CN106596059B - A kind of measurement method of the stress birfringence amount of non-spherical element - Google Patents

Abstract

The present invention relates to a kind of measurement method of the stress birfringence amount of non-spherical element, the measurement method comprises determining that the initial position of test point and light source on non-spherical element and obtains the deflection angle of the light source according to the angle of current test point and non-spherical element optical axis；The position of the detector of the stress birfringence equipment is determined according to the position of current test point；The detector is moved into corresponding position according to the position of the detector；The stress birfringence amount of current test point is obtained by detector；Multiple specified angles that the non-spherical element turns on same circumference are corresponded in test point by rotating the testboard, and multiple stress birfringence amounts that multiple specified angles on same circumference correspond to test point are obtained by detector；Into the initial position of the test point and light source determined on non-spherical element, the step of obtaining the deflection angle of the light source according to the angle of current test point and light source optical axis, until all test point measurements finish.

Description

A Measuring Method of Stress Birefringence of Aspheric Element

technical field

The invention relates to the technical field of optical element detection, in particular to a method for measuring the stress birefringence of an aspheric element.

Background technique

With the development of the semiconductor industry, the feature size of large-scale integrated circuits is getting smaller and smaller. Photolithography, as a key technology for manufacturing semiconductor devices, is facing new challenges. In order to improve the resolution of the lithography system, the wavelength of the exposure light source is continuously reduced, from the near ultraviolet of 436nm and 355nm to the deep ultraviolet of 248nm and 193nm. Taking 193nm ArF excimer laser lithography as an example, it has broken through the 90nm, 65nm and 45nm nodes and has become the current mainstream exposure technology.

In the deep ultraviolet band, since the number of elements in the optical system is limited by the absorption of materials, this leads to a large number of applications of aspheric elements. Aspherical components need to go through processes such as processing, coating, integration and assembly from the blank to a part of the optical system. In these processes, new stresses will be applied or introduced to the components. At this time, it is necessary to compare the stress birefringence measurement results of the components before and after the treatment. However, the current stress birefringence test system can only measure the stress birefringence retardation of planar and spherical components. The amount of stress birefringence of aspheric surfaces cannot be measured.

Contents of the invention

The invention aims to solve the technical problem that the stress birefringence of the aspheric surface cannot be measured in the prior art, and provides a stress birefringence of the aspheric element with a simple measurement process and low cost, which can realize the stress birefringence Quantity measurement method.

The invention provides a method for measuring the stress birefringence of an aspheric element, the measuring method comprising:

Determining the test point on the aspheric element and the initial position of the light source and obtaining the deflection angle of the light source according to the angle between the current test point and the optical axis of the aspheric element;

Obtain the displacement distance of the light source according to the size of the aspheric element, the position of the current test point and the distance from the current test point to the light source;

adjusting the concentricity of the aspheric element and the test bench;

moving the light source to a corresponding position according to the deflection angle of the light source and the displacement distance of the light source;

determining the position of the detector of the stress birefringence device according to the position of the current test point;

move the detector to a corresponding position according to the position of the detector

Obtain the stress birefringence of the current test point through the detector;

By rotating the test table, the aspheric element is rotated to test points corresponding to multiple specified angles on the same circumference, and multiple stress birefringence values corresponding to multiple specified angles on the same circumference are obtained by the detector ;

Enter the step of determining the test point on the aspheric element and the initial position of the light source, and obtain the deflection angle of the light source according to the angle between the current test point and the optical axis of the light source, until all the test points are measured.

Compared with the prior art, the technical solution of the present invention has beneficial effects in that: no need to upgrade the equipment, no need to use software programming, only need to measure the size of the equipment, and the size of the component to be measured, the aspheric equation and the refractive index are known The measurement of stress birefringence can be carried out; in addition, it is only necessary to calculate the position of the light source and the position of the detector corresponding to a radial test point, and then the stress birefringence delay on the circle can be measured, which makes the measurement process of this measurement method simple and cost-effective. Low.

Description of drawings

FIG. 1 is a flow chart of an embodiment of the method for measuring eccentricity of an aspheric mirror according to the present invention.

Fig. 2 is the structural representation of aspherical element;

Fig. 3 is a schematic diagram of the positions of the aspheric element, the detector and the light source.

In the figure, 31, a detector; 32, an aspheric element; 33, a light source; 34, a test point.

