JPS596059B2 - Semiconductor surface identification device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for identifying the surface of a semiconductor chip, particularly an electrode position, used in a semiconductor device assembly apparatus or the like.

When wire bonding is performed on the surface of a light-emitting semiconductor chip such as GaAsp or GaP on which an electrode is formed, the surface of the semiconductor chip is irradiated with light and the reflected light is projected through an ITV camera to read the electrode position. The direction and amount of movement of the capillary for wire supply are controlled.

Here, while the light-emitting semiconductor chip has a relatively mirror-finished surface, the lead frame to which the chip is attached has a severely uneven surface and causes most of the light to be diffusely reflected when it is irradiated with light. Therefore, when a lead frame to which a semiconductor chip is attached is irradiated with light, it is relatively easy to recognize the semiconductor chip area with respect to the lead frame. However, in a wire bonding process, etc., it is insufficient to simply recognize the semiconductor chip area; in order to perform highly accurate bonding, it is necessary to reliably recognize the positions of electrodes formed on the semiconductor chip surface. The present invention provides a semiconductor surface identification device that can easily recognize electrode regions formed on a semiconductor chip by utilizing the light absorption characteristics of a semiconductor substrate.

First, the principle of the present invention will be explained. Band cap (Eg)
When a semiconductor substrate of is irradiated with light with an energy (Reν) larger than this band gap (Eg), the absorption of light is theoretically expressed as α・Reν=B(Reν above g)2 It will be done.

where α: absorption coefficient, ν: photon energy, B:
Constant and Eg: band gap. '' When irradiated with light with energy smaller than the energy gap Eg of the semiconductor substrate, the light passes through the semiconductor substrate.On the other hand, light irradiated onto the electrode portion formed by a metal film on the surface of the semiconductor substrate does not pass through. Therefore, in order to recognize the position of the electrode formed on the surface of the semiconductor substrate c, the light to be irradiated onto the surface of the semiconductor substrate should be selected to have an energy smaller than the energy gap Eg. In addition to immediately reflecting the light, the irradiated light is made to enter the semiconductor substrate at the semiconductor substrate portion, and the incident light is diffusely reflected or absorbed by the bottom surface of the semiconductor substrate to minimize the light that exits to the surface of the semiconductor substrate. Electrode position information can be obtained by producing a clear difference from the reflected light from the part.5 Next, the present invention will be explained in detail with reference to Examples.

In FIG. 1, reference numeral 1 denotes a semiconductor chip, for example, a light emitting diode, which is vertically fixed to a lead frame 2. On the surface of the semiconductor chip 1, there is a chip, for example, almost the entire surface of the chip, as shown in FIG. An electrode 11 made of a thin metal film such as Al is located in the center.
A peripheral part 12 surrounding the electrode 11 constitutes a light emitting part of the semiconductor substrate, and the surrounding area of the light emitting part is covered with an oxide film 13.

The semiconductor chip 1 is bonded to a lead frame 2 at the surface opposite to the surface on which the electrodes 1 are provided. A conductive adhesive or the like is used for the adhesive surface of the semiconductor chip 1 with the lead frame 2, but the bottom surface of the semiconductor chip 1 prevents specular reflection so that the light incident on the semiconductor substrate is not directed in a fixed direction. The surface may be textured to cause diffuse reflection, or an adhesive with light absorption properties may be used. An ITV camera 4 is installed facing the semiconductor chip 1 and receives light from the semiconductor chip surface via an optical system 3 to form an image corresponding to the incident light. The optical system 3 includes a halogen lamp 5 having light emission characteristics as shown in FIG.
is provided as a light source, and irradiates the surface of the semiconductor chip 1 with light. On the optical path between the light source 5 and the semiconductor chip 1,
For example, a filter 6 is inserted at position A or position B to select the emitted light from the light source 5. The semiconductor chip 1 is G
aASO. 6pO. 4, the energy gap Eg is approximately 1.9e, and this energy gap corresponds to a wavelength of approximately 650 nm, so the filter 6 transmits light longer than light with a wavelength of 650 nm. A filter 6 having transmission characteristics as shown in FIG. 4 is installed at position A or position B. Figure 5a
is a video output signal projected onto the camera 4 through the optical system in which the filter 6 is installed, and FIG. 5b shows the video output signal after being further amplified through an operational amplifier.

