WO1992007250A1

WO1992007250A1 - Process and device for automated monitoring of the manufacture of semiconductor components

Info

Publication number: WO1992007250A1
Application number: PCT/EP1991/001648
Authority: WO
Inventors: Antonius Beckmann; Bernd Sommer
Original assignee: Abos Automation, Bildverarbeitung Optische System Gmbh
Priority date: 1990-10-11
Filing date: 1991-08-30
Publication date: 1992-04-30
Also published as: DE4032327C2; DE4032327A1

Abstract

During the manufacture of semiconductor components, the surface quality of the semiconductor chips as well as their relative position with respect to a housing, in particular the bonding pads between the chip and the connection elements in the housing, must be monitored. For that purpose, the semiconductor components are lighted by means of a lighting device and observed by means of a camera that can supply video output signals to a video signal processing device for recognizing defects of manufacture. The effective lighting directions are determined according to a pattern recognition process, so that contrast-rich images of the structures of interest or their profiles may be reproducibly recognized.

Description

Method and device for the automated monitoring of the production of semiconductor components

description

The invention relates to a method for the automatic monitoring of the production of semiconductor components according to the preamble of claim 1 and a corresponding device according to the preamble of claim 6.

A major problem in the semiconductor industry is that the reliability of manufactured components must be guaranteed by the manufacturer. The reliability of the components depends on the quality of the installation of the chip in the housing, provided the chip is correctly manufactured. This includes both the state in which the chip is installed, the position of the chip in the housing and the type and quality of the electrical connections between the chip and the housing connection contacts. For this reason, the chip surfaces are checked for mechanical damage or soiling, the position of the chip in the housing, the adhesive points between the chip and the housing, and the bond wire connections between the chip and the housing connection contacts. So far, this inspection has essentially been carried out exclusively by human personnel using microscopes. On the one hand, this process is very tiring for the staff and cost-intensive for the entrepreneur, on the other hand, at today's high production speeds, only spot checks of the components are possible.

Methods and devices of the type mentioned at the outset are known from EP 0 159 354 B1. The arrangement shown there is extremely complicated. The objects to be examined are in fact scanned point by point by means of a laser mirror system, the data obtained providing information

REPLACEMENT LEAF allow about the spatial shape of the object surface. At this

Arrangement requires a considerable time to scan a surface. In addition, there is such a large amount of data that has to be processed that even when using a very fast computer, only samples from a production can be checked.

From DE-OS 24 31 931 it is known to compare stored sets of image signals with other sets of image signals for determining spatial shape data of semiconductor components. How the image signals are obtained in detail cannot be found in detail in the publication.

From DE 38 06 209 AI a structure defect detection system is known which can be used for example for an integrated semiconductor circuit. In this system, a camera delivers image output signals, which are recorded in an image signal processing device and displayed on a monitor. This publication also does not contain any details as to how the image signals can be obtained in detail.

The invention is based on the object of further developing methods and devices of the type mentioned at the outset such that the essential data for detecting errors in the production of semiconductor components can be derived and checked in a simple manner.

This object is achieved procedurally by the features specified in the characterizing part of claim 1. A device for performing the method is specified in claim 6.

If one considers the problem of assessing bond wire connections or courses, knowledge of the course in the X-Y plane is often sufficient, although it is known that the wires run essentially in an arc shape above this plane. If one now illuminates in the previously known manner by means of light running coaxially to the camera axis, the chip surface appears bright due to its diffusely reflecting properties, while the bond wire appears bright

REPLACEMENT its curvature and very smooth surface practically does not throw light back into the camera - it appears black. Only a single surface area or a few surface areas of the bonding wire run in a plane which is located in relation to the incident light and to the camera axis such that the illumination light is reflected into the camera. However, this reflection is so intense again that this point is very bright relative to the surroundings. If it is too bright, a blooming effect can result. Now, however, the bond wire does not run exclusively over the chip surface, but rather runs from the chip to the connection contact via other surface sections of the housing, which also appear dark when viewed by means of the structure mentioned above. The course of the bond wire cannot be seen at all in these areas.

