Alignment system, alignment method and image sensor

Abstract

A system (10) for actively aligning a lens module (100) and an image sensor (105) comprises a movable, rotatable stage (101) for supporting the lens module (100), a stage (107) for supporting the image sensor (105), an illumination source (115), and a camera (120). The illumination source (115) is configured to illuminate a main surface (106) of the image sensor (105) via the lens module (100). The camera (120) is configured to take a picture of the illuminated main surface (106) of the image sensor (105) via the lens module (100). The sys- tem further comprises a control device (125) configured to determine a movement of the movable stage ((101) based on the picture taken by the camera (120).

Description

[0001] ALIGNMENT SYSTEM, ALIGNMENT METHOD AND IMAGE SENSOR

[0002] The present disclosure relates to an alignment system, an alignment method and an image sensor for use in the alignment system .

[0003] The accurate active alignment of an image sensor, e . g . a CMOS image sensor with a lens is an integral and important part of assembling a camera module .

[0004] Generally, ef forts are being made to improve the alignment system and alignment method .

[0005] It is an obj ect of the present disclosure to provide an improved alignment system and an improved alignment method . Further, it is an obj ect to provide an image sensor for use in the alignment system .

[0006] SUMMARY

[0007] According to embodiments , the above obj ect is achieved by the claimed matter according to the independent claims . Further developments are defined in the dependent claims .

[0008] According to embodiments , a system for actively aligning a lens module and an image sensor comprises a movable stage for supporting the lens module , a stage for supporting the image sensor, an illumination source , and a camera . The illumination source is configured to illuminate a main surface of the image sensor via the lens module . The camera is configured to take a picture of the illuminated main surface of the image sensor via the lens module . The system further comprises a control device that is configured to determine a movement of the movable stage based on the picture taken by the camera . For example , the system may further comprise an optical system . The illumination source may be configured to illuminate the main surface of the image sensor via the optical system and the lens module .

[0009] According to further embodiments , the system may further comprise a mask between the illumination source and the optical system .

[0010] For example , the mask may be an amplitude mask . According to further embodiments , the mask may be a phase mask .

[0011] According to embodiments , a method for actively aligning a lens module and an image sensor comprises illuminating a main surface of the image sensor via the lens module , and taking a picture of the illuminated main surface of the image sensor via the lens module by an external camera . The method further comprises determining a movement of the lens module based on the picture .

[0012] The method may further comprise moving the lens module in accordance with the determined movement .

[0013] Further embodiments refer to an image sensor for use in the system as described above . The image sensor comprises a plurality of pixels , wherein the plurality of pixels comprise modi fied and original pixels , the blocked pixels being arranged according to a speci fic pattern .

[0014] For example , the image sensor may be a CMOS image sensor .

[0015] BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings are included to provide a further understanding of embodiments of the invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles. Other embodiments of the invention and many of the intended advantages will be readily appreciated, as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numbers designate corresponding similar parts.

[0016] Fig. 1 is a schematic view of an alignment system according to embodiments .

[0017] Fig. 2A shows an example of a main surface of an image sensor.

[0018] Fig. 2B is a further example of a main surface of an image sensor .

[0019] Fig. 3 shows a schematic view of an alignment system according to further embodiments.

[0020] Fig. 4 summarizes a method according to embodiments.

[0021] DETAILED DESCRIPTION

[0022] In the following detailed description reference is made to the accompanying drawings, which form a part hereof and in which are illustrated by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology such as "top", "bottom", "front", "back", "over", "on", "above", "leading", "trailing" etc. is used with reference to the orientation of the Figures being described. Since components of embodiments of the invention can be positioned in a number of di f ferent orientations , the directional terminology is used for purposes of illustration and is in no way limiting . It is to be understood that other embodiments may be utili zed and structural or logical changes may be made without departing from the scope defined by the claims .

[0023] The description of the embodiments is not limiting . In particular, elements of the embodiments described hereinafter may be combined with elements of di f ferent embodiments .

[0024] Fig . 1 is a schematic view of an alignment system 10 according to embodiments . As will be discussed in the following, the alignment system 10 is a system for actively aligning a lens module 100 and an image sensor 105 . The alignment system 10 comprises a movable stage 101 for supporting the lens module 100 and a stage 107 for supporting the image sensor 105 . For example , the stage 101 and, optionally, the stage 107 may be rotatable about arbitrary axes or configured to be shi fted in any arbitrary direction . In addition, the stage 101 and, optionally, the stage 107 may be conf igured to perform a tip or a tilt movement . For example , a stage may be typically implemented as a 6 axis ( or even higher ) stage .

