CN115939009A

CN115939009A - Optical alignment method

Info

Publication number: CN115939009A
Application number: CN202310044370.4A
Authority: CN
Inventors: 么之光; 母凤文; 王晓宇
Original assignee: Tianjin Zhongke Jinghe Electronic Technology Co ltd
Current assignee: Tianjin Zhongke Jinghe Electronic Technology Co ltd
Priority date: 2023-01-30
Filing date: 2023-01-30
Publication date: 2023-04-07

Abstract

The embodiment of the invention discloses an optical alignment method, which is applied to an optical alignment system and used for aligning two opposite wafers, and comprises the following steps: firstly, moving an optical alignment system until two wafers are respectively arranged on light emitting paths of a first channel and a second channel; then, imaging the two opposite wafers respectively by using the first channel, the second channel and the first imaging optical path to form a first image and a second image; then determining the dislocation condition of the two wafers according to the positions of the mark points on the wafers in the first image and the second image; and finally, carrying out dislocation compensation in the process of aligning the two wafers according to the dislocation condition of the two wafers. By using the method, aiming at the flip chip bonding technology, the movement of the wafer can be reduced, the accumulated error and the repeated positioning error in the optical alignment process can be effectively reduced, and the alignment precision before the wafer bonding is improved.

Description

Optical alignment method

Technical Field

The embodiment of the invention relates to the technical field of optics, in particular to an optical alignment method.

Background

Bonding is a critical step in semiconductor packaging technology, and as the number of contacts per unit area of a chip increases, the bonding accuracy determines the yield and performance of chip production to a great extent. In the existing alignment process before chip bonding, the chip moves to cause positioning errors. In addition, the existing optical alignment system has a large volume, which causes cumulative errors and repeated positioning errors during alignment, thereby affecting the alignment accuracy of bonding.

Disclosure of Invention

The embodiment of the invention provides an optical alignment method, which aims at the flip chip bonding technology to improve the alignment precision before bonding and effectively reduce accumulated errors and repeated positioning errors in the optical alignment process.

The embodiment of the invention provides an optical alignment method, which is applied to an optical alignment system, wherein the optical alignment system comprises an alignment detection light path; the alignment detection light path comprises a first channel, a second channel and a first imaging light path, the first channel and the second channel share the first imaging light path, and light emitting light paths of the first channel and the second channel deviate from each other;

the optical alignment method is used for aligning two opposite wafers and comprises the following steps:

moving the optical alignment system until the two wafers are respectively arranged on the light emergent light paths of the first channel and the second channel;

imaging the two wafers which are opposite to each other by using the first channel, the second channel and the first imaging optical path to form a first image and a second image;

determining the dislocation condition of the two wafers according to the positions of the mark points on the wafers in the first image and the second image;

and according to the dislocation condition of the two wafers, performing dislocation compensation in the process of aligning the two wafers.

Optionally, the optical alignment system further includes a parallelism detection optical path; the parallelism detection optical path comprises a third channel, a fourth channel and a second imaging optical path, the third channel and the fourth channel share the second imaging optical path, and the first imaging optical path is multiplexed into the second imaging optical path;

moving the optical alignment system until the two wafers are respectively placed on the light-emitting paths of the first channel and the second channel, further comprising:

moving the optical alignment system until the two wafers are respectively arranged on the light emergent paths of the third channel and the fourth channel;

emitting two coaxial parallel lights with opposite directions by using the third channel and the fourth channel;

and adjusting the inclination angle of at least one wafer by utilizing images formed by reflecting the two beams of parallel light on the two wafers respectively so as to enable the two wafers to be parallel to each other.

Optionally, before the two coaxial parallel lights with opposite directions are emitted by using the third channel and the fourth channel, the method further includes:

and adjusting the light emitting direction of the third channel and/or the fourth channel so that the light beams emitted by the third channel and the fourth channel are coaxial and have opposite directions.

Optionally, the third channel includes a first half mirror, the fourth channel includes a second half mirror and an adjustment base, and the second half mirror is disposed on the adjustment base;

the two wafers comprise a first wafer and a second wafer; the third channel emits a third laser beam, and the fourth channel emits a fourth laser beam;

adjusting the light emitting direction of the third channel and/or the fourth channel so that the light beams emitted by the third channel and the fourth channel are coaxial and opposite in direction, and the method comprises the following steps:

adjusting the inclination angle of the first wafer according to the imaging of the reflected light of the third laser beam on the first wafer through the third channel and the second imaging optical path, so that the third laser beam is perpendicular to the first wafer, and recording the imaging position of the reflected light of the third laser beam on the first wafer;

moving the first wafer to a light-emitting light path of the fourth channel along a first direction, wherein the first direction is vertical to the first wafer;

and rotating the adjusting base and driving the second semi-transparent semi-reflective mirror to adjust the light emitting direction of the fourth laser beam, so that the reflected light of the fourth laser beam on the second wafer is superposed with the reflected light of the third laser beam on the first wafer through the imaging of the fourth channel and the second imaging optical path.

Optionally, the optical alignment system further includes a pressing head and a jig, the pressing head fixes the jig by suction, and the jig clamps the wafer and exposes two opposite surfaces of the wafer;

adjusting the tilt angle of the first wafer according to the imaging of the reflected light of the third laser beam on the first wafer through the third channel and the second imaging optical path, so that the third laser beam is perpendicular to the first wafer, comprising:

and adjusting the inclination angle of the pressure head until the imaging position of the reflected light of the third laser beam on the first wafer, which passes through the third channel and the second imaging optical path, is unchanged when the pressure head is moved along the first direction and drives the first wafer.

Optionally, adjusting the inclination of the ram comprises:

rotating the ram about a second direction and a third direction, respectively; wherein the second direction intersects with the third direction, and intersects with the first direction respectively.

Optionally, the two wafers comprise a first wafer and a second wafer;

imaging the two opposing wafers using the first and second channels and the first imaging optical path, respectively, to form a first image and a second image, comprising:

imaging the first wafer through the first channel and the first imaging light path to form the first image, and recording the position of a mark point on the wafer in the first image;

moving the first wafer to a light-emitting optical path of the second channel along a first direction, wherein the first direction is vertical to the first wafer;

adjusting the inclination angle of the optical alignment system to enable the mark points on the wafer in the imaging of the first wafer passing through the second channel and the first imaging optical path to coincide with the positions of the mark points on the wafer in the first image;

and maintaining the inclination angle of the optical alignment system, moving the second wafer to the light-emitting optical path of the second channel along the first direction, and imaging through the second channel and the first imaging optical path to form the second image.