An essential idea of the invention is that for each individual point (not in the mathematical sense) an optimal direction of illumination and / or illumination intensity is possible in such a way that this point can be seen with high contrast above the background. This means that either the point is bright (highly reflective) and the background dark all around or - conversely - the background in this area is well illuminated, but the point on the bond wire appears dark. These useful lighting directions are obtained by varying the possible lighting directions with simultaneous evaluation of the image signals. Here, for example, starting from a known point (for example a contact point on the chip), the lighting can be varied so that a currently selected lighting direction is recognized as the useful lighting direction whenever the corresponding light source or Illumination from precisely this direction produces a point of high contrast which immediately adjoins the previously found point (or starting point). Of course, the pattern recognition can be limited to a narrowly limited area following the line point just found, with only the lighting directions as useful lighting directions in To be considered are those which do not differ too much from the previously found useful lighting direction, since one can assume a certain continuity of the line course (bond wire course) and exclude discontinuous or abrupt transitions. Furthermore, a field between a known start point and a known end point of the contour to be examined (bonding wire) can also be defined, within which the pattern recognition method evaluates image signals and outside which all information is rejected as "uninteresting".

As soon as the useful lighting directions necessary for the pattern recognition (on average) are determined from a sample component or a certain number of sample components, the further checking of series components can take place on the basis of the "lighting setting" defined in this way.

For each individual point, the illuminance can furthermore be set in such a way that, on the one hand, a sufficient contrast to the background is guaranteed, and, on the other hand, a blooming effect is avoided, in which overexposure and thus a type of optical enlargement or blurring of the reflective point occurs. When using a conventional camera that integrates the amount of light falling into the camera during a predetermined longer time interval (approx. 50 ms), the illuminance can take place via a pulse duration, pulse frequency or pulse number control of the light sources for the individual directions of illumination.

In another preferred embodiment of the invention, lighting is simultaneously carried out from all the lighting directions provided in the corresponding device, but each lighting direction is assigned a specific light color or color combination. In this case, a useful lighting direction is then defined on the basis of one color, so that (when using a color camera) other colors are "hidden" in the pattern recognition. In this embodiment of the method,

REPLACEMENTB early advantage that diffusely reflecting surfaces, such as the chip surface, appear white, since a mixture of all colors takes place there. A corresponding signal can be derived from a color camera, so that the pattern recognition process is simplified.

Individually controllable light sources are suitable as lighting sources, e.g. LEDs, which are then controlled by a computer. If a different color or color combination is assigned to each of the different directions of illumination, this can be done via suitable color filters which are illuminated by a (single) light source which emits at least the essential spectral components transmitted by the color filter. Such a color filter can e.g. be produced from a slide positive film with which a standardized color spectrum (from blue to red) was photographed.

In order to achieve a higher effectiveness of the lighting (a color filter also results in an attenuation at the transmitted wavelength), in a preferred embodiment light emitted by a white light source is broken down into its spectral components (e.g. through a prism), with a corresponding number behind the prism of light guides with their input ends is arranged such that each light guide is assigned a defined color. The other ends of the light guides then represent "light sources" which, with a corresponding arrangement, illuminate a component to be examined with a specific color from a corresponding direction of illumination.

Special embodiments result from the subclaims. The following description of preferred embodiments of the invention, which are explained in more detail with the aid of figures. Here show:

1 shows an embodiment of the invention in a schematic representation; Fig. 2 AC schematic image sections for bond wire localization;

3 shows a perspective partial illustration of a chip with bond wire;

4 shows a schematic sketch to explain the effect of different directions of illumination;

5 A, B show further illustrations to explain bond wire profiles;

Fig. 6 shows a further embodiment of the invention in a schematic representation similar to that of FIG. 1; and

Fig. 7 is a partial perspective view along the line VIII-VIII of Fig. 6;

8 shows an embodiment of a light guide illumination with light of different colors.