[0025] The system further comprises an illumination source 115 and a camera 120 . The illumination source 115 is configured to illuminate a main surface 106 o f the image sensor 105 via the lens module 100 . The camera 120 is configured to take a picture of the illuminated main surface 106 of the image sensor 105 via the lens module 100 . The system further comprises a control device 125 which is configured to determine a movement of the movable stage 101 based on the picture taken by the camera 120 . For example , the image sensor 105 may be based on a semiconductor material and may comprise further layers and patterns over the surface of the semiconductor material , e . g . a metal grid array, color filters , or one or more metal or organic layer ( s ) . The term "main surface of the image sensor" 105 may refer to e . g . to a topmost surface of the image sensor . For example , this may be the surface of the topmost further layer or patterns over the surface of the semiconductor material .

[0026] For example , the alignment system 10 may further comprise an optical system 110 . The electromagnetic radiation 15 emitted by the illumination source illuminates the main surface 106 of the image sensor 105 via the optical system 110 . The main surface 106 of the image sensor 105 may imaged by the optical system 110 . Due to the optical system 10 a higher throughput may be achieved while maintaining good alignment accuracy . For example , the optical system 110 may comprise a first lens 111 , a second lens 112 , and a third lens 113 . For example , the first lens 111 may be arranged in front of the camera 120 . Further, the second lens 112 may be arranged in front of the illumination source 115 . The optical system 110 may further comprise a beam splitter 114 which may be configured to redirect light emitted by the illumination source 115 and transmitted by the second lens 112 , towards the image sensor 105 . Further, the beam splitter 114 may be configured to transmit light that has been reflected by the image sensor 105 via the lens module 100 and the third lens 113 to the camera 120 .

[0027] For example , any of the lenses described herein may be implemented by more than one single lens . In particular, the term " lens" may comprise a lens system .

[0028] The third lens 113 may be arranged in front of the lens module 100 . The third lens 113 may be implemented as a low NA optical system, e . g . as a lens having a low numerical aperture . As a consequence , nearly collimated beams may be transmitted by the third lens 113 . The illumination source 115 may e.g. be an incoherent or coherent illumination source, e.g. a laser. For example, the illumination source 115 may be a broadband or white light source or a narrowband light source. For example, the illumination source 115 may be configured to image features, which will be discussed in more detail below, on the image sensor 105 at a specific wavelength .

[0029] As is indicated in Fig. 1, the entire system comprising the optical system 110, the illumination source 115 and the camera 120 may be mounted on a further stage which may be rotated about arbitrary axes or shifted in any arbitrary direction. In addition, the stage may perform a tip or a tilt movement. For example, a stage may be typically implemented as a 6 axis (or even higher) stage.

[0030] When the main surface 106 of the image sensor 105 is illuminated by electromagnetic radiation emitted by the illumination source 115, structural features on the main surface 106 may be imaged onto the camera 120 via the lens module 100. Examples of structural features which may be arranged on the main surface 106 of the image sensor 105 will be discussed below. For example, the lens module 100 may comprise several lenses for assembly with the image sensor 105. The lens module 100 may be implemented as a wafer-level optics lens.

[0031] The camera 120 takes a picture of the structural features on the main surface 106. The camera 120 or a control device 125 may compare the picture taken with a reference image. For example, the reference image may be an image of an image sensor 105 which is perfectly aligned with respect to the lens module 100. A control device 125 performs the comparison. Based on the comparison result, the control device may move, e.g. shift or rotate the movable stage 101. For example, this movement may be performed until a perfect alignment between the lens module 100 and the image sensor 105 has been achieved. According to further embodiments, the control device 125 may analyse an image quality. According to embodiments, the control device 125 may further determine if the alignment needs to proceed or not.

[0032] Due to the presence of the camera 120, an active alignment of the image sensor 105 with respect to the lens module 100 may be performed without the need of electrically connecting the image sensor 105 to a power supply or a driver module. In more detail, the picture is taken from the main surface 106 of the image sensor 105 by means of the camera 120 which is also connected to a power source and which is connected to a control device 125. Further, the image sensor 105 is disconnected from a voltage source. As a consequence, active alignment may be performed at a higher speed and in a more efficient and compact manner in comparison with cases in which the image sensor itself takes a picture for active alignment.

