JPS6246531A - Detection of etching end point of metallic layer - Google Patents

Abstract

PURPOSE:To prevent any side etching from happening by a method wherein a metallic layer on a wafer is etched while controlling the etching rate thereof so that the etching rate may be detected as a current value whose minimum value is considered to show an end point of the etching. CONSTITUTION:A different kind of metallic layer 31 is provided directly below a metallic layer 32. A wafer 3, a platinum plate 5 are immersed in an etching vessel 1. Current flows between an anode electrode 4 and a cathode electrode 6 through the intermediary of etching solution. The metallic layer 32 on the wafer 3 is etched controlling the etching rate thereof by properly setting up the current value using a variable power supply 7. When immersion time t2 elapsed, the etching process of metallic layer 32 is finished subject to the minimum current value of i1. Therefore the true etching terminal can be detected by means of setting up said current value i1 as the current value at etching terminal to check the current value for finishing the etching process.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting the end point of etching when patterning a metal layer by electrolytic etching.

2. Description of the Related Art In general, when forming wiring patterns for semiconductor devices, it is important to reliably confirm the end point of etching. Various methods for detecting the etching end point have been proposed and implemented depending on the type of etching.

Therefore, a method of detecting the end point of etching when forming a wiring pattern by electrolytic etching will be described as a conventional technique.

To carry out electrolytic etching, an anode electrode is connected to the facet of the wafer on which the metal layer to be etched is deposited and patterned with a resist as a mask;
Connect the cathode electrode to a separately prepared platinum plate.

Both electrodes are immersed in an etching bath. In this state, a current is passed between the two electrodes to pattern the metal layer while controlling the etching rate of the metal layer. Incidentally, in order to detect the end point of etching, an ammeter is connected between the two electrodes, and the amount of etching of the metal layer is detected as a current value. In other words, since the current value decreases as etching progresses, when the current value is minimum, this is determined to be the end point of etching. Note that after the etching end point of the metal layer, the metal layer covered with the resist, that is, the metal layer remaining as a pattern, is side-etched, so that the current value does not become zero but becomes a substantially constant current value.

The initial value of this current was determined as the end point of etching.

By the way, in electrolytic etching, the metal layer is etched from the periphery to the center of the wafer, so even if the metal layer near the facet where the anode electrode is attached is etched, , a metal layer may remain near the center of the wafer.The metal layer remaining near the center is not electrically connected to the anode electrode, so when the metal layer near the facets of the wafer is etched, the current will eventually flow. The value becomes the minimum, and this point becomes the end point of etching.

In this way, with the conventional method, even if the end point of etching is confirmed, there is a lump of etching residue near the center of the wafer, so it cannot be said that the true end point has been detected. , it was necessary to provide extra time for etching the etching residue. Moreover, during this estimated time, electrolytic etching is just 't+? It can be said that it is inefficient because it changes to R-etching, that is, chemical etching.

This invention was devised in view of the above circumstances, and the end point of etching can be detected when the metal layer near the center of the wafer has been etched, eliminating the need to provide an estimated time for etching the remaining etching as in the conventional method. It is an object of the present invention to provide a method for detecting the etching end point of a metal layer.

Means for Solving the Problems In order to achieve the above object, in the present invention, a different metal layer different from the metal layer to be etched is formed on all the wafers to be etched. This dissimilar metal layer is placed directly below the gold mN deposited on the wafer. Then, an anode electrode is attached to the facet part of the wafer,
A cathode electrode is attached to a separately prepared platinum plate, and both are immersed in an etching bath. In this state, a current is passed between the two electrodes to etch the metal layer of the wafer while controlling the etching rate of the metal layer. Moreover, an ammeter is connected between the anode electrode and the cathode electrode to detect the etching amount of the metal layer as a current, and the end point of etching is determined when this current value becomes the minimum. .

■ Even when the facet area of the wafer, that is, the area where the anode electrode is attached, is etched and the metal layer near the center of the wafer remains, the metal layer near the center is etched through the dissimilar metal layer directly below it. Since it is electrically connected to the anode electrode, the etching rate of the metal layer near the center is controlled until the end, and the current value becomes smaller until the metal layer is etched.

FIG. 1 is an explanatory diagram showing an outline of an embodiment of the present invention.