Optionally, adjusting the tilt angle of the optical alignment system comprises:

rotating the optical alignment system about a second direction and a third direction, respectively; wherein the second direction intersects with the third direction, and intersects with the first direction respectively.

Optionally, determining the misalignment of the two wafers according to the positions of the marked points on the wafers in the first image and the second image includes:

determining the dislocation direction and the dislocation distance between the two wafers according to the positions of the marked points on the wafers in the first image and the second image;

according to the dislocation situation of the two wafers, the dislocation compensation is carried out in the process of aligning the two wafers, and the method comprises the following steps:

moving the first wafer and/or the second wafer along the dislocation direction and according to the dislocation distance on a first plane, wherein the first plane is a plane vertical to the first direction;

and aligning the two wafers along the first direction.

Optionally, the alignment detection optical path further includes a first illumination optical path, the first channel and the second channel share the first illumination optical path, and the first illumination optical path emits parallel light;

the parallelism detection light path further comprises a second illumination light path, the third channel and the fourth channel share the second illumination light path, and the second illumination light path emits cross parallel laser;

before imaging the two wafers facing each other by using the first and second channels and the first imaging optical path to form a first image and a second image, the method further includes:

turning on the first illumination light path;

before two coaxial parallel lights with opposite directions are emitted by using the third channel and the fourth channel, the method further comprises the following steps:

and opening the second illumination light path.

The embodiment of the invention provides an optical alignment method, which is applied to an optical alignment system, wherein the optical alignment system comprises an alignment detection light path; the alignment detection light path comprises a first channel, a second channel and a first imaging light path, the first channel and the second channel share the first imaging light path, and light emitting light paths of the first channel and the second channel deviate from each other; the optical alignment method is used for aligning two opposite wafers and comprises the following steps: firstly, moving an optical alignment system until two wafers are respectively arranged on light emitting paths of a first channel and a second channel; then, imaging the two opposite wafers by using the first channel, the second channel and the first imaging optical path respectively to form a first image and a second image; then determining the dislocation condition of the two wafers according to the positions of the mark points on the wafers in the first image and the second image; and finally, carrying out dislocation compensation in the process of aligning the two wafers according to the dislocation condition of the two wafers. By using the method, aiming at the flip chip bonding technology, the movement of the wafer can be reduced, the accumulated error and the repeated positioning error in the optical alignment process can be effectively reduced, and the alignment precision before wafer bonding is improved.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a conventional optical alignment system;

FIG. 2 is a first alignment diagram of a prior art optical alignment system;

FIG. 3 is a second alignment diagram of a prior art optical alignment system;

fig. 4 is a schematic optical path diagram of an optical alignment system according to an embodiment of the present invention;

FIG. 5 is a flowchart illustrating an optical alignment method according to an embodiment of the present invention;

FIG. 6 is a schematic optical path diagram of another optical alignment system provided in an embodiment of the present invention;

FIG. 7 is a flow chart of another optical alignment method according to an embodiment of the present invention;

fig. 8 is a schematic flowchart of another optical alignment method according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and are not to be construed as limiting the invention. It should be further noted that, for the convenience of description, only some of the structures related to the present invention are shown in the drawings, not all of the structures.

The terminology used in the embodiments of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It should be noted that the terms "upper", "lower", "left", "right", and the like used in the description of the embodiments of the present invention are used in the angle shown in the drawings, and should not be construed as limiting the embodiments of the present invention. In addition, in this context, it will also be understood that when an element is referred to as being "on" or "under" another element, it can be directly formed on "or" under "the other element or be indirectly formed on" or "under" the other element through intervening elements. The terms "first," "second," and the like, are used for descriptive purposes only and are not intended to denote any order, quantity, or importance, but rather are used to distinguish one element from another. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

The term "include" and variations thereof as used herein are intended to be open-ended, i.e., "including but not limited to". The term "based on" is "based, at least in part, on". The term "one embodiment" means "at least one embodiment".

It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are only used for distinguishing corresponding contents, and are not used for limiting the order or interdependence relationship.

It is noted that references to "a", "an", and "the" modifications in the present invention are intended to be illustrative rather than limiting, and that those skilled in the art will recognize that reference to "one or more" unless the context clearly dictates otherwise.

Fig. 1 is a schematic structural diagram of a conventional optical alignment system, fig. 2 is a schematic first alignment diagram of the conventional optical alignment system, and fig. 3 is a schematic second alignment diagram of the conventional optical alignment system, and as shown in fig. 1, fig. 2 and fig. 3, the conventional optical alignment system is composed of two vertically symmetrical parts. In the alignment process, the displacement platform 108 carries the first sample 109 to move to the optical axis position of the objective lens 103, the light beam emitted from the light source 105 is transmitted to the objective lens 103 through the beam splitter 104, and then is reflected to the beam splitter 104 through the surface of the first sample 109, and then the beam splitter 104 reflects the light beam to the imaging mirror 106, and finally an image with a mark (symbol mark) of the first sample 107 is displayed in the camera 107. Then, the displacement platform 108 carries the first sample 109 to move back to the original position, the displacement platform 101 carries the second sample 102 to move to the optical axis position of the objective lens 110, the light beam emitted from the light source 112 is transmitted to the objective lens 110 through the beam splitter 111, and is reflected to the beam splitter 111 through the surface of the second sample 102, and then the beam splitter 111 reflects the light beam to the imaging mirror 113, and finally the image with mark of the second sample 102 is displayed in the camera 114 and is stored. The translation stage 101 then moves back to its original position carrying the second sample 102. The image with mark stored by the camera 107 is overlapped with the image with mark stored by the camera 114, and the center position deviation of the two images is calculated by an image processing method. The position of one of the displacement stage 101 and the displacement stage 108 is finely adjusted based on the center position deviation of the two images, and the center position deviation between the first sample 109 and the second sample 102 is corrected, thereby completing the alignment process. However, with the above method, the alignment accuracy is greatly affected by the moving positioning accuracy of the moving platform 101 and the moving platform 108, an accumulated error and a repeated positioning error are generated during the moving process of the sample carried by the moving platform, and the error between the moving displacement of the theoretical moving platform and the actual moving displacement of the moving platform also affects the alignment accuracy of the alignment system by calculating the center position deviation of the two images through the image processing method. In addition, in the alignment process of the alignment system, the parallelism between the first sample 109 and the second sample 102 is not detected and calibrated, and bonding misalignment may be caused by the inclination angle of the sample itself in the subsequent bonding process.

