A dual side interferometer

Abstract

The present application relates to a kind of double-sided interferometer, the collimating mirror of one side interferometer is provided with first light blocking device between reference mirror, first light blocking device is provided with first through hole, the aperture of first through hole is greater than the outer diameter of the non-transparent substrate to be measured and less than the aperture of the reference mirror of this side interferometer, for blocking the interference of this side interferometer to the opposite side interferometer in the measurement cavity topography.By setting light blocking device, the output light of one side in the measurement cavity topography is prevented from interfering with the other side interferometer, the topography between two reference mirrors can be obtained while measuring the topography of the front and back of non-transparent substrate, especially the first-order tilt information.

Description

Technical Field

[0001] This invention relates to the field of semiconductor measurement, and more specifically to a two-sided interferometer. Background Technology

[0002] As the feature size of photolithography continues to shrink, the surface morphology of wafers (e.g., silicon wafers) has an increasingly significant impact on photolithography performance. As a special type of large-size non-transparent substrate, it is necessary to measure the geometric parameters of the wafer surface.

[0003] A two-sided interferometer is disclosed in the prior art, for example, as shown in the figure. Figure 1 The two-sided Fizeau interferometer shown or such Figure 7 The illustrated two-sided Thyman-Green interferometer can be used to simultaneously measure the geometric parameters of both sides of a non-transparent substrate. Taking the two-sided Fizeau interferometer as an example, its structure is as follows: Figure 1 As shown, the system includes two Fizeau interferometers, with their optical axes aligned. Wafer 4 is placed within the cavity formed by the reference mirrors of the two Fizeau interferometers. If the distance distribution of the front side of wafer 4 relative to the first reference mirror 2 is a; the distance distribution of the back side relative to the second reference mirror 3 is b; and the distance distribution between the two reference mirrors is c, then the wafer thickness variation is t = cab.

[0004] To ensure the accuracy of the wafer thickness distribution, the cavity thickness distribution *c* needs to be pre-calibrated. Since the first-order tilt between the reference mirrors changes due to their mechanical fixing structure under conditions of temperature, vibration, and air pressure, the first-order tilt of the cavity between the two interferometer reference mirrors needs to be measured simultaneously with the measurement of the geometric parameters of the wafer's front and back sides. Then, the measured first-order tilt replaces the corresponding first-order tilt component in the pre-calibrated cavity distance distribution *c*, resulting in the updated cavity distance distribution *c*. Finally, the wafer thickness distribution is obtained using CAB. Specifically, the first-order tilt component between the reference mirrors is calculated by measuring the morphology of the annular region outside the wafer aperture of the interferometer reference mirrors. Figure 2 As shown, Figure 2 This is a schematic diagram of interference fringes obtained by measuring one side of the interferometer, including a wafer region and a ring region. The former is formed by the interference of the measured light and the reference light on the wafer, while the latter is formed by the interference of the reference plane of the first reference mirror 2 and the reference plane of the second reference mirror 3. The latter can be used to calculate the morphology between the two reference mirrors, such as obtaining the first-order tilt information between the two reference mirrors.

[0005] When using a two-sided interferometer to measure geometric parameters such as thickness distribution, it is crucial to ensure that the output beams from both interferometers do not interfere with each other, making effective beam isolation essential for accurate measurement results. However, in practical measurements, relying solely on the polarization orthogonality of the beams is insufficient to effectively attenuate the output beams from both interferometers. This results in the output beam from one side affecting the interferometric measurement from the other side, adversely impacting measurements of cavities (e.g., measurements of the first-order tilt of a cavity) while simultaneously measuring the front and back of a non-transparent substrate. Consequently, a higher demand is placed on beam isolation in two-sided interferometers. Summary of the Invention

[0006] This invention addresses the technical problems existing in the prior art by providing a dual-sided interferometer, which prevents the output light from one side of the cavity topography measurement from interfering with the other side of the interferometer by setting a light blocking device.

