JPS6199806A - groove depth measuring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a device for measuring the depth of a deep groove formed in, for example, a semiconductor wafer.

[Background of the invention]

In recent years, as semiconductor devices have become highly integrated, device structures have progressed from two-dimensional planar structures to three-dimensional three-dimensional structures. For example, in order to maintain electrical insulation between adjacent different elements, it is becoming practical to create deep grooves between adjacent elements. Since the shape and depth of these grooves or holes greatly affect the device characteristics, it is necessary to measure them by some means. When performing these measurements, non-contact measurement means are strongly desired in order to avoid changes in the characteristics of semiconductor elements due to contamination.

Conventionally, methods and devices for measuring minute heights and intervals in a non-contact manner include (a) static kick capacitance micrometer, (b)
) air micrometer, (Q) microscope, and (d) interferometer. However, these methods and devices can accurately measure differences in level or gentle unevenness, but for example, when the width is about 104 mm. In the case of a groove whose depth is 5 to 10 times the width, the measurement accuracy deteriorates, and in fact, it was not possible to measure L.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a groove depth measuring device capable of measuring the depth of a minute deep groove, which has been difficult to measure in the past.

[Summary of the invention]

The principle of measuring the groove depth used in the present invention will be explained. Figure 7 shows the shape of the groove. The groove is dug perpendicular to the sample surface, and the bottom surface is assumed to be perpendicular to the side surface of the groove. A parallel light beam is made incident on this groove. When the incident angle is O, the light incident on the sample surface is reflected by the surface and travels in the direction of the reflection angle θ. On the other hand, the light incident on the groove opening is
After being reflected repeatedly by the side walls and bottom of the groove, it reaches the opening of the groove again and exits the groove. Let the width of the groove be a and the depth be d, and as shown in Figure 8, the incident angle O of the light is θ = jan-''
Consider the case of (−) (] ). In this case, the light incident on the inside of the groove is first reflected from the right side surface of the groove and directed toward the bottom surface of the groove, and the light further reflected from the bottom surface proceeds toward the left side surface. After being reflected off the left side surface, it reaches the opening of the groove and exits the groove. The direction of the light exiting from the inside of the groove is in this case the same direction as the reflected light reflected from the sample surface. In general, the angle of incidence θ
is θ, = tan"" (-) where n: even number...
- In the case of (2) d, the light reflected from inside travels in the same direction as the light reflected by the sample surface, as in the above case.

Next, consider the case where the angle of incidence is θ=tan""() (3)d. In this case, as shown in FIG. 9, the light incident on the left side from the center of the opening of the groove first directly enters the bottom surface. The light reflected from the bottom is directed toward the right side, and the light further reflected from the right side travels in the direction opposite to the incident light and exits from the groove. As in this case, the condition for the reflected light from the inside square of the groove to travel in the opposite direction to the incident light is that the incident angle of the light incident on the groove is expressed by the following equation.

8, = tan-” (-) where n: odd number-
(4) d If the incident angle of light is other than θ□ and θ2,
The light incident on the groove is divided into two parts, with a part going in the direction of the reflected light from the sample surface and the rest going in the direction opposite to the incident light, and is reflected from inside the groove. The amount of light reflected in these two directions depends on the angle of incidence, and especially when the angle of incidence is the value expressed by equation (2), all of the light reflected from inside the groove is reflected from the sample surface. The amount of reflected light that is in the same direction and goes opposite to the incident light is zero. Therefore, the depth d of the groove is calculated by measuring the angle of incidence θ, when the amount of reflected light going against the incident light is zero, and substituting that value and the groove width 8 into equation (2). be able to.

Specifically, the incident angle θ is changed while measuring the light intensity IR of reflected light that goes against the incident light, and the incident angle θR at which TR becomes zero is determined.
Measure. When the value of the incident angle is changed from 0 degrees, the formula (
In 2), several incident angles OR at which TR becomes zero are measured when n is set to 2.4.6. If the incident angle corresponding to n is 2 is ORz, θR2 is expressed by the following formula.

a θR1=jan-” (-) d Therefore, using this equation, the depth d of the groove can be expressed as follows.