In view of the above technical problems, an embodiment of the present invention provides an optical alignment method, which is applied to an optical alignment system. Fig. 4 is a schematic optical path diagram of an optical alignment system according to an embodiment of the present invention, and fig. 5 is a schematic flow chart of an optical alignment method according to an embodiment of the present invention, as shown in fig. 4 and fig. 5, the optical alignment system includes an alignment detection optical path; the alignment detection optical path comprises a first channel 31, a second channel 32 and a first imaging optical path 33, the first channel 31 and the second channel 32 share the first imaging optical path 33, and light emitting optical paths of the first channel 31 and the second channel 32 deviate from each other; the optical alignment method is used for aligning two opposite wafers, and comprises the following steps:

and S110, moving the optical alignment system until the two wafers are respectively arranged on the light emergent paths of the first channel and the second channel.

Specifically, with reference to fig. 4, the optical alignment system is moved as a whole, the optical alignment system should be located in an area between two opposite wafers, the light-emitting optical paths of the first channel 31 and the second channel 32 are deviated from each other, the optical alignment system is moved until one wafer is placed on the light-emitting optical path of the first channel 31, the other wafer is placed on the light-emitting optical path of the second channel 32, the optical alignment system can simultaneously align and detect the two wafers, and the optical alignment system moves without moving the two wafers, so that a positioning error caused by the movement of the wafers can be avoided.

And S120, respectively imaging the two opposite wafers by using the first channel, the second channel and the first imaging optical path to form a first image and a second image.

Specifically, with continued reference to fig. 4, the alignment detection optical path includes a first channel 31, a second channel 32 and a first imaging optical path 33, a wafer is placed on the light emitting optical path of the first channel 31, the first imaging optical path 33 is located on the optical path of the reflected light after the laser beam emitted from the first channel 31 is reflected by the surface of the wafer, and the first imaging optical path 33 includes the tube lens 14 and the camera 15, and is displayed and stored as a first image in the camera 15. The other wafer is placed on the light-emitting path of the second channel 32, and after the laser beam emitted from the second channel 32 is reflected by the wafer surface, the first imaging optical path 33 is also located on the optical path of the reflected light, and is displayed and saved as the second image in the camera 15. The first channel 31 and the second channel 32 share the first imaging optical path 33, and two opposite wafers are imaged in the same camera 15, so that consistency of imaging is ensured, that is, the two wafers are based on the same imaging optical path as a reference system, and the position relationship of the two wafers is determined by using the imaging positions, so that the condition that subsequent alignment accuracy is influenced due to different imaging optical paths of the two wafers can be avoided. In addition, the first channel 31 and the second channel 32 can be strictly arranged in an equal optical path, so that the consistency of the imaging scale and distortion of the first channel 31 and the second channel 32 is ensured, the imaging difference can be avoided, and the alignment error is effectively reduced.

S130, determining the dislocation condition of the two wafers according to the positions of the marked points on the wafers in the first image and the second image.

Specifically, with continued reference to fig. 4, the wafer placed on the light exit path of the first channel 31 is formed into a first image in the camera 15 by using the first channel 31 and the first imaging optical path 33, the first image being an image with a mark point corresponding to the wafer. The second channel 32 and the first imaging optical path 33 are used to form a second image of the wafer placed on the light-emitting optical path of the second channel 32 in the camera 15, wherein the second image is an image with the mark points corresponding to the wafer. The first image and the second image are imaged in the same camera 15, and the dislocation condition of the two wafers can be obtained according to the positions of the marked points on the wafers in the first image and the second image.

And S140, according to the dislocation situation of the two wafers, performing dislocation compensation in the process of aligning the two wafers.

Specifically, with reference to fig. 4, based on the misalignment condition obtained from the positions of the mark points on the wafers in the first image and the second image of the two wafers, the misalignment condition between the two wafers can be obtained accordingly, and the misalignment compensation is performed during the alignment of the two wafers, for example, the misalignment compensation may be at least one of the two wafers moving left and right until the positions of the mark points on the wafers in the first image and the second image, which are formed by imaging the two wafers opposite to each other in the camera 15, coincide, and at this time, the misalignment condition between the two opposite wafers is compensated, so that the alignment accuracy before bonding is improved, and the subsequent bonding accuracy can also be effectively improved.

The technical scheme in the embodiment of the invention is applied to an optical alignment system, wherein the optical alignment system comprises an alignment detection light path; the alignment detection light path comprises a first channel, a second channel and a first imaging light path, the first channel and the second channel share the first imaging light path, and light emitting light paths of the first channel and the second channel deviate from each other; the optical alignment method is used for aligning two opposite wafers and comprises the following steps: firstly, moving an optical alignment system until two wafers are respectively arranged on light emitting paths of a first channel and a second channel; then, imaging the two opposite wafers by using the first channel, the second channel and the first imaging optical path respectively to form a first image and a second image; then determining the dislocation condition of the two wafers according to the positions of the mark points on the wafers in the first image and the second image; and finally, according to the dislocation situation of the two wafers, performing dislocation compensation in the process of aligning the two wafers. By using the method, aiming at the flip chip bonding technology, the movement of the wafer can be reduced, the accumulated error and the repeated positioning error in the optical alignment process can be effectively reduced, and the alignment precision before the wafer bonding is improved.

Optionally, the alignment detection optical path further includes a first illumination optical path, the first channel and the second channel share the first illumination optical path, and the first illumination optical path emits parallel light. Before imaging the two opposite wafers respectively by using the first channel, the second channel and the first imaging optical path to form a first image and a second image, the method further comprises the following steps: the first illumination light path is turned on.