[0007] Specifically, in the aforementioned bilateral interferometer, a first light-blocking device is provided between the collimating mirror and the reference mirror of one side interferometer. The first light-blocking device has a first through hole. The diameter of the first through hole is larger than the outer diameter of the non-transparent substrate to be measured and smaller than the aperture of the reference mirror of the same side interferometer, in order to block the interference of the same side interferometer to the other side interferometer in measuring the cavity morphology.

[0008] Furthermore, the first light-blocking device is configured such that the width of the annular region around the non-transparent substrate under test, used for measuring the cavity morphology between the reference mirrors, meets a preset width.

[0009] Furthermore, the aperture of the first through hole and / or the position of the non-transparent substrate are adjusted so that the width of the annular region is within a preset width range.

[0010] Furthermore, the preset width range is 2 to 15 mm.

[0011] Furthermore, the first light-blocking device is an aperture.

[0012] Furthermore, both sides of the aperture are made of light-absorbing material and are subjected to matte oxidation treatment or coated with an anti-reflection absorption film.

[0013] Furthermore, the distance between the aperture and the reference mirror is no greater than 10mm.

[0014] Furthermore, the aperture is a variable aperture.

[0015] Furthermore, the first light-blocking device is an anti-reflection absorption film coated on one side of the collimating mirror of the reference mirror near the interferometer on this side, and the anti-reflection absorption film has a ring structure.

[0016] Furthermore, a second light-blocking device is provided between the collimating mirror and the reference mirror of the interferometer on the other side opposite to the first light-blocking device. The second light-blocking device has a second through hole with a diameter different from that of the first through hole. This is used to block the interference of the interferometer on this side to the interferometer on the other side in measuring the cavity morphology, and to ensure that the width of the annular region around the non-transparent substrate to be measured for measuring the cavity morphology between the reference mirrors meets the preset width.

[0017] The beneficial effects of this invention are: through the above-described scheme, interference from the output light on one side of the cavity morphology measurement to the interferometer on the other side can be effectively prevented. The morphology between two reference mirrors can be obtained simultaneously while measuring the morphology of the front and back surfaces of a non-transparent substrate, especially obtaining first-order tilt information. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a double-sided Fizeau interferometer in the prior art.

[0019] Figure 2 This is a schematic diagram of the interference fringes obtained by measuring one side of the interferometer.

[0020] Figure 3 The first light-blocking device provided in this embodiment of the invention is a schematic diagram of a double-sided Fizeau interferometer structure with an aperture.

[0021] Figure 4 A schematic diagram illustrating the working principle of a two-sided Fizeau interferometer provided in an embodiment of the present invention.

[0022] Figure 5 This is a schematic diagram of the aperture blade provided in an embodiment of the present invention.

[0023] Figure 6 The first light-blocking device provided in the embodiment of the present invention is a schematic diagram of a two-sided Fizeau interferometer structure with an anti-reverse absorption film.

[0024] Figure 7 This is a schematic diagram of the structure of a bilateral Thyman Green interferometer in the prior art.

[0025] Figure 8 A schematic diagram of the structure of the double-sided Thyman Green interferometer provided in an embodiment of the present invention.

[0026] The attached diagram lists the components represented by each number as follows:

[0027] 1. Collimating lens, 2. First reference lens, 3. Second reference lens, 4. Wafer, 5. Aperture, 6. Anti-reflection coating, 7. Collimating lens, 8. Beam splitter, 9. Third reference lens, 10. Condenser lens, 11. Imaging lens. Detailed Implementation

[0028] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] This invention provides a two-sided interferometer, which can be a two-sided Fizeau interferometer or a two-sided Twyman-Green interferometer. Taking a two-sided Fizeau interferometer as an example, as follows... Figures 3-6 As shown, a first light-blocking device is provided between the collimating lens 1 and the first reference lens 2 of one side interferometer. The first light-blocking device has a first through hole (for example, located at its center). The diameter of the first through hole is larger than the outer diameter of the non-transparent substrate to be measured (for example, wafer 4) and smaller than the aperture of the first reference lens 2 of the interferometer on this side (the side interferometer with the first light-blocking device). This is used to block the output light of the interferometer on the side with the first light-blocking device whose aperture is larger than the aperture of the first through hole of the first light-blocking device, so as to block the interference of the interferometer on this side to the interferometer on the other side in measuring the cavity morphology.

