JPS5928988B2 - Evaluation method for metal corrosion - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal corrosion evaluation method used for evaluating corrosion of metal patterns in ICs.

A conventional method for evaluating At corrosion in an IC will be explained with reference to FIG.

First, the sasopuru to be evaluated is divided into chips and assembled (Fig. 1a). Next, the assembled sample is subjected to the pressure-jerker test (FIG. 1b). During this period, electrical characteristics such as circuit function, element characteristics, metal resistance, etc. are periodically measured (FIG. 1c). Finally, MTTF (mean time failure) and median life are calculated from the measurement data, and quantitative evaluation of At corrosion is performed (Fig. 1d). However, this method has the disadvantage that it takes a very long time to produce results because samples are assembled and evaluated.

The present invention has been made in view of the above points, and an object of the present invention is to provide a metal corrosion evaluation method that can evaluate corrosion of a metal pattern in an ICK in a wafer state in a short time.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing a first embodiment of the invention.

As shown in this figure, in the first embodiment, a sample in a wafer state is first subjected to a pressure vacuum test under conditions of, for example, 120° C., 2Ay/Cd, and 50H (FIGS. 2a and 2b). Thereafter, the reflectance curve of the sample is measured (FIG. 2c). The third reflectance curve measurement device
As shown in the figure. To explain this device, 1 is a W (tungsten) or deuterium lamp, and the light from this lamp 1 is made monochromatic by a grating spectrometer 2, and then divided into double beams VC by a rotating mirror 3. One of the lights 4 passes through reflecting mirrors 61 and 62 and is directly incident on the detector T. The other light 5 is incident on the sample 10 via a reflecting mirror 60, a half mirror 8, and an objective lens 9. Then, the light reflected by the susable 10 is returned to the objective lens 9,
The light passes through a half mirror 8 and enters a detector 7, and the detector 7 measures the ratio of the intensities of the light 4 and the light 5.
The results are displayed on the display device 11VC. Display. Such a reflectance curve measuring device is provided with an illumination device 13 for focusing the sample 10. Further, a microscope (not shown) for observing the sample 10 is provided. To describe the measurement using the above device in detail, first, the sample 10 is irradiated by the illumination device 13, and the focus is focused on, for example, a bonding pad using a microscope.

Next, the illumination device 13 is turned off, and the wavelength of at least 400 to 5
The sample 10 is irradiated with light 5 having a wavelength of 00 nm, and its reflectance curve is measured. Once the reflectance curve has been measured in this way, next, from the reflectance curve, the wavelength 400
Reflectance R4OO at nm and reflectance R at wavelength 500 nm
,OO, ΔR=(R4OO−R,OO)/R5OO
is calculated, and the degree of corrosion is quantitatively evaluated based on the magnitude relationship of ΔR (Fig. 2 d). The reason for evaluating the degree of corrosion using ΔR will be described below.

FIG. 4 shows reflectance curves for various samples. Curve a is a reflectance curve of uncorroded At, which has a characteristic that it decreases monotonically as the wavelength becomes shorter. On the other hand, if this is corroded using the pressure tester test PCT,
Reflectance curves B, c, and d are obtained depending on the degree of corrosion. This can be explained as follows. FIG. 5 is a diagram schematically showing the behavior of reflected light on the sample of reflectance curves A, b, c, and d in FIG. 4.

As shown in FIG. 5a, when At on the Si substrate 15 is not corroded, its skin depth is small, so the incident light 16 is reflected at the very surface of Atl4, and only the reflected light 17 from the surface of Atl4 is reflected at the surface of Atl4. Enter the detector 7 of the device in Figure 3, A
t (curve a in FIG. 4). On the other hand, when corroded, At
Since the corrosion layer 19 such as (0H)3 is formed, the reflected light is divided into the reflected light 18 from the surface of the corrosion layer 19 and the residual Atl4'
Both of the reflected lights 17' and 1r from the surface cause interference. However, the z reflected light 17' from the surface of the residual Atl4'
, 17I are attenuated depending on the thickness of the corrosion layer 19 due to absorption effects. Therefore, when the corrosion layer 19 is thick as shown in FIG. 5c, the intensity of the reflected light 17I from the surface of the residual Atl 4' is weaker than that of the reflected light 17' when the corrosion layer 19 is thin as shown in FIG. 5b. Become. Also, of course, the reflected light 17' is weaker than the reflected light 17 from Atl4 when there is no corrosion. From the above, the reflection characteristics when corrosion occurs are a combination of the reflection characteristics of the corroded layer surface and the reflection characteristics of the residual Al surface. In this case, if the corroded layer is thick, the reflective properties of the corroded layer surface become more dominant of both components. Therefore,
Even if corrosion occurs, the reflectance curves in Figures 5b and 5c are different; in the case of Figure 5b, the curve b in Figure 4 is the same, and in the case of Figure 5c, the curve c in Figure 4 is different. becomes. Next, when the corrosion progresses and all At turns into a corrosion layer 19 as shown in FIG. 5d, the reflected light 18 from the surface of the corrosion layer 19
Therefore, the reflectance curve becomes curve d in FIG. 4, which is different from the reflectance curve of At (curve a in FIG. 4). A deceased person, A
The reflection characteristics of the corrosion layer consisting of t(0H)3 are at a wavelength of 450
It increases from around nm. In order to utilize the point that the reflectance curve changes according to the degree of VCAt corrosion as described above, the reflectance R, OO at a wavelength of 500 nm where no interference effect is observed, and the reflectance depending on the degree of At corrosion are determined. From the reflectance R4OO at the wavelength of 400 nm where it changes the most, ΔR=
(R4OO−R5OO)/R,OO was used as a parameter for corrosion degree evaluation.

