WO2011091894A1

WO2011091894A1 - Method for inspecting structures of test substrates

Info

Publication number: WO2011091894A1
Application number: PCT/EP2010/068996
Authority: WO
Inventors: Michael Teich; Frank Fehrmann; Thomas THÄRIGEN; Jens Fiedler; Ulf Hackius
Original assignee: Cascade Microtech Dresden Gmbh
Priority date: 2010-02-01
Filing date: 2010-12-06
Publication date: 2011-08-04
Also published as: DE102010006607A1

Abstract

The invention relates to a method for inspecting test substrates in a sampler which comprises a chuck for holding the test substrate (2), an inspection unit having a camera for inspecting the test substrate (2), a moving device for moving the chuck and/or the inspection unit, a control unit for controlling the moving device and a display for showing an image recorded by means of the camera. For inspection an overview image (1) of the test substrate (2) is produced by recording a plurality of individual images (4) in various positions of the test substrate (2) and combining them into the overview image (1) on the display. Each individual image (4) is stored together with the co-ordinates of the position in in which it was recorded. For navigation on the test substrate an individual image (4) in the overview image (1) is selected, and then a position associated with the individual image (4) is approached by means of the moving device and there an image is produced of the detail of the test substrate (2) which is then located in the field of view (6) of the inspection unit.

Description

Method of Inspecting Structures of Test Substrates The invention relates generally to a method for

Inspection of test substrates by means of a

Inspection unit of a Probers. In particular, it relates to the inspection of test substrates that are larger than the field of view of the inspection unit, so that the area to be inspected must be positioned in the field of view by means of a movement device of the tester in order to inspect the entire test substrate or regions of the test substrate lying outside the field of view.

As is known, a wide variety of test substrates are tested for various properties or subjected to special tests. The test substrates can be used in different production and integration stages

available. So are tests of semiconductor chips,

Hybrid components, micromechanical and micro-optical components and the like carried out, which are still in the wafer composite or isolated or already integrated in more or less complex circuits.

In the following, the component to be inspected is the test substrate. This can be both an entire wafer as well as its individual components or already isolated components, depending on the current

Inspection task. It is equally possible that initially a single component of a wafer and

then another to be inspected, and in each case using the same inspection method once on the individual component and the other on the entire wafer.

For testing and inspection of test substrates

Test stations used a chuck with one

Surface for receiving test substrates include. Of the Chuck is usually movable by means of a movement device at least in the X and Y directions. The inspection station also has an inspection unit, a camera and / or a microscope, with which the test substrates can be inspected. This takes place, for example, before or during the contacting of the contact pads of the test substrates by probe tips.

In the manual inspection of structures of

As a result of the limited field of view of the inspection unit, only a part of the entire wafer or only a part of the test substrate is visible to test substrates. The size of the image depends on the one hand on the size and resolution of the lens used in the inspection unit and / or the sensor used. The bigger the

Lens enlargement, the smaller the region of the test substrate to be displayed in an image, generally as

Image field called. In a partial representation of the test substrate, the inspection unit must be so by the operator of the inspection station, the operator, relative to the chuck

be positioned that for the inspection

interesting part in their field of vision is.

The positioning of the inspection unit relative to the chuck is often done solely by a movement of the chuck.

Alternatively, however, probes are known whose

Inspection unit is movable, so that also chuck and inspection unit to each other or only the

Inspection unit be delivered to the chuck. In the following, the description will be described by way of example with reference to the movement of the chuck alone. A limitation to such positioning for inspection purposes is not intended.

Are structures to be inspected one and the same

Test substrate spatially far apart, so they no longer fit simultaneously in the field of view of the inspection unit. The operator must manually enter the required positions approach. This process is time consuming and monotonous, especially with frequent repetition. Quick manual inspection of a test substrate is possible only insofar as the structures to be inspected are close to each other or within the image field.

The invention has for its object to expand the image field of an inspection unit of a Probers and the

To improve navigation on the test substrate during the inspection. There is provided an inspection method with which the image field of the inspection unit is virtually expanded by creating a virtual overview image of the test substrate or at least part of it. The overview image is obtained by two-dimensional juxtaposition of images recorded by a camera, so-called

Tiling, which was taken at different positions of the chuck. The individual tiles of the

Overview image can be either in different

Chuck positions can be included within the X-Y plane. However, they can also include Z-direction jumps, depending on the structure of the test substrate and the target of the inspection.

