• US Class Current: 348/92
• CPC Class Codes: G01N 2021/95676 Masks, reticles, shadow masks
• CPC Class Codes: G01N 21/95607 using a comparative method
• CPC Class Codes: G03F 1/84 Inspecting

Abstract

The present invention provides a reticle defect inspection method and a reticle defect inspection apparatus capable of calibrating the offset and gain of a sensor amplifier using a product reticle even though black and white regions each sufficiently wider than a TDI sensor imaging area do not exist in the product reticle. An output of each pixel of the TDI sensor is amplified by the sensor amplifier. A bottom value of the amplified amount-of-light signal of each pixel is stored by bottom value storing means of offset/gain calibrating means, and a peak value thereof is stored by peak value storing means. The offset of each pixel is calculated by offset calculating means based on the bottom value of each pixel. The gain of each pixel is calculated by gain calculating means based on the offset of each pixel and the peak value of each pixel. The calculated offset and gain of each pixel are stored in a register and thereby the offset and gain of the sensor amplifier are calibrated.

Claims

1. A reticle defect inspection method in which an image sensor is moved relative to a reticle, and an optical image obtained by amplifying an output of each pixel of the image sensor by a sensor amplifier is compared with a reference image defined as a standard image relative to the optical image to perform a defect inspection of the reticle,

the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel, the reticle defect inspection method comprising, before the defect inspection:

imaging some of patterns of the reticle by the image sensor, and storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier, wherein when the bottom and peak values of each of the pixels are stored, a relative moving speed of the reticle is set slower than a pixel moving speed determined according to a pixel size and an imaging period of the image sensor;

setting a plurality of offsets in the sensor amplifier by setting each offset of a signal amplitude for each pixel of the sensor amplifier, based on the stored bottom value of each pixel; and

setting a plurality of gains in the sensor amplifier by setting each gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude of each pixel and on the stored peak value of each pixel.

2. A reticle defect inspection method in which an image sensor is moved relative to a reticle, and an optical image obtained by amplifying an output of each pixel of the image sensor by a sensor amplifier is compared with a reference image defined as a standard image relative to the optical image to perform a defect inspection of the reticle, wherein the image sensor is a TDI sensor having a plurality of stages of lines,

the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel, the reticle defect inspection method comprising, before the defect inspection:

imaging some of patterns of the reticle by the image sensor, and storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier, wherein when the bottom and peak values of each of the pixels are stored, the relative moving speed of the reticle is set slower than a TDI operating speed of the TDI sensor;

setting a plurality of offsets in the sensor amplifier by setting each offset of a signal amplitude for each pixel of the sensor amplifier, based on the stored bottom value of each pixel; and

setting a plurality of gains in the sensor amplifier by setting each gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude of each pixel and on the stored peak value of each pixel.

3. A reticle defect inspection method in which an image sensor is moved relative to a reticle, and an optical image obtained by amplifying an output of each pixel of the image sensor by a sensor amplifier is compared with a reference image defined as a standard image relative to the optical image to perform a defect inspection of the reticle,

the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel, the reticle defect inspection method comprising, before the defect inspection:

imaging some of patterns of the reticle by the image sensor, and storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier;

setting a plurality of offsets in the sensor amplifier by setting each offset of a signal amplitude for each pixel of the sensor amplifier, based on the stored bottom value of each pixel; and

setting a plurality of gains in the sensor amplifier by setting each gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude of each pixel and on the stored peak value of each pixel;

acquiring edge positions at plural spots of reticle patterns each approximately parallel to a relative moving direction of the image sensor upon storing the bottom and peak values of the respective pixels;

calculating degrees of rotational error of the reticle from acquired edge positions; and

executing a rotational alignment of the reticle, based on the calculated degrees of rotational error.

4. The reticle defect inspection method according to claim 3 wherein, in the acquiring the edge positions, amount-of-light and coordinates of the pixels, which are obtained by imaging the neighborhood of the edge positions, are acquired, and edge positions each brought to a predetermined amount-of-light are calculated, based on the acquired amount-of-light and coordinates of the pixels.

5. A reticle defect inspection method in which an image sensor is moved relative to a reticle, and an optical image obtained by amplifying an output of each pixel of the image sensor, wherein the image sensor is a TDI sensor having a plurality of stages of lines, by a sensor amplifier is compared with a reference image defined as a standard image relative to the optical image to perform a defect inspection of the reticle,

the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel, the reticle defect inspection method comprising, before the defect inspection:

imaging some of patterns of the reticle by the image sensor, and storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier, wherein when some of the patterns of the reticle are imaged by the TDI sensor while the stage with the reticle placed thereon is being moved in one direction, imaging is done by the image sensor while the stage is being moved in the other direction orthogonal to the one direction where each arbitrary pixel of the TDI sensor do not reach both light-shielding and light-transmitted portions of the reticle;

setting a plurality of offsets in the sensor amplifier by setting each offset of a signal amplitude for each pixel of the sensor amplifier, based on the stored bottom value of each pixel; and

setting a plurality of gains in the sensor amplifier by setting each gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude of each pixel and on the stored peak value of each pixel;

wherein a stage moving speed in the other direction is set slower than a TDI operating speed of the TDI sensor.