As is clear from the video output signal in the same figure, the video output signal also has signals A and b of different levels corresponding to the outer shape A, the light emitting area B, and the electrode area C of the semiconductor chip 1 shown in FIG.
, e are output and even without amplification processing, the output signal in electrode area C is 20 to 40 m higher than that in the surrounding semiconductor substrate area B, and if amplification processing is performed, a level difference of about 1V can be obtained. I can do it. By setting the slice level to an appropriate value between the level differences based on the occurrence of level differences in the output signals in this way, the electrode positions can be recognized from the binarized video signal. i.e. electrode)
The light irradiated on the semiconductor substrate section 11 is reflected and reaches the camera 4, but the light irradiated on the semiconductor substrate section 12 has optical energy smaller than the band gap, so it enters the inside of the substrate rather than being reflected and reaches the bottom of the substrate. reflected or absorbed.

Therefore, almost no light reaches the surface of the semiconductor substrate and enters the camera 4, and a difference in intensity occurs between the light reflected from the electrode section and a level difference in the output signal between the semiconductor substrate section and the electrode section. , the surface condition of a semiconductor chip can be recognized. 6a and 6b show the video output signal of the camera 4 and the video output signal obtained when the surface of the semiconductor chip 1 is irradiated with light emitted from the light source 5 without interposing the filter 6. This shows the output signal after amplifying the .

Since the filter 6 is not inserted, light with energy greater than the band gap is also irradiated, and this high energy light is reflected by the semiconductor surface and transmitted to the camera 4.
and contributes to the formation of a video output signal. Therefore, there is no clear level difference between the video output signals from the semiconductor substrate region and the electrode region, and it is extremely difficult to distinguish between the two regions. As described above, according to the present invention, in an apparatus for recognizing electrodes formed on a semiconductor chip, the semiconductor chip is irradiated with light having an energy smaller than the bandgap of the semiconductor material, and the light reflected from the electrode portion and the semiconductor By creating a clear difference in the level of the video output signal formed by the camera between the light incident on the substrate and the level of the video output signal formed by the camera, the electrode position can be recognized easily and more reliably, making it particularly useful in the assembly of semiconductor devices. It is possible to improve assembly accuracy in processes such as wire bonding and improve the reliability of semiconductor devices.

The present invention is not limited to the vertical epi-illumination method as in the embodiment, but can be similarly implemented in the case of a reflective method in which illumination is performed obliquely at an angle θ (0<θ<90 limit).

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment according to the present invention, FIG. 2 is a front view of a semiconductor chip, and FIG. 3 is a diagram of light emission characteristics of a light source.
Figure 4 is a transmission characteristic diagram of the filter, Figures 5A and b are video output signal diagrams when the filter according to the present invention is used, and Figures 6A and b are video output signal diagrams when the filter is not used. . 1: semiconductor chip, 11: electrode section, 12: semiconductor substrate section, 3: optical system, 4: IT camera, 5: optical system, 6: filter.

Claims (1)

[Scope of Claims] 1. An apparatus for forming an image of a semiconductor chip surface having an electrode region formed on the surface, comprising: an optical system that projects light with an energy smaller than the bandgap of a semiconductor chip substrate; A semiconductor surface identification device comprising an image forming means for forming a video output signal using an image of a chip surface as an input signal. 2. The semiconductor surface identification device according to claim 1, wherein the semiconductor chip is mounted on a lead frame whose surface is processed to have a diffused reflection surface or a light absorption surface.