This overview image composed of individual images is a still image that is only updated by explicit user interaction. It serves as a reference for further navigation for the inspection unit, e.g. as part of the setting or inspection of the contact position of

Probe tips. The size of the virtual image field of the overview image is chosen so that on a

Test substrate, which is larger than that with the

Inspection unit imageable image detail, with

can be roughly navigated with sufficient accuracy. The fine positioning then takes place in the live image, which after starting the position selected in the overview image

is won. To produce the overview image, the chuck positions of interest are approached. In every

Position a single picture is taken, this the

associated X and Y coordinates of Chuckposition and possibly also Z coordinates and scaling data and stored the image in connection with these data in the memory of the control unit of the Probers. The recording of the individual images can be done in various ways. So is an automated recording with

presettable positioning steps of the chuck within a previously, e.g. Manual, limited area on the test substrate possible. This can be done, in particular, if regular structures on the test substrate are to be inspected, such as e.g. Contact pad rows or

Contact pad arrays. Also manual positioning for

Recording any picture or a combination of both are possible. The individual images to be photographed can then be completely directly next to one another, the area of interest of the test substrate or only selected areas thereof.

The frames with the associated data will be

hereafter referred to as tiles. From these tiles is determined by criteria appropriate for each

Inspection task is favorable, the overview picture

composed. Most of these criteria will be due to the spatial relationship of the individual tiles. Alternatively, however, functional relationships resulting from the image content can also be decisive for the

Stringing the individual. In any case, the tiles are assembled on the basis of the coordinates without consideration of the image content. It follows from the latter that no positioning errors in the desired chuck position or lens distortions that would require image recognition methods are taken into account. A clue to the number of tiles ever

Overview image is in addition to the inspection task and the memory requirements, which must be taken into account that both the individual tiles as well as the overview image must be held at least briefly parallel and the

Overview image can also be saved in full resolution. So it can be helpful to save the images only in black and white, because in the case of colored images, both the computational and associated time expenditure as well as the storage requirements multiply. A reduction of the memory requirement can alternatively or additionally also be effected by a downward scaling of the resolution of the individual images. This has no on the later inspection

Influence, since the tiles serve only the navigation and the inspection after starting the with the tile

connected coordinates on the image then obtained, the live image takes place.

The overview image is displayed on a display of the control unit of the prober, preferably together with the current live image of the test substrate to be obtained with the inspection unit. By means of a cursor, either a mouse pointer, a crosshair or similar, the operator can select and activate each of the tiles in the overview image. Upon activation of a tile, a signal is generated in the control unit to the movement device, which causes the start of the chuck position in which the activated tile was taken.

In the case of this so-called static positioning, coordinates and data of the activated tile always relate to the area of the test substrate recorded for the creation of the overview image, regardless of how far away the current position is from the location of the tile.

In one embodiment of the invention, the so-called dynamic positioning, the coordinates of the

Tiles of the overview image transferred to regularly recurring, comparable substructures of the test substrate by the step size of the repetition of the substructure on the coordinates of each tile of the overview image

is counted. Each coordinate of each tile is corrected by a multiple of the values in the X-, Y and possibly also Z-direction, which is the position of two adjacent

Define substructures to each other. Based on the comparison of the current position with the recording range of the

Overview image is the number of repetitions of the

Determine the substructure that lies between the two positions and thus how often and in which directions the

Corrections of the X, Y and Z coordinates are to be applied. The recording area of the overview image is e.g. using a reference tile to define.

