Real-time registration in lithography systems

Abstract

An apparatus for measuring a reference point in real time during photolithography printing includes a light source for providing an exposure beam, a light modulator for modulating the exposure beam according to an exposure pattern, a measurement system configured to measure the positions of a plurality of alignment marks pre-arranged on a substrate, and an exposure optical system including a control unit. The exposure optical system transmits the modulated exposure beam as an image provided by the light modulator onto the substrate, and the exposure system control unit is configured to calculate the orientation of the substrate based on the positions of the alignment marks and control the transmission of the modulated exposure beam relative to the calculated substrate orientation.

Description

Summary of the invention

[0001] The present invention relates to a method and apparatus for exposing photosensitive materials for fine-line direct imaging lithography requiring a large number of measured reference points, wherein camera capture, imaging analysis, calculation and real-time data transmission and printing are all completed in real time.

[0002] Laser direct imaging (LDI) and direct imaging (DI) lithography machines are well proven in the market and are used in various lithography applications such as PCB and wafer lithography.

[0003] Orbotech's Novougo and Schmoll's MDI TT are typical examples of such machines.

[0004] LDI and DI machines have some limitations because they require registration / measurement of fiducials and reference points to take advantage of position, rotation, and pattern warpage compared to traditional contact lithography machines and aligners. Registration is time consuming, and direct imaging lithography is generally slower than traditional contact lithography machines and aligners. However, when using smaller and smaller lines / spaces in the lithography pattern, accuracy advantages can be achieved through registration and calculation of position, rotation, and warpage, allowing for more accurate layer-by-layer printing.

[0005] In (laser) direct imaging lithography systems (LDI, DI), the measurement of reference points / fiducials in the medium to be exposed (PCB, wafer, RDL, display, film, etc.) is an essential part of the process. The medium containing the photosensitive material to be exposed with the pattern is subject to position errors and rotation errors when it is placed in the lithography machine. Furthermore, such a medium may already have a printed pattern exposed on one or both sides. The pattern to be printed needs to fit the position and rotation of the medium, the existing pattern, the existing reference points and the interconnection points between the existing pattern and the new pattern to be applied to the medium. Therefore, reference points / registration points are defined in these patterns to be measured and then the pattern to be printed must be changed to adapt to the actual position, rotation and warping of the medium and the existing or to-be-exposed pattern.

[0006] The measured positions / coordinates of these reference points are transmitted from the capture camera and analysis system to the printing part of the lithography system. A lithography machine with a registration system and printing system will typically use a laser scanner (e.g. Orbotech's Nouvogo) or a modulated light projector (DLP / LCOS, etc.) (e.g. Schmoll-maschinen's MDI TT), which are used to calculate the position, rotation and warp of the pattern to be printed.

[0007] Typically these registration coordinates will be transferred to a lithography calculation / printing system and a new pattern file will be calculated and then printed based on these calculations. This is done more or less in real time, with some systems using software to transfer data to and from the computer / CPU, while other systems will use an FPGA / video processor or similar device to change the pattern in real time.

[0008] Such measurements are typically made at a few to a few hundred reference points. Registration of these reference points is time consuming and slows down the throughput of such a lithography system. This can be compensated by having a lithography machine with a measurement station on the first medium while printing the second medium, so that the measurement is made using the actual printed shadow time. However, the print time of such a lithography system is typically a few seconds to a few minutes, so if many lithography machines are used, there is a limit to how many measurements can be made before starting to slow down the throughput of the system or method.

[0009] When the number of reference points / fiducials is too large, measurement becomes very time-consuming. Combined with the smaller feature sizes in patterning, the Figure 1b ), require higher measurement accuracy and even higher time consumption. A typical DI PCB lithography machine will be able to perform coordinated registration / measurement with a panel side to panel side accuracy of 5-15μm. New fine line applications require registration accuracy down to 1μm and below to the nanometer region.

