CN116202664A

CN116202664A - Film stress detection system and method suitable for transparent wafer

Info

Publication number: CN116202664A
Application number: CN202310231713.8A
Authority: CN
Inventors: 陈剑; 俞胜武; 刘明东; 戴丹蕾
Original assignee: Wuxi Zhuohai Technology Co ltd
Current assignee: Wuxi Zhuohai Technology Co ltd
Priority date: 2023-03-10
Filing date: 2023-03-10
Publication date: 2023-06-02
Anticipated expiration: 2043-03-10
Also published as: CN116202664B

Abstract

The invention relates to a thin film stress detection system and a thin film stress detection method suitable for a transparent wafer. It includes light path unit, and light path unit includes: a laser; the incident beam regulating and controlling part comprises a beam waist control mechanism for compressing the beam waist radius of the incident laser beam, wherein the beam waist radius of the incident laser beam is compressed by the beam waist control mechanism and then is matched with the maximum allowable beam waist radius of the wafer to be subjected to film stress detection; the reflected light beam regulating part comprises a focusing lens group used for focusing reflected light, wherein the reflected laser beam formed by reflection is focused on the two-dimensional position sensor through the focusing lens group so as to detect the film stress of the wafer based on the position point of the reflected laser beam on the two-dimensional position sensor. The invention can effectively realize the film stress detection of the wafer, is particularly suitable for the film stress detection of the transparent wafer, and improves the range, stability and reliability of the film stress detection.

Description

Film stress detection system and method suitable for transparent wafer

Technical Field

The present invention relates to a stress detection system and method, and more particularly, to a system and method for detecting stress of a thin film suitable for a transparent wafer.

Background

The document with publication number CN113267278A discloses a film stress detection method, which specifically comprises the following steps: the laser with two different wavelengths is regulated to a common light path by a beam splitter prism, and after the laser irradiates the surface of the wafer, the reflected light is reflected to a position sensor by a reflecting mirror. When the slope of the tangential plane at a point on the wafer surface changes, the position of the reflected light impinging on the position sensor changes. By collecting the light spot position signals on the position sensor corresponding to each scanning point on the wafer surface, the tangential plane slope of each point on the wafer surface can be calculated, and the curvature radius of the wafer surface can be calculated. The film stress of the wafer can be calculated by measuring the surface curvature radius of the wafer before and after film coating.

In the prior art disclosed in the above patent application, there are mainly some disadvantages in calculating the radius of curvature of the wafer surface:

1) 2 different wavelength lasers are used to ensure that when the reflectivity of one of the wavelengths is too low for a certain wafer material, a laser of another wavelength is also adequate. However, for the wafers made of special materials (such as transparent materials, lithium niobate, lithium carbonate, etc.), the reflectivity for 2 wavelengths is very low, and at this time, lasers with other wave bands or lasers with higher light intensity are required to meet the requirements.

2) The following problems are encountered when using a bonding surface of a 45 ° prism as a reflecting surface: a) The light intensity of the bonding surface is increased, the glue is easy to crack, and the service life of the bonding beam-splitting prism is greatly reduced; b) The semi-transparent and semi-reflective film of the 45-degree beam splitting prism cannot meet the measurement requirements well in terms of transmittance and reflectivity, which inevitably leads to great light energy loss, and for some wafer materials with lower reflectivity at 670nm wavelength, the light intensity irradiated to the position sensor is very small and cannot meet the measurement requirements due to great system light energy loss.

3) The transparent wafer cannot be measured. Because the reflectivity of the transparent wafer to 2 wavelengths is very low, and the reflected light on the upper surface and the lower surface of the transparent wafer interfere, the optical signals collected by the position sensor are greatly affected by interference, the shape outline of the outer surface of the wafer cannot be accurately represented, and a large measurement error is caused.

4) The emergent light spots of the 2 lasers are elliptical light spots, and are not shaped, so that the resolution of system measurement is affected.

5) In operation, the optical path of the system is required not to change too much. In the actual measurement process, factors such as the thickness of the wafer, the surface bending degree, whether the carrier is level-adjusted and the like have great influence on the optical path of the system, especially for different measuring sheets and different adjustment processes of the laser and the reflector frame, the optical path values are different, and the actual optical path of the system and the theoretical optical path are necessarily different. The unstable optical path value caused by the above reasons will necessarily directly lead to unstable measurement values of the wafer radius of curvature and the film stress value.

6) The system must be leveled before normal use. Based on the optical path design scheme, when the carrier is inclined, reflected light corresponding to the scanning points with equal slope of the two tangential planes is directly influenced to irradiate the position points on the position sensor, namely the slope of the tangential planes of the two scanning points can be mistakenly considered to be different by system software, so that measurement errors are caused.

7) The value of the radius of curvature measured by this method is necessarily different for wafers of the same radius of curvature but different thicknesses. This is because the wafer thickness has an effect on the actual optical path length.

8) For a wafer with a certain curvature (i.e. convex or concave), there must be different heights of different scanning points, which also causes different actual optical paths of different scanning points of the same wafer, resulting in measurement errors.

9) Without focusing optics, the size of the mirrors and position sensors is limited, resulting in limited object angle of view of the light rays directed onto the mirrors and position sensors, which directly results in limited minimum radius of curvature of the wafer that the instrument can measure.

10 A single wafer placement can only measure the curvature radius of one diameter of the wafer, so that the measurement efficiency is affected; and meanwhile, placing and measuring diameters of different angles for multiple times can introduce placement errors.

The document with publication number CN105509796A discloses a film stress detection method, which specifically comprises the following steps: and two independent laser light sources (with the wavelength of 650 nm) which are placed at a certain angle are utilized to form two parallel light beams at a certain angle after being collimated by two aspheric focusing lenses respectively. When two parallel light beams irradiate on the same plane reflecting surface, the reflected light can irradiate on the same position of the CCD; when two parallel light beams are irradiated on the same reflecting surface with certain warpage (namely, surface curvature radius), the reflected light beams can be irradiated on two different positions of the CCD, and a light spot position distance difference is generated. The warp (i.e., radius of curvature) of the reflecting surface can be calculated using the distance difference.

In the prior art disclosed in the above patent application, there are some drawbacks to calculating the radius of curvature of the wafer surface:

1) It is also required that the system optical path cannot vary too much. The unstable optical path value (namely the distance from the aspheric lens to the reflecting surface to be measured) will inevitably lead to the fact that the double independent laser light sources cannot reflect to the same position of the CCD after being irradiated on the ideal plane reflecting surface, thereby leading to measurement errors.

2) Although an aspherical focusing lens is used, the lens only has the function of collimating an output light spot of the laser into approximately parallel light, and measurement errors caused by unstable optical path values of a system cannot be solved.

3) And the aspherical lens is used, so that the processing is difficult and the manufacturing cost is high.

4) And a double independent same-kind laser light source is used, so that a quarter wave plate is also required to be introduced in order to reduce the influence of coherent light interference on system measurement, and the device cost is increased.

5) The laser source with single wave band is used and the gradient control of the light intensity is not carried out, so that the wafer material with lower reflectivity at the wavelength of 650nm can not be measured due to the insufficient light intensity on the CCD.