Specifically, with continued reference to fig. 4, the alignment detection optical path further includes a first illumination optical path 41, the first channel 31 and the second channel 32 share the first illumination optical path 41, and the first illumination optical path 41 emits parallel light. The first illumination light path 41 includes a parallel light illumination light source 1, a converging lens 3, a third half mirror 4 and a fourth half mirror 6, and the third half mirror 4 and the fourth half mirror 6 are sequentially located on a light emitting path of the parallel light illumination light source 1. In addition, the first channel 31 and the second channel 32 share the parallel light illumination light source 1, so that parallax caused by different light source positions can be avoided, the measurement accuracy is effectively improved, and the volume of the optical alignment system is reduced. The first illumination light path 41 emits parallel light, so that more complicated light path modulation can be avoided, the light path structure is simplified, the imaging effect of the first image and the imaging effect of the second image can be clearly observed through the first illumination light path 41, and then the dislocation condition between the position of the mark point on the corresponding wafer in the first image and the position of the mark point on the corresponding wafer in the second image is judged, so that the dislocation compensation between the two wafers is carried out.

In the bonding process of two opposing wafers, a positioning error, an accumulated error, and the like between the two wafers may cause a misalignment between the two wafers, which may affect the bonding accuracy. In addition, the parallel relationship between the two wafers also affects the bonding accuracy, and the inclination angle between the two wafers may cause displacement during the pressure bonding. Therefore, before aligning two opposite wafers, the laser beams emitted by the third channel and the fourth channel are required to be adjusted to be coaxial and opposite in direction, when an inclined angle exists between the emitted laser beams and the wafers, the image position formed through the imaging optical path is not accurate, and the alignment precision is influenced by judging the parallelism of the wafers by the inaccurate image position, so that the two wafers are calibrated to be parallel to each other, the imaging deviation caused by the mutual inclination of the wafers is avoided, and the deviation is prevented from being mistaken as the dislocation of the wafers. Fig. 6 is a schematic flow chart of another optical alignment method according to an embodiment of the present invention, which is expanded based on the foregoing embodiments. In this embodiment, optionally, the optical alignment system further includes a parallelism detection optical path; the parallelism detection optical path comprises a third channel, a fourth channel and a second imaging optical path, the third channel and the fourth channel share the second imaging optical path, and the first imaging optical path is multiplexed into the second imaging optical path;

moving the optical alignment system until the two wafers are respectively arranged on the light-emitting paths of the first channel and the second channel, further comprising:

moving the optical alignment system until the two wafers are respectively arranged on the light emitting paths of the third channel and the fourth channel;

emitting two coaxial parallel lights with opposite directions by using a third channel and a fourth channel;

two beams of parallel light are respectively reflected on two wafers to form images, and the inclination angle of at least one wafer is adjusted so that the two wafers are parallel to each other.

For a detailed description of the present embodiment, please refer to the above embodiments. As shown in fig. 6, the optical alignment method includes:

s210, moving the optical alignment system until the two wafers are respectively arranged on the light emitting paths of the third channel and the fourth channel.

Specifically, fig. 7 is a schematic optical path diagram of another optical alignment system according to an embodiment of the present invention, as shown in fig. 7, the optical alignment system is moved as a whole, the optical alignment system should be located in an area between two opposite wafers, the optical alignment system is moved until one wafer is located on the light-emitting path of the third channel 34, and the other wafer is located on the light-emitting path of the fourth channel 35, the optical alignment system can align the two wafers at the same time, and the optical alignment system moves without moving the two wafers, so that a positioning error caused by the movement of the wafers can be avoided.

And S220, emitting two coaxial parallel lights in opposite directions by using the third channel and the fourth channel.

Specifically, with reference to fig. 7, one wafer is disposed on the light emitting path of the third channel 34, the other wafer is disposed on the light emitting path of the fourth channel 35, the third channel 34 and the fourth channel 35 share the second imaging optical path 36, and the first imaging optical path 33 is multiplexed as the second imaging optical path 36, and two opposite wafers are imaged in the same camera 15, so that consistency of imaging is ensured, and the situation that subsequent alignment accuracy is affected due to different imaging optical paths of the two wafers can be avoided, and the first imaging optical path 33 is multiplexed as the second imaging optical path 36, so that the overall volume of the optical alignment system can be effectively reduced, and the number of used optical elements is reduced. After two coaxial parallel lights with opposite directions emitted by the third channel 34 and the fourth channel 35 are reflected by the surface of the wafer, if the imaging positions of the two wafers in the camera 15 are coincident, the two wafers are parallel, and if the imaging positions of the two wafers in the camera 15 are not coincident, the two wafers are not parallel, and the parallelism of the two wafers needs to be adjusted.

Optionally, before two coaxial parallel lights with opposite directions are emitted by using the third channel and the fourth channel, the method further includes: and S280, adjusting the light emitting direction of the third channel and/or the fourth channel so that the light beams emitted by the third channel and the light beams emitted by the fourth channel are coaxial and have opposite directions. Furthermore, the third channel comprises a first semi-transparent semi-reflective mirror, the fourth channel comprises a second semi-transparent semi-reflective mirror and an adjusting base, and the second semi-transparent semi-reflective mirror is arranged on the adjusting base; the two wafers include a first wafer and a second wafer; the third channel emits a third laser beam, and the fourth channel emits a fourth laser beam; adjusting the light emitting direction of the third channel and/or the fourth channel so that the light beams emitted by the third channel and the fourth channel are coaxial and opposite in direction, and the method comprises the following steps:

s2801, adjusting the tilt angle of the first wafer according to the imaging of the reflected light of the third laser beam on the first wafer through the third channel and the second imaging optical path, so that the third laser beam is perpendicular to the first wafer, and recording the imaging position of the reflected light of the third laser beam on the first wafer.

Specifically, with continued reference to fig. 7, the third channel 34 includes the first half mirror 19, the third channel 34 emits the third laser beam, the first wafer 13 is located on the light-emitting path of the third channel 34, the tilt angle of the first wafer 13 is properly adjusted with reference to the third laser beam, so that the third laser beam is perpendicular to the first wafer 13, and the imaging position of the reflected light of the third laser beam on the first wafer 13 in the camera 15 is recorded.