[0010] Such precise measurements are difficult to achieve, and special measurement equipment such as the Rudolph Firefly series is used on existing high-precision and fine-line (10um-x00nm line / space) lithography systems (such as lithography machines, such as Rudolph's Jetstep 2300 system). When using a measurement machine, the measurement data will need to be transmitted back to the lithography system to calculate a new pattern, or use a pattern that has already been calculated and changed from external processing (position, warp rotation, etc.). This process is usually slow and is done through the factory process SW, not in real time. In addition, the measurement is done outside the lithography system, so the required accuracy may be difficult to achieve because the measurement and lithography equipment do not share the same optomechanical system. Sharing the optomechanical system is an advantage in terms of the optomechanical thermal effects of the camera system and the lithography system. This will require more accurate and complex calibration and create uncertainties that may affect yield and the entire factory. When these two optomechanical systems are combined, higher registration measurement accuracy can be achieved, see Visitech lithography system LLS optoelectronic sensor heads LLS 10 and LLS 04, where the registration camera is positioned so that the camera and projector share the same optical path and therefore have the same optomechanical. See Visitech European patent application number: 14200630.3. The system is as Figure 1a shown.

[0011] Therefore, LDI and DI machine / direct imaging lithography systems have throughput and cost limiting factors if the number of reference points is excessive and / or the registration accuracy requirement is very high.

[0012] New approaches to advanced packaging, embedded wafers, FOWLP, FOPLP, 2,5 and 3D electronic components and higher precision requirements for pattern line / space require very small line / spaces, such as below 10μm and down to the nanometer region. These fine line / space requirements also require higher registration and position / warp accuracy.

[0013] As known to those skilled in the art, in the context of integrated circuits, a wafer is a small piece of semiconductor material on which a given functional circuit is manufactured. In embedded wafer packaging, components are embedded within a substrate using a multi-step manufacturing process. A wafer, multiple wafers, MEMS or passive devices can be embedded in a core of an organic laminate substrate in a side-by-side manner. The object of the present invention is to provide a method and apparatus for real-time measurement of reference points during photolithography printing to reduce the problems of the prior art.

[0014] The objects of the invention are achieved by the features of the patent claims.

[0015] In one embodiment, an apparatus for measuring reference points in real time during photolithography includes a light source providing an exposure beam, a light modulator modulating the exposure beam according to an exposure pattern, a measurement system configured to measure positions of a plurality of alignment marks pre-arranged on a substrate, and an exposure optical system including a control unit.

[0016] The exposure beam source may be, for example, a UV light source. The measurement system may, for example, use a beam of visible light or any other suitable wavelength of light.

[0017] In one embodiment, the light source comprises a plurality of light sources, such as a plurality of LED units, having at least one wavelength.

[0018] The exposure optical system transmits a modulated exposure beam as an image provided by the light modulator to the substrate. The modulated exposure beam represents the image to be exposed on the photolithographic printing material.

[0019] In one embodiment, the exposure optical system includes a projection lens and the light source / light sources are positioned to be optically coupled through the projection lens. In other embodiments, the light source may be located at the bottom of the exposure optical system, surrounding the projection lens.

[0020] The alignment marks may be special marks printed or physically placed or arranged on the substrate in any other manner. The alignment marks may be any suitable marks already on the substrate whose positions are known, so that the orientation of the substrate can be calculated. In one embodiment, electrical connection pads on the wafer are used as alignment marks. In alternative embodiments, the body or body portion of the wafer may be used as alignment marks.

[0021] The measuring system is a system for measuring the position of the alignment mark. The exposure optical system control unit is configured to calculate the orientation of the substrate based on the position of the alignment mark and control the transmission of the modulated exposure beam relative to the calculated substrate orientation.

[0022] In one embodiment, the measurement system comprises a camera or camera system. The camera or camera system can be arranged to use direct high data rate transmission directly from the camera chip to an FPGA (field programmable gate array) or processor for fast analysis and data transmission to a pattern calculation module inside the exposure optical system control.

[0023] Contemporary field programmable gate arrays (FPGAs) have a large number of logic gates and RAM block resources to implement complex digital calculations, making them suitable for high data rate calculations.