Detailed ways

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

The present invention provides a method for measuring the stress birefringence of the aspheric element of an embodiment, as shown in Figure 1, the measurement method includes:

Step S11, determining the test point on the aspheric element and the initial position of the light source, and obtaining the deflection angle of the light source according to the angle between the current test point and the optical axis of the light source;

Step S12, obtaining the displacement distance of the light source according to the size of the aspheric element, the position of the current test point and the distance from the current test point to the light source;

Step S13, adjusting the concentricity of the aspheric element and the test bench of the stress birefringence device;

Step S14, moving the light source to a corresponding position according to the deflection angle of the light source and the displacement distance of the light source;

Step S15, determining the position of the detector of the stress birefringence device according to the position of the current test point;

Step S16, moving the detector to a corresponding position according to the position of the detector;

Step S17, obtaining the stress birefringence of the current test point through the detector;

Step S18, by rotating the test bench, the aspheric element is rotated to test points corresponding to multiple specified angles on the same circumference, and multiple stresses of multiple specified angles corresponding to test points on the same circumference are obtained by the detector Birefringence amount; enter step S11;

Step S19, until all test points are measured.

In step S13 , the concentricity between the aspheric element and the test stand of the stress birefringence device is adjusted manually by placing the aspheric element on the test stand of the stress birefringence device.

In a specific implementation, the deflection angle of the light source is equal to the angle between the normal of the current test point and the optical axis of the aspheric element minus the incident angle of light in the air, that is, assuming that the light is inside the aspheric element along the optical axis Direction propagation, calculate the incident angle of light in the air, that is, the incident angle of light at the current test point, and convert it into the deflection angle of the light source.

In a specific implementation, the stress birefringence device uses polar coordinates when testing the aspheric element, wherein the center point of the aspheric element is the reference point, and the horizontal vector to the right of the center point is the polar axis. Coincident with the polar axis is the 0° position, and the polar axis is rotated 90° counterclockwise to be the 90° position.

In specific implementation, step S11 is specifically:

In the radial direction of the aspheric element, select N test points whose unit interval is the first preset distance from the center of the aspheric element, where N is a positive integer greater than or equal to 1. Each first preset distance has two test points with angles of 0° and 90° on the same circumference. Of course, each first preset distance has two test points with angles of 0°, 90°, Four test points at 180° and 270°. For example, when the first preset distance is 5mm and the radius of the aspheric element is 35mm, the test points are specifically four points whose distance from the center of the aspheric element is 5mm, and the distance from the center of the aspheric element is 10mm. Four points, four points at a distance of 25mm, and four points at a distance of 30mm. In addition, the angles on the circumference of two points at which the distance between the centers of the aspherical elements is 5 mm are 0°, 90°, 180°, and 270°.

In a specific implementation, the initial position of the light source is: the displacement is 0mm, and the deflection angle is 0°

In a specific implementation, the concentricity between the aspheric element and the test bench is less than or equal to 0.1 mm.

In a specific implementation, the aspheric element may be a double-sided polished element and an element coated with matching liquid on the matte surface.

In a specific implementation, step S15 is specifically: moving the detector of the stress birefringence device directly below the current test point. When measuring the stress birefringence device, the test light propagates along the optical axis in the aspheric element, that is, the vertical direction. Specifically, the lower surface of the aspheric element is flat, and the light propagating vertically is perpendicular to the lower surface of the aspheric element without refraction, so the light exit position is the same as the incident position, and the detector only needs to be below the test point of the aspheric element , the complete exit light can be detected.

In a specific implementation, in step S18, it further includes: obtaining the specified angle according to the number M of test points selected in the circumferential direction of the aspheric element, wherein M is a positive integer greater than or equal to 1. The number M of test points selected in the circumferential direction of the aspheric element is determined according to the actual situation of the measurement. When the number M of test points is larger, the measurement result is more accurate. For example, the number M of test points can be 4, 8 or 12, etc. . When the number of test points M is 2, the multiple specified angles are: 0° and 90°. When the number of test points M is 4, the specified angles are: 0°, 90°, 180° and 270°. That is to say, when the current test point is one of the four test points with angles of 0°, 90°, 180° and 270°, multiple specified angles on the same circle correspond to test points with angles of 0°, 90°, For the remaining three of the four angles of 180° and 270°, the next test point is one of the test points corresponding to multiple specified angles on the same circumference, and the four test points with the same first preset distance in the radial direction are detected Afterwards, proceed to step S11, and then measure the rest of the test points.

In a specific implementation, the method for measuring the stress birefringence of the aspheric element is described in detail by taking the aspheric element in FIG. 2 as an example. The formula of the aspheric surface I of the aspheric element:

Wherein, the diameter r ₀ of the aspheric surface I = 100 mm, the coefficient k of the aspheric surface I = -1.329873206, the diameter length of the aspheric surface element x = 104 mm, and the center thickness y = 10 mm.