Optionally, the optical alignment system further comprises a pressing head and a jig, wherein the pressing head adsorbs and fixes the jig, and the jig clamps the wafer and exposes two opposite surfaces of the wafer; according to the imaging of the reflected light of the third laser beam on the first wafer through the third channel and the second imaging optical path, adjusting the inclination angle of the first wafer to enable the third laser beam to be vertical to the first wafer, the method comprises the following steps: and adjusting the inclination angle of the pressure head until the pressure head is moved along the first direction and drives the first wafer, wherein the imaging positions of the reflected light of the third laser beam on the first wafer through the third channel and the second imaging optical path are unchanged. Further, adjusting the inclination of the ram includes: rotating the ram about the second direction and the third direction, respectively; the second direction and the third direction are intersected and are respectively intersected with the first direction.

Specifically, with reference to fig. 7, the optical alignment system further includes a pressing head 20 and a fixture 21, the pressing head 20 can absorb and fix the fixture 21, and the fixture 21 can hold the wafer and expose two opposite surfaces of the wafer. In adjusting the inclination of the first wafer 13, by adjusting the inclination of the indenter 20 to adjust the inclination of the first wafer 13, the indenter 20 may be rotated about the second direction X and the third direction Y, respectively, wherein the second direction X and the third direction Y intersect and are respectively intersected with the first direction Z, exemplarily, the second direction X and the third direction Y are perpendicular and are respectively intersected with the first direction Z, and an angle of rotation of the indenter 20 about the second direction X is denoted as θ and an angle of rotation of the indenter 20 about the third direction Y is denoted as γ. When the inclination angle of the pressure head 20 is adjusted, and the pressure head 20 is moved along the first direction Z and drives the first wafer 13 to move, an included angle with a certain angle between the third laser beam and the first wafer 13 can be determined according to the change of the imaging positions of the reflected light of the third laser beam on the first wafer 13 through the third channel 34 and the second imaging optical path 36, which is not a perpendicular relation, and at this time, when the pressure head 20 is moved along the first direction Z and drives the first wafer 13, the imaging positions of the reflected light of the third laser beam on the first wafer 13 through the third channel 34 and the second imaging optical path 36 are not fixed. The tilt of the indenter 20 should be continuously adjusted until the indenter 20 is moved in the first direction Z and the first wafer 13 is driven, the imaging position of the reflected light of the third laser beam on the first wafer 13 via the third channel 34 and the second imaging optical path 36 is unchanged, and the third laser beam is perpendicular to the first wafer 13, and the imaging position of the first wafer 13 at that time in the camera 15 is recorded.

S2802, moving the first wafer to a light-emitting path of the fourth channel along a first direction, where the first direction is perpendicular to the first wafer.

Specifically, with continued reference to fig. 7, the fourth channel 35 includes a second half mirror 17 and an adjusting pedestal 18, the second half mirror 17 is disposed on the adjusting pedestal 18, and the fourth channel 35 emits a fourth laser beam to move the first wafer 13 along a first direction Z to an optical path of the fourth channel 35, where the first direction Z is perpendicular to the first wafer 13. At this time, the third laser beam emitted from the third channel 34 is perpendicular to the first wafer 13, and based on the perpendicular relation to the first wafer 13, the fourth laser beam emitted from the fourth channel 35 should be continuously adjusted to be also perpendicular to the first wafer 13, so that it can be determined that the fourth laser beam emitted from the fourth channel 35 and the third laser beam emitted from the third channel 34 are coaxial and opposite in direction.

And S2803, rotating the adjusting base and driving the second half-mirror to adjust the light emitting direction of the fourth laser beam, so that the reflected light of the fourth laser beam on the second wafer is imaged through the fourth channel and the second imaging optical path and is superposed with the reflected light of the third laser beam on the first wafer through the third channel and the second imaging optical path.

Specifically, with reference to fig. 7, due to the processing error and the assembling error of the first half mirror 19 and the second half mirror 17, the third laser beam emitted from the third channel 34 and the fourth laser beam emitted from the fourth channel 35 may not be coaxial and opposite in direction, so that the light emitting directions of the two laser beams need to be calibrated before the optical alignment system is used, and after the light emitting directions of the third laser beam and the fourth laser beam are ensured to be coaxial and opposite in direction, the parallelism of the two opposite wafers calibrated by the optical alignment system is more accurate, and the occurrence of bonding misalignment caused by wafer inclination is reduced. After the inclination angle of the first wafer 13 is adjusted to make the third laser beam perpendicular to the first wafer 13 and the first wafer 13 is moved to the light-emitting optical path of the fourth channel 35 along the first direction Z, the second half mirror 17 can be driven to rotate by rotating the adjusting pedestal 18, so as to change the light-emitting direction of the fourth laser beam. When the parallelism of the first wafer 13 is used as a reference, the indenter 20 is moved along the first direction Z and the first wafer 13 is driven to move, the imaging positions of the reflected light of the fourth laser beam on the first wafer 13 through the fourth channel 35 and the second imaging optical path 36 are not fixed, and it can be determined that an included angle with a certain angle exists between the fourth laser beam and the first wafer 13, which is not a perpendicular relation, and at this time, the fourth laser beam and the third laser beam are not coaxial and opposite in direction. The adjustment base 18 should be rotated continuously and drive the second half mirror 17 to rotate, and the light emitting direction of the fourth laser beam is changed until the pressure head 20 is moved along the first direction Z and the first wafer 13 is driven, the reflected light of the fourth laser beam on the first wafer 13 passes through the fourth channel 35 and the imaging position of the second imaging optical path 36 is fixed, it can be determined that the adjusted fourth laser beam and the adjusted third laser beam are both perpendicular to the first wafer 13, and the light emitting directions of the fourth laser beam and the third laser beam are coaxial and opposite. In addition, after the laser beams emitted from the third channel 34 and the fourth channel 35 are adjusted to be coaxial and in opposite directions, the first wafer 13 can be moved back to the original position, the second wafer 9 is moved to the optical path of the fourth laser beam, and in the process that the second wafer 9 is driven by the pressure head 20 to move along the first direction Z, i.e. perpendicular to the second wafer 9, if the imaging position is fixed, it is indicated that the second wafer 9 is perpendicular to the fourth laser beam, and the second wafer 9 is parallel to the first wafer 13. If the imaging position moves, it means that the second wafer 9 is not perpendicular to the fourth laser beam and is not parallel to the first wafer 13, and at this time, the tilt angle of the second wafer 9 can be changed by adjusting the tilt angle of the indenter 20 to make it parallel to the first wafer 13, thereby completing the calibration process of the two laser beams.