[0033] For example, the image sensor stage 107 may be stationary. According to further embodiments, the image sensor stage 107 may be moved, e.g. in a horizontal or a vertical direction.

[0034] Fig. 2A shows an example of a main surface 106 of an image sensor 105. Generally, the image sensor, e.g. a CMOS ("complementary metal-oxide semiconductor") sensor comprises a plurality of pixels which may e.g. be arranged in rows and columns. The pixels may comprise original pixels 128 and modified pixels 129. For performing the active alignment, a specific pattern of blocked pixels 129 may be arranged over the main surface 106. For example, the term "original pixel" may refer to a pixel having a surface which has not been especially processed for the purpose of the alignment method described herein. For example, the term "original pixel" may refer to an unblocked pixel. The original pixels 128 may be pixels without a specific coating for changing an absorptance or reflectivity of the pixel. For example, the term "modified pixel" may refer to a pixel which may have been further processed for the purpose of the alignment method described herein. For example, a modified pixel may be coated by a reflective material, e.g. a metal. According to further implementations, the term "blocked" pixel may refer to a pixel which is covered by a color filter, e.g. an organic or inorganic dye which changes the reflectivity e.g. in dependence from a specific illumination wavelength. For example, the illumination source 115 may be a broadband or white light source or a narrowband light source which may be used to image features on the image sensor 105 at a specific wavelength.

[0035] As is shown in Fig. 2A, a specific mask may be built into the main surface 106 of the image sensor 105. Accordingly, a certain reflectivity map at a specific wavelength may be created. This specific reflectivity map may be used to image and align the lens module 100 with the image sensor 105. For example, a certain number of pixels (blocked pixels) may be chosen to be coated with a suitable metal, e.g. tungsten or aluminum. When e.g. illuminated by blue light, the semiconductor material of the unblocked pixels 128, e.g. silicon which absorbs most of blue light, appears black in the reflection imaging mode. In contrast, the blocked pixels 129 appear bright or white. This inherent contrast may be used to achieve active alignment.

[0036] According to further implementations, as is shown in Fig. 2B, the structural features on the main surface 106 of the image sensor 105 may be implemented by a metal grid 127, which may comprise a metal and which may e.g. be formed by horizontal and vertical lines crossing each other. According to further embodiments, the metal grid may comprise grid marks 126. For example, grid marks 126 may be which are present to facilitate an assessment whether the lens module 100 and the image sensor 105 are properly aligned.

[0037] Fig. 3 shows an example of a further alignment system 10. The alignment system 10 of Fig. 3 comprises similar or identical components as the alignment system 10 shown in Fig. 1. Further, the alignment system 10 of Fig. 3 may comprise a mask 122 which may be arranged between the illumination source 115 and the second lens 112. For example, the mask 122 may be implemented as a transmission mask which causes a certain intensity and phase pattern which is imposed by the illumination source 115. For example, when the mask 122 is an amplitude mask, e.g. comprising transparent and opaque portions, the illumination source 115 may be a broadband source. When the mask 122 is a phase mask comprising portions having a different optical path lengths, the illumination source 115 may be implemented as a laser.

[0038] For example, the mask may be used in combination with an image sensor 105 comprising a metal grid which has been described with reference to Fig. 2B. As a result, the alignment accuracy may be further improved.

[0039] When the mask 122 is implemented as a phase mask and the illumination source 115 is implemented by a laser device, the alignment system 10 may further comprise an interferometer in the optical path.

[0040] The third lens may be implemented in a manner that it mostly collimates light from the optical system into the lens module 100. As a result, only a small FOV ("field of view") which may be approximately 0°, corresponding to collimated light having a normal incidence into the lens module 100, is used. As has been described, due to the speci fic implementation of the alignment system comprising a dedicated camera 120 for taking a picture of the main surface 106 of the image sensor 105 , the active alignment system 10 may be further improved . In particular, no electrical connections for power and data are necessary to be connected to the image sensor 105 . As a further consequence , the throughput of the alignment system 10 is increased, thereby decreasing the cost .

