JPH0225988B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling discharge impedance of a magnetron type sputtering device.

Conventionally, this type of device has an Al or other target placed opposite to a substrate holder to which a substrate such as a Si wafer is attached in a vacuum chamber, and, for example, a potential difference is applied between the holder and the target by a DC power supply, and a voltage is applied to the front side of the target. Generally, a magnetic field of an electromagnet or a permanent magnet is applied to generate a magnetron discharge, and the target material is sputtered to form a thin film of the material on the surface of the substrate. The target gradually scatters and becomes thinner due to the progress of erosion accompanying the spatter, and as the target becomes thinner, the actual magnetic flux density of the electromagnet in front of the target increases, as follows. causing inconvenience.
In other words, as the magnetic flux density increases, the discharge impedance decreases, and at this time the sputtering current gradually increases, and eventually reaches the rated value of the sputtering power supply, making it difficult to control a constant power, and it is difficult to control a constant power, and it is difficult to control the sputtering current in a fixed amount of time. When thin films are sequentially formed, there is a disadvantage that the film thickness of the initially processed substrate and the film thickness of the final processed substrate differ greatly, and it is not economical because many substrates cannot be processed with one target.

The present invention is aimed at solving these inconveniences, and includes providing a target opposite to a substrate holder to which a substrate is attached in a vacuum chamber, applying a negative potential to the target by a sputter power source, and installing an electromagnet in front of the target. In this method, a magnetron discharge is generated by applying a magnetic field to sputter the target, and the current flowing through the electromagnet is gradually lowered so as to maintain the discharge impedance substantially constant.

An embodiment of the present invention will be described with reference to the drawings. Reference numeral 1 indicates an evacuated vacuum chamber, 2 a substrate on which a thin film is formed, 3 a substrate holder to which the substrate 2 is attached, and 4 a target. are provided facing each other in the vacuum chamber 1, as shown in the figure.
A DC or RF sputter power supply 5 is connected to provide a potential difference between the holder 3 and the target 4, for example. 6 is an electromagnet provided behind the target 4 via a bucking plate 7, and 8 is a DC power source for exciting the electromagnet 6.

The sputtering device with the above configuration is conventionally known, and is capable of evacuating the vacuum chamber 1 and
When Ar or other rare gas is injected, the electromagnet 6 is excited, and the sputter power source 5 is turned on, the target 4 is
A magnetron discharge occurs in front of the substrate 2, and the substance of the target 4 sputtered by the excited ions adheres to the surface of the substrate 2 in the form of a thin film. The target 4 is made of Al with a thickness of, for example, 3 cm, and a magnetic field with a horizontal magnetic flux density of, for example, about 250 Gauss is applied to its surface by an electromagnet 6. Further, the substrates 2 are positioned facing the target 4 in turn.

The target 4 gradually becomes thinner as shown by the dotted line 9 due to the erosion of the sputter, and the magnetic flux density on its surface increases, resulting in a decrease in discharge impedance, so that the sputter power supply 5 reaches its full current rating when operating at constant power.

The present invention pays close attention to changes in discharge impedance due to thinning of the target 4 through changes in the current or voltage of the sputter power source 5, and in the embodiment, it is determined whether the current increases until it approaches the full rated current or not. When the voltage drops to a set value, the current of the electromagnet 6 is lowered to control the discharge impedance to be approximately constant.

To further explain this, as the erosion of the target 4 progresses, the current and voltage of the sputter power source 5 gradually rise and fall as shown by A and B in FIG. 2, respectively, and the current A Point C
The ammeter 11 of the circuit 10 indicates that the current reaches the full rated value or close to the full rating as shown by , or that the voltage B has fallen below the set value E as shown by point D.
Alternatively, it is detected by the voltmeter 12 and the current F of the electromagnet 6 is lowered as shown by point G. As a result, the discharge impedance is controlled to be approximately constant as shown by the curve H, and a large number of substrates 2 can be processed without exceeding the rated output of the sputter power supply 5. As shown by the curve, the film thickness of the substrate 2 is also approximately constant. You can get a certain amount. Comparing this with the conventional case, when the number of processed substrates 2 exceeds about 1400 at a film formation rate of 200 Å/sec, the discharge impedance decreases and the sputter power supply 5 reaches its rated current output, so the target 4 had to be replaced with a new one, but as in the present invention, the electromagnet 6
By lowering the current, the discharge impedance can be kept approximately constant even when the number of sheets processed exceeds 1400, and the target 4 can be used effectively until it becomes extremely thin.

The reason why the discharge impedance becomes substantially constant by lowering the current of the electromagnet 6 is that the magnetic flux density in front of the target 4 decreases by lowering the current.

In the embodiment, when the voltage of the sputter circuit 10 fell below 500V, the current of the electromagnet 6 was controlled to be lowered by 1A.
The current of the power source 8 of the electromagnet 6 may be controlled by a calculator 13 connected to the electromagnet 6.
It is also possible to gradually lower the current in more circuits, and it is also possible to lower the current continuously. In this way, according to the present invention, the current of the electromagnet is gradually lowered to maintain the discharge impedance approximately constant, so that even if the erosion of the target progresses, sputtering can be performed with constant power without causing a shortage of power in the sputtering power supply. It is possible to process a large number of substrates for a long time without changing the target.
This method improves work efficiency, makes effective use of the target, is economical, and allows the thin plate formed on the substrate to have a substantially constant thickness.

[Brief explanation of drawings]

FIG. 1 is a diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the number of processed substrates, current, voltage, and discharge impedance. 1... Vacuum chamber, 2... Substrate, 3... Substrate holder, 4... Target, 5... Sputter power supply, 6
……electromagnet.

Claims (1)

[Claims] 1. A target is provided facing the substrate holder to which the substrate is mounted in the vacuum chamber, and a negative potential is applied to the target by a sputter power supply, and a magnetic field of an electromagnet is applied to the front surface of the target to generate a magnetron discharge, thereby causing the target to 1. A method for controlling discharge impedance of a sputtering apparatus, characterized in that, in a sputtering type apparatus, a current flowing through the electromagnet is gradually lowered so as to maintain a substantially constant discharge impedance.