[0024] The measurement system and the exposure optical system have at least partially parallel optical paths. For example, a camera as part of the measurement system and its image path can be placed in the optical path of the exposure optical system. The camera can share the same optical elements (such as dichroic beam splitter prisms and projection lenses, etc.) with the exposure optical system. The camera can share the optomechanical structure (optical component mounting unit) with the light source modulator. The light source modulator is, for example, an electronic projector based on DMD technology or similar technology. Since the exposure optical system and the registration camera share the same mechanical and optical paths, any position changes of the exposure image provided by the exposure optical system caused by the exposure internal (such as the optical mechanical device of the optical component mounting unit) and external (exposure optical system frame and chassis mechanical device) will also be adapted to the position of the registration camera. Therefore, there is no need to frequently calibrate the relative position offset of the exposure optical system and the registration camera.

[0025] In one embodiment, the image region of interest of the camera is proximate to and mechanically coupled to the exposure optics.

[0026] The image region of interest of a camera is a feature that specifies a portion of a sensor line. During operation, only pixel information from the specified portion of the line is transferred out of the camera. The image region of interest of a camera can also specify the width of the frame. Since CMOS sensors read out pixels in parallel compared to CCD sensors, many CMOS sensors also offer the possibility to read out only a portion of the image, thus being able to focus on the image area that contains information relevant for image processing.

[0027] In one embodiment, the measurement system defines a camera region of interest to optimize fast camera data transmission. For example, the measurement system can define a special camera region of interest for autofocus laser reflection detection similar to a line sensor, and use the defined special camera region of interest for fast camera data transmission for autofocus calculation and autofocus adjustment.

[0028] A method for measuring reference points in real time during photolithography printing may also be provided. In one embodiment, the method comprises the following steps:

[0029] - modulating the exposure beam according to an exposure pattern;

[0030] - measuring the positions of a plurality of alignment marks previously patterned on the substrate,

[0031] - transmitting the modulated exposure light beam as an image provided by the light modulator onto the substrate;

[0032] - Calculate the orientation of the substrate based on the positions of the alignment marks and

[0033] - Controlling the delivery of the modulated exposure beam relative to the calculated orientation of the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The present invention will now be described in more detail with reference to the accompanying drawings.

[0035] Figure 1a An example of an exposure system for direct imaging lithography is shown.

[0036] Figure 1b Various examples of direct imaging lithography applications are schematically shown.

[0037] Figure 1c to Figure 1d An example of a component having high requirements on pattern accuracy is shown.

[0038] Figure 2a to Figure 2b An example of an embedded die is shown.

[0039] Figures 3 to 5 A typical process for advanced packaging with embedded die is shown.

[0040] Figure 6a to Figure 6b Examples of wafers and panels containing embedded die are shown.

[0041] Figures 7 to 13 An example of the configuration of optical elements for exposure and camera capture of an apparatus for direct imaging lithography is shown.

[0042] Figures 14a to 14dDetails of different embodiments of the exposure and camera capture optics of an apparatus for direct imaging lithography are shown.

[0043] Fig.15a and Fig.15b Details of different embodiments of the exposure and camera capture optics of an apparatus for direct imaging lithography are shown. DETAILED DESCRIPTION

[0044] Figure 1a An example of an exposure system is shown, comprising a light source 302 providing an exposure beam 306, light modulators 301, 302 modulating the exposure beam 306 according to an exposure pattern, and exposure optical systems 303, 304, 308 transmitting the modulated exposure beam as an image 311 provided by the light modulator onto a substrate 307. Measurement systems 303, 304, 305, 308, 309 are incorporated in the exposure apparatus and are configured to measure the position of alignment (reference) marks patterned in advance on the substrate. In this embodiment, the exposure optical system and the measurement system have at least partially parallel optical paths.

[0045] In the following description, the term "photoelectric sensing head" will sometimes be used as a collective term including optical elements of an exposure system.

[0046] The exposure system may further include a control unit (not shown) configured to calculate the orientation of the substrate based on the positions of the alignment marks and to control the delivery of the modulated exposure beam relative to the calculated orientation of the substrate. This will be described in more detail below.

[0047] Figure 1b Various applications are shown, where smaller feature sizes are required in patterning due to the increasing demand for smaller devices. For this reason, higher precision in the measurement of alignment marks is required without significantly increasing the time consumption of the process.