In this way, both a repetition in one direction and in several directions must be considered. In addition, this extension of navigation to a variety of comparable structures, e.g. at

Components in the wafer composite, even without image recognition applicable. The current position is alone from the

Coordinate comparison to determine if the increment of repetitions is known or previously determined. This allows navigation in the environment of the live image and on the substructure depicted there, even if the inspection unit is outside the range of the

Overview screen is located. With each activation of a tile in the overview image will automatically into a position

within the current, i. pictured in the live image

Partial structure converted. It is also possible to navigate around the live image, but this assumes that the overview image has captured a complete substructure. The invention will be described below with reference to a Embodiments will be explained in more detail. In the accompanying drawing shows

Fig. 1 is composed of four times four tiles

Overlooks image;

FIGS. 2A and 2B show a real overview and live image with the image data according to FIG. 1;

3 is a real overview image with respect to FIG

2A larger field of view;

Fig. 4 shows a wafer with a grid of components as repeating partial structures, with spatial

Assignment of an overview picture and substructures adjacent to it;

5 shows a display of an overview image and a live

Picture.

FIG. 1 shows an overview image 1, which is of a chip 2, in the exemplary embodiment the one to be inspected

Test substrate 2, is created. The chip 2 is part of a wafer 3 comprising a plurality of chips 2. If the wafer were to be 3 or inspected, the wafer would be 3

according to the terminology outlined above

alike be a test substrate 2.

The 16 frames 4 are successively picked up by the chip 2 by repositioning the wafer 3 correspondingly for each frame 4. Each frame 4 is stored together with the position coordinates at which the frame 4 was taken and the image resolution. The stored individual images 4 are provided with suitable software for the overview image 1

and can be displayed to the operator of a prober on a display.

The overview picture 1 was made of four by four tiles created, the individual images slightly overlapping each other represent the entire chip 2, which should be illustrated by the reduced copy of the overview image 1 on the wafer 3 in conjunction with the connecting lines. The individual images 4 each have a resolution of 2048 x 2048 pixels. The exact data can be found in the following table:

Based on the size of a live image of 3 by 3 mm, the theoretical tiling of the selected tiling is 12 by 12 mm ² . The difference to the actual

Image field size of in the exemplary embodiment 10 times 10 mm ² is due to the overlap 5 of the individual images 4, which was made here with about 20%. The image information in overlapping image areas is either overlaid or exclusively combined, if necessary parameterized.

A real overview picture 1 with a comparable one

Tiling and resolution is shown in FIG. 2A. The individual images 4 fit together almost seamlessly. By means of a suitable overlap of the individual images 4 are

Edge effects on the frame 4, e.g. affect the representation in the edge area, minimizable. in the

Embodiment, the individual images 4 were not

Scaled down so that the high resolution in the Details of the overview picture 1 is preserved. For better illustration in FIG. 2A, however, not all 16 individual images 4 are shown.

Fig. 2B shows a detail of the center of

Overview diagram 1 shown in FIG. 2A. The structures of the test substrate 1 are shown clearly and sharply.

In the exemplary embodiment according to FIG. 3, a significantly larger image field has been shown in the overview image 1. It is composed of 50 by 50 individual images 4 and gives an image field size of 150 by 150 mm ² , in this case without

Overlap. To the total resolution of the overview image 1 to save storage capacity and computing time

To keep as small as possible, the individual images 4 were scaled down sharply this time. The data can be the following

Table be taken:

Due to the lower in this embodiment

Detailed resolution, a single image 4 would only be clear

give blurred contours of the test substrate 2, but which still suffice to produce e.g. Detect contact pads. With a correspondingly low structural resolution, sufficient storage capacity and computing time, a complete imaging of a wafer 3 in the overview image 1 would also be possible.

Fig. 4 shows a wafer according to Fig. 1, in which of a the chips 2 an overview image 1 of two times two tiles 4 was created with an overlap 5. in the

Embodiment according to FIG. 4, this overview image 1 is also applied to other chips 2 of the wafer 3 used for navigation by the above-described dynamic positioning on other chips 2 not used for the production of the overview image 1. To distinguish the starting position in which the overview image 1 was recorded, from the later

Positions where the same overview image 1 is applied only to the repetitive, comparably structured chips 2 on the wafer 3, the former position is surrounded by a solid line, whereas all others

Positions have a dashed border.

In the illustrated dynamic positioning of a chip 2 for inspection purposes, the wafer 3 by means of

Movement device of chopper of Probers (not

represented) relative to the stationary inspection unit (not shown), in this case a camera, so far moved that the field of view 6 of the camera is located away from the area of the recorded overview image 1. In the illustration according to FIG. 4, the field of view 6 is shown displaced relative to the wafer 3 for the sake of a better overview.