6) The following problems are encountered when using a bonding surface of a 45 ° prism as a reflecting surface: a) The light intensity of the bonding surface is increased, the glue is easy to crack, and the service life of the bonding beam-splitting prism is greatly reduced; b) The semi-transparent and semi-reflective film cannot meet the measurement requirements well in terms of both transmittance and reflectivity, which inevitably leads to great light energy loss of the system, and for some wafer materials with lower reflectivity at the wavelength of 650nm, the light intensity irradiated onto the CCD is very small and cannot meet the measurement requirements probably because of great light energy loss of the system; c) Some light is directly returned to the laser after passing through the beam splitter prism twice. And the spot energy returned to the interior of the laser will be very concentrated due to the focusing action of the aspherical lens. This will significantly reduce the lifetime of the laser, causing damage to the laser.

The document with publication number CN104634760A discloses a film stress detection method, which specifically comprises the following steps: the stress of the optical film is detected by using diffraction gratings formed on the front and back surfaces of the long substrate by using surface acoustic waves. The emergent light of the laser is collimated and expanded by a beam expander and irradiates on a strip substrate provided with a surface acoustic wave generator and a sound absorber, and the surface acoustic wave generator generates acoustic waves on the front surface and the rear surface of the strip substrate to form a diffraction grating. After passing through the diffraction grating, the laser is focused on the detector through a focusing lens. And obtaining the cycle length of the zero-order or +/-1-order diffraction light intensity distribution by the received diffraction light signals, calculating the curvature radius of the substrate from the cycle length, and obtaining the film stress by a Stoney formula.

1) The desired substrate is a long substrate, or a wafer of not very large dimensions. Because the method is based on the light diffraction principle, the linear degree requirement on a certain direction of the piece to be measured cannot be too large, otherwise, the diffraction effect is not obvious, and the measurement cannot be performed.

2) Although the beam expander and the focusing lens are utilized, the beam expander only plays a role in collimating and expanding beams, so that the size of a light spot irradiated on a piece to be measured is ensured; the focusing lens only focuses the emergent light passing through the piece to be measured on the detector to form diffraction light spots, and the radius of curvature of the piece to be measured is calculated through the diffraction light intensity distribution period. The former has low requirements on the installation position of the beam expander; however, the latter requires that the detector must be accurately positioned at the back focal length of the focusing lens, and a slight deviation in position will cause deviation in the distribution period of the diffraction spots, resulting in measurement errors. Thus, the problem of measurement errors caused by the position errors of the installation of the parts is still not solved.

In summary, the existing film stress detection system for wafers has various defects, so that effective measurement of wafer film stress is difficult to meet, and the system is especially not suitable for detecting transparent wafer film stress.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a film stress detection system and method suitable for a transparent wafer, which can effectively realize film stress detection of the wafer, are particularly suitable for film stress detection of the transparent wafer, and improve the range, stability and reliability of film stress detection.

According to the technical scheme provided by the invention, the film stress detection system suitable for the transparent wafer comprises an optical path unit, wherein the optical path unit comprises:

a laser for generating an incident laser beam incident on a wafer to be subjected to film stress detection;

the incident beam regulating and controlling part is configured on the light path of the incident laser beam and comprises a beam waist control mechanism for compressing the beam waist radius of the incident laser beam, wherein the beam waist radius of the incident laser beam is compressed by the beam waist control mechanism and then is matched with the maximum allowable beam waist radius of the wafer to be subjected to film stress detection;

the reflected light beam regulating and controlling part is configured on a light path of an incident laser beam which is reflected by a wafer to be subjected to film stress detection to form a reflected laser beam, and comprises a focusing lens group used for focusing the reflected light, wherein the reflected laser beam formed by reflection is focused on a two-dimensional position sensor through the focusing lens group so as to detect the film stress of the wafer based on the position point of the reflected laser beam on the two-dimensional position sensor.

For an incident laser beam, the beam waist control mechanism configures a beam waist position of the incident laser beam to an upper surface of a wafer to be subjected to film stress detection, wherein,

the beam waist control mechanism comprises a divergent lens group and a collimating lens group which are sequentially arranged on the light path of the incident laser beam.

The incident light beam regulating part also comprises a polaroid and/or a cylindrical lens group for shaping light spots, wherein,

converting an incident laser beam generated by a laser into a linear polarized incident laser beam polarized in a preset direction through a polarizing plate, and sequentially passing through a beam waist control mechanism and a cylindrical lens group;

the beam waist radius of the incident laser beam compressed by the beam waist control mechanism is shaped into a circular light spot by the cylindrical lens group.

And also comprises a light intensity adjusting mechanism for adjusting the light intensity of the laser, wherein,

the light intensity adjusting mechanism comprises an adjustable attenuation sheet arranged on the light path of the incident laser beam and/or an adjustable optical gate arranged on the light path of the emitted laser beam;

reducing the laser intensity of an incident laser beam incident on a wafer to be subjected to film stress detection through an adjustable attenuation sheet;

the intensity of the laser beam reflected by the tunable grating is reduced to be incident on the two-dimensional position sensor.

The incident laser beam after being shaped by the column lens group is incident on a wafer to be subjected to film stress detection through the adjustable attenuation sheet;

the reflected laser beams are focused on the two-dimensional position sensor after sequentially passing through the focusing lens group, the reflecting mirror and the adjustable optical gate;

the adjustable attenuation sheet is moved into or out of the optical path of the incident laser beam through the adjustable attenuation sheet moving driving mechanism.

The focusing lens group comprises a focusing first convex lens, a focusing concave lens and a focusing second convex lens which are sequentially arranged, wherein,

the refractive indexes of the focusing first convex lens, the focusing concave lens and the focusing second convex lens are matched correspondingly, and abbe numbers are different.

Also comprises a detection cabinet for detecting the film stress, wherein,

the detection cabinet comprises an optical path heat insulation closed bin for accommodating the optical path unit and a wafer accommodating bin for accommodating wafers to be subjected to film stress detection, wherein the wafer accommodating bin is positioned below the optical path heat insulation closed bin, and the optical path heat insulation closed bin is isolated from the wafer accommodating bin through a bin body partition plate;

a light path unit movement driving mechanism for driving the scanning movement of the light path unit is arranged in the light path heat insulation closed bin;

a heat insulation protection light-transmitting plate is arranged in the partition plate of the bin body;

A wafer carrying platform for placing a wafer to be subjected to film stress detection is arranged in the wafer accommodating bin, and the wafer carrying platform is positioned right below the heat insulation protection light-transmitting plate;

the incident laser beam is incident on the wafer carrier through the thermal insulation protection light-transmitting plate, and the reflected laser beam formed by the reflection of the wafer is focused on the two-dimensional position sensor through the thermal insulation protection light-transmitting plate and the focusing lens group.

The light path unit driving mechanism comprises an X-axis screw rod, a Y-axis screw rod and a Z-axis screw rod which are sequentially and adaptively connected,

the optical path unit is assembled on the Z-axis lead screw, and the X-axis lead screw is assembled on the bin body partition plate;

and the X-axis lead screw, the Y-axis lead screw and the Z-axis lead screw are matched to drive the optical path unit to scan any diameter of the surface of the wafer.

A film stress detection method suitable for transparent wafers is characterized in that the film stress detection system is used for detecting the film stress of any wafer.

The wafer is a transparent wafer, a semitransparent wafer or an opaque wafer.