[0048] Figure 1c to Figure 1d An example of a component with such high demands on pattern accuracy is shown. Typically, an embedded wafer with connection pads will have small pads / electrical connection points ranging in size from 25-100 microns or less.

[0049] In order to optimize the spacing available for fine line patterning, the available spacing between pads on the wafer needs to be optimized. The "channel" optimization of the available spacing requires high positioning accuracy when applying the wafer and pads to the substrate. In addition, for cost reasons, if the "channel" is optimized, the number of redistribution layers (RDL) can be reduced.

[0050] Typical applications are fan-out panel level packaging process FOPLP or fan-out wafer level packaging process FOWLP.

[0051] Examples of such application processes can be found in Figures 2a to 5 .

[0052] exist Figure 2b and Figure 3 The first step is illustrated in FIG. A temporary base layer 20, such as a wafer, is created with a tape 21 or layer placed on top. Wafers 22 are positioned and arranged on the adhesive layer / tape 21 with the connection pads facing the tape. Each wafer may be positioned using a "pick and place" machine, for example, and the process will produce some positional and rotational errors due to the precision limitations of such pick and place equipment which requires high speed and throughput.

[0053] Such dies are typically 1-10 mm2 and hundreds or thousands of them can be mounted on a 300 mm round wafer or a 600 mm x 600 mm panel. Figure 6 shows an example of two wafers with dies mounted on them. Figure 6a shows an example of fan-out wafer-level packaging (FOWLP), while Figure 6b An example of fan-out panel-level packaging (FOPLP) is shown.

[0054] The wafer is now overmolded with the composite material 23, during which the wafer may move or rotate slightly. The base layer and tape / material 20, 21 are then removed in a special process. The result is a composite material layer 24 with the wafer and wafer pads / electrical connection points visible from one side.

[0055] In order to be able to use the wafer to optimize the pattern to be printed onto the composite layer, the position and rotation of the wafer needs to be registered / measured. This optimization is often required in fan-out processes, where the pads / electrical connection points are redistributed over a wider area so that they can be connected to a solderable system with larger and more widely distributed connection pads. Other cases can include fanning out the connection points to a larger interconnect system (such as a substrate, PCB or RDL) so that the wafer connection points can be routed and connected to other electrical components on the same substrate. This avoids this wafer-embedded wafer packaging process.

[0056] For example, a registration / measurement accuracy of 1um or higher is required. In such a system, one or more points on each wafer are measured to be able to measure and calculate position errors and rotations, so the number of measurements required can reach a value range of 1.000-100.000. Such a large number of high-precision measurements will challenge the entire process, as this is very time-consuming for the equipment currently used, such as the registration system in the DI machine and / or the measurement machine.

[0057] DI machines based on systems with light modulators (e.g. DLP, LCOS, etc.) typically print a stripe pattern, where each projector / photoelectric sensor head will print one or more stripes. Multiple photoelectric sensor heads can also be arranged to increase the capacity / throughput of the machine. Figures 7 to 13 The use of multiple optoelectronic sensing heads and multiple registration cameras having different position configurations is shown.

[0058] DI machines, such as Schmol's MDI TT Ultra using Visitech's LLS 2500 photoelectric sensor head, or other machines capable of printing 2μm line / space specifications, will typically print 10-30 strips per photoelectric sensor head, depending on the configuration. Therefore, the photoelectric sensor head mechanical system will scan several times over the area to be printed.

[0059] By applying a registration camera to the projector mechanical system and capturing / registering alignment / reference marks in real time, this along with the position / rotation calculations and data feeds can be applied to the real-time pattern warping system in the opto-sensing head. The opto-sensing head can then print the calculated resulting pattern on the fly. Fig.14a This process is shown.

[0060] exist Fig.14a , Fig.14d In the example of , the imaging optics and the optics of the camera are combined or arranged close to each other. The camera is used here as a line sensor.

