JP5141632B2 - Wafer with inspection electrode and method of measuring refractive index - Google Patents

Description

  The present invention relates to a technique for measuring a refractive index of an electrode in a manufacturing process of an optical waveguide element in which an optical waveguide and an electrode are formed.

  An optical modulator in which a Mach-Zehnder type optical waveguide and a traveling wave type electrode are formed on a ferroelectric substrate having an electro-optic effect has been developed and used for optical communication and optical measurement (see, for example, Patent Document 1). In order to enable the optical modulator of this configuration to operate in a wide band, it is necessary to match the speed of the optical signal propagating through the optical waveguide and the microwave traveling through the electrode. It is important to measure the refractive index of the electrode with respect to microwaves.

JP-A-4-288518

  The process of manufacturing the above optical modulator is generally as follows. First, a large number of optical waveguide patterns and electrode patterns are formed on a single wafer using a thin film forming process and a photolithography process. Next, the electrical characteristics of the electrode pattern in the wafer are inspected. For example, in this inspection process, microwaves are input to the electrodes, the refractive index of the electrodes with respect to the microwaves is measured as described above, and the quality is determined based on the obtained refractive index value. Next, the wafer is cut into individual optical modulator shapes, and each optical modulator is formed into a chip. Next, a non-defective product and a defective product of each of the optical modulators formed into chips are selected based on the electrical property inspection results before chip formation and the optical property inspection results of the optical waveguide performed after chip formation.

  As described above, conventionally, since all the electrode patterns are inspected even when the refractive index of the microwave is poor over the entire surface of the wafer, the number of times of measuring the refractive index is large and the inspection takes time. It was. Also, in the electrode pattern in which the electrode routing wiring is formed long, the portion affects the measurement of the refractive index, and the electric field application portion of the electrode where the microwave and the optical signal actually interact (arranged in parallel with the optical waveguide). The refractive index of the portion provided) could not be measured accurately. In addition, the drawing wiring has a different drawing direction from that of the electric field application part, so the refractive index of the drawing wiring shows a different value from the refractive index of the electric field application part due to the crystal anisotropy of the wafer. This is one of the reasons that the refractive index of the electric field application part cannot be measured accurately.

  The present invention has been made in view of the above points, and an object of the present invention is to easily and accurately measure the refractive index of an electrode in a manufacturing process of an optical waveguide element in which an optical waveguide and an electrode are formed. An object of the present invention is to provide a wafer with an inspection electrode and a refractive index measurement method.

  The present invention has been made to solve the above-described problems, and includes a plurality of optical waveguides, and a hot electrode and a ground electrode arranged along the optical waveguide on a wafer having an electro-optic effect. A plurality of traveling-wave control electrodes for controlling the light propagating through the optical waveguide by passing an electric signal therebetween, and having the same cross-sectional shape and the same extending direction as the hot electrode, and at least different in length A wafer with inspection electrodes, characterized in that two inspection electrodes are formed.

  Further, the present invention provides the above-mentioned wafer with inspection electrodes, wherein the electric field application portions of the plurality of traveling wave type control electrodes have a plurality of types of cross-sectional shapes, and the at least two types of inspection use for each type of the cross-sectional shapes An electrode is provided.

  Further, the present invention is characterized in that, in the wafer with an inspection electrode, the same film configuration is formed between the hot electrode and the wafer and between the inspection electrode and the wafer.

  Further, the present invention provides a wafer having an electro-optic effect, wherein a plurality of optical waveguides and a hot electrode and a ground electrode are disposed along the optical waveguide, and an electric signal is advanced between the electrodes to cause the optical waveguide to travel. A traveling-wave control electrode for controlling light propagating through the hot electrode, and at least two inspection electrodes having the same cross-sectional shape and the same extending direction as the hot electrode, and having different lengths, and the inspection An electrical signal is input to at least two of the test electrodes, and the delay time required for each electrical signal to propagate through the test electrode is measured. The length of each test electrode and the measured delay time The refractive index measurement method is characterized in that a refractive index with respect to an electric signal of the inspection electrode is obtained based on the inclination of the above.

  According to the present invention, an electrical signal is input to inspection electrodes formed on wafers having different lengths and the delay time is measured, and the inclination between the length of each inspection electrode and the measured delay time is determined. As a result, the refractive index of the electrode can be easily measured before the wafer is made into chips, and the refractive index of the electrode can be accurately measured without being affected by the electrode handling portion.

1 is an overall configuration diagram of a wafer with inspection electrodes according to an embodiment of the present invention. It is a detailed block diagram of the electrode for a test | inspection. It is an example of the measurement result which measured the refractive index with respect to a microwave using the electrode for a test | inspection.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an overall configuration diagram of a wafer with electrodes for inspection according to an embodiment of the present invention. The wafer 1 is made of a material having an electro-optic effect, for example, lithium niobate. In the first area 10 of the wafer 1, a plurality of optical waveguide patterns 101 and electrode patterns of optical waveguide elements which are actual products are arranged in the row direction and the column direction. The planar shape of the optical waveguide pattern 101 is a Mach-Zehnder type optical waveguide. Although not shown, the electrode pattern is a traveling wave electrode in which a hot electrode and a ground electrode are arranged along the arm of the Mach-Zehnder optical waveguide. The hot electrode and the ground electrode are connected to the outside of the electric field applying unit disposed in parallel with the optical waveguide so that the electric field is applied to the optical waveguide by the microwave traveling between the electrodes. It consists of a routing wiring part to the terminal. This one Mach-Zehnder type optical waveguide and the traveling wave type electrode corresponding thereto constitute one optical modulator. After the individual optical modulators are made into chips from the wafer 1, when a microwave is input to the traveling wave type electrode, an electric field is applied from the electric field applying unit to the optical waveguide, and the refractive index of the optical waveguide changes due to the electrooptic effect, The light propagating through the Mach-Zehnder type optical waveguide is modulated.