Next, select 10 points with an interval of 5mm from the center in the radial direction of the above-mentioned aspheric element to be tested, and select two points at 0° and 90° on each circumference for testing, taking 1 point 20mm from the center as an example, As shown in FIG. 3 , the specific steps of the measurement method are as follows: determine the initial positions of the test point 34 and the light source 33 on the aspheric element 32 , for example, the angle of the test point 34 is 0°. Then assuming that the light propagates along the optical axis inside the element, calculate the incident angle of the light in the air, and convert it into a light source deflection angle of 5.216°; according to the size of the aspheric element 32, the position of the selected test point 34 and the position Calculate the light source displacement distance of 53 mm; place the aspheric element 32 on the test bench of the stress birefringence device, adjust the concentricity between the sample and the test bench to 0.02 mm; move the light source according to the calculated deflection angle and displacement, as shown in Figure 3 As shown, the detector 31 moves to 20mm directly below the test point 34; measures and records the data; rotates the sample to a specified angle, since the current angle of the test point 34 is 0°, rotate the sample to 20mm from the center and the angle is 90° Measure and record the data, that is, after one week of measurement, select a test point with a distance of 25 mm from the center and an angle of 0° to repeat the above steps, and process all the test data of the aspheric element 32 to obtain the stress birefringence of the aspheric element quantity.

The measurement method of the present invention does not need to upgrade the equipment, does not need to use software programming, only needs to measure the size of the equipment, and the stress birefringence can be measured when the size of the component to be measured, the aspheric surface equation and the refractive index are known; in addition, only The stress birefringence delay on the circumference can be measured by calculating the position of the light source and the position of the detector corresponding to a test point in the radial direction, which makes the measurement process of the measurement method simple and low in cost.

What described in above-mentioned embodiment and description just illustrate the principle of the present invention and preferred embodiment, under the premise of not departing from the spirit and scope of the present invention, the present invention also can have various changes and improvements, and these changes and improvements all fall into within the scope of the claimed invention.

Claims (10)

1. a kind of measurement method of the stress birfringence amount of non-spherical element, it is characterised in that: the measurement method includes:

Determine the initial position of the test point and light source on non-spherical element and according to current test point and non-spherical element light The angle of axis obtains the deflection angle of the light source；

According to the size of non-spherical element, the distance of the position of current test point and current test point to light source obtains the light source Shift length；

Adjust the concentricity of the non-spherical element and testboard；

The light source is moved into corresponding position according to the shift length of the deflection angle of the light source and the light source；

The position of the detector of the stress birfringence equipment is determined according to the position of current test point；

The detector is moved into corresponding position according to the position of the detector；

The stress birfringence amount of current test point is obtained by detector；

The non-spherical element is turned into the corresponding test of multiple specified angles on same circumference by rotating the testboard On point, and multiple stress birfringence amounts that multiple specified angles on same circumference correspond to test point are obtained by detector；

Into the initial position of the test point and light source determined on non-spherical element, according to the angle of current test point and light source optical axis The step of degree obtains the deflection angle of the light source, until all test point measurements finish.

2. measurement method according to claim 1, it is characterised in that: the initial position of the light source are as follows: displacement is 0mm, deflection angle are 0 °.

3. measurement method according to claim 1, it is characterised in that: the stress birfringence equipment tests non-spherical element The polar mode of Shi Caiyong, wherein point on the basis of the central point of non-spherical element, the vector of central point horizontally to the right are polar axis.

4. measurement method according to claim 3, it is characterised in that: the step of the test point on the determining non-spherical element Suddenly, specifically:

Select unit gap for the first pre-determined distance since the center of non-spherical element in the radial direction in non-spherical element N number of test point, wherein N is positive integer more than or equal to 1.

5. measurement method according to claim 4, it is characterised in that: it is described in non-spherical element in the radial direction from non- The center of aspherical elements starts the N number of test point for selecting unit gap as the first pre-determined distance, specifically:

It is 0 °, 90 °, 180 ° and 270 ° of four test points that each first pre-determined distance has angle on the same circumference.

6. measurement method according to claim 5, it is characterised in that: the corresponding test of multiple specified angles on same circumference Point, specifically:

When current test point be four test points that angle is 0 °, 90 °, 180 ° and 270 ° for the moment, it is multiple on same circumference Specified angle corresponds to remaining three that test point is four angles that angle is 0 °, 90 °, 180 ° and 270 °.

7. measurement method according to claim 1, it is characterised in that: the non-spherical element is concentric with the testboard Degree is less than or equal to 0.1mm.

8. measurement method according to claim 1, it is characterised in that: the current test point of the basis and non-spherical element Optical axis angle obtains the deflection angle of the light source, specifically:

Light is propagated in the inside of non-spherical element along optical axis direction, and the aerial incidence angle of light is calculated；

It is aerial that the angle of normal and non-spherical element optical axis that the light source deflection angle is equal to current test point subtracts light Incidence angle.

9. measurement method according to claim 1, it is characterised in that: described according to the determination of the position of current test point The position of the detector of stress birfringence equipment, specifically:

The detector of stress birfringence equipment is moved to the underface of current test point.

10. measurement method according to claim 1, it is characterised in that: the non-spherical element be twin polishing element and The element of hair side painting matching fluid.