The invention has the advantages that:

1. the optical path unit is driven by the optical path unit motion driving mechanism to scan and realize full-diameter detection of the wafer, and the existing method based on non-one-dimensional linear motion drives the optical path to scan, and the rotation, lifting and vacuum adsorption of the wafer carrier realize full-diameter detection of the wafer, so that the placement position error caused by the rotation and the movement of the wafer in the full-diameter detection process of the wafer can be avoided, and the uniqueness of the single placement wafer detection position is ensured.

2. The Z-axis lead screw and the adjustable optical gate are matched to compensate the optical path of the actual optical path to the optical path of the theoretical optical path, and the traditional stress detection system has no degree of freedom.

3. The heat insulation protection light-transmitting plate can realize the functions of light-transmitting window, heat insulation and dust prevention, increases the functions of heat insulation and dust prevention, is favorable for ensuring the cleanness during detection, and provides possibility for increasing the heating function for the wafer carrier.

4. Only one laser is used, and the light intensity of the laser irradiated on the two-dimensional position sensor is regulated through the light intensity regulating mechanism, so that the problem that the conventional stress detection system still cannot be compatible with the detection of wafers made of various materials by using two lasers is solved.

5. The laser beam intensity and the beam waist position of the incident laser beam emitted by the laser are adjusted, the light intensity of the reflected laser beam on the two-dimensional position sensor is controlled, and then the reflected light on the upper surface and the lower surface of the transparent wafer is focused on the same position point on the two-dimensional position sensor by the focusing lens group, so that the defect that the traditional stress detection system cannot detect the transparent wafer is overcome, the minimum laser spot size on the wafer can be ensured, and the wafer detection resolution is improved.

6. The elliptical light spot emitted by the laser is shaped into a circular light spot through the cylindrical lens group, so that compared with the traditional stress detection system which scans by utilizing the short axis direction of the elliptical light spot, the scanning position point can be positioned more accurately, and the wafer detection resolution ratio can be improved. Meanwhile, the scanning detection mode that the X-axis lead screw and the Y-axis lead screw are matched with each other to scan all the diameters of the wafer is considered, and the scanning light spots are required to be round light spots, so that the light spot shape is symmetrical relative to the diameter direction when the inclined diameter is scanned.

7. The multi-stage regulation and control of the light intensity of the laser irradiated on the two-dimensional position sensor can be realized through the adjustable attenuation sheet and the adjustable optical gate, and the light intensity is ensured to be matched with the main flow of non-transparent/semitransparent/transparent wafer materials and film materials.

8. The calibration of the light path unit realizes semi-automation, and the problems existing in the traditional stress detection system for calibrating the light path purely manually are solved.

9. The focusing lens group is utilized to focus the problems existing in the prior art that the optical path value is needed to participate in the measurement value calculation, the measurement value is calculated by optimizing the effective focal length EFL of the lens group, the effective focal length EFL of the focusing lens group cannot change, and the defect that the measurement error is unstable due to the change of the optical path value in the stress measurement process in the prior art can be thoroughly solved.

10. When the wafer carrier is inclined, the reflected laser line with ideal measurement diameter is a group of parallel light, and is focused on the same position point of the two-dimensional position sensor after being focused by the focusing lens group; therefore, the leveling operation on the wafer carrier is not needed, the mechanical design is simplified, and the operation flow of personnel is simplified.

11. When wafers with different thicknesses and different curvature radiuses are processed, the difference of the heights of the measuring points only affects the position of reflected light irradiated on the focusing lens group, and the focusing position is not affected; therefore, the defect that different system errors exist in measurement of different wafers is overcome, and the instrument calibration error caused by the fact that the thickness of the measurement standard wafer is obviously larger than that of the wafer is overcome.

12. The measuring error caused by the system optical path change due to the adjustable support of the reflecting mirror is solved.

13. Due to the focusing effect of the focusing lens group, the size of an aperture angle of an image space is compressed, the upper limit of the size of an object space angle is improved under the condition that the sizes of the reflecting mirror and the two-dimensional position sensor are limited, the problem that the measuring range of the wafer curvature radius is limited due to the size limitation of the reflecting mirror and the two-dimensional position sensor is solved, and the measuring range is enlarged.

14. The adjustable optical gate can filter out stray light (including background stray light, scattered light of laser, and the like) irradiated on the two-dimensional position sensor, and the accuracy of signal acquisition is ensured.

15. The two-dimensional position sensor is adopted to replace a one-dimensional position sensor of a traditional stress detection system, whether the system light path has offset on the sagittal plane of the system light path can be recognized, and the offset of the light path can be compensated through the light path unit motion driving mechanism.

Drawings

FIG. 1 is a schematic view of an embodiment of the detection cabinet of the present invention.

FIG. 2 is a schematic view of the optical path thermal insulation closed chamber and the wafer storage chamber in an open state.

Fig. 3 is a schematic diagram of an embodiment of the optical path unit of the present invention.

Figure 4 is a schematic diagram of one embodiment of wafer surface parameters.

Reference numerals illustrate: 1-detecting cabinet, 2-wafer, 3-cabin partition board, 4-thermal insulation protection light-transmitting plate, 5-light path unit, 6-X axis screw, 7-X axis drag chain, 8-Y axis screw, 9-Z axis screw, 10-Y axis drag chain, 11-wafer carrying platform, 12-counterweight guide rail, 13-laser, 14-laser adjustable seat, 15-polaroid, 16-divergent lens group, 17-collimating lens group, 18-column lens group, 19-adjustable attenuation sheet, 20-adjustable attenuation sheet moving driving mechanism, 21-reflector adjustable bracket, 22-adjustable light gate, 23-focusing lens group, 24-reflector, 25-two-dimensional position sensor, 26-sensor plate and 27-light path unit seat.

Detailed Description

The invention will be further described with reference to the following specific drawings and examples.

In order to effectively implement the film stress detection on the wafer 2, especially suitable for the film stress detection of the transparent wafer, the film stress detection system suitable for the transparent wafer comprises an optical path unit 5, wherein the optical path unit 5 comprises:

a laser 13 for generating an incident laser beam incident on the wafer 2 to be inspected for film stress;

the incident beam regulating and controlling part is configured on the light path of the incident laser beam and comprises a beam waist control mechanism for compressing the beam waist radius of the incident laser beam, wherein the beam waist radius of the incident laser beam is compressed by the beam waist control mechanism and then is matched with the maximum allowable beam waist radius of the wafer 2 for detecting the film stress;

The reflected beam adjusting and controlling part is configured on the light path of the incident laser beam reflected by the wafer 2 to be detected by the film stress to form a reflected laser beam, and comprises a focusing lens group 23 for focusing the reflected laser beam, wherein the reflected laser beam formed by reflection is focused on the two-dimensional position sensor 25 by the focusing lens group 23 so as to detect the film stress of the wafer 2 based on the position point of the reflected laser beam on the two-dimensional position sensor 25.

Specifically, when the optical path unit 5 is used to detect the film stress on the wafer 2, the wafer 2 is the wafer to be detected by the film stress, the wafer 2 may be in a conventional common form, and the wafers 2 in the following are all wafers to be detected by the film stress.

As can be seen from the above description, when the film stress of the wafer 2 is detected, a laser beam is required to be used, and therefore, the optical path unit 5 needs to include the laser 13, the laser 13 may take a conventional form, and the laser 13 may generate or emit an incident laser beam, which is specifically a laser beam incident on the wafer 2. In order to improve the stability and reliability of the film stress detection, the incident laser beam emitted by the laser 13 needs to be modulated by an incident beam modulating section.