[0030] It should be noted that the present invention requires the cavity size to be larger than the size of the non-transparent substrate to be tested, so that while imaging the non-transparent substrate to be tested, an interference ring region can be generated between the two reference mirrors, and then the cavity morphology can be obtained based on the interference fringes in the ring region.

[0031] In this embodiment, the non-transparent substrate is wafer 4. For example... Figure 2 As shown, when wafer 4 is imaged by an interferometer on one side, there is a gap between the wafer region and the annular region. Interference fringes may exist in the gap region, or the interference fringes may be sparse or even non-existent due to the edge roll-off effect of wafer 4.

[0032] In this embodiment, the structures of one interferometer and the other interferometer are identical. The optical axes of the two interferometers along the incident direction onto the non-transparent substrate are collinear, and the non-transparent substrate is disposed within the cavity formed by the two reference mirrors. Exemplarily, the optical axis is horizontal, and the non-transparent substrate is placed vertically in the cavity; or the optical axis is vertical, and the non-transparent substrate is placed horizontally in the cavity. In this embodiment, the non-transparent substrate is placed in the middle of the cavity, and the distance between the non-transparent substrate and the two reference mirrors is the same, but this is not limited to this; that is, the distance between the non-transparent substrate and the two reference mirrors can be different.

[0033] In this embodiment, an excessively narrow annular region may cause deviations in the topography measurement between the two reference mirrors, while an excessively wide region would increase the manufacturing cost and size of the interferometer. Therefore, a first light-blocking device is provided to ensure that the width of the annular region surrounding the wafer 4 used for measuring the cavity topography between the reference mirrors meets a preset width. Specifically, the aperture of the first through-hole of the first light-blocking device and / or the position of the wafer are adjusted to ensure that the width of the annular region is within the preset width range.

[0034] The first light-blocking device may be installed in an interferometer on only one side, or in an interferometer on both sides, including a first light-blocking device and a second light-blocking device.

[0035] In one embodiment of the present invention, the first light-blocking device is provided only in the interferometer on one side. On the one hand, the cost is lower when the light-blocking device is provided on only one side; on the other hand, when light-blocking devices are provided on both sides, if the light-blocking devices with the same aperture are provided on both sides, the output light on either side will be partially blocked by the light-blocking device, making it difficult to generate a ring region of sufficient width or even no ring region. This makes it impossible to ensure that the morphology between the two reference mirrors, especially the first-order tilt information, is measured simultaneously when measuring the morphology of the non-transparent substrate.

[0036] In another embodiment of the present invention, a light-blocking device is provided between the collimating mirror and the reference mirror of both interferometers, that is, a first light-blocking device is provided on one side and a second light-blocking device is provided on the other side. A second through hole is provided on the second light-blocking device (for example, at the center). The diameter of the second through hole is different from that of the first through hole. It is used to block the interference of the interferometer on this side (either side interferometer) to the interferometer on the other side (the other side interferometer) in measuring the cavity morphology, and to make the width of the annular region around the non-transparent substrate to be measured for measuring the cavity morphology between the reference mirrors meet the preset width.

[0037] In this embodiment, the first light-blocking device is an aperture 5, such as... Figure 3 As shown. On one side where the aperture 5 is set, because the aperture of the aperture 5 is larger than the outer diameter of the wafer 4 under test and smaller than the aperture of the first reference mirror 2, part of the output on that side will be blocked by the aperture 5, while the other side will not be blocked by the aperture 5, as shown. Figure 4 As shown, the reflected light from the first reference surface of the first reference mirror 2 and the reflected light from the second reference surface of the second reference mirror 3 interfere to form the annular region. The reference light from the first reference surface and the measurement light from the wafer 4 interfere to form the wafer region. The aperture 5 is set in the collimating mirror 1 (not in the collimating mirror 1). Figure 4 The aperture between the wafer (illustrated in the diagram) and the first reference mirror 2 ensures that the morphology between the two reference mirrors, especially the first-order tilt information, can be measured simultaneously while measuring the wafer morphology. Taking a 12-inch wafer as an example, the preferred aperture diameter is 301mm to 310mm.