6. A reticle defect inspection apparatus comprising:

a light irradiating mechanism for irradiating a reticle formed with each pattern with light;

a driving unit for driving a stage which holds the reticle thereon;

an image sensor for detecting an amount-of-light signal of light transmitted through or reflected from the reticle at a plurality of pixels;

a sensor amplifier for amplifying an output of each pixel of the image sensor every pixel and generating an optical image, the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel;

a reference image generating unit for generating a reference image defined as a standard image relative to the optical image;

a detecting unit for comparing the optical image with the reference image thereby to detect a defect of each pattern of the reticle;

a storing unit, when the stage is driven by the driving unit before the inspection by the detecting unit to image some of the patterns by the image sensor, for storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier, wherein a stage moving speed at the time that the bottom and peak values are stored by the storing unit, is set slower than a pixel moving speed determined according to a pixel size and an imaging period of the image sensor;

an offset setting unit for setting an offset of a signal amplitude for each pixel of the sensor amplifier, based on the bottom value of each pixel stored by the storing unit; and

a gain setting unit for setting a gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude for each pixel and the peak value of each pixel stored by the storing unit.

7. A reticle defect inspection apparatus comprising:

a light irradiating mechanism for irradiating a reticle formed with each pattern with light;

a driving unit for driving a stage which holds the reticle thereon;

an image sensor for detecting an amount-of-light signal of light transmitted through or reflected from the reticle at a plurality of pixels, wherein the image sensor is a TDI sensor that stores the amount-of-light signal on each of a plurality of stages of lines;

a sensor amplifier for amplifying an output of each pixel of the image sensor every pixel and generating an optical image, the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel;

a reference image generating unit for generating a reference image defined as a standard image relative to the optical image;

a detecting unit for comparing the optical image with the reference image thereby to detect a defect of each pattern of the reticle;

a storing unit, when the stage is driven by the driving unit before the inspection by the detecting unit to image some of the patterns by the image sensor, for storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier, wherein a stage moving speed at the time that the bottom and peak values are stored by the storing unit is set slower than a TDI operating speed of the TDI sensor;

an offset setting unit for setting an offset of a signal amplitude for each pixel of the sensor amplifier, based on the bottom value of each pixel stored by the storing unit; and

a gain setting unit for setting a gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude for each pixel and the peak value of each pixel stored by the storing unit.

8. A reticle defect inspection apparatus comprising:

a light irradiating mechanism for irradiating a reticle formed with each pattern with light;

a driving unit for driving a stage which holds the reticle thereon;

an image sensor for detecting an amount-of-light signal of light transmitted through or reflected from the reticle at a plurality of pixels;

a sensor amplifier for amplifying an output of each pixel of the image sensor every pixel and generating an optical image, the sensor amplifier being capable of calibrating a gain and an offset of a signal amplitude every pixel;

a reference image generating unit for generating a reference image defined as a standard image relative to the optical image;

a detecting unit for comparing the optical image with the reference image thereby to detect a defect of each pattern of the reticle;

a storing unit, when the stage is driven by the driving unit before the inspection by the detecting unit to image some of the patterns by the image sensor, for storing bottom and peak values of an amount-of-light signal of each pixel amplified by the sensor amplifier;

an offset setting unit for setting an offset of a signal amplitude for each pixel of the sensor amplifier, based on the bottom value of each pixel stored by the storing unit; and

a gain setting unit for setting a gain of a signal amplitude for each pixel of the sensor amplifier, based on the offset of the signal amplitude for each pixel and the peak value of each pixel stored by the storing unit;

an edge position acquiring unit for acquiring edge positions at plural spots of reticle patterns each approximately parallel to a relative moving direction of the image sensor,

a degrees-of-rotational error calculating unit for calculating degrees of rotational error of the reticle from the edge positions acquired by the edge position acquiring unit, and

an alignment unit for executing a rotational alignment of the reticle, based on the degrees of rotational error calculated by the degrees-of-rotational error calculating unit.

9. The reticle defect inspection method according to claim 8, wherein the edge position acquiring unit calculates edge positions each brought to a predetermined amount-of-light, based on amounts of light and coordinates of the pixels, which are obtained by imaging the neighborhood of the edge positions.