1 schematically shows an embodiment of a device for monitoring the production of semiconductor components. This comprises a holder 22 to which a number of individual light sources 16a to 16n are attached. The individual light sources 16a-16n are arranged at certain angular distances from one another and directed towards a common center. A holder (not shown) is provided under the holder 22 with the light sources 16a-16n, on which a semiconductor component to be examined can be positioned. The semiconductor component is indicated in the drawing by the schematic representation of a chip 10, the connection points of which are connected via bond wires 12 and connection contacts 13 of a housing (not shown).

A (CCD) camera 14 is held above the semiconductor component such that the optical axis O of its objective 25 is essentially perpendicular to the surface 11 of the chip 10.

REPLACEMENT LEAF A beam splitter 24 is attached behind the lens 25 of the camera 14 in such a way that a light source 23 arranged next to the camera 14 can illuminate the semiconductor component coaxially to the optical axis O.

All the illumination sources 16a-16n and 23 are in a controlled connection with a processing device 17, to which the image output signals of the camera 14 are also fed. With this arrangement it is possible to illuminate the component to be examined from different directions in accordance with the light sources controlled by the processing device 17 and to record the image signals generated in the camera 14 for further processing.

The accompanying FIGS. 3 and 4 are intended to explain the description of the method according to the invention made at the beginning. 3 shows a schematic representation of a semiconductor component in which a chip 10 is mounted (glued) on a substrate 15. Terminal contacts on the surface 11 of the chip 10 are connected via bonding wires 12 to terminal contacts 13, which are connected to contact pins (not shown) protruding outwards (out of the housing). As a result of the bonding methods known per se, each bonding wire 12 is guided in an arc between the corresponding connection point on the chip 10 and the contact 3, so that the bonding wire 12 runs essentially in a plane A which is practically perpendicular to the surface 11 of the chip 10 is. The surface 11 runs in an X-Y plane, the bond wires thus extend upwards in a direction Z beyond the surface 11 of the chip 10.

If one now illuminates such a bonding wire 12 from a certain angle, assumed in FIG. 4 with approximately 10 ° to the surface 11 of the chip 10, then, as shown in FIG. 4, only one becomes due to the curvature of the bonding wire 12 small proportion of the incident light, corresponding to a small surface section 28a of the bonding wire 12, is reflected into the lens of the camera 14. The remaining light components are

REPLACEMENT LEAF their directions radiated. In order to illuminate a certain point or area 28a of the bonding wire 12 strongly, a first light beam In from a first useful lighting direction is required. A subsequent point or region 28b of the bonding wire 12 must be illuminated from another direction of illumination by means of a light beam Im, as shown in FIG. 4. Although the illumination from almost all (possible) directions of illumination also leads to the fact that light from the chip surface enters the lens of the camera 14, the luminance of the light emitted by the areas 28 on the bonding wire 12 is much higher because the bond wire 12 reflects due to its surface quality with only minor losses, but the chip surface scatters very strongly.

5A and 5B, from which it can be seen that, depending on the course of the bonding wire, the region 28 of the bonding wire 12 reflecting into the camera 14 can be of different lengths.

The effect of the illumination of a bond wire from two directions is shown again in FIGS. 2A-C. This then results in a brightness pattern 26 for the background, a brightness image 28 for the area in which the respective bonding wire 12 reflects, and a brightness pattern 27 which corresponds to a shadow which the respective bonding wire casts on the background for each of the images . With simultaneous illumination or difference measurement, the image according to FIG. 2C results, in which the (dark) shadow region 27, which in the two images according to FIGS. 2A and 2B lies at the same point (in the XY plane), is rich in contrast against the lighter background. This corresponds to a reversal of the image compared to the examples shown above.

A further preferred embodiment is described in more detail below with reference to FIGS. 6 and 7.

REPLACEMENT SADDLE In this embodiment, instead of a multiplicity of light sources löa-I6n, an illumination unit consisting of a plurality of white light sources 31 is provided, the light of which is transmitted through a color filter 32 attached in a holder 22 to the chip 10 to be examined. The color filter 32 is designed such that a defined color is assigned to each lighting direction. For example, the color filter 32 in FIGS. 6 and 7 can run through the color spectrum from blue to red from bottom to top. It comes here

10 indicates that each direction from which the chip 10 is illuminated can be assigned a specific color.