In order to meet the detection of the transparent wafer, the incident laser beam is regulated and controlled by the incident beam regulating and controlling part, at least the beam waist radius of the incident laser beam is compressed, and the purpose of compressing the beam waist radius of the laser beam is to reduce the influence of light interference of the corresponding reflected laser beams on the upper surface and the lower surface of the transparent wafer to an acceptable range, so that the detection system can realize the detection of the transparent wafer. In particular, the incident laser beam generated/emitted by the laser 13 is a gaussian beam, and the propagation rule of the intensity of the gaussian beam is not a straight line propagation of geometrical optics, but a hyperbola, and the beam waist is the position of the apex of the hyperbola.

For wafers 2 of different materials, the wafers 2 generally have corresponding maximum allowable beam waist radii according to different material characteristics, so that when the incident laser beam is regulated by the incident beam regulating part, at least the maximum allowable beam waist radius of the incident laser beam is adapted to the wafer 2 to be tested for film stress after the beam waist radius of the incident laser beam is compressed by the beam waist control mechanism, and the adapted maximum allowable beam waist radius is specifically not more than the maximum allowable beam waist radius of the wafer 2.

Further, for an incident laser beam, the beam waist control means configures a beam waist position of the incident laser beam to an upper surface of the wafer 2 to be subjected to film stress detection, wherein,

the beam waist control mechanism comprises a divergent lens group 16 and a collimating lens group 17 which are sequentially arranged on the light path of the incident laser beam.

An embodiment of the optical path unit 5 is shown in fig. 1, in which the beam waist control mechanism includes a divergent lens group 16 and a collimator lens group 17, and a manner of controlling the radius and position of the beam waist by the divergent lens group 16 and the collimator lens group 17 will be described in detail.

In specific implementation, the divergence lens group 4 increases the far field divergence angle of the incident laser beam, and then focuses and collimates the incident laser beam through the collimation lens group 17, and meanwhile, the beam waist position of the incident laser beam is ensured to be on the upper surface of the wafer 2. According to the theory of laser physics, the light intensity variation of reflected light caused by the light interference of the reflected laser beams on the upper and lower surfaces of the transparent wafer is reduced to be less than epsilon, and the beam waist radius W ₀ The following should be satisfied:

wherein d is the thickness of the transparent material (transparent substrate or transparent film); n is the refractive index of the laser in the transparent material; t is t ₁ The transmissivity of the upper surface of the transparent material to laser; r is (r) ₁ The reflectivity of the upper surface of the transparent material to laser; r is (r) ₂ The reflectivity of the lower surface of the transparent material to laser; epsilon is the maximum interference effect acceptable, generally epsilon=1×10 is desirable ^-5 The method comprises the steps of carrying out a first treatment on the surface of the θ is the angle of incidence of the incident laser beam.

As can be seen from the above expression, when the incident angle of the incident laser beam to the upper surface of the wafer 2 is fixed, the difference in thickness, refractive index, reflectivity, and transmissivity of the different transparent materials causes the difference in maximum allowable beam waist radius, and the smaller the incident angle θ of the incident laser beam, the maximum allowable beam waist radius W _max The smaller.

In practice, for transparent/semitransparent materials (such as glass, lithium niobate, lithium carbonate, etc.) commonly used for film stress detection, only the maximum allowable beam waist radius W satisfying the above materials needs to be calculated _max Then pass through the diverging lens group 16 and the collimating lens group 17Beam waist radius W of incident laser beam ₀ Limited to W _max The reflected light intensity of the above various transparent/translucent materials can be ensured not to be affected by interference.

In addition, the diverging lens group 16 and the collimating lens group 17 can also adjust the beam waist position of the incident laser beam to the upper surface position of the wafer, at this time, the incident angle of the incident laser beam irradiated on the wafer 2 can be ensured to be consistent with the incident angle of the optical axis, and meanwhile, the laser spot size on the wafer 2 can be ensured to be minimum, so that the wafer detection resolution is improved.

In practice, the diverging lens group 16 may be a 0.5 inch negative lens, the collimating lens group 17 may be a 0.5 inch positive lens, and both of them may be required to combine the laser beam waist radius W ₀ The limitation is according to equation 1. For a glass wafer with d.apprxeq.1 mm, there are:

bringing the above parameters into equation (1), there are: w (W) ₀ Less than or equal to 0.02mm. The beam waist radius W of the incident laser beam can be easily calculated by using optical simulation software (such as ZEMAX, CODEV, etc.) ₀ Limited to less than 0.02mm.

In operation, an incident laser beam having a beam waist radius compressed by the beam waist control mechanism is incident on the wafer 2, and is reflected by the wafer 2 to form a reflected laser beam, which needs to be focused on the two-dimensional position sensor 25 when detecting the film stress.

When the wafer 2 is a transparent wafer, if the reflected light on the upper and lower surfaces of the transparent wafer is not focused, the reflected light will not irradiate the same position point of the two-dimensional position sensor 25, which will cause 2 light spots on the two-dimensional position sensor 25 and strike at different positions, which will cause deviation of the position signal output by the two-dimensional position sensor 25, resulting in measurement error of the slope of the measurement point of the wafer 2 and further result in measurement error of the radius of curvature.

Therefore, as is clear from the above description, although the problem of the influence of the light interference of the reflected laser beams on the upper and lower surfaces of the transparent wafer is solved by the beam waist control mechanism, the shift of the optical axes of the reflected laser beams on the upper and lower surfaces of the transparent wafer causes the positions of the two reflected light beams on the two-dimensional position sensor 25 to be different. However, considering that the upper and lower surfaces of the wafer 2 and the upper and lower surfaces of the thin film are parallel (which is the premise derived by Stoney's formula), the two reflected light beams are also parallel. In one embodiment of the present invention, the focusing lens group 23 is disposed on the optical path of the reflected laser beam, and due to the presence of the focusing lens group 23, the two reflected light beams can be focused to the same position point on the two-dimensional position sensor 25, thereby solving the problem of optical axis deviation of the two reflected light beams.

In one embodiment of the present invention, the design intent of the focusing lens group 23 is to:

1) Focusing the reflected laser lines reflecting different fields of view at the wafer 2 onto the two-dimensional position sensor 25;

2) Uniformly focusing parallel reflected laser lines of the same field of view reflected at the wafer 2 to the same position point on the two-dimensional position sensor 25;

3) For lasers with various different wavelengths, the laser can be focused on the same position point on the two-dimensional position sensor 25, namely, the chromatic aberration of the focusing lens group 23 is controlled to be in a very small range;

4) The transmittance of the focusing lens group 23 is controlled to be not lower than 90%, so that the light intensity on the two-dimensional position sensor 25 is ensured to meet the measurement requirement;

5) Considering the limitation of the assembly space, the aperture of the focusing lens group 23 is limited, and meanwhile, the compatibility of a slightly large view field is ensured as much as possible, so that the range of the instrument is enlarged.

6) And the bonding lens is not used as much as possible, so that the cracking of the bonding surface caused by laser is prevented.

7) On the premise of considering the limitation of the assembly space, the effective focal length of the focusing lens group 23 is increased as much as possible, and insufficient measurement accuracy caused by too small effective focal length is prevented.

8) The reflected laser lines on the upper and lower surfaces of the wafer 2 based on the transparent/translucent material are focused to the same position point on the two-dimensional position sensor 25.

The operation principle of the focusing lens group 23 will be specifically described below.

