JPS62144002A - Apparatus for measuring thickness of metal membrane - Google Patents

Abstract

PURPOSE:To make it possible to measure the thickness of a metal membrane with high accuracy without minding the arrangement accuracy of detection coils, by providing a relative moving means for relatively moving a body to be measured and the detection coils between a pair of detection coils. CONSTITUTION:The position slightly lower than the position downwardly separated by a distance dc from the under surface of a first detection coil 4a is set as a start point position d1 and, at first, said detection coil 4a is moved upwardly from said start point position d1 at a rough pitch, for example, at a pitch of 0.1mm and oscillation amplitude values P1, P2, P3, P4 are plotted at pitch positions d1, d2, d3, d4. In this case, as a body 1 to be measured 1 approaches a center position dc, oscillation amplitude values become small and become large when exceed said center position dc and, therefore, when P4>P3 was formed, the rising movement of the body 1 to be measured is stopped. Next, the body 1 to be measured falls and the min. value Pm of the oscillation amplitude value at each pitch position is calculated. By finding out the min. value Pm by this method, the thickness of a metal membrane 3 corresponding to said value can be accurately calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an apparatus for measuring the thickness of a metal thin film by a high-frequency film thickness measurement method that reduces thin current loss.

(Prior Art) FIG. 3 shows the mechanical configuration of a conventional film thickness measuring device using eddy current loss, and FIG. 4 shows the circuit configuration of the conventional device.

In the figure, the object to be measured 1 consists of a wafer (substrate) 2 on which a metal thin film 3 is formed, and a detection coil 4 is arranged near the surface of the metal thin film 3 at a constant distance d. This detection coil 4 is connected to a transistor 5 as shown in FIG.
, and capacitors 6 and 7. By applying an alternating magnetic field to the metal thin film 3 from the detection coil 4, the film of the metal thin film 3 is activated as follows. Thickness measurements were being taken.

That is, when the alternating magnetic field generated by the detection coil 4 crosses the object to be measured 1, an eddy current flows in the thin metal M3 at right angles to the alternating magnetic field, lowering the Q of the detection coil 4. As a result, the oscillation amplitude of the oscillation circuit 8 changes. The aspect of this change is shown in FIG. In the figure, the horizontal axis indicates the distance d between the detection coil 4 and the metal thin film 3, and the vertical axis indicates the oscillation amplitude of the oscillation circuit 8. On this coordinate, characteristic curves as shown by broken lines are obtained for the film thicknesses T1', T2', and T3' of each metal thin film 3.

Therefore, if the oscillation amplitude and distance d are known, the film thickness can be determined from the characteristic curve passing through the intersection. By the way, as is clear from the figure, it can be understood that even if the film thickness is the same, if the distance d changes slightly, the oscillation amplitude changes greatly. For this reason, for example, in order to measure a pure aluminum thin film with a thickness of 1 μm with an accuracy of 1%, it is necessary to keep the accuracy of the distance d within ±0.01 +u+. When measuring a metal thin film 3 on a wafer 2 (semiconductor substrate), it is extremely difficult to install the detection coil 4 within this accuracy range, and it is difficult to obtain a satisfactory measurement accuracy. This method has drawbacks such as requiring a large-scale device configuration and requiring a high level of skill to handle it.

In recent years, in order to eliminate such problems as much as possible, an improved device as shown in FIG. 5 has been provided. This improved device divides the detection coil 4 of the oscillation circuit 8 into two, a first detection coil 4a and a second detection coil 4b, as shown in FIG. 1 detection coil 4
a and the second detection coil 4b are connected to the thin metal a of the object to be measured 1.
They are arranged vertically facing each other with the surface of No. 3 as the center position. When this improved device is used, the characteristics of the oscillation circuit 8 become solid curves as shown in FIG. 7 for each film thickness Tl, T2, and T3. and the intermediate position d between the second detection coil 4b. Near this minimum value, the oscillation amplitude hardly changes as the distance d changes. Therefore, for example, when measuring a thickness of 1 μm of a pure aluminum metal thin film 3 with an accuracy of 1%, the distance d between the first detection coil 4a and the metal thin film 3 is adjusted by ±0.1 so that d=dc. It has been demonstrated that it is sufficient to maintain an accuracy of mm.