[0041] Fig . 4 summari zes a method according to embodiments . As is shown, a method for actively aligning a lens module and an image sensor comprises illuminating ( S 100 ) a main surface of the image sensor via the lens module , taking ( S 110 ) a picture of the illuminated main surface of the image sensor via the lens module by an external camera, and determining ( S 120 ) a relative movement of the lens module based on the picture .

[0042] The picture of the illuminated main surface of the image sensor is taken by an external camera, i . e . a camera which is not the image sensor itsel f but which may be a component of an alignment system .

[0043] For example , the method may further comprise relatively moving ( S 130 ) the lens module in accordance with the determined relative movement .

[0044] For example , the method may further comprise comparing the picture with a reference image , wherein the movement of the lens module is based on this comparison .

[0045] The method may still further comprise taking a further picture of the illuminated main surface after relatively moving the lens module and performing analysis of an image quality to determine a further relative movement of the lens module . In this context the terms "relative movement" and "relatively moved" refer to a relative movement of lens module and image sensor. Accordingly, the lens module may be moved and / or the image sensor may be moved so that e.g. a distance, e.g. in a horizontal or vertical direction is changed.

[0046] The term "move" does not only refer to a linear movement, e.g. a shift in a certain direction. The term "move" may as well refer to a rotation about an arbitrary axis, e.g. a roll axis, a pitch axis or a yaw axis. For example, the term "determine a movement" may comprise determining a rotation angle about any axis. Further, the term "determine a movement" may comprise determining an amount of linear movement.

[0047] In a similar manner, the term "movable" may refer to any kind of movement, comprising a linear movement or a rotation about one or more arbitrary axes. The terms "movable" and "move" may further refer to a tilt or a tip movement.

[0048] While embodiments of the invention have been described above, it is obvious that further embodiments may be implemented. For example, further embodiments may comprise any sub combination of features recited in the claims or any subcombination of elements described in the examples given above. Accordingly, this spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein . LIST OF REFERENCES alignment system electromagnetic radiation lens module movable stage image sensor main surface image sensor stage optical system first lens second lens third lens beam splitter illumination source camera mask control device grid mark metal grid unblocked pixel blocked pixel

Claims

CLAIMS1. A system (10) for actively aligning a lens module (100) and an image sensor (105) comprising: a movable stage (101) for supporting the lens module (100) ; a stage (107) for supporting the image sensor (105) ; an illumination source (115) , and a camera (120) , the illumination source (115) being configured to illuminate a main surface (106) of the image sensor (105) via the lens module (100) , the camera (120) being configured to take a picture of the illuminated main surface (106) of the image sensor (105) via the lens module (100) , the system further comprising a control device (125) configured to determine a movement of the movable stage ( (101) based on the picture taken by the camera (120) .

2. The system (10) according to claim 1 further comprising an optical system (110) , wherein the illumination source (115) is configured to illuminate the main surface (1069 of the image sensor (105) via the optical system (110) and the lens module (100) .

3. The system (10) according to claim 2, further comprising a mask (112) between the illumination source (115) and the optical system (110) .

4. The system (10) according to claim 3, wherein the mask (112) is an amplitude mask.

5. The system (10) according to claim 3, wherein the mask (112) is a phase mask.

6. A method for actively aligning a lens module (100) and an image sensor (105) , comprising: illuminating (S100) a main surface (106) of the image sensor (105) via the lens module (100) ; taking (S110) a picture of the illuminated main surface (106) of the image sensor (105) via the lens module (100) by an external camera (120) ; and determining a relative movement of the lens module (100) based on the picture.

7. The method according to claim 6, further comprising relatively moving the lens module (100) in accordance with the determined movement.

8. The method according to claim 6 or 7, further comprising comparing the picture with a reference image, wherein the relative movement of the lens module (100) is based on this comparison .

9. The method according to claims 7 or 8, further comprising taking a further picture of the illuminated main surface (106) after relatively moving the lens module (100) and performing analysis of an image quality to determine a further relative movement of the lens module (100) .

10. An image sensor (105) for use in the system (10) according to any of claims 1 to 5, the image sensor (105) comprising a plurality of pixels, wherein the plurality of pixels comprises modified (129) and unmodified pixels (128) , the blocked pixels (129) being arranged according to a specific pattern .

11. The image sensor (105) according to claim 8, wherein the image sensor (105) is a CMOS image sensor.

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