[0038] In one embodiment, the annular region is not limited to having a uniform width; when it has a non-uniform width, its width should also meet the preset width range.

[0039] In one embodiment, the annular region has a uniform width, which is a set value within a preset width range. The width satisfies the preset width, meaning it is a set value within the preset width range. For example, the preset width range is 2–15 mm. For instance, the width of the annular region can be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 mm.

[0040] In one embodiment, the width of the annular region satisfies a preset width, i.e., the width is within a preset width range. When the annular region has a uniform width, the width of the annular region can be a set value within the preset width range; when the width of the annular region is non-uniform, the width of the annular region has multiple width values, but all satisfy the preset width range. For example, the preset width range is 2 to 15 mm. For instance, if the annular region has a non-uniform width, any width of the annular region is greater than or equal to 2 mm and less than or equal to 15 mm.

[0041] In one embodiment, both sides of the aperture 5 are made of light-absorbing material and are subjected to matte oxidation treatment or coated with an anti-reflection absorption film. The aperture 5 should be an excellent light-absorbing material, such as carbon fiber nanotubes; it can also be a base material such as aluminum alloy or stainless steel, with a matte oxidation treatment on the surface; or it can be a metal or non-metal material with an anti-reflection absorption film coated on the surface, such as black nickel plating.

[0042] In one embodiment, the aperture 5 should be positioned between the collimating lens 1 and the reference lens 2, with the distance between the aperture 5 and the reference lens 2 being less than 10 mm, preferably less than 5 mm; the blade thickness of the aperture 5 is preferably 0.2-0.5 mm. A schematic diagram of the aperture 5 is shown below. Figure 5 As shown.

[0043] Based on the above embodiments, in order to cope with the measurement of non-transparent substrates of different sizes, the aperture 5 can be set as a variable aperture to meet the needs of different preset widths of the annular region when measuring non-transparent substrates of different sizes.

[0044] In one embodiment, the aperture 5 is disposed between the collimating lens 1 and the first reference lens 2, and one side of the aperture 5 is in contact with the side of the first reference lens 2 that is closer to the collimating lens 1.

[0045] In one embodiment, the Fizeau interferometer on either side further includes a beam splitter, a quarter-wave plate, a mirror, an imaging mirror, and a detector. The working principle of the Fizeau interferometer is prior art and will not be described in detail here. Exemplarily, the interferometer on either side includes a light source, but is not limited thereto; the interferometers on both sides may share a single light source.

[0046] In another embodiment, the first light-blocking device is an anti-reverse absorption film 6. For example... Figure 6As shown, a black nickel or similar coating is deposited on the side of the reference mirror 2 of one interferometer near the collimating mirror 1 to form an anti-reflection film 6 with a preferred thickness of 5-20 nm. The anti-reflection film has a ring structure, for example, forming a uniformly wide ring. The reference mirror on the other side does not need to be coated. To ensure the integrity of the test area on the non-transparent substrate, the aperture (i.e., inner diameter) of the anti-reflection film 6 is larger than the outer diameter of the non-transparent substrate and smaller than the aperture of the first reference mirror 2 of the interferometer on this side. Taking a 12-inch wafer as an example, the preferred aperture diameter is 301 mm to 310 mm. For example, the preset width of the ring region needs to be 2 to 15 mm.

[0047] The anti-reflection coating effectively blocks the output light from the interferometer on the side with the aperture installed from being larger than the aperture of the anti-reflection coating, thus preventing interference to the interferometer on the opposite side during cavity topology measurement. The interferometer on the side without the anti-reflection coating can measure the annular region outside the aperture of the anti-reflection coating, and obtain the cavity topology based on the interference fringes of the annular region, for example, calculating the first-order tilt between the two reference mirrors. Compared with the scheme with aperture 5 mentioned above, the distance between the anti-reflection coating 6 and the non-transparent substrate under test is usually closer, resulting in better illumination of the interferometer, weaker penumbra effect, and better interferometric imaging.