Or adjacent θR values, for example ORn and θRn+
Using the value of a, the depth d of the groove can be determined as follows.

In the above example, the depth of the groove was determined from the angle of incidence at which the amount of light traveling in the direction opposite to the incident light was zero, but conversely, the depth of the groove was found in the same way from the angle of incidence at which the amount of light traveling in the jφ direction to the incident light was maximum. can be found. That is, the groove depth measuring device according to the present invention includes means for irradiating a parallel beam of light onto a groove having two parallel surfaces and a plane orthogonal to the two surfaces, and of the light reflected from the groove. and means for measuring the amount of reflected light in the direction opposite to the incident light.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of a groove depth measuring device according to the present invention, FIG. 2 is a sectional view of the light transmitting/receiving head of the above embodiment, and FIG. 3 is a diagram showing a second embodiment of the present invention. FIG. 4 is a cross-sectional view of the light transmitting and receiving head of the above embodiment, FIG. 5 is a block diagram showing the third embodiment of the present invention, and FIG. FIG. 3 is a cross-sectional view showing a state of irradiation.

In FIG. 1, laser light 111 emitted from a laser light source 11 is focused on the end face of an optical fiber 13 by a lens 12 and guided to a light transmitting/receiving head 14. As shown in FIG. 2, the structure of the light transmitting/receiving head 14 includes a groove that converts the light sent by the optical fiber 13 into parallel light beams using a lens 15, and transmits the light through a semi-transparent mirror prism 16 to measure the depth. A certain sample 17 is irradiated. In order to absorb the reflected light generated when the laser beam passes through the semi-transparent mirror prism 16 from the lens 15 side, a light-absorbing film 23 is coated on the side surface of the semi-transparent mirror prism 16.

The light transmitting/receiving head 14 receives the reflected light in the direction opposite to the incident light on the sample 17, reflects the reflected light by the semi-transparent mirror prism 16, and converts it into an electrical signal by the photoelectric conversion element 18. The converted electrical signal is measured by the voltage H119, and the presence or absence of reflected light from the sample 17 is detected. 20 in FIG. 4 is a power source for the photoelectric conversion element 18. In FIG. The slider 21 attached to the light transmitting/receiving head 14 moves along an arc-shaped arm 22 with graduations, and the angle of incidence of the light irradiating the sample 17 can be read from the graduations. To measure the depth of the groove using the above device, the light transmitting/receiving head 14 is slid along the arm 22 while irradiating the sample 17 with laser light, and at the same time the intensity of the reflected light is measured at the voltage indicated by the voltmeter 19. Measured by The angle of incidence of light on the sample 17 is gradually increased from around 0 degrees, and the angle of incidence of light when the reading on the voltmeter 19 reaches the smallest value is set to A-1.
Read from the %22 scale. The incident angle fl of the light at this time
The depth d of the groove can be calculated by substituting R and the width a of the opening of the groove separately measured using a microscope or the like into the above equation (1).

In this example, a laser light source is used as the light source to obtain perfectly parallel light beams, and the light reflected from the sample surface and the reflected light that is reflected from the inside of the groove and that travels in the opposite direction to the incident light are in the direction of light propagation. Since they are different from each other, they can be efficiently separated, and the incident angle θ at which the reflected light intensity becomes zero can be easily measured.

In addition, since an optical fiber is used to irradiate the parallel light beam from the light source, the optical path between the light source and the light transmitting/receiving head is not physically fixed, which prevents the configuration of the device from becoming too large.
Moreover, the trouble of adjusting the optical axis can be avoided, and the entire device can be made compact and easy to operate.

