JPH0562816B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field 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 Generally, when forming a wiring pattern for a semiconductor device, 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 perform electrolytic etching, an anode electrode is connected to the facet of the wafer on which the metal layer to be etched has been deposited and patterned with a resist as a mask, and a cathode electrode is connected 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.

Problems to be Solved by the Invention Incidentally, in electrolytic etching, the metal layer is etched from the periphery of the wafer toward the center, so even if the metal layer near the facet portion where the anode electrode is attached is etched, , a metal layer may remain near the center of the wafer. Since the metal layer remaining near the center is not electrically connected to the anode electrode, the current value becomes minimum when the metal layer near the facet of the wafer is etched, and this point is the etching end point. In this way, with the conventional method, even if the end point of etching is confirmed, there is a lump-like etching residue near the center of the wafer, so it cannot be said that the true end point has been detected. Therefore, it was necessary to provide extra time for etching the etching residue. Furthermore, during this estimated time, electrolytic etching turns into mere immersion etching, that is, chemical etching, which can be said to be inefficient.

This invention was created due to the above circumstances,
To provide a method for detecting the end point of etching of a metal layer, which can detect the end point of etching when the metal layer near the center of a wafer is etched, and eliminates the need to set an estimated time for etching the remaining etching as in the conventional method. It is an object.

Means for Solving the Problems In order to achieve the above object, in the present invention, a dissimilar metal layer different from the metal layer to be etched is formed on all wafers to be etched. This dissimilar metal layer is disposed directly below the metal layer deposited on the wafer. Then, an anode electrode is attached to the facet portion of this 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 while controlling the etching rate of the metal bath of the wafer. Furthermore, 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. .

Function: Even when the area near the facet 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.

Embodiment 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,
In this embodiment, it is formed to have the same shape as the wafer 3. A cathode electrode 6 is attached to the platinum plate 5, and 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 structure as shown in FIG. That is, on the surface of the wafer 3, a layer 31 of a different metal such as Ti--W is formed with a thickness of about 1000 Å, and on the surface of this different metal layer 31, a layer 32 of a metal such as aluminum is formed with 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, the patterned metal layer 3
2 is etched 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 current using the variable power supply 7, the metal layer 32 of the wafer 3 is etched while controlling the etching rate of the metal layer 32.

The progress of this etching is shown in Figures 3 and 4.
This will be explained according to the diagram. First, during the immersion time period _t0 to _t1 , etching of the metal layer 32 progresses as shown in FIG. 4a, and the current value based on the amount of etching at that time becomes constant at _i2 . Between the immersion time _t1 and _t2 ,
As shown in FIG. 4b, the metal layer 32 remains in a lumpy state, and the current value gradually decreases from _i2 to _i1 . Then, when the immersion time _t2 comes, the etching of the metal layer 32 is completed, as shown in FIG. 4c, and the current value reaches its minimum value at _i1 . Therefore, the current value
If i ₁ is set as the current value at the end point of etching, and the current value i ₁ is checked to end the etching in advance, it can be said that the true end point of etching has been detected. Note that the current value after the immersion time _t2 remains approximately constant at the minimum value _i1 , 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
2 is electrically connected to the anode electrode 4 via the dissimilar metal layer 31 provided directly below it, the current value i ₂ to _{i 1}
The current value at the end point of etching is not yet indicated. However, conventionally, this point indicates the end point of etching, and therefore an estimated time is required for etching the remaining metal layer 32.

Effects of the Invention 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 electrode through the dissimilar metal layer directly below it. Since it is conducting, the current value on the ammeter will be 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.

Additionally, in the past, etching within the estimated time had to be replaced with chemical etching, but with this invention, etching can be performed while reliably controlling the etching rate of the metal layer on the wafer until the end, making it more efficient. I can say that.

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 overview of an embodiment of the present invention, Fig. 2 is an explanatory cross-sectional diagram of a wafer 3, Fig. 3 is a diagram showing the relationship between immersion time and current value, and Fig. 4 is a diagram showing the progress of etching. FIG. 1... Etching tank, 3... Wafer, 31...
Different metal layer, 32...metal layer, 4...anode electrode, 6...cathode electrode, 8...ammeter.

Claims (1)

[Claims] 1. First, a dissimilar metal layer different from the metal layer is formed immediately 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 tank. , the cathode electrode is also immersed in the etching bath, 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, so that the metal layer to be etched is 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.