JPS60122308A - Evaluating method of bonding - Google Patents

Abstract

PURPOSE:To evaluate the quality of bonding quantitatively and accurately by projecting a parallel light beam upon an aluminum vapor-deposited film which is adhered to a base and to which a wire is bonded almost at right angles. CONSTITUTION:A light source 6 is provided at one terminal of an optical path body 5 and two lenses 7 and 7 for making light from the light source 6 into a circular parallel light beam are provided at the center part of the optical path body 5. Then, a mirror 8 slanting at a specific angle to the other terminal of the optical path body 5 so that the parallel light beam transmitted through the lenses 7 and 7 is incident at right angles to the surface of the wafer 2 through a through hole 4. consequently, it is possible to discriminate between the crystal growth of vapordeposited aluminum which is hardly found by visual inspection and the influence of residual gas, thereby pevaluating the quality of bonding quantitatively and accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a bondability evaluation method for evaluating the bondability of a wire to an aluminum vapor-deposited film.

[Technical background of the invention and its problems]

In the production of semiconductor products, forming an aluminum vapor deposition film is an essential step. That is, thin aluminum or gold wires are used to connect one individual device to an external terminal, and an aluminum vapor-deposited film is used as a thin film to which these thin wires are bonded. therefore,
Aluminum vapor deposited films are always required to have stable bonding properties. Conventionally, the above-mentioned bonding property is judged as good or bad.

Visual inspection of the surface of the wafer on which the aluminum deposited film was deposited was relied upon. Generally, the surface of an aluminum vapor deposited film loses its smoothness and becomes rough due to the influence of residual gas in the aluminum vapor deposited film, so that it appears cloudy when visually observed. In this case, the surface of the aluminum vapor deposited film becomes rough and the bonding properties deteriorate. Therefore, by visually inspecting whether the surface of the aluminum vapor deposited film is cloudy,
It is possible to judge whether the state of aluminum vapor deposition is good or bad. However, if the wafer temperature is raised during vapor deposition.

Alternatively, if the film thickness is increased to 2 μm or more, bonding properties are not affected, but aluminum crystals grow, so even in these cases, the aluminum vapor deposited film is affected by residual gas. The surface appears white, just like when it is washed. As a result, in visual inspection, cloudiness due to residual gas was often confused with cloudiness due to crystal growth, and a product whose surface became whitish due to the crystal growth was erroneously judged as having poor bonding properties. Therefore, there is a need for a method that can quantitatively distinguish between the two.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a bonding performance evaluation method that can quantitatively and accurately evaluate the quality of bonding of a wire to a chika layer. do.

[Summary of the invention]

Parallel light is projected onto the aluminum vapor deposited film whose bonding properties are to be evaluated, and the reflected light from the aluminum vapor deposited film at this time is photoelectrically converted to obtain a reflection distribution curve.The aluminum vapor deposition of the wire is performed based on the reflection distribution curve. It is designed to judge whether the bonding property to the film is good or bad.

[Embodiments of the invention]

The present invention will be described below based on one embodiment with reference to the drawings.

FIG. 1 shows a bondability evaluation device used in the bondability evaluation method of this embodiment. In this figure, a wafer (2) made of single-crystal silicon (St) is placed on the inside bottom of a housing (1) that can be opened and closed by a door (not shown) and a dark box that blocks external light. Placement stand (3)
is provided. A through hole (4) is provided in the center of the upper plate of the housing (1), and both ends of the outer upper part of the housing (1) including the through hole (4) are sealed to block outside light. A completely blocking cylindrical light path body (5) is attached.

A light source (6) is provided at one end inside the light path body (5), and two light sources are provided at the center of the light path body (5) to convert the light from the light source (6) into parallel rays with a circular cross section. lens (7
), (force is provided. The part of the other end of the optical path body (5) that contacts the top of the housing (1) is open and communicates with the first through hole (4). , the other end of the optical path body (5) is provided with a light beam (8) so that the parallel light beam that has passed through the lens (7) i7) enters the surface of the wafer (2) perpendicularly from the through hole (4). It is tilted at a certain angle. And the optical path body (5) and the light source (6).