After the overview image 1 was taken in the lower region of the wafer 3 and the wafer 3 was moved so far that the field of view 6 in the upper region of the wafer. 3

Static positioning would result in a selection and activation of one of the four tiles 4 of the overview image 1 of the wafer 3 automatically so

was moved back that the activated tile 4 of the originally recorded chip 2 is exactly in the field of view 6 of the camera.

In the case of dynamic positioning, the difference between the currently approached position and the field of view of the camera whose x and y coordinates are known and Position coordinates of the activated tile 4 determines how many chips 2 lie between these two positions in both the X and Y directions. From the knowledge of the size of each chip in the X and Y direction, the

Coordinates of the activated tile 4 converted to those of the chip 2, located in the immediate vicinity of the

Field of view 6 is located, i. where the largest

Overlap with the field of view 6 results. This largest overlap can e.g. be determined by

it is determined over which chip 2 the center of the field of view 6 is located.

After the used chip 2 the tiles 4 of the

Assigned overview image 1, the corrected tile 4 of this chip 2 is approached. In this way, initially roughly a region on the wafer 3 can be approached and there the overview image 1 can be applied to the chips 2 located in the vicinity of the field of view 6, in order to there

navigate. In Fig. 4, this dynamic positioning has been repeated in a plurality of distinctly spaced regions of a wafer 3.

5 shows the display an overview image 1 and a live image 7 on a display 10. The overview image 1 is composed of 4 tiles. Since the live image 7 is the one which can be accommodated in the current position with the camera, it corresponds to the field of view of the camera according to FIG. 4.

In the overview screen 1 on the display is by means of a

Reticle 11, which serves as a cursor, the current field of view 6 of the camera, i. the inspectable area of a test substrate 2 is shown. In Fig. 5, this is a

Excerpt from a chip 2. Accordingly, the live image 7 represents this section, but with a higher resolution. If another section is to be displayed, the overview picture 1 is navigated by moving the crosshair 11 until the desired section in the crosshair 11 lies. At this point, the tile 4 is activated by clicking with the crosshair 11, which is located under the crosshair. As a result of the activation of the tile 4, the movement device of the Probers (not

displayed) and the chuck is positioned so that the activated tile 4 or a dynamically corrected tile 4 is in the field of view of the camera.

Method for inspecting test substrates Reference symbol overview image

Test substrate, chip

wafer

Single picture, tile

overlap

field of view

Display, display

Cursor, crosshair

Claims

Method for inspection of test substrates Claims

A method of inspecting test substrates in a prober comprising a chuck for holding the test substrate (2), an inspection unit with a camera for inspecting the test substrate (2), a moving device for

Movement of the chuck and / or the inspection unit relative to each other, a control unit for controlling the

Moving device and a display for displaying a captured by means of the camera image, comprising the following method steps:

holding the test substrate (2) on the support surface of the chuck and positioning the test substrate (2) by means of the movement device in the field of vision (6)

Inspection unit, - generate an overview image (1) of at least

a portion of the test substrate (2) by means of the camera, wherein a plurality of individual images (4) of said portion in different positions of the test substrate (2) relative to the field of view (6) of

Inspection unit recorded and displayed on the display

Overview picture (1) can be put together

- Save each frame (4) together with the

Coordinates of the position in which it was taken

- Select a single image (4) in the overview image

(1), whereupon a control signal is generated in the control unit for approaching a position associated with the single image (4) by means of

Movement device and - Approaching this position and image of the present in this position in the field of view (6) of the inspection unit section of the test substrate (2).

2. The method of claim 1, wherein the coordinates of the position stored with a single image (4) are corrected by an integer multiple of a

predefined increment and the number of correction steps are determined from the distance that exists between a position during generation of the

Overview screen (1) and a currently set, deviating position exists.

3. The method according to any one of the preceding claims, wherein the coordinates of the position of each frame (4) and the scaling of the individual images (4), in particular their resolution is stored.

4. The method according to any one of the preceding claims, wherein the overview image (1) completely images a test substrate (2).