JPH03197878A - Light wave interference type ic tester - Google Patents

Abstract

PURPOSE:To decide whether or not heat diffusion is normal as to all ICs in a short time of several seconds by analyzing a heat expansion process pertaining the heat generation of an IC by a light wave interference type displacement gauge and a differentiating means. CONSTITUTION:A body 80 to be measured is moved by an XY stage 60 which is controlled by a control means 10 and an XY stage controller 30 so that a specific place is irradiated with a laser spot which is converged by an objective lens 90. Then an IC driver 40 which is controlled by the control means 10 as well supplies a specific current to a part to be measured and the body 80 to be measured generates heat. The quantity of heat expansion (displacement quantity) of the body 80 to be measured which expands thermally by the heat generation is measured extremely accurately to order of angstrom by, for example, the light wave interference type displacement gauge 100 which uses the phase shift of reflected light from the body 80 to be measured. Consequently, if can be decided whether or not the heat diffusion is normal as to all the ICs in a short time of several seconds.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a light wave interference type IC tester for ICs typified by LSI, ULSI, and the like.

(Prior Art) Currently, all large-scale systems represented by electric power, railways, banking, etc. are made up of semiconductor ICs such as LSIs, and their integration and density are progressing at an accelerating rate year by year.

It has been pointed out that the higher integration and density of ICs increases the heat generation of the ICs themselves, leading to thermal deterioration of the ICs, shortening their lifespans, and resulting in system failures.

Conventionally, tests for such semiconductor ICs include operating life tests consisting of continuous and intermittent operation tests, shelf life tests consisting of high temperature storage life tests, low temperature storage life tests, etc.
Alternatively, environmental tests consisting of temperature cycle tests and thermal shock tests were conducted.

(Problem to be Solved by the Invention) However, the above test was a sampling test, and each test required an enormous amount of time, 1000 hours. In addition, it is difficult to conclude that there is a complete correlation with element life in forced deterioration tests in which the stress is increased above the rated value, and it also takes time.

The present invention was made in order to solve the above-mentioned problems, and the thermal expansion process accompanying the heat generation of an IC is analyzed by thermal diffusion using a light wave interference displacement meter and a differentiator. An object of the present invention is to provide a light wave interference type IC tester that can determine the quality of thermal diffusion of an IC.

(Means for Solving the Problems) In order to achieve this object, the present invention provides a method for causing a predetermined current to flow through a predetermined element in an object to be measured, such as an IC, such as a transistor or a resistor, to generate heat. An IC driver, a light wave interference type displacement meter for measuring thermal expansion due to the heat generation, a differentiating means for measuring a differential value from a time change in the amount of thermal expansion, and a laser spot at a predetermined position on the object to be measured. It is equipped with an XY moving means for setting.

(Function) In the present invention having the above configuration, the XY moving means moves the object to be measured so that a predetermined position is irradiated with a laser spot. The IC driver causes a predetermined current to flow through a predetermined element of the object to be measured to generate heat. The light wave interference type displacement meter measures the amount of displacement caused by expansion due to heat generation, and determines whether the object to be measured is good or bad based on the output of the differentiating means.

(Example) Hereinafter, an example in which the present invention is integrated will be described with reference to the drawings.

FIG. 1 shows a block diagram of the present invention.

The IC/LSI sample, that is, the object to be measured 80 is
The laser beam is moved by an XY stage 60 controlled by a control means 10 and an XY stage controller 30 so that a laser spot focused by 0 is irradiated onto a predetermined location. Thereafter, the device under test 80 is controlled by the IC/LSI driver 40 which is also controlled by the control means 10.
As a result, a predetermined current is passed through the measurement point, causing it to generate heat. The object to be measured 8 has thermally expanded due to heat generation.
For example, the amount of thermal expansion (displacement) of 0 is based on the phase change of the reflected light from the object to be measured 80.
The measurement can be performed very precisely on the order of angstroms using a light wave interference type displacement meter 100 such as No. 977 (optical heterodyne interference surface shape measuring device).

For example, if the object to be measured 80 is an IC, the resistance R in the IC
The amount of temperature rise ΔT when a current I is passed through for t seconds is given by the following equation.

△T-12R/λ-[1-exp (-λt/me)] Where, m: Mass of IC chip c: Specific heat of IC chip t: Time Also, the relationship between the amount of thermal expansion ΔL and the amount of temperature rise △T is simply △L=to・L・△T, so △L(λ)=to・L−I2R/λ・[1−exp
(-λt/mc)]...(1
) However, a constant of proportionality is established, and the displacement amount ΔL measured by the light wave interferometric displacement meter 100 is a function of the thermal conductivity λ. In other words, I.C.
/When the LSI chip has no voids or poor adhesion and the heat sink is good, the thermal conductivity λ is sufficiently large, so the curve representing thermal diffusion as shown in Figure 2 is formed, and the differential coefficient at 1=0 is αo, t = The differential coefficient at i is α1, and their ratio is the coefficient ratio r, then r=al/α0=exp (-λt / m c )λ
, mSc>0, and r(1. In other words, this means that thermal diffusion is working as designed and the IC life will be longer. However, there are voids and When there is poor adhesion and the heat sink is insufficient, the thermal conductivity λ becomes relatively small, so equation (1) is approximated by equation (2).
The linear shape is expressed as .