As described above, in the first example, the reflectance curve of the sample after being subjected to the pressure Kutzker test was measured,
From the reflectance curve, the reflectance R4O at a wavelength of 400 nm
ΔRO(
By calculating R4OO-R5OO)/R,OO, ΔR
Since the degree of corrosion is quantitatively evaluated based on the magnitude relationship of , it is possible to evaluate the corrosion of metal patterns on ICs in a short time on a wafer.

In the first embodiment, it was explained that the degree of corrosion can be evaluated using the ΔR value, but even if interference waves on the long wavelength side shown by the reflectance curve c in Fig. 4 are used, corrosion can be evaluated based on the relationship between the thickness of the corroded layer. It is possible to quantitatively evaluate the degree of

This is the second embodiment, and in this case,
After subjecting the sample to the Pressure-Jakutsker test, the reflectance curve of the sample was determined using the equipment shown in Figure 3.
Measured at one position, and from the reflectance curve, d=? 2nΔK (where n: refractive index of the corroded layer, ΔK: wave number difference between interference peaks) is calculated, and the degree of corrosion is quantitatively evaluated based on the magnitude relationship of the thickness d of the corroded layer.

This second embodiment also provides the same effects as the first embodiment. As detailed above, in the present invention, after subjecting a sample to the Brassier Kutzker test, the reflectance curve of the sample is measured,
From the reflectance curve, ΔR=? Calculate Rλ - refractive index, ΔK: wave number difference between interference peaks),
Since the degree of corrosion is quantitatively evaluated based on the magnitude relationship of ΔR or the thickness d of the corrosion layer, the corrosion evaluation of the metal pattern at C can be performed in a short time in the wafer state.

Therefore, the present invention can be used to analyze various factors affecting metal corrosion, and to evaluate the effectiveness of post-treatment for removing corrosive substances that are generally adsorbed during metal dry etching.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the procedure of the conventional At corrosion evaluation method, Fig. 2 is a diagram showing the procedure of the first embodiment of the metal corrosion evaluation method of the present invention, and Fig. 3 is a reflectance curve measuring device. Fig. 4 is a diagram showing a typical example of a reflectance curve measured using the apparatus shown in Fig. 3, and Fig. 5 shows the behavior of reflected light on a sample of the reflectance curve in Fig. 4. It is a figure shown typically. 1... Lamp, 4, 5... Shu, 7... Detector, 10...
··sample.

Claims (1)

[Claims] 1. In metal evaluation of metal patterns in IC,
First, the sample to be evaluated is subjected to the Pressure Schucker Test PCT, then the reflectance curve of the sample is measured, and from the reflectance curve, the reflectance Rλ_1 at the wavelength λ_1 is calculated.
and reflectance Rλ_2 at wavelength λ_2, ΔR=(Rλ_
1-Rλ_2) (Rλ_2) and evaluating the degree of corrosion based on the magnitude of ΔR. 2 Wavelength λ_1 is 400 nm, wavelength λ_2 is 500 nm
A method for evaluating metal corrosion according to claim 1, characterized in that: 3 In evaluating corrosion of metal patterns in ICs,
First, the sample to be evaluated is subjected to the Pressure Schucker Test PCT, and then the reflectance curve of the sample is measured. From the reflectance curve, d = (1) / (2nΔK) (where n: the refractive index of the corroded layer) , ΔK=wave number difference between interference peaks), and evaluates the degree of corrosion based on the relationship between the thickness d of the corrosion layer.