In the second embodiment shown in FIG. 3, a laser beam 111 emitted from a laser light source 11 passes through a semi-transparent mirror prism 24, is focused on an optical fiber 13 by a lens 12, and is transmitted through the optical fiber 13. The light is guided to a light transmitting/receiving head 14'. In the light transmitting/receiving head 14', as shown in FIG. 4, the laser beam is again converted into a parallel beam by the lens 15 and irradiated onto the sample 17. The light reflected from the groove provided in the sample 17 in the direction opposite to the incident light is transmitted to the light transmitting/receiving head 14'.
further passes through the optical fiber 13 to the lens 12
guided by. This reflected light is converted into a parallel light beam by the lens 12, then reflected by the semi-transparent mirror prism 24, and enters the photoelectric conversion element 18. The output voltage of the photoelectric conversion element 18 is measured with a voltmeter 19. 20 in the figure is a power source for the photoelectric conversion element. The voltage measured by the voltmeter 19 corresponds to the intensity of reflected light from the groove of the sample 17 whose depth is to be measured. Along the arm 22, a light transmitting/receiving head 14'
is moved to increase the angle of incidence of the laser beam irradiating the groove from 0 degrees, and at the same time, the voltmeter 19 measures changes in the intensity of the light reflected from the groove to the light transmitting/receiving head 14'. Then, the incident angle θ when the indicated voltage of the voltmeter 19 becomes the lowest is read from the scale attached to the arm. In this example, sample 17
Among the light reflected from the irradiating light to the light transmitting/receiving head 14', only the light that completely travels along the φ line with respect to the irradiated light is focused on the optical fiber 13. can be detected. As a result, measurements can be easily made;
It is characterized by being able to measure the depth of grooves with high precision.

In the third embodiment shown in FIG. 5, a laser beam emitted from a laser light source 11 is focused by a lens 12 and guided to an optical fiber 13, and the laser beam guided by the optical fiber 13 is converted into a parallel beam by a lens 25. and enters the semi-transparent mirror prism 26. A portion of the laser light incident on the semitransparent mirror prism 26 is reflected toward the lens 27 and focused on the opening of the groove of the sample 17. In this case, the distance between the lens 27 and the sample 17 is such that the 'il 1 line light beam incident on the lens 27 is
It is made equal to the focal length f of the lens 27 so that it enters the opening of the upper groove. A shielding plate 2 that covers at least half of the lens 27 when the laser beam passes through the lens 27
8 blocks a portion of the laser light incident on the lens 27. Therefore, the state of incidence of light entering the groove of the sample 17 is as shown in FIG. 6, and the numerical aperture of the lens 27 is N, A
re), the angle of incidence is from 0 degrees to the maximum sin''' (
Light of up to N, A) degrees will be incident at the same time. Of the light incident on the groove, all the light whose incident angle corresponds to equation (2) is reflected by the lens 2 as shown in reflected light 29 in FIG.
It is reflected by the portion covered by the shielding plate 28 of No. 7. Therefore, the amount of light reflected on the portion of the lens 27 that is not covered by the shielding plate 28 becomes zero. A portion of the incident light having an incident angle of the groove other than the value of equation (2) is reflected by the portion of the lens 27 that is not covered by the shielding plate 28. This light passes through the lens 27 in the direction of the irradiation light; and enters the semi-transparent mirror prism 26. Part of the light incident on the semi-transparent mirror prism 26 is transmitted, and the remaining light is reflected by the semi-transparent mirror prism 26 and travels toward the lens 25. The light transmitted through the semi-transparent mirror prism 26 enters the eyepiece 29.