In the film stress detection method disclosed in publication No. CN113267278A, the radius of curvature R of the wafer surface is calculated using the following formula:

where k is the slope of the fitted line,

Δx is the center-to-center distance of the position points on the surface of the wafer 2, and Δy is the spot position reading of the two-dimensional position sensor 25 corresponding to the position points on the wafer 2. L is the system optical path, and the detection of the radius of the surface area of the wafer is defective due to the instability of the optical path L.

Fig. 4 is a schematic diagram of parameters of a wafer 2, wherein let the outer diameter of the wafer 2 be D, the bow height be H, and the zenith angle of a position point from the center Δx be θ; then there is an approximate relationship:

from the above expression, it is clear from the geometric relationship that 2θ is the object-side half field angle of the focusing lens group 23 corresponding to the position point of the wafer 2.

Let the effective focal length of the focusing lens group 23 be f, the photosurface of the two-dimensional position sensor 25 is exactly located on the image-side focal plane of the focusing lens group 23. From the geometrical relationship, it is clear that the vertical axis image height Δy=f×tan (2θ).

In an actual stress detection system, the object half field angle 2θ is small, typically not exceeding 2 °. Therefore, with the approximate relationship tan (2θ) =2θ, the position reading Δy of the two-dimensional position sensor 25 corresponding to the position point of the wafer 2 is:

at this time, there are: />

As can be seen from the above description, in one embodiment of the present invention, compared with the prior art, by adding the focusing lens group 23, the optical path L is changed to the effective focal length f of the focusing lens group 23, so as to facilitate calculation of the profit detection. Meanwhile, since the effective focal length f of the focusing lens group 23 does not change, stability and reliability can be greatly improved compared with a method of calculating the radius of curvature of the surface of the wafer 2 by using the optical path L.

In one embodiment of the present invention, the focusing lens group 23 includes a focusing first convex lens, a focusing concave lens, and a focusing second convex lens, which are sequentially disposed, wherein,

Specifically, the focus lens group 23 forms a convex-concave-convex three-piece structure by focusing the first convex lens, focusing the concave lens, and focusing the second convex lens. For the focusing lens group 23, there are:

1) The first convex lens and the second convex lens can be made of crown glass, the concave lens can be made of flint glass, the refractive index matching of the first convex lens, the concave lens and the second convex lens can be guaranteed, the Abbe numbers are different, and chromatic aberration can be effectively corrected. The refractive indexes of the first convex lens, the concave lens and the second convex lens are matched, that is, the refractive indexes of the first convex lens, the concave lens and the second convex lens are similar, or the difference of the refractive indexes is in an allowable range, and the allowable range can be generally selected and determined according to actual requirements.

When the focusing lens group 23 is formed by adopting the focusing first convex lens, the focusing concave lens and the focusing second convex lens, the chromatic aberration of the focusing lens group 23 is not more than 1 mu m in a wavelength range of 670 nm-780 nm and under a half view field of 2 degrees, the measuring error of the curvature radius of the wafer 2 is less than 1%, and the measuring precision requirement is met. The measurement error due to chromatic aberration is further compressed in consideration of the fact that separate corrections are made for the 670nm and 780nm bands.

2) In one embodiment of the present invention, the focusing first convex lens, the focusing concave lens and the focusing second convex lens are all standard spherical lenses with low cost, and the convex-concave-convex three-piece structure can well perform positive and negative spherical aberration compensation. Specifically, the spherical aberration of the lens group 23 may not exceed 0.6λ, λ is the laser wavelength, and the spherical aberration of the full band may not exceed 0.5 μm, so as to meet the measurement accuracy requirement.

3) Since the light-sensitive surface of the two-dimensional position sensor 25 is a plane, the actual focal surface of the focusing lens group 23 must be as close to the plane as possible to minimize the influence of curvature of field (or coma). When the focusing lens group 23 is formed by adopting the focusing first convex lens, the focusing concave lens and the focusing second convex lens, the meridian field curvature of the focusing lens group 23 is not more than 1.7 mu m, the sagittal field curvature is not more than 15.4 mu m, and the assembly precision requirement is met.

4) Since the two-dimensional position sensor 25 is insensitive to the laser spot size on the photosurface and is sensitive only to the central position of the spot, the influence of distortion on the measurement is very small and no correction of distortion is necessary.

5) Since the two-dimensional position sensor 25 is selected to be one-dimensional and linear, astigmatism has no influence on the measurement of the instrument, and no correction of astigmatism is required.

As can be seen from the above description, the focusing lens group 23 can focus the light rays of different object angles on different positions on the photosensitive surface of the two-dimensional position sensor 25; meanwhile, for parallel rays of the same object field angle, the focusing lens group 23 can focus them on the same position point on the photosurface of the two-dimensional position sensor 25. In one embodiment of the present invention, the front and rear surfaces of the focusing first convex lens, the focusing concave lens and the focusing second convex lens are coated with antireflection films, so that the energy attenuation of the laser passing through the focusing lens group 23 is less than 10%, and the light spot energy on the two-dimensional position sensor 25 is ensured to meet the use requirement.

Due to the focusing effect of the focusing lens group 23, the size of the aperture angle of the image space is compressed, the upper limit of the size of the angle of view of the object space is improved under the condition that the sizes of the reflecting mirror 24 and the two-dimensional position sensor 25 are limited, the limitation of the measuring range of the curvature radius of the wafer 2 caused by the size limitation of the reflecting mirror 24 and the two-dimensional position sensor 25 is solved, and the measuring range of an instrument is enlarged.

Unlike the solutions disclosed in publication numbers CN105509796a and 104634760a, in one embodiment of the present invention, the focusing lens group 23 is not simply used for focusing, collimating or expanding the outgoing light of the laser, but rather, solves the systematic measurement errors caused by instability and measurement inaccuracy of the important parameter "optical path value" in the calculation formula of the radius of curvature of the wafer 2. The following description will be made in terms of several cases.

1) The stage being non-parallel to the scanning direction

In the measurement scheme disclosed in CN113267278A, the stage for placing the wafer 2 needs to be leveled. If the stage 2 is not parallel to the scanning direction, when the focusing lens group 23 is not arranged in the optical path, the reflected light does not irradiate the same position point on the position sensor when scanning a certain diameter of an ideal plane mirror serving as a calibration tool, because the height of different scanning points can be different due to the unevenness of the stage. This can lead to the system misunderstanding that there is warping of the surface of the ideal planar mirror as a calibration tool, resulting in measurement errors. The light rays corresponding to different scanning points are a group of parallel light rays, and the optical path values of the light rays are different, which also causes calculation errors of measured values.

When the focusing lens group 23 is added in the optical path, a group of parallel scanning light rays caused by uneven carrier will be focused on the same position point of the position sensor uniformly, so that the measurement error caused by uneven carrier and unstable optical path value is solved. Meanwhile, the measuring system does not need to adjust levelness of the carrier, and structural design and system adjustment steps are simplified.

2) The thickness of the wafer 2 to be measured is different and the curvature radius is the same

In the measurement scheme disclosed in CN113267278A, the measured values of the radius of curvature measured by the system are different for the wafers 2 to be measured having the same radius of curvature and different thicknesses. When the focusing lens group 23 is not present in the optical path, the reflected light does not strike the ideal position point on the position sensor when scanning a certain diameter of an ideal plane mirror as a calibration tool, because the different thicknesses of the wafers 2 cause the scan point heights of the different wafers to be different. At this time, the light corresponding to the wafers 2 with different thicknesses is a set of parallel light, and their optical path values are different, which leads to calculation errors of the measured values.