Optionally, the parallelism detection optical path further includes a second illumination optical path, the third channel and the fourth channel share the second illumination optical path, and the second illumination optical path emits cross parallel laser. Before two coaxial parallel lights with opposite directions are emitted by using the third channel and the fourth channel, the method further comprises the following steps: and opening a second illumination light path.

Specifically, with continued reference to fig. 7, the parallelism detection optical path further includes a second illumination optical path 42, the third channel 34 and the fourth channel 35 share the second illumination optical path 42, and the second illumination optical path 42 emits cross-parallel laser light. The second illumination light path 42 includes a cross-shaped parallel light illumination light source 16, a third half mirror 4 and a fourth half mirror 6, and the third half mirror 4 and the fourth half mirror 6 are sequentially located on a light emitting path of the cross-shaped parallel light illumination light source 16. In addition, the third channel 34 and the fourth channel 35 share the cross-shaped parallel light illuminating source 16, so that parallax caused by different light source positions can be avoided, the measurement accuracy is effectively improved, and the volume of the optical alignment system is reduced. The second illumination light path 42 emits the cross parallel laser, so that more complex light path modulation can be avoided, the light path structure is simplified, the imaging effect of the first image and the imaging effect of the second image can be accurately observed through the second illumination light path 42, the dislocation condition of the cross laser images with the same size in the first image and the second image is further judged, and the parallelism between the two wafers is adjusted.

And S230, adjusting the inclination angle of at least one wafer by utilizing images formed by reflecting the two parallel beams on the two wafers respectively so as to enable the two wafers to be parallel to each other.

In particular, with continued reference to fig. 7, the third channel 34 and the fourth channel 35 emit two coaxial parallel lights with opposite directions, and the two parallel lights can be imaged in the camera 15 after being reflected by the wafer surface. Using the third channel 34 and the second imaging optical path 36, the wafer placed on the light exit path of the third channel 34 forms a third image in the camera 15, the third image being an image of a sharp cross laser beam. The fourth channel 35 and the second imaging beam path 36 are used to form a fourth image of the wafer placed on the light exit path of the fourth channel 35 in the camera 15, the fourth image being a sharp image of the cross laser beam. The third image and the fourth image are imaged in the same camera 15, the parallelism of the two wafers can be obtained according to the dislocation between the positions of the cross laser beams in the third image and the fourth image, the inclination angle of the corresponding wafer is changed by adjusting the inclination angle of the pressure head 20, the pressure head 20 is moved along the first direction Z and drives the corresponding wafer until the positions of the cross laser beams in the third image and the fourth image formed by imaging the two opposite wafers in the camera 15 respectively are not changed, the two wafers are parallel to each other, the laser beams emitted by the third channel 34 and the fourth channel 35 are coaxial and have opposite directions, the third laser beam is in a vertical relation with the first wafer 13, and the fourth laser beam is in a vertical relation with the second wafer 9.

S240, moving the optical alignment system until the two wafers are respectively arranged on the light emitting paths of the first channel and the second channel.

And S250, respectively imaging the two opposite wafers by using the first channel, the second channel and the first imaging optical path to form a first image and a second image.

And S260, determining the dislocation condition of the two wafers according to the positions of the marked points on the wafers in the first image and the second image.

S270, according to the dislocation situation of the two wafers, dislocation compensation is carried out in the process of aligning the two wafers.

According to the technical scheme, firstly, an optical alignment system is moved until two wafers are respectively arranged on light emergent paths of a third channel and a fourth channel; then, a third channel and a fourth channel are utilized to emit two coaxial parallel lights with opposite directions; and finally, adjusting the inclination angle of at least one wafer by utilizing images formed by reflecting two beams of parallel light on the two wafers respectively so as to enable the two wafers to be parallel to each other. By using the method, the optical alignment system is moved without moving the two wafers, so that the positioning error caused by the movement of the two wafers can be avoided, the parallelism of the two wafers needs to be detected and adjusted before the two opposite wafers are aligned, the two wafers are ensured to be parallel to each other, the situation that the dislocation error is judged to occur in the parallelism of the two opposite wafers because the laser beams emitted by the third channel and the fourth channel are not coaxial and have opposite directions is avoided, and the subsequent bonding precision can be effectively improved.

During alignment inspection of two opposing wafers, positioning errors and accumulated errors between the two wafers can cause misalignment conditions, which in turn affect bonding accuracy. In addition, bonding accuracy is also affected by machining errors and/or assembly errors of optical elements in the optical alignment system. Therefore, before aligning the two opposite wafers, it is necessary to adjust the laser beams emitted from the first and second channels to be coaxial and opposite, and then to correct the misalignment of the two wafers. Fig. 8 is a schematic flow chart of another optical alignment method according to an embodiment of the present invention, which is optimized based on the foregoing embodiment. In this embodiment, optionally, the two wafers include a first wafer and a second wafer; forming a first image and a second image by imaging the two opposed wafers respectively using the first and second channels and the first imaging optical path, comprising:

imaging the first wafer through the first channel and the first imaging light path to form a first image, and recording the positions of the marking points on the wafer in the first image;

moving the first wafer to a light-emitting light path of the second channel along a first direction, wherein the first direction is vertical to the first wafer;

and keeping the inclination angle of the optical alignment system, moving the second wafer to the light-emitting optical path of the second channel along the first direction, and imaging through the second channel and the first imaging optical path to form a second image.

For a detailed description of the present embodiment, please refer to the above embodiments. As shown in fig. 8, the optical alignment method includes:

s301, moving the optical alignment system until the two wafers are respectively arranged on the light emitting paths of the third channel and the fourth channel.

And S302, emitting two coaxial parallel lights with opposite directions by using the third channel and the fourth channel.