Used for visual groove [6]. Further, the end face of the optical fiber array 30 is arranged between the lens 25 and the semitransparent mirror prism 26. What is the sum of the distance Q1 between the lens 27 and the semi-transparent mirror prism 26 and the distance between the semi-transparent mirror prism 26 and the end face of the fiber array 30?
The fiber array 30
Match the end faces of. Generally, on the focal plane of a lens, light incident on the lens is focused at different points depending on the angle of incidence. Therefore, the reflected light reflected from the groove to the lens 27 is separated into angles of incidence of the reflected light to the lens 27 at the end face of the fiber array 30. Since the angle of incidence of the reflected light on the lens 27 is equal to the angle of incidence when the reflected light enters the groove, the light condensed on the end face -1 of the fiber array 30 is separated. For example, on the end face of the fiber array 30, a distance m perpendicular to the optical axis
The light that is condensed at a point that is far away is light that has entered the groove at an angle of incidence expressed by the following equation.

0 = tan-” (-) (5
) The light incident on each optical fiber of the fiber array 30 is converted into an electrical signal by the photoelectric conversion element array 31 coupled to the rear end face of the fiber array 30, and the electrical signal is measured by a voltmeter or ammeter 32, and -30 Detects an optical fiber in which the amount of light reflected from the end face is zero. When the distance between the tip of the optical fiber and the optical axis is m, the angle of incidence of the irradiated light at which the reflected light becomes zero is expressed by equation (5). formula(
Using the value of 5) and equation (2), the depth d of the groove can be determined as follows.

becomes. As described above, in this embodiment, the depth of the groove, which could not be measured conventionally, can be easily measured, and the groove to be measured can be observed with the naked eye.

Although each of the above embodiments has been described with respect to the measurement of fine grooves, it goes without saying that the present invention can also be applied to the measurement of the depth of a hole having parallel side surfaces and a bottom surface perpendicular to the side surfaces.

〔Effect of the invention〕

As described above, the groove depth measuring device according to the present invention includes means for irradiating a parallel beam of light onto a groove having two parallel surfaces and a plane perpendicular to the two surfaces, Equipped with a means to measure the μ of reflected light in the direction opposite to the incident light, it is now possible to easily measure the depth of minute grooves, which was previously extremely difficult to measure, in a non-contact and non-destructive manner. It is particularly suitable for measuring the depth of grooves in semiconductor wafers where contamination is a problem.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a first embodiment of a groove depth measuring device according to the present invention, Fig. 2 is a sectional view of a light transmitting/receiving head of the second embodiment, and Fig. 3 is a diagram showing a second embodiment of the present invention. Block diagram showing an example, No. 4
The figure is a sectional view of the light transmitting/receiving head of the above embodiment, FIG. 5 is a configuration diagram showing the third embodiment of the present invention, and FIG. Fig. 7 is a cross-sectional view showing the state of reflection of the parallel light beam irradiated onto the groove;
This figure and FIG. 9 are diagrams showing the state of reflection of the parallel light beam irradiated onto the groove. +1...Laser light source 12.15.25.27...Lens 13...Optical fiber 14.14'...Light transmitting/receiving head 16.24.26...Semi-transparent mirror prism 17...Sample 18... Photoelectric conversion element 19... Voltmeter 28... Shielding plate 29... Eyepiece 30... Optical fiber array 31... Photoelectric conversion element array 32... Voltmeter or ammeter

Claims (5)

[Claims] (1) A means for irradiating a parallel beam of light onto a groove having two parallel surfaces and a plane orthogonal to the two surfaces; A groove depth measuring device comprising means for measuring the depth of a groove. (2) The means for irradiating the parallel light flux includes means for dividing the parallel light flux into two, and the means for measuring the reflected light includes means for observing the groove using a part of the reflected light. A groove depth measuring device as set forth in claim 1. (3) The groove depth measuring device according to claim 2, wherein the means for measuring the amount of reflected light is an optical fiber array. (4) The groove depth measuring device according to any one of claims 1 to 3, wherein the parallel light beam is a laser beam. (5) The groove depth measuring device according to any one of claims 1 to 4, wherein the means for irradiating the parallel beam of light uses an optical fiber. .