  Two inspection electrodes 201 and 202 are formed in the second area 20 of the wafer 1. FIG. 2 is a detailed configuration diagram of the inspection electrodes 201 and 202. The inspection electrodes 201 and 202 are composed of linear electrode portions 201a and 202a and pad electrode portions 201b and 202b at both ends of the linear electrode portions 201a and 202a. The straight electrode portions 201 a and 202 a are provided in parallel with the hot electrode of the optical modulator formed in the first area 10. The straight electrode portions 201a and 202a are formed to have the same cross-sectional shape as the electric field applying portion of the hot electrode, that is, the same film thickness and pattern width as the electric field applying portion of the hot electrode. Further, the length of one linear electrode portion 201a is longer than the length of the other linear electrode portion 202a. Further, the pad electrode portion 201b and the pad electrode portion 202b have the same shape.

  A method of measuring the refractive index of the inspection electrodes 201 and 202 with respect to the microwave is as follows. The refractive index is measured in the state of one wafer before the wafer 1 is cut into chips. In this wafer state, an inspection probe is connected to the pad electrode portion 201b of the inspection electrode 201, a measurement signal is input from the inspection probe using a network analyzer, and the delay time of the reflected signal is measured by the time domain method. To do. At this time, the delay time t1 is expressed as t1 = Nm · 2 · (L1 + ΔL) / c. Where Nm is the refractive index of the inspection electrode with respect to the microwave, L1 is the length of the straight electrode portion 201a, ΔL is the length of the pad electrode portion 201b, and c is the speed of light. Similarly, the delay time is also measured for the inspection electrode 202. At this time, the delay time t2 is expressed as t2 = Nm · 2 · (L2 + ΔL) / c. However, L2 is the length of the linear electrode part 202a.

These two measurement results are plotted on a graph with the horizontal axis representing the length of the straight electrode portion and the vertical axis representing the delay time. FIG. 3 shows an example of the measurement result. When the slope of the straight line connecting the two plotted points is α, the refractive index Nm of the inspection electrode with respect to the microwave is
Nm = (α / 2) · c
It can ask for.

  Thus, according to the present invention, the refractive index of the electrode can be easily measured before the wafer is chipped. In addition, the delay time of the two test electrodes is measured, and the refractive index is obtained from the slope of the graph of FIG. 3, so that the refractive index of the electrode can be accurately measured without being affected by the electrode handling portion or the pad electrode. can do.

As described above, the embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to the above, and various design changes and the like can be made without departing from the scope of the present invention. It is possible to
For example, the number of inspection electrodes may be three or more. In this case, the number of plot points in the graph of FIG. 3 is three or more, but the measurement accuracy of the refractive index can be improved by performing statistical processing.
In addition, the measurement of the delay time of the inspection electrode may be performed by measuring the delay time of a signal transmitted from the pad electrode portion on one end side to the pad electrode portion on the other end side. In this case, the equation for obtaining the refractive index is Nm = α / c.
In addition, when there are a plurality of types of cross-sectional shapes of the electric field application portion of the hot electrode in one wafer, it is preferable to provide an inspection electrode for each type of cross-sectional shape of the electric field application portion.
Further, it is desirable that the hot film and the wafer and the inspection electrode and the wafer have the same film configuration (the same material and the same film thickness).

  DESCRIPTION OF SYMBOLS 1 ... Wafer 101 ... Optical waveguide pattern 201, 202 ... Inspection electrode 201a, 202a ... Linear electrode part 201b, 202b ... Pad electrode part

Claims (4)

For wafers with electro-optic effect,
A plurality of optical waveguides;
A plurality of traveling-wave control electrodes for controlling light propagating through the optical waveguide by advancing an electrical signal between the electrodes, wherein a hot electrode and a ground electrode are disposed along the optical waveguide;
At least two inspection electrodes having the same cross-sectional shape and the same extending direction as the hot electrode, each having a different length;
A wafer with an inspection electrode, characterized in that is formed. The electric field application portions of the plurality of traveling wave type control electrodes have a plurality of types of cross-sectional shapes,
The wafer with inspection electrodes according to claim 1, wherein the at least two inspection electrodes are provided for each type of the cross-sectional shape.   The wafer with an inspection electrode according to claim 1 or 2, wherein the film structure is the same between the hot electrode and the wafer and between the inspection electrode and the wafer. A plurality of optical waveguides and a hot electrode and a ground electrode are arranged along the optical waveguide on a wafer having an electro-optic effect, and an electric signal is advanced between the electrodes to control light propagating through the optical waveguide. A traveling wave type control electrode, and at least two inspection electrodes having the same cross-sectional shape and the same extending direction as the hot electrode, and different lengths from each other,
An electrical signal is input to at least two of the inspection electrodes, and a delay time required for each electrical signal to propagate through the inspection electrode is measured.
A refractive index measurement method, wherein a refractive index with respect to an electrical signal of the inspection electrode is obtained based on a slope between the length of each inspection electrode and each measured delay time.

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