The camera 14 is designed as a color camera, so that a signal (analog or digital) can be obtained from its output signal via a color signal converter 30, from which those color values are extracted, which directions of useful lighting, and those color values are suppressed which correspond to unfavorable directions of illumination.

6 can also be a section through a

20 hollow spherical lighting device (with camera) can be understood, the color filter then being preferably axially symmetrical to the optical axis 0 of the camera 14.

In the preferred embodiment shown in FIG. 8, the light from a (single) white light source 31 is sent through a prism 18 and broken down into its spectral components. The spectrum falls on the input ends of light guides L1-Ln, so that each light guide is assigned a color (wavelength)

30 is ordered and the light guide only emits light of this wavelength at its other end.

The other ends of the light guides L1-Ln are arranged in the holder 22 corresponding to the multiplicity of light sources 16a-16n 35 from FIG. 1, so that each light source 16a-16n, that is to say each light-guide end, has a light beam 11 -Inn speaks, which is directed to the chip 10. Here, too, the camera 14 is again a color camera, so that the lighting directions (useful lighting directions) identified as favorable

REPLACEMENT LEAF 10 can be defined as color values of the camera output signal.

For the list of characters

ln, m beam of light

Claims

1. A method for the automatic monitoring of the production of semiconductor components, in which the semiconductor components are illuminated by means of an illumination device and observed via a camera, the image output signals of which can be fed to an image signal processing device for recognizing manufacturing errors, the semiconductor component to be examined taking at least a first reproducible illumination angle region is illuminated and, on the basis of image or brightness and / or color contrasts, linear regions such as contours, edges, wires or the like are determined in a pattern recognition process with regard to their position data in such a way that the position data are also determined Predefined standard data are comparable, characterized in that the illumination of the semiconductor components takes place from a certain number of directions when the camera is stationary, with several useful directions of illumination being determined from the image signals earth, each of which enables detection of at least a section of the line-shaped regions, and that the semiconductor components are illuminated from the useful lighting directions in order to record image signals from which the position data can be determined.

2. The method according to claim 1, characterized in that the useful lighting directions are determined by means of a limited number of sample semiconductor components and are used for checking further series components.

3. The method according to any one of the preceding claims, characterized in that the lighting intensity (amount of light per Raumwin¬ angle and time unit) for the different lighting directions is chosen such that optimal contrasts between the sections and the image signals belonging to the environment arise.

4. The method according to any one of the preceding claims, d a d u r c h g e k e n n z e i c h n e t that the lighting from the various illuminating directions with the aid of light of different Wavelengths or colors or color combinations.

5. The method according to any one of the preceding claims, characterized in that a limited field, in particular a start and / or an end area is defined, within which the linear area must lie, and that the (subsequent) pattern recognition method on an evaluation of image signals within this Area is carried out limited.

6. Device for performing the method according to one of the preceding claims, with lighting devices (16) for illuminating the semiconductor components (10), a camera (14) for image recording and an image signal processing device (17) for detecting manufacturing errors of the Semiconductor component (10), characterized in that the lighting devices (16) are designed and arranged to form a semiconductor component to be examined in such a way that it can be illuminated from defined useful lighting directions, which are based on a pattern recognition method with the aid of the image signal processing device (17 ) can be determined.

7. The device according to claim 6, d a d u r c h g e k e n n z e i c h n e t,

REPLACEMENT3LATT that the lighting devices (16) comprise a plurality of individual lighting sources (16a-16n).

8. The device according to claim 7, d a d u r c h g e k e n n z e i c h n e t that the individual lighting sources (16a - 16n) comprise LEDs.

9. Device according to one of claims 6 or 7, so that the individual lighting sources (16a-16n) comprise first ends of light guides, in the second ends of which light of different colors can be introduced.

10. The device according to claim 6, characterized in that the lighting devices (16) comprise a light-emitting surface (29) which is designed such that different light spectra (colors) are assigned to different locations of the light-emitting surface, and that the camera (14 ) is formed for generating image signals which include color signals.

REPLACEMENT LEAF