When the focusing lens group 23 is added in the optical path, a group of parallel scanning light rays caused by different thicknesses of the wafer 2 are uniformly focused on the same position point of the position sensor, so that measurement errors caused by different thicknesses of the wafer 2 and unstable optical path values are solved. This also allows the measurement system to be compatible with measurements of wafers of different thickness without systematic errors.

3) The wafer 2 has a certain warpage (i.e. radius of curvature)

In the measurement scheme disclosed in CN113267278A, there is a systematic error in the measured radius of curvature measurements for a wafer 2 having a certain warp (i.e., radius of curvature). When there is no focusing lens group 23 in the optical path, the heights of different scanning points are different when a certain diameter of the wafer 2 is scanned, and their optical path values are different, which may lead to calculation errors of measured values. The measured values are accurate only if the scanning points of different heights on the surface of the wafer 2 are uniformly compensated to a uniform height.

After the focusing lens group 23 is added in the optical path, the scanning light rays translate due to different heights of the scanning points and are uniformly focused on the same position point of the position sensor, so that measurement errors caused by different heights of different scanning points and unstable optical path values of the wafer 2 are solved. This also allows the measurement system to be compatible with measurements of wafers 2 of different radii of curvature without systematic errors.

4) The actual optical path value cannot be measured

In the measurement scheme disclosed in CN113267278A, the measurement values are calculated using the system theoretical optical path values. However, after the actual system is assembled and adjusted, due to factors such as component machining errors, assembly errors, different adjustment positions of the adjustable lens frame and the like, the actual optical path value and the theoretical optical path value of the system are inevitably deviated, and at the moment, the theoretical optical path is utilized to calculate the measured value, so that systematic errors are inevitably generated.

In addition, in one embodiment of the invention, the problem that the measuring range of the curvature radius of the wafer 2 is limited due to the size limitation of the reflecting mirror and the position sensor is solved, and the measuring range of the instrument is enlarged. In the prior art, when the focusing lens group 23 is not present in the optical path, the warp of the surface of the wafer 2 is the maximum wafer warp measurable by the system when the light irradiates the edge of the mirror or the edge of the position sensor. The wafer 2 with surface warpage exceeding this limit cannot be measured by the system at all scan points on its diameter. The addition of the focusing lens group 23 improves this situation by compressing the angle of incidence of the mirror 24 with the focusing effect, thereby expanding the measurable maximum wafer warpage.

In one embodiment of the invention, the incident beam adjusting part further comprises a polarizing plate 15 and/or a cylindrical lens group 18 for spot shaping, wherein,

the incident laser beam generated by the laser 13 is converted into a linearly polarized incident laser beam polarized in a predetermined direction by the polarizing plate 15, and the converted linearly polarized incident laser beam sequentially passes through the beam waist control mechanism and the cylindrical lens group 18;

the beam waist radius of the incident laser beam compressed by the beam waist control mechanism is shaped into a circular spot by the cylindrical lens group 18.

For one embodiment of the optical path unit 5 shown in fig. 3, the polarizer 15 is located on the optical path of the laser 13, and the incident laser line generally passes through the polarizer 15, then the beam waist control mechanism, and the cylindrical lens group 18. The polarizing plate 15 may take a conventionally used form, and the incident laser beam may be converted into a linearly polarized laser beam in a predetermined direction by the polarizing plate 15, and the manner of converting the incident laser beam into the linearly polarized laser beam by the polarizing plate 15 is consistent with the conventional one. In addition, the polarizer 15 may be configured to be rotatable, and the rotation may take a conventional form, in particular, in order to meet the rotation requirement of the polarizer 15.

The cylindrical lens group 18 is used for spot shaping, the spot of the incident laser beam emitted by the laser 13 is generally elliptical, and after being shaped by the cylindrical lens group 18, the incident laser beam can be shaped into a circular spot, compared with the traditional stress detection, the scanning is performed by utilizing the short axis direction of the elliptical spot, the scanning position point can be positioned more accurately, and the detection resolution of the wafer 2 can be improved. In specific implementation, the cylindrical lens group 18 may select two positive lenses with a size of 20×20mm, and of course, the cylindrical lens group 18 may also adopt other implementation forms, so as to be capable of meeting the requirement of performing spot shaping on an incident laser beam.

In operation, an incident laser beam emitted by the laser beam 13 is converted into a linear polarized beam through the polarizing plate 15, then the linear polarized beam is subjected to beam waist radius compression through the beam waist control mechanism, and finally the linear polarized beam is subjected to spot shaping through the cylindrical lens group 18.

In one embodiment of the invention, the laser processing device further comprises a light intensity adjusting mechanism for adjusting the light intensity of the laser, wherein,

the light intensity adjusting mechanism comprises an adjustable attenuation piece 19 arranged on the light path of the incident laser beam and/or an adjustable shutter 22 arranged on the light path of the emitted laser beam;

the intensity of the laser beam incident on the wafer 2 to be subjected to film stress detection is reduced by the adjustable attenuation piece 19;

The intensity of the laser light of the reflected laser beam incident on the two-dimensional position sensor 25 is reduced via the adjustable shutter 22.

As is clear from the above description, in the case of performing film stress detection, since only one laser 13 is used, the type of the laser 13 with a strong emission intensity is selected, specifically, the laser 13 can be selected to have a 670nm band with a power of 10-20 mW. In fig. 1, the laser 13 is mounted on the laser adjustable seat 14, the laser 13 can rotate in the laser adjustable seat 14, and can pitch or swing, and the laser 13 and the laser adjustable seat 14 can adopt the conventional common mode so as to meet the requirement of adjusting the position or state of the laser 13. The adjustable base 14 of the laser is mounted on the base 27 of the light path unit, of course, the incident beam adjusting and controlling part and the outgoing beam adjusting and controlling part are also mounted on the base 27 of the light path unit, and the base 27 of the light path unit can adopt the conventional common mode so as to meet the requirement of assembling the light path unit 5.

As can be seen from the above description, since the laser 13 is of a type with stronger emergent light intensity, in order to adapt to the requirements of film stress detection of different scenes, a light intensity adjusting mechanism is required to be matched with the laser 13, and in one embodiment of the present invention, the light intensity adjusting mechanism includes an adjustable attenuation sheet 19 and an adjustable light gate 22, wherein the light intensity of the incident laser line can be attenuated by the adjustable attenuation sheet 19, and the light intensity of the reflected laser line can be attenuated by the adjustable light gate 22.

In particular, when the wafer 2 is an opaque wafer, the light intensity of the laser focused on the two-dimensional position sensor 25 can be automatically reduced to a reasonable range by the adjustable attenuation sheet 19 and the adjustable optical gate 22, wherein the reasonable range specifically refers to the light intensity located in the measuring range of the two-dimensional position sensor 25, and the reasonable ranges of different two-dimensional position sensors 25 are different and specifically related to the type of the two-dimensional position sensor 25. When the wafer 2 is a transparent/semitransparent wafer, the intensity of the laser light on the two-dimensional position sensor 25 can be automatically enhanced to a reasonable range by opening the adjustable shutter 22 and moving the electrically adjustable attenuator 19 out of the optical path of the incident laser beam. Specifically, the adjustable gate 22 is opened or closed, specifically, the size of the central opening of the gate is adjusted to be larger or smaller, which is consistent with the existing processing direction of the adjustable gate 22. By adjusting the size of the central opening of the adjustable shutter 22, it is possible to control whether or not a portion of the light spot on the adjustable shutter 22 is blocked by the adjustable shutter, and how much the light spot is blocked by the adjustable shutter, and thus to control the intensity of the light on the two-dimensional position sensor 25, which is in accordance with the existing manner of adjusting the light intensity by using the shutter.