(Problem to be solved by the invention) By using the above improved device, the placement accuracy of the detection coil 4 (first detection coil 4a and second detection coil 4b) with respect to the object to be measured 1 (metal FI H3) can be improved. can now be alleviated considerably.

However, even with this improved device, the placement accuracy of the detection coil 4 must still be kept within ±0.1 mm, and it is difficult to satisfy this requirement with a simple device.

The present invention was made in order to solve the above-mentioned conventional problems, and its purpose is to provide a metal thin film that can measure the thickness of a thin metal film with high precision without worrying about the placement accuracy of the detection coil. An object of the present invention is to provide a thin film thickness measuring device.

(Means for Solving the Problems) In order to achieve the above object, the present invention is configured as follows. That is, the present invention includes: at least a pair of detection coils that are arranged at a constant distance from each other across an object to be measured on which a thin metal film is formed, and generate an alternating magnetic field; A detection circuit whose characteristics change depending on the detection circuit; and a measurement circuit that measures the output of the detection circuit.

In the metal thin film film thickness measuring device that measures the film thickness of the metal thin film from a change in the characteristics of a detection circuit corresponding to eddy current loss that changes depending on the film thickness of the metal thin film, The apparatus for measuring the thickness of a metal thin film is provided with a relative movement means for reciprocatingly moving the object to be measured and the detection coil relative to each other.

(Function) In the present invention having the above configuration, the thickness of the metal thin film formed on the object to be measured is measured as follows. first,
The relative movement means is operated to perform relative movement between the detection coil and the object to be measured.

For example, the object to be measured is moved upward in steps at a rough pitch from a position below between a pair of detection coils arranged one above the other. Due to this movement of the object to be measured, the object to be measured approaches the center position between the detection coils, and as the object approaches, the output value of the detection circuit gradually decreases. Furthermore, if the object to be measured continues to move upward, the output value of the detection circuit will increase more than the previous value, but the upward movement of the object to be measured will be stopped at the position where this increase starts.6 In other words, the detection circuit When the output value exceeds the minimum value, the upward movement of the object to be measured is stopped.

Next, for example, using the stop position as the turning point, the object to be measured is lowered at a fine feed pitch, and the minimum value of the output value output from the detection circuit is determined. The thickness of the metal thin film is ultimately determined from the characteristic curve of the detection circuit having the value. As described above, in the present invention, first, the position near the minimum value of the output value output from the detection circuit is quickly found by relative movement of the rough feed, and then the position near the minimum value is connected to the object to be measured and the detection coil. By relatively moving the film at a fine pitch, it is possible to accurately determine the minimum value of the output of the detection circuit, that is, the film thickness.

(Example) Hereinafter, one example of the present invention will be described based on the drawings. In the description of this embodiment, the same components as those of the conventional example are given the same reference numerals, and the description thereof will be omitted. FIG. 1 shows the configuration of an embodiment according to the present invention. In the figure, a pair of holding legs 10 and 11 are horizontally protruded apart from the side plate 9 at a certain distance, and a first detection coil 4a is fixed to one holding leg 10, and the other holding leg A second detection coil 4b is fixed to the leg 11.

This first detection coil 4a and second detection coil 4b
4i It constitutes a part of the oscillation circuit 8 similarly to the conventional improved device.

The detailed circuit configuration of this oscillation circuit 8 is similar to the conventional circuit configuration shown in FIG. 6, and has a configuration in which the detection coil 4 is divided into two, a first detection coil 4a and a second detection coil 4b. There is. The object to be measured 1 is arranged between the first detection coil 4a and the second detection coil 4b.

Therefore, by outputting an alternating magnetic field from the first detection coil 4a and the second detection coil 4b, eddy current is generated within the metal thin film 3.

The magnitude of this eddy current corresponds to the thickness of the metal thin film 3, and therefore, the detection coil 4
Q changes. In other words, the eddy current of the detection coil 4 changes depending on the film thickness. As a result, the oscillation circuit 8 outputs a signal having an analog oscillation amplitude corresponding to the thickness of the metal thin film 3. This oscillation amplitude signal is applied to a high-speed analog-to-digital conversion circuit 12, where it is converted from an analog signal to a digital signal.