In the figure, 1 is an etching tank filled with an etching solution. A plurality of wafers 3 housed in a wafer carrier 2 are immersed in the etching bath 1. A clip-shaped anode electrode 4 is attached to the facet portion of the wafer 3. 5 is a platinum plate, which is formed in the same shape as the wafer 3 in this embodiment. This platinum plate 5 has a cathode electrode 6
A variable power source 7 is connected between the cathode electrode 6 and the anode electrode 4, and an ammeter 8 is also connected.

Each wafer 3 shown in FIG. 1 has a configuration as shown in FIG. That is, on the surface of the wafer 3, T i −W
About 1000 dissimilar metal layers 31 such as
On the surface of this dissimilar metal layer 31, a metal layer 32 made of aluminum or the like is formed to a thickness of about 1 μm. A resist 33 serving as a mask is patterned on the surface of this metal layer 32. That is, the dissimilar metal layer 31 is provided directly below the metal layer 32. As described above, the thickness of the dissimilar metal layer 31 is made very thin, and after patterning the metal layer 32, it is etched using the patterned metal layer 32 as a mask. Ultimately, the wiring pattern has a multilayer structure consisting of a dissimilar metal layer 31 and a metal layer 32.

The wafer 3 and platinum plate 5 are then immersed in the etching bath 1. A current flows between the anode electrode 4 and the cathode electrode 6 via the etching solution in the etching bath 1 . By appropriately setting the amount of this current using the variable power source 7, the metal layer 32 is etched while controlling the etching rate of the gold fii 32 on the wafer 3.

The progress of this etching will be explained with reference to FIGS. 3 and 4. First, for the immersion time 1 (, -1°, the 4th
As shown in Figure 4 (al), the etching of the metal layer 32 progresses, and the current value based on the amount of etching at that time becomes constant at 12. The layer 32 remains in a lumpy state, and the current value gradually decreases from 12 to 11. Then?
i? At 74 hours t2, the etching of the metal layer 32 is completed as shown in FIG. 4(C), and the current value reaches its minimum value at 11. Therefore, if the current value i is set as the current value at the end point of etching, and the etching is terminated by checking this current value i, the true end point of etching can be detected. I can say that.

Note that the current value after the immersion time L2 remains substantially constant at the minimum value i, but does not show 0. This is because the side etching of the metal layer 32 to be left, that is, the portion that will become the wiring pattern, progresses slightly.

Therefore, if a part of the metal layer 32 of each wafer 3 that is not covered with the resist 33 remains near the center of the wafer 3, the remaining metal layer 32 is replaced by a dissimilar metal layer provided directly below it. Since it is electrically connected to the anode electrode 4 through 31, the current value is between 12 and 11, and does not yet indicate the current value at the end point of etching. However, conventionally, this point marked the end of etching, so
After this, an estimated time was required for etching the remaining metal layer 32.

As explained above, according to the present invention, when a part of the metal layer remains near the center of the wafer, the remaining metal layer is connected to the anode through the dissimilar metal layer directly below it. Since the electrode is conducting, the current value on the ammeter becomes even smaller. In other words, since the ammeter does not indicate the minimum value until the metal layer has been etched so that no part of the metal layer remains to be etched, the expected time to etch the remainder after detecting the end point of etching as in the conventional method is There is no need to go out of your way to provide one.

In addition, in the past, etching in estimated time had to be replaced with chemical etching, but
This invention can be said to be efficient since it is possible to perform etching while reliably controlling the etching rate of gold mN on a wafer until the end.

Based on these facts, the present invention allows wiring patterns with good reproducibility to be easily manufactured.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an outline of an embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing the relationship between immersion time and current value, and FIG. 4 is a cross-sectional diagram of the wafer 3 showing the progress of etching. 1...Etching bath 3...Wafer 31...Different metal layer 32...Metal layer 4...Anode electrode 6...Cathode electrode 8...Ammeter Patent applicant Agent of ROHM Co., Ltd. Patent Attorney Takaharu Onishi Figure 1 Figure 2 Figure 3 to tlt Z 11st ノ')” * m

Claims (1)

[Claims] (1) First, a dissimilar metal layer different from the metal layer is formed directly below all the metal layers of the wafer to be etched, and then an anode electrode is attached to the facet of the wafer and the wafer is immersed in an etching bath. At the same time, the cathode electrode is also immersed in the etching tank, and a current is passed between the two electrodes to etch the metal layer of the wafer while controlling the etching rate of the metal layer to be etched. A method for detecting the end point of etching of a metal layer, characterized in that when the dissimilar metal layer is etched until it is exposed, a current value based on the amount of etching is determined as the end point of etching.