Further, the incident laser beam shaped by the cylindrical lens group 18 is incident on the wafer 2 to be subjected to film stress detection through the adjustable attenuation piece 19;

The reflected laser beams are focused on the two-dimensional position sensor 25 after passing through the focusing lens group 23, the reflecting mirror 24 and the adjustable optical shutter 22 in sequence;

the adjustable attenuator 19 is moved into or out of the optical path of the incident laser beam via an adjustable attenuator movement driving mechanism 20.

As can be seen from the above description, the adjustable attenuator 19 is selectively used for different wafers 2. In order to meet the requirements of different application scenes, the position of the adjustable attenuation sheet 19 is adjusted by using the adjustable attenuation sheet moving driving mechanism 20, and the adjustable attenuation sheet moving driving mechanism 20 can be in a conventional common form, specifically, the requirements of adjusting the position of the adjustable attenuation sheet 19 and adjusting the light intensity of the incident laser beam can be met.

In practice, the adjustable attenuator 19 and the adjustable attenuator moving driving mechanism 20 serve to attenuate the light intensity of the incident laser light by a certain proportion. The electric adjustable attenuation piece 19 is controlled to move in or out of the optical path where the incident laser beam is located by the adjustable attenuation piece moving driving mechanism 20, so that the light intensity of the incident laser beam is controlled. The adjustable attenuator 19 may generally include two attenuators to form a two-stage adjustable attenuation, so as to achieve multi-stage adjustment of the light intensity of the incident laser beam, and after passing through the adjustable attenuator 19, the light intensity of the incident laser beam is the product of the light intensity of the incident laser beam which is not strong through the adjustable attenuator 19 and the transmittance of the two attenuators, and generally, the transmittance of the two attenuators is respectively selected to be 70% and 60%.

In fig. 3, the reflecting mirror 24 is mounted on the reflecting mirror adjustable support 21, the reflecting mirror adjustable support 21 is mounted on the optical path unit base, the rotational degrees of freedom of the reflecting mirror adjustable support 21 in two directions can be adjusted, it can be ensured that the reflected light of the reflecting mirror 24 is not inclined after being adjusted, and the reflected light can accurately irradiate the corresponding position on the two-dimensional position sensor 25.

The mirror adjustable mount 21 is similar in principle to the laser adjustable mount 14, enabling attitude adjustment of the mirror 24 in 2 degrees of rotational freedom. When the mirror 24 rotates with the adjustable mirror support 21, the optical path length of the reflected laser beam (i.e. the optical path length from the wafer 22 to the two-dimensional position sensor 25) also changes, resulting in a system optical path change. If the radius of curvature of the wafer is calculated by using the conventional calculation formula of the optical path, measurement errors are necessarily caused.

In one embodiment of the present invention, the effective focal length of the focusing lens group 23 is used to replace the system optical path to calculate the radius of curvature of the wafer, so as to avoid the measurement error caused by the system optical path change due to the rotation of the reflecting mirror 21, i.e. solve the measurement error caused by the system optical path change due to the reflecting mirror adjustable bracket 21.

The adjustable shutter 22 is a small aperture diaphragm with an automatically adjustable aperture size, and its functions include:

1) In cooperation with the adjustable attenuator 19, the intensity of the laser light irradiated on the two-dimensional position sensor 25 is controlled.

2) And filtering clutter. The adjustable optical shutter 22 can filter out stray light (including background stray light, scattered light of laser, etc.) irradiated on the two-dimensional position sensor 25, and ensure accuracy of signal acquisition of the two-dimensional position sensor 25.

In one embodiment of the invention, the film stress detection device also comprises a detection cabinet 1 for detecting the film stress, wherein,

the detection cabinet comprises an optical path heat insulation closed bin for accommodating the optical path unit and a wafer accommodating bin for accommodating wafers to be subjected to film stress detection, wherein the wafer accommodating bin is positioned below the optical path heat insulation closed bin, and the optical path heat insulation closed bin is isolated from the wafer accommodating bin through a bin body partition plate 3;

a light path unit movement driving mechanism for driving the scanning movement of the light path unit 5 is arranged in the light path heat insulation closed bin;

a heat insulation protection light-transmitting plate 4 is arranged in the bin body partition plate 3;

a wafer carrying platform 11 for placing a wafer 2 to be subjected to film stress detection is arranged in the wafer accommodating bin, and the wafer carrying platform 11 is positioned right below the heat insulation protection light-transmitting plate 4;

the incident laser beam is incident on the wafer 2 on the wafer stage 11 through the thermal insulation protection light-transmitting plate 4, and the reflected laser beam formed by the reflection of the wafer 2 is focused on the two-dimensional position sensor 25 through the thermal insulation protection light-transmitting plate 4 and the focusing lens group 23.

Specifically, when the optical path unit 5 is used to perform film stress detection on the wafer 2, the optical path unit 5 and the wafer 2 need to be placed in the detection cabinet 1. In order to meet the requirement of film stress detection, the detection cabinet 1 generally needs to include an optical path thermal insulation closed bin and a wafer accommodating bin, as shown in fig. 1 and 2. The optical path thermal insulation closed bin provides a closed environment for the optical path unit 5, and the wafer accommodating bin is used for placing and detecting the wafer 2. In fig. 1 and 2, the optical path thermal insulation closed bin is positioned right above the wafer accommodating bin in the detection cabinet 1, and the optical path thermal insulation closed bin and the wafer accommodating bin are separated by the bin body partition plate 3.

In order to realize effective detection of the film stress of the wafer 2, the optical path unit driving mechanism is utilized to drive the optical path unit 5 to move in the optical path heat insulation closed bin so as to realize scanning of any diameter on the surface of the wafer 2. The heat insulation protection light-transmitting plate 4 is arranged in the bin body partition plate 3, and the heat insulation protection light-transmitting plate 4 can play roles of heat insulation, light-transmitting window and dust prevention. The heat-insulating protective transparent plate 4 may be a glass plate, and heat-insulating films are coated on both surfaces of the glass plate. The wafer carrier 11 is disposed in the wafer storage bin, and the wafer carrier 11 is used for supporting the wafer 2, so that the wafer 2 is positioned under the thermal insulation protection light-transmitting plate 4 when the wafer 2 is placed on the wafer carrier 11. For the wafer carrier 11, a fixed design is adopted, and a tray for supporting the wafer 2 is subjected to fine sand blasting treatment, so that specular reflection does not occur on the surface of the tray when transparent/semitransparent wafers are measured.

An embodiment of the optical path unit driving mechanism is shown in fig. 1 and 2, specifically, the optical path unit driving mechanism includes an X-axis screw 6, a Y-axis screw 8, and a Z-axis screw 9 which are sequentially connected in an adapted manner, wherein,

the light path unit 5 is assembled on the Z-axis lead screw 9, and the X-axis lead screw 6 is assembled on the bin body partition plate 3;

the scanning of the optical path unit 5 to any diameter of the surface of the wafer 2 is driven by the X-axis screw 6, the Y-axis screw 8 and the Z-axis screw 9.