S303, utilizing images formed by reflecting the two parallel beams on the two wafers respectively, and adjusting the inclination angle of at least one wafer to enable the two wafers to be parallel to each other.

S304, moving the optical alignment system until the two wafers are respectively arranged on the light emitting paths of the first channel and the second channel.

S305, imaging the first wafer through the first channel and the first imaging light path to form a first image, and recording the position of the mark point on the wafer in the first image.

Specifically, with reference to fig. 4, the first channel 31 includes a first reflection prism 11 and a first microscope objective 12, the first channel 31 emits a first laser beam, the first wafer 13 is located on the light emitting path of the first channel 31, the first wafer 13 is imaged through the first channel 31 and the first imaging optical path 33 to form a first image, and the position of the mark point on the first wafer 13 in the first image is recorded.

S306, moving the first wafer to the light-emitting optical path of the second channel along a first direction, wherein the first direction is vertical to the first wafer.

Specifically, with reference to fig. 4, the second channel 32 includes the pentagonal prism 7 and the second micro objective 8, the second channel 32 emits the second laser beam, and due to processing errors and assembly errors of optical elements in the optical alignment system, the first laser beam emitted from the first channel 31 and the second laser beam emitted from the second channel 32 may not be coaxial and opposite in direction, which may affect alignment accuracy of two opposite wafers, and after the two opposite wafers are adjusted to be parallel, it is also necessary to adjust the first laser beam emitted from the first channel 31 and the second laser beam emitted from the second channel 32 to be coaxial and opposite in direction. Taking the first wafer 13 as a reference, the first wafer 13 is imaged through the first channel 31 and the first imaging optical path 33, and the position of the mark point on the first wafer 13 in the lower image is recorded, and then the first wafer 13 is moved to the light-emitting optical path of the second channel 32 along the first direction Z, wherein the first direction Z is perpendicular to the first wafer 13, and the first wafer 13 is imaged through the second channel 32 and the first imaging optical path 33.

And S307, adjusting the inclination angle of the optical alignment system to enable the mark points on the wafer in the imaging of the first wafer passing through the second channel and the first imaging optical path to coincide with the positions of the mark points on the wafer in the first image.

Specifically, with reference to fig. 4, the first wafer 13 is imaged through the first channel 31 and the first imaging optical path 33, then the first wafer 13 is moved to the light-emitting optical path of the second channel 32 along the first direction Z, the first wafer 13 is imaged through the second channel 32 and the first imaging optical path 33, the first wafer 13 is used as a reference, the tilt angle of the optical alignment system is adjusted to coincide the two imaged images, and at this time, the first laser beam emitted from the first channel 31 and the second laser beam emitted from the second channel 32 are coaxial and opposite in direction. Optionally, adjusting the tilt angle of the optical alignment system, taking the optical alignment system as a whole, includes: the optical alignment system is rotated around a second direction X and a third direction Y, respectively, wherein the second direction X and the third direction Y intersect and intersect with the first direction Z, exemplarily, the second direction X and the third direction Y are perpendicular and perpendicular to the first direction Z, respectively, and an angle of rotation of the optical alignment system around the second direction X is recorded as θ and an angle of rotation of the optical alignment system around the third direction Y is recorded as γ. The inclination angle of the optical alignment system is adjusted, so that the first wafer 13 is imaged through the second channel 32 and the first imaging optical path 33, the position of the mark point on the first wafer 13 in the formed image is overlapped with the position of the mark point on the first wafer 13 in the formed image formed by imaging the first wafer 13 through the first channel 31 and the first imaging optical path 33, at this time, even if the first wafer 13 and the second wafer 9 are not imaged at the same time, the included angle between the first laser beam emitted from the first channel 31 and the first wafer 13 and the included angle between the second laser beam emitted from the second channel 32 and the first wafer 13 before and after the optical alignment system is rotated are the same, and thus it can be determined that the first laser beam emitted from the first channel 31 and the second laser beam emitted from the second channel 32 are coaxial and have opposite directions.

And S308, keeping the inclination angle of the optical alignment system, moving the second wafer to the light-emitting optical path of the second channel along the first direction, and imaging through the second channel and the first imaging optical path to form a second image.

Specifically, with reference to fig. 4, the tilt angle of the optical alignment system is maintained, and at this time, the first laser beam emitted from the first channel 31 and the second laser beam emitted from the second channel 32 are coaxial and opposite in direction, the second wafer 9 can be moved along the first direction Z into the light-emitting optical path of the second channel 32, the second channel 32 includes the pentagonal prism 7 and the second microscope objective 8, the second channel 32 emits the second laser beam, the reflected light of the second laser beam from the second wafer 9 is imaged through the second channel 32 and the first imaging optical path 33 to form a second image, and the position of the mark point on the second wafer 9 in the second image is recorded. If there is no misalignment between the second wafer 9 and the first wafer 13, the image formed by the second laser beam on the second wafer 9 should theoretically coincide with the image formed by the first laser beam on the first wafer 13 before the optical alignment system is rotated. If the image formed by the second wafer 9 at this time is misaligned with the image formed by the first laser beam before the optical alignment system is rotated with respect to the first wafer 13, the misalignment between the first wafer 13 and the second wafer 9 can be directly indicated.

S309, determining the dislocation direction and the dislocation distance between the two wafers according to the positions of the marked points on the wafers in the first image and the second image.

Specifically, with continued reference to fig. 4, the first wafer 13 placed on the light exit path of the first channel 31 is imaged to form a first image by using the first channel 31 and the first imaging optical path 33, and the position of the mark point on the first wafer 13 in the first image is recorded. The second wafer 9 placed on the light-emitting path of the second channel 32 is imaged to form a second image by using the second channel 32 and the first imaging optical path 33, and the position of the mark point on the second wafer 9 in the second image is recorded. After the first laser beam and the second laser beam are adjusted to be coaxial and opposite in direction, the position of the mark point on the first wafer 13 in the first image is compared with the position of the mark point on the second wafer 9 in the second image, and the dislocation direction and the dislocation distance between the two wafers can be obtained.

S310, moving the first wafer and/or the second wafer on the first plane along the dislocation direction and according to the dislocation distance, wherein the first plane is a plane vertical to the first direction.