The lens (power, (7), fi mirror 8) is the light projecting part (9)
It consists of Furthermore, on the inside upper part of the casing (1), on the wafer (2), the parallel light rays from the circular light source (6) are evenly distributed at 45° intervals around the normal P set at the center a@ of the parallel light rays from the circular light source (6). (See Figure 2), and eight rod-shaped photoreceptors (lla) formed in an arc centered on the center 00, (I
lb)... is installed. That is, the photoreceptor (
Ila), (llb) is the photoreceptor (IIC) in the X direction.
, (lld) are photoreceptors (11e), (o
f) is arranged in the R1 direction, and the photoreceptors (IIJ) and (llb) are arranged in the R2 direction, and these photoreceptors (lla
), (llb), (IIC), (lid),'
(IC), (llf), (ll'f).

(llh) is installed along a great circle on the same spherical surface centered on the center α0. Furthermore, each of the photoreceptors (11a), (Ilb)... has the normal P set to 0.
A light receiving element (121...) such as a photo diode or a solar cell is fitted at every 10 degrees as 10 degrees to receive the diffusely reflected light from Ueno (2).
By specifying a certain light receiving element (12+), the reflection angle can be determined.
), photoreceptor (lla), (llb) ・, photoreceptor (
LJ... constitutes a light receiving section (131). On the other hand, as shown in FIG. (I4) is connected separately to the input side of
The output side of this changeover switch I is connected to the input side of an analog-to-digital converter (IQ) via an amplifier Q5. Part (1
7) is connected to the input side. Furthermore, the output side of the arithmetic control section side.

For example, it is connected to a display section 08 such as a cathode ray tube or a printer.

Next, the bonding property evaluation method of this example will be described.

First, a wafer (2) coated with an aluminum vapor-deposited film whose bonding properties are to be evaluated is placed on a mounting table (3) in a casing (1) that is shielded from external light. Afterwards, the light source (
6) A parallel ray is projected from the lens (7), (7) and a mirror (8) in the direction of the arrow (11), that is, in a direction orthogonal to the wafer (2) surface.This parallel ray is incident. Light is reflected from the surface of the wafer (2).Of the reflected light, diffuse reflection light is transmitted to each light receiving element (11)...
An electrical signal SA whose size corresponds to the amount of light received at
It is converted to... The electrical signal SA... is simultaneously input to the change-over switch α and sequentially output to L amplifiers (L), and the amplified electrical signal SA... is analog - output to the digital converter σ6).The electrical signal SA... amplified in this analog-to-digital converter α0 is converted into a digital signal SB..., and these digital signals SB... The arithmetic control unit (I7) outputs the received light from each light receiving element α in each direction of the X direction, Y direction, AI direction, and R2 direction. In other words, a digital value proportional to the amount of light reflected from the surface of the wafer (2) is stored in the memory Ml together with the value of the corresponding reflection angle.
In the memory M2 of the arithmetic control unit αη, the digital value of the reflected light when the surface of the wafer (2) is normal, that is, when it is in a mirror-like state, is stored in advance together with the corresponding reflection angle ( at the beginning of the test.

The data is stored in the memory M2 using the wafer (2) as a standard specimen. ). By the way, Figure 4 shows the wafer (
2) shows nine reflection distribution curves corresponding to various vapor deposition states of aluminum. Here, the reflection distribution curve (4) shows a case where the vapor deposition state is a good specular surface, and as the 1 reflection angle increases, the amount of reflection decreases rapidly. Conversely, near the reflection angle O0, the amount of reflection is extremely large. Most of the light reflected by the tab is specularly reflected, and there is almost no diffusely reflected light. In addition, the reflection distribution curve Q1) shows the case where, although the above-mentioned vapor-deposited aluminum becomes cloudy due to crystal growth, it does not impede the bondability of the wire to the vapor-deposited aluminum, and the reflection angle is 20-3
There is a maximum value near 0°, and as the reflection angle increases, the amount of reflection gradually decreases.

On the other hand, the reflection distribution curve Q4 is a case where the wire bondability to the vapor-deposited aluminum becomes cloudy due to the influence of residual gas, and the amount of reflected light becomes monotonous as the reflection angle increases. has decreased to There is no maximum value in the L reflection distribution curve except for the part at 1 reflection angle O0. Therefore, it is possible to clearly distinguish between the case where the vapor-deposited aluminum has grown as a crystal, which is difficult to distinguish by visual inspection, and the case where the vapor-deposited aluminum has been affected by residual gas from the shape of the reflection distribution curve.