[0061] As each strip is exposed, the system measures the position of the alignment marks in the same strip and / or the next strip to be printed. At the same time, the XY position and rotation matrix of each alignment mark is calculated in real time. The exposure system then uses the calculated position / rotation to control the positioning of subsequent exposure images.

[0062] The relative distance and rolling speed of the substrate known to the system can be used to determine the image capture, position calculation, data transmission and image warping time windows.

[0063] Further, by analyzing the given pattern and reference data, one or more regions of the camera image can be used to determine the camera region of interest. This will reduce the number of camera pixels to be captured for transmission and analysis compared to the entire camera image, thereby optimizing the camera data transmission and subsequent calculations to increase the speed of data transmission to the computing module.

[0064] Typically, cameras measure Figures 14a to 14d Alignment marks in front of the projected pattern as shown, or as Fig.15a and Fig.15bThe example shown in FIG. 1 shows the alignment marks on the next strip to be printed (N+1, N+2, etc.). The choice of embodiment may depend on the time required for capture, calculation and transmission of coordinate data as well as positioning and warping when printing.

[0065] By applying a system as described herein, the time-consuming problem of large numbers of high-precision measurements in fine-line lithography applications can be significantly reduced.

Claims

1. An apparatus for real-time measurement of reference points during photolithography, comprising a light source providing an exposure beam; - a light modulator for modulating the exposure light beam according to an exposure pattern; - a measurement system comprising a camera and configured to define at least one camera region of interest to optimize fast camera data transmission and to measure the positions of a plurality of alignment marks pre-arranged on a substrate, - an exposure optical system, comprising a control unit, which transmits a modulated exposure light beam as an image provided by the light modulator onto the substrate; Wherein, the exposure system control unit is configured as: - calculating the orientation of the substrate simultaneously with the exposure based on the positions of the alignment marks, and - controlling the delivery of a modulated exposure beam relative to the calculated orientation of the substrate to control the positioning of a subsequent exposure image on the substrate.

2. The device according to claim 1, wherein: The XY position and rotation matrix of each alignment mark is calculated concurrently with exposure, and wherein the calculated position / rotation is used in the exposure system to control the positioning of subsequent exposure images.

3. The device according to claim 2, wherein: The exposure pattern is provided in the form of strips and as each strip is exposed the positions of the registration marks in the same strip and / or in the next strip to be printed are measured.

4. A device according to any one of the preceding claims, wherein: Electrical connection pads on the wafer are used as alignment marks.

5. The device according to claim 4, wherein: The bulk of the wafer or parts of the bulk are used as alignment marks.

6. The device according to claim 1, wherein: The measuring system and the exposure optical system have at least partially parallel optical paths.

7. The device according to claim 1, wherein: An image region of interest of the camera is positioned proximate to the exposure optical system and is mechanically coupled to the exposure optical system.

8. The device according to claim 1, wherein: The measurement system defines a special camera region of interest for autofocus laser reflection detection similar to a line sensor, and utilizes the defined special camera region of interest for fast camera data transmission for autofocus calculation and autofocus adjustment.

9. The device according to claim 1, wherein: The light source includes a plurality of light sources having at least one wavelength.

10. The device according to claim 9, wherein: The exposure optical system includes a projection lens, and the light source is positioned and optically coupled through the projection lens.

11. A method for measuring reference points in real time during photolithography, comprising the following steps: - modulating the exposure beam according to an exposure pattern; - defining at least one camera region of interest to optimize fast camera data transmission and measure the positions of a plurality of alignment marks pre-arranged on a substrate, - transmitting a modulated exposure light beam onto the substrate as an image provided by a light modulator; - calculating the orientation of the substrate simultaneously with the exposure based on the positions of the alignment marks, and - controlling the delivery of a modulated exposure beam relative to the calculated orientation of the substrate to control the positioning of a subsequent exposure image on the substrate.

12. A method according to claim 11, comprising calculating the XY position and rotation matrix of each alignment mark simultaneously with exposure, and using the calculated position / rotation in the exposure system to control the positioning of subsequent exposure images.

13. A method according to claim 12, comprising providing the exposure pattern in strips and, as each strip is exposed, measuring the positions of registration marks in the same strip and / or in the next strip to be printed.

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