[0048] By setting an aperture or coating, the output light of the interferometer on the side with the aperture / coating larger than the aperture / coating aperture can be effectively blocked, so as to prevent the output light on this side from interfering with the interferometer on the other side when measuring the cavity morphology; the morphology between two reference mirrors can be obtained while measuring the morphology of the front and back of the non-transparent substrate, especially the first-order tilt information.

[0049] In one embodiment, the second light-blocking device is either the aperture 5 or the anti-reflection absorption film 6. The first light-blocking device and the second light-blocking device can both be aperture 5, or both can be anti-reflection absorption film 6, or one can be aperture 5 and the other anti-reflection absorption film 6.

[0050] In one embodiment of the present invention, the two-sided interferometer can be specifically a two-sided Twyman Green interferometer, which is used to simultaneously measure the geometric parameters of the front and back surfaces of a non-transparent substrate. The technical solutions in the previous embodiments are also applicable to the two-sided Twyman Green interferometer, and will not be repeated here.

[0051] In one embodiment of the present invention, the bilateral Twyman Green interferometer can be... Figure 8 The optical path structure shown in the diagram includes a Thyman Green interferometer on one side, comprising a light source, a collimating mirror 7, a beam splitter 8, a third reference mirror 9, a first light-blocking device (e.g., an aperture 5 or an anti-reflection absorption film 6), a first reference mirror 2, a condenser mirror 10, an imaging mirror 11, and a detector. The Thyman Green interferometer on the other side has the same structure. The working principle of the Thyman Green interferometer is prior art and will not be described in detail here.

[0052] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0053] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A two-sided interferometer, characterized in that, The two-sided interferometer is a two-sided Fizeau interferometer or a two-sided Thyman Green interferometer; in the two-sided interferometer, a first light-blocking device is provided between the collimating mirror and the reference mirror of one side interferometer. The first light-blocking device has a first through hole. The diameter of the first through hole is larger than the outer diameter of the non-transparent substrate to be measured and smaller than the aperture of the reference mirror of the same side interferometer, so as to block the interference of the same side interferometer to the other side interferometer in the measurement cavity morphology.

2. The two-sided interferometer according to claim 1, characterized in that, The first light-blocking device is configured such that the width of the annular region around the non-transparent substrate under test, used for measuring the cavity morphology between the reference mirrors, meets a preset width.

3. The two-sided interferometer according to claim 2, characterized in that, Adjust the diameter of the first through hole and / or the position of the non-transparent substrate so that the width of the annular region is within a preset width range.

4. The two-sided interferometer according to claim 2, characterized in that, The preset width range is 2~15mm.

5. The two-sided interferometer according to claim 1, characterized in that, The first light-blocking device is an aperture.

6. The two-sided interferometer according to claim 5, characterized in that, Both sides of the aperture are made of light-absorbing material and are treated with matte oxidation or coated with an anti-reflection absorption film.

7. The two-sided interferometer according to claim 5, characterized in that, The distance between the aperture and the reference mirror is no more than 10mm.

8. The two-sided interferometer according to claim 5, characterized in that, The aperture is a variable aperture.

9. The two-sided interferometer according to claim 1, characterized in that, The first light-blocking device is an anti-reflection absorption film coated on one side of the collimating mirror of the reference mirror near the interferometer on this side. The anti-reflection absorption film has a ring structure.

10. The two-sided interferometer according to claim 1, characterized in that, A second light-blocking device is also provided between the collimating mirror and the reference mirror of the interferometer on the other side opposite to the first light-blocking device. The second light-blocking device has a second through hole with a diameter different from that of the first through hole. It is used to block the interference of the interferometer on this side to the interferometer on the other side in measuring the cavity morphology, and to ensure that the width of the annular region around the non-transparent substrate to be measured for measuring the cavity morphology between the reference mirrors meets the preset width.

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