Specifically, the light path unit 5 is assembled on the Z-axis screw rod 9, and the light path unit 5 can be driven to move in the light path heat insulation closed cabin through the X-axis screw rod 6, the Y-axis screw rod 8 and the Z-axis screw rod 9. The specific process of driving the optical path unit 5 to move in the optical path heat insulation closed bin through the X-axis screw 6, the Y-axis screw 8 and the Z-axis screw 9 can be consistent with the prior art, and the specific process can meet the movement of the optical path unit 5 and realize the required scanning detection of the wafer 2.

In the implementation, the wafer carrier 11 can be added with a heating function without considering the heat insulation problem of electric devices and cables; because the wafer carrier 11 has no moving system, the curvature radius of the whole diameter of the wafer 2 can be measured only by placing the wafer 2 once, and the wafer 2 does not need to be moved or rotated, so that the placement position error caused by the movement or rotation of the wafer 2 is avoided, and the uniqueness of the detection position of the wafer 2 is ensured; the wafer carrier 11 does not need to be adjusted in level, and is in a fixed installation mode, so that the structure of the wafer carrier 11 is simplified.

Because there may be an installation error between the optical path unit 5 and the wafer stage 11, the actual reflected laser beam cannot be just irradiated on the center position of the two-dimensional position sensor 25 like an ideal light, and at this time, the Z-axis position of the optical path unit 5 may be finely adjusted by the Z-axis screw 9 to ensure that the actual reflected laser beam optical path coincides with the ideal optical path. In the specific implementation, the function of the Z-axis screw 9 is to compensate for the mechanical assembly error, so that the reflected laser beam accurately irradiates the center position of the adjustable shutter 22 and the center position of the two-dimensional position sensor 25, and at this time, the final position of the optical path unit 5 in the Z-axis automatic positioning can be obtained.

Specifically, in the calibration of the optical circuit unit 5, in the pre-calibration stage, the center positions of the adjustable shutter 22 and the two-dimensional position sensor 25 are first adjusted to the same horizontal line. The adjustable shutter 22 is positioned accurately by means of a mechanical positioning pin, and the center position of the two-dimensional position sensor 25 can be finely adjusted by means of its mounting screw.

In a specific implementation, the two-dimensional position sensor 25 is mounted on the sensor board 26, and is used for collecting the reflected light signal, and calculating the curvature radius of the surface of the wafer 2 by an upper computer algorithm after the reflected light signal is processed by a subsequent signal processing circuit. Because the motion scheme adopts triaxial linear motion, when measuring the diameter of the wafer 2 with different angles, the X-axis lead screw 6 and the Y-axis lead screw 8 are required to cooperate to realize linear scanning motion in the diagonal direction, at this time, the position point irradiated on the two-dimensional position sensor 25 is also a diagonal line, and the one-dimensional position sensor cannot meet the detection requirement. The mounting position of the sensor plate 26 on the optical path unit seat 27 can be adjusted by its mounting screw.

The installation position of the two-dimensional position sensor 25 is finely adjusted by using the parallel light of the collimator tube after passing through the adjustable floodgate 22. After the pre-adjustment is completed, the Z-axis position of the optical path unit 5 is adjusted by moving the Z-axis screw 9, and the reflection light is adjusted to pass through the center position of the adjustable shutter 22 (the diaphragm size is adjusted to a proper size in advance) and irradiated on the center position (i.e., the 0-position difference position) of the two-dimensional position sensor 25 in cooperation with the adjustment mirror adjustable bracket 21, and at this time, the Z-axis position calibration of the optical path unit 5 can be considered to be completed.

In specific implementation, the X-axis screw rod 6 and the Y-axis screw rod 8 can select the low dust emission series of the electric sliding table EZS of the eastern motor, and the maximum travel of the low dust emission series ensures that the constant speed section covers the diameter of the largest wafer to be tested. The Z-axis screw rod 9 can select the low dust emission series of the eastern motor electric sliding table EZS, and the maximum stroke only needs to ensure that the accumulated assembly errors affecting the optical path are covered. The X-axis drag chain 7 and the Y-axis drag chain 10 are mainly used for accommodating wire harnesses used by the X-axis screw rod 6 and the Y-axis screw rod 8, and the X-axis drag chain 7 and the Y-axis drag chain 10 can be selected from an easy-dust-free drag chain series.

In addition, a counterweight guide rail 12 is provided on the compartment partition plate 3, and the counterweight guide rail 12 corresponds to both ends of the X-axis screw 6 and the Y-axis screw 8, respectively. The weight guide rail 12 mainly balances the weight of the X-axis lead screw 6 on the bin partition plate 3. The counterweight guide rail 12 can be a THK series guide rail.

In summary, a film stress detection method suitable for transparent wafers can be obtained, and in one embodiment of the present invention, the film stress detection system is used to perform film stress detection on any wafer 2.

From the above description, the wafer 2 is a transparent wafer, a semitransparent wafer or an opaque wafer; that is, for the film stress detection system, the curvature radius of the wafer 2 (i.e., the wafer substrate, such as the Si substrate, the SiC substrate, etc.) without the film coating can be detected, and the curvature radius of the wafer 2 after the film coating can be measured. For transparent wafers, the wafer substrate may be a transparent material (e.g., glass) or the plating material may be a transparent material. In addition, when the film stress detection is performed, the stress detection of the uncoated transparent wafer and the coated transparent film wafer is adapted. The method and process for detecting the film stress by using the film stress detection system can be referred to above.

Claims

1. A thin film stress detection system for a transparent wafer, comprising an optical path unit comprising:

2. The thin film stress detection system for transparent wafers of claim 1, wherein: for an incident laser beam, the beam waist control mechanism configures a beam waist position of the incident laser beam to an upper surface of a wafer to be subjected to film stress detection, wherein,

3. The thin film stress detection system for transparent wafers of claim 1, wherein: the incident light beam regulating part also comprises a polaroid and/or a cylindrical lens group for shaping light spots, wherein,

4. A thin film stress detection system for a transparent wafer according to claim 3, wherein: and also comprises a light intensity adjusting mechanism for adjusting the light intensity of the laser, wherein,

5. The thin film stress detection system for transparent wafers of claim 4 wherein: the incident laser beam after being shaped by the column lens group is incident on a wafer to be subjected to film stress detection through the adjustable attenuation sheet;

6. A thin film stress detection system for transparent wafers as claimed in any one of claims 1 to 5, wherein: the focusing lens group comprises a focusing first convex lens, a focusing concave lens and a focusing second convex lens which are sequentially arranged, wherein,

7. A thin film stress detection system for transparent wafers as claimed in any one of claims 1 to 5, wherein: also comprises a detection cabinet for detecting the film stress, wherein,

8. The thin film stress detection system for transparent wafers of claim 7 wherein: the light path unit driving mechanism comprises an X-axis screw rod, a Y-axis screw rod and a Z-axis screw rod which are sequentially and adaptively connected,

9. A method of detecting film stress for a transparent wafer, wherein the film stress detection system according to any one of claims 1 to 8 is used for detecting film stress for any one of the wafers.

10. The method of claim 9, wherein the wafer is a transparent wafer, a translucent wafer, or an opaque wafer.