This digital signal is then applied to the data processing circuit 1-3 to perform desired data processing. In this embodiment, a measuring circuit 14 is constituted by the high-speed analog-to-digital conversion circuit 12 and the data processing circuit 13.

By the way, a characteristic feature of this embodiment is that a relative moving means 15 is provided for vertically moving the object to be measured 1 between the first detection coil 4a and the second detection coil 4b. be.

In this embodiment, the relative moving means 15 includes a holding member 16 that holds the object to be measured 1, a feed screw 17 that is screwed into the holding member 16, and rotates the feed screw 17 in a desired direction of normal rotation and reverse rotation as appropriate. It is composed of a pulse smoke 18 to be driven and a control circuit 19 that controls the rotation of this pulse motor 18.

The holding member 16 is slidably disposed along a guide groove (not shown) provided in a fixed wall (not shown), and the object 1 to be measured is attached to and removed from the holding portion of the holding member 16. freely held.

Further, a through hole is provided at a desired position of the holding member 16, and a threaded groove is formed on the circumferential surface of this through hole. A feed screw 17 is screwed into this thread groove in a penetrating state, and the base end of the feed screw 17 is connected to the output shaft of a pulse motor 18 via a coupling (not shown).

The pulse motor 18 receives commands from the control circuit 19 and rotates stepwise in the forward or reverse direction in a desired direction, and the width of the step can be arbitrarily varied. Therefore, by controlling the rotation of the pulse motor 18, the relative threading rotation between the feed screw 17 and the holding member 16 is performed, and the holding member 16 slides up and down along the guide groove. Control of the vertical movement is achieved.

A control signal outputted from one of the control circuits is applied not only to the pulse motor 18 but also to the data processing circuit 13. The data processing circuit 13 operates as shown in FIG. 2 based on the digital oscillation amplitude information applied from the high-speed analog-to-digital conversion circuit 12 and the control signal (position information of the measured object) applied from one control circuit. Next, a characteristic diagram is created by plotting the relationship between the oscillation amplitude of the oscillation circuit 8 and the moving distance d of the object to be measured 1 (metal thin film 3).

Therefore, by looking at this characteristic diagram, it is possible to determine the accurate minimum value of the oscillation amplitude at a glance.

In this embodiment, when determining the minimum value of this oscillation amplitude, the object to be measured 1 is connected to the first detection coil 4a and the second detection coil 4.
The starting point is a position slightly below the center position of b, that is, a position slightly below the position cic downward from the bottom surface of the first detection coil 4a (a position d downward from the first detection coil). d1, first, this starting point fd,
From d1. Same d2. Oscillation amplitude value P1 at d and d4. Same P2. Same P3 and Same P
Plot 4. In this case, as the measured object 1 approaches the center position dC, the oscillation amplitude value becomes smaller (PI>
P2>P, ), and the oscillation amplitude value increases again when the center position Wdc is exceeded, so when P 4 > P 3, that is, when the measured object 1 exceeds the center position dc, the measured object 1 Stop the upward movement of 1. Next, the object 1 to be measured is lowered at a fine pitch in the opposite direction using the position of d4 or a slightly higher position than this as a turning point, and the oscillation amplitude value at each pitch position is plotted as a plot. The minimum value Pm of the oscillation amplitude value is determined from the figure.

By finding the minimum value P, n in this way, the minimum value P. It becomes possible to accurately determine the film thickness of the metal thin film 3 corresponding to .

As described above, according to this embodiment, the object to be measured 1 is moved at a rough pitch to roughly estimate the position of the minimum value of the oscillation amplitude, and then the area where the oscillation amplitude has been estimated is searched at a fine pitch. By doing so, the minimum value of the oscillation amplitude, that is,
The thickness of the thin metal WA3 can be measured accurately and quickly. Furthermore, since there is no need for the complicated and troublesome high-precision positioning and fixing work of the detection coil 4, which was essential in conventional devices, the film thickness measurement work is extremely easy. Since no special mechanism is required, the device configuration can be greatly simplified.