Therefore, the calculation control unit αη obtains the reflection distribution curve of the wafer (2) based on the digital value indicating the amount of diffuse reflection stored in the memo IJMI and the reflection angle corresponding to the digital value. First, an integral value is calculated for this reflection distribution curve. Similarly, an integral value is calculated in advance for the wafer (2) serving as a standard specimen in the memory M2, and a reference value is set by setting an allowable limit for this integral value. In the arithmetic control unit (17), the integral value obtained based on the memory contents of the memo IJMI is compared with the reference value, and if it exceeds the reference value, it is determined that the bonding property is poor. do. Next, for the wafer (2) whose bondability has been determined to be poor, it is checked whether or not there are extreme values on both sides of the zero reflection angle region of the reflection distribution curve, and if there are extreme values.

Since this is a case where the aluminum vapor deposited film described above has grown as a crystal, this is re-judged as good bonding and excluded from the list of sea urchins with poor bonding.

On the other hand, if the maximum value does not exist, this is due to the influence of the residual gas mentioned above, so it is reconfirmed that the bonding is defective and is displayed on the 1 display section (1'I).

At the same time, the digital values stored in the memories M1 and M2 are simultaneously output for each reflection angle, and the inspector can visually check whether the judgment result by the arithmetic control unit αη is correct or not on the display unit α. Check.

Observe such reflection distribution curves in the X and Y directions.

This is carried out in the R1 direction and the R2 direction to determine whether the bonding properties of the vapor-deposited aluminum deposited on the wafer (2) are good or bad.

In addition, the light receiving elements αυ... are each light receiving body (10a), (
10b)...Although it is provided above, it is also possible to provide the light receiving element (Ll)... outside the housing (1) by using an optical fiber. Furthermore, each photoreceptor (10a),
(10b)... Each photoreceptor (10a), (10b)... can be covered by one photoreceptor (11) without fixing multiple photoreceptors (l)... on top. It may also be scanned.

In addition, various changes can be made without departing from the gist of the present invention.

〔Effect of the invention〕

As described above, in the bonding property evaluation method of the present invention, an object to be measured coated with vapor-deposited aluminum is placed in a case that is shielded from external light, and a parallel light beam perpendicular to the surface of the object is projected. Then, the diffusely reflected light is photoelectrically converted by a light receiving element,
The bondability of wires to vapor-deposited aluminum is determined based on photoelectrically converted electrical signals from the aluminum vapor-deposited film. To accurately distinguish between a case where there is no problem in bonding property due to crystal growth of aluminum and a case where bonding property is poor due to surface roughening of the aluminum vapor deposited film due to residual gas, based on the difference in the shape of the reflection distribution curve between the two. As a result, losses due to misjudgment are reduced and product yield is improved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of a bondability evaluation device used in a bondability evaluation method according to an embodiment of the present invention, and FIG.
The figure shows the arrangement of the photoreceptor and light-receiving element in Fig. 1, Fig. 3 is an electric circuit diagram of the bonding property evaluation device shown in Fig. 1, and Fig. 4 shows the reflection distribution curve from aluminum deposited on the wafer. FIG. (1): Housing, (2): Wafer (substrate). (6): Light source, a: Light receiving element. (2): Light receiving section, right? ): Arithmetic control unit. Agent Patent Attorney Noriyuki Chika (and 1 other person)...'';l-Note Yl''Ig JP-A-Sho GO-122308 (5) 7j12=' 12 Y 12 ' 11c T217. ( , //12 1312 ＼ If

Claims (1)

[Claims] tl is a step of projecting a parallel beam in a direction perpendicular to the aluminum vapor deposited film that is adhered to the substrate and to which the wire is bonded, and a process of projecting a parallel light beam onto the aluminum vapor deposited film on a spherical surface centered on the projection position of the parallel light beam. a step of receiving reflected light from the aluminum vapor deposited film along a great circle and converting it into an electrical signal indicating the amount of received light, and based on the electrical signal, the amount of received light and the projection position of the light receiving position corresponding to the amount of received light; The step of obtaining a reflection distribution curve showing the relationship between the reflection angle and the reflection angle with the normal direction set at zero; and a step of determining whether the bonding property is good or bad based on a large amount of light received in the diffuse reflection area of the reflection distribution curve, and the reflection distribution curve of the aluminum vapor deposited film whose bonding property is determined to be poor. A method for evaluating bonding properties, characterized in that an aluminum vapor deposited film having extreme values on both sides of a region in which the reflection angle is zero is re-judged to have good bonding properties.