△L(λ)=ni・L−I2R/mC−t・・・・・・(
2): Constant of proportionality This can be expressed graphically as shown in Figure 3. In other words, heat diffusion is insufficient, and heat accumulates unilaterally. Similarly, if we take the coefficient ratio r when 1=0 and t=1, then r
= 1. In other words, the smaller the thermal conductivity λ, that is, the closer the coefficient ratio r is to 1, the worse the heat sink of the IC/LSI chip is, that is, the shorter the life span.

In other words, the user uses, for example, r sh = 0 as a criterion.
By selecting a value between .degree.5 and 0.6, the control means can judge whether the heat diffusion of the IC/LSI chip is good or bad, that is, whether the product is good or bad. The relationship between the coefficient ratio r and the thermal conductivity λ is shown in FIG. 4, and the relationship between the coefficient ratio r and the life span is shown in FIG.

Next, a method for determining this r will be specifically explained based on an example.

First, the control means 10 sends a predetermined code to the IC driver 40 via the bus 20 based on a program.

The IC driver 40 decodes the code and causes a pulse current to flow through a predetermined element. At the same time, the control means 10
A measurement trigger signal is sent to the timing generation circuit 230 of the differentiator circuit 50 via the bus 20 . Timing generation circuit 23
0 sends a latch signal to the latch 1 in synchronization with the measurement trigger signal and takes in the data of the light wave interference type displacement meter 100 in the buffer 200 to the latch 1. Next, for example, 0.01
After a second, a latch signal is sent to latch 2, and data after 0.01 seconds is taken into latch 2. The data in latch 1 and latch 2 are subtracted by a subtraction circuit 240 to calculate a differential value αO at t=0, which is then taken into latch 3 at the next timing. This data is output to the bus 20 and stored in the RAM 10I by the control means 10.

After one second, the control means 10 again activates the timing generation circuit 230.
A measurement trigger signal is issued at , and the differential value α1 at t=1 is obtained through the same process. and r=α1/αO
The calculation is performed and the judgment is made by comparing with the pass/fail judgment criteria rsh inputted in advance by the user. Therefore, the measurement time that conventionally required about 1000 hours is only a few seconds in this embodiment.

In the above embodiment, the differentiating circuit is constructed of a digital circuit as shown in FIG. 6, but as a modification, an analog differentiating circuit as shown in FIG. 7 may be used. In addition, various other circuits can be considered for extracting the characteristics of this thermal diffusion curve, although they are not illustrated, and modifications are permitted as long as they do not depart from the main idea.

(Effects of the Invention) As is clear from the detailed description above, according to the present invention, a specific part of an IC is energized and heated by an IC driver, and the amount of expansion is measured by a light wave interference displacement meter, for example, on the order of angstroms. This method is revolutionary compared to conventional technology, which takes time, as it measures accurately and uses a differentiator to determine the change in displacement to determine the quality of thermal diffusion, in other words, to estimate the future life of the semiconductor IC. It can be measured at a speed of Of course, it goes without saying that it is non-contact and non-destructive. Furthermore, while the conventional technology involves sampling inspection, the present invention allows for easy inspection of all parts, contributing to the reliability of semiconductor ICs.

[Brief explanation of drawings]

Figures 1 to 7 show embodiments embodying the present invention. Figure 1 is a system block diagram, and Figure 2 shows time and heat in the case of high thermal conductivity, that is, a good product. FIG. 3 is a diagram illustrating the relationship between the amount of expansion and time for a product with low thermal conductivity, that is, a defective product. FIG. FIG. 5 is a diagram illustrating the relationship between the coefficient ratio r and the overall thermal conductivity λ, which is a judgment criterion; FIG. 5 is a diagram illustrating the relationship between the coefficient ratio and IC life;
The figure is a block diagram of the differentiating circuit, and FIG. 7 is a diagram showing a modification of the differentiating circuit. 0 0 0 0 0 0 0 0 00 Control means XY stage controller IC controller Differential circuit XY stage IC board Semiconductor IC Objective lens Light wave interference type displacement meter

Claims (1)

[Claims] An IC driver that specifies an element or wiring in an IC and causes it to generate heat by passing a predetermined current through it; and a light wave interference system that irradiates light to the specified location and measures the amount of thermal expansion, or displacement, from the phase change of the reflected light. 1. A light wave interference type IC tester comprising a type displacement meter, a differentiating means for measuring a change in the amount of displacement over time, and an XY moving means for setting a laser spot at a predetermined location on an object to be measured.