In the above embodiment, the object to be measured 1 is configured to move relative to the detection coil 4 (the first detection coil 4a and the second detection coil 4b). 1
may be fixed, and the first detection coil 4a and second detection coil 4b may be configured to move integrally using a similar feed screw configuration. Furthermore, the relative movement between the object to be measured 1 and the first detection coil 4a and second detection coil 4b is not necessarily limited to the combination mechanism of the pulse motor 18 and the feed screw 17 as in this embodiment. However, as long as it is possible to control these relative movement amounts minute by minute, other desired means may be used as appropriate.

Further, in the above embodiment, the oscillation circuit 8 is used as a detection circuit that changes characteristics due to eddy current loss, but it is not necessarily limited to this, and it is also possible to configure it with other circuits, for example. , a bridge circuit may be constructed in which one side of the bridge is a detection coil whose coil constant changes due to eddy current loss. In this case as well, the thickness of the metal thin film 3 can be quickly and accurately determined as in the above embodiment. It is possible to measure.

Further, in the above embodiment, the minimum value of the oscillation amplitude is determined based on the plotting result of the data processing circuit 13, but the analog signal of the oscillation amplitude output from the oscillation circuit 8 is guided to the display, and the The minimum value of the oscillation amplitude may be determined by observing the deflection of the display hand.

(Effects of the Invention) Since the present invention has the configuration and operation as described above, the thickness of the metal thin film can be measured quickly and with high accuracy regardless of the positioning accuracy of the detection coil. Also,
Since positioning accuracy of the detection coil is not required, a complicated mechanism for high-precision positioning is not required, thereby making it possible to significantly simplify the device configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a schematic diagram of film thickness measurement using the device of this embodiment, and Fig. 3 is a block diagram of a conventional film thickness measuring device before improvement. Figure 4 is a circuit diagram of the oscillation circuit used in the device shown in Figure 3, Figure 5 is a block diagram of a conventional improved device, Figure 6 is a circuit diagram of the oscillation circuit used in the device shown in Figure 5, and Figure 7. is a characteristic diagram showing the relationship between the relative movement distance d of a metal thin film and the oscillation amplitude with the film thickness as a parameter. 1...Object to be measured, 2...Wafer,
3...metal thin film, 4...detection coil, 4a...first detection coil, 4b...
...Second detection coil, 5...Transistor, 6.7...Capacitor, 8...
Oscillation circuit, 9...Side plate, 10.11...
... Holding leg, 12 ... High-speed analog-to-digital conversion circuit, 13 ... Data processing circuit,
14... Measuring circuit, 15... Relative movement means, 16... Holding member, 17...
...Feed screw, 18...Pulse motor,
19...Control circuit. Agent Patent Attorney Yoshi Yahata Usuba / Figure 2 Figure do Shingo - Figure 4 Figure 3 Figure 6 Figure 5 Reason 4''

Claims (5)

[Claims] (1) at least a pair of detection coils that are arranged at a constant interval across the object to be measured on which a thin metal film is formed and generate an alternating magnetic field; A detection circuit whose characteristics change; and a measurement circuit which measures the output of the detection circuit; and the thickness of the metal thin film can be determined from changes in the characteristics of the detection circuit corresponding to eddy current loss which changes depending on the thickness of the metal thin film. A thin metal film thickness measuring device for measuring the thickness of a thin metal film, further comprising a relative movement means for relatively moving the object to be measured and the detection coil between the pair of detection coils. Thickness measuring device. (2) The relative movement means is characterized by comprising: a pulse motor; a control circuit that controls the rotation of the pulse motor; and a feed screw that converts the rotational motion of the pulse motor into linear motion of the object to be measured. A film thickness measuring device for a metal thin film according to claim (1). (3) The relative movement means consists of a pulse motor; a control circuit that controls the rotation of the pulse motor; and a feed screw that converts the rotational motion of the pulse motor into integral linear motion of a pair of detection coils. An apparatus for measuring the thickness of a thin metal film according to claim (1). (4) The metal thin film according to any one of claims (1) to (3), wherein the detection circuit comprises an oscillation circuit whose oscillation amplitude changes due to eddy current loss. Thickness measuring device. (5) The detection circuit comprises a bridge circuit in which one side of the bridge is a detection coil whose coil constant changes due to eddy current loss. A film thickness measuring device for a metal thin film according to claim 1.