Specifically, with reference to fig. 4, according to the misalignment between the position of the mark point on the first wafer 13 in the first image and the position of the mark point on the second wafer 9 in the second image, the misalignment direction and the misalignment distance between the two wafers can be obtained accordingly, and the misalignment compensation is performed during the alignment of the two wafers, thereby greatly improving the subsequent bonding accuracy. The first wafer 13 can be moved in a dislocation direction and at a dislocation distance on a first plane, which is a plane perpendicular to the first direction Z. On the first plane, the second wafer 9 may also be moved in the misalignment direction by the misalignment distance, or the first wafer 13 may also be moved in the misalignment direction by half the misalignment distance, and the second wafer 9 may also be moved in the misalignment direction by half the misalignment distance until the position of the mark point on the first wafer 13 in the first image coincides with the position of the mark point on the second wafer 9 in the second image.

And S311, aligning the two wafers along the first direction.

Specifically, with reference to fig. 4, when the position of the mark point on the first wafer 13 in the first image and the position of the mark point on the second wafer 9 in the second image coincide, the optical alignment system is moved out of the position of the area between the two wafers, where the two wafers are parallel, the projections of the two wafers along the first direction Z coincide, and the opposing first wafer 13 and second wafer 9 are aligned along the first direction Z, which effectively improves the bonding accuracy of the wafers.

According to the technical scheme, the alignment detection process of the optical alignment system is specifically refined, firstly, a first wafer is imaged through a first channel and a first imaging light path to form a first image, the position of a mark point on the wafer in the first image is recorded, then the first wafer is moved to a light-emitting light path of a second channel along a first direction, the first direction is perpendicular to the first wafer, then the inclination angle of the optical alignment system is adjusted, so that the mark point on the wafer in the imaging process of the first wafer through the second channel and the first imaging light path is overlapped with the position of the mark point on the wafer in the first image, finally the inclination angle of the optical alignment system is kept, the second wafer is moved to the light-emitting light path of the second channel along the first direction, and imaging is carried out through the second channel and the first imaging light path to form a second image. And determining a dislocation orientation and a dislocation distance between the two wafers according to the positions of the marked points on the wafers in the first image and the second image, and moving the first wafer and/or the second wafer along the dislocation orientation and according to the dislocation distance on the first plane. By using the method, aiming at the flip chip bonding technology, before alignment detection of the wafer is carried out, the first laser beam and the second laser beam are adjusted to be coaxial and opposite in direction, so that wafer alignment errors caused by processing errors and assembly errors of optical elements can be avoided, and by adjusting the position of the mark point on the first wafer in the first image to be superposed with the position of the mark point on the second wafer in the second image, the alignment precision of the wafer before bonding is improved, and the accumulated errors and repeated positioning errors in the optical alignment process are effectively reduced.

It is to be noted that the foregoing is only illustrative of the preferred embodiments of the present invention and the technical principles employed. It will be understood by those skilled in the art that the present invention is not limited to the particular embodiments described herein, but is capable of various obvious modifications, rearrangements, combinations and substitutions as will now become apparent to those skilled in the art without departing from the scope of the invention. Therefore, although the present invention has been described in greater detail by the above embodiments, the present invention is not limited to the above embodiments, and may include other equivalent embodiments without departing from the spirit of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. An optical alignment method is applied to an optical alignment system, wherein the optical alignment system comprises an alignment detection optical path; the alignment detection light path comprises a first channel, a second channel and a first imaging light path, the first channel and the second channel share the first imaging light path, and light emitting light paths of the first channel and the second channel deviate from each other;

2. The optical alignment method of claim 1, wherein the optical alignment system further comprises a parallelism detection optical path; the parallelism detection optical path comprises a third channel, a fourth channel and a second imaging optical path, the third channel and the fourth channel share the second imaging optical path, and the first imaging optical path is multiplexed into the second imaging optical path;

3. The optical alignment method of claim 2, wherein before two coaxial parallel lights with opposite directions are emitted by the third channel and the fourth channel, the method further comprises:

4. The optical alignment method of claim 3, wherein the third channel comprises a first half mirror, the fourth channel comprises a second half mirror and an adjusting base, and the second half mirror is disposed on the adjusting base;

moving the first wafer to a light-emitting optical path of the fourth channel along a first direction, wherein the first direction is vertical to the first wafer;

and rotating the adjusting base and driving the second half mirror to adjust the light emitting direction of the fourth laser beam, so that the reflected light of the fourth laser beam on the second wafer is coincided with the reflected light of the third laser beam on the first wafer through the imaging of the fourth channel and the second imaging optical path.

5. The optical alignment method as claimed in claim 4, wherein the optical alignment system further comprises a pressing head and a fixture, the pressing head is used for fixing the fixture by suction, and the fixture is used for holding the wafer and exposing two opposite surfaces of the wafer;

6. The optical alignment method of claim 5, wherein adjusting the tilt angle of the indenter comprises:

rotating the ram about a second direction and a third direction, respectively; wherein the second direction and the third direction intersect, and intersect with the first direction, respectively.

7. The optical alignment method of claim 2, wherein the two wafers comprise a first wafer and a second wafer;

using the first and second channels and the first imaging optical path to image the two opposing wafers, respectively, to form a first image and a second image, comprising:

8. The optical alignment method of claim 7, wherein adjusting the tilt angle of the optical alignment system comprises:

rotating the optical alignment system about a second direction and a third direction, respectively; wherein the second direction and the third direction intersect, and intersect with the first direction, respectively.

9. The optical alignment method of claim 7, wherein determining the misalignment between the two wafers according to the positions of the marks on the wafers in the first image and the second image comprises:

moving the first wafer and/or the second wafer on a first plane along the dislocation direction and according to the dislocation distance, wherein the first plane is a plane vertical to the first direction;

and aligning the two wafers along the first direction.

10. The optical alignment method of claim 2, wherein the alignment detection optical path further comprises a first illumination optical path, the first channel and the second channel share the first illumination optical path, and the first illumination optical path emits parallel light;

before the two wafers which are opposite to each other are respectively imaged by using the first channel, the second channel and the first imaging optical path to form a first image and a second image, the method further comprises the following steps:

turning on the first illumination light path;

and opening the second illumination light path.