JP2000046756A - Method of measuring conductivity at metal layer interface - Google Patents

Abstract

(57) Abstract: A novel measurement method capable of measuring the conductivity of an interface between a metal layer and a dielectric substrate is provided. A metal layer (4) and a dielectric substrate (5) in an object to be measured comprising a dielectric substrate (5) having a metal layer (4) adhered to a surface thereof.
A method for measuring the conductivity at the interface with the substrate, wherein both end faces of the dielectric cylinder 6 having a known relative dielectric constant and dielectric loss tangent are sandwiched so that the dielectric substrate 5 faces the dielectric cylinder 6, Alternatively, a dielectric resonator A or B having one end face of the dielectric cylinder 6 opposed to the dielectric substrate 5 and the other end face opposed to the conductor plate 7 having a known conductivity is formed to form a dielectric resonator. The resonance frequency f ₀ measured from the resonance waveform of the TE 0 _mn mode (m = 1, 2, 3,..., N = 1, 2, 3,...) Generated by the body resonator A or B and no load Q,
Based on Qu, the high-frequency conductivity at the interface between the metal layer 4 and the dielectric substrate 5 is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the conductivity of a metal layer formed on the surface of a dielectric substrate at the interface with the dielectric substrate, particularly the conductivity in a high frequency region and a millimeter wave region. It is.

[0002]

2. Description of the Related Art In general, measurement of electrical conductivity is one of the most basic measurements of electrical material properties. In particular, the IC element is mounted on the surface of the dielectric substrate,
In a package for a semiconductor element on which a metal wiring layer electrically connected to the C element is formed and a circuit board, its characteristic value is an important factor in design.

Conventionally, conductivity has been measured by measuring the direct current resistance of a metal layer. This will measure the conductivity of the bulk body. However, when the frequency of the electric signal increases, the current concentrates on the surface of the metal layer or the interface with the dielectric substrate on which the metal layer is adhered due to the skin effect. On the surface of the metal layer, the conductivity deteriorates due to oxidation and surface roughness, and at the interface of the metal layer with the dielectric substrate, the unevenness of the interface and diffusion of conductor atoms into the dielectric substrate, reaction between the metal layer and the dielectric substrate As a result, the electrical conductivity deteriorates.

[0004] Therefore, in a package for a semiconductor element or a circuit board for a high frequency which handles a high frequency signal, it is important to measure the conductivity of the interface as well as the surface of the metal layer adhered to the surface of the dielectric substrate.

A technique for measuring the conductivity of a conductive material in the microwave region with high accuracy is required in the measurement of the complex permittivity of a dielectric substance. Measurem
ent of Dielectric Properties of Low-Loss Materials
by the Dielectric Rod Resonator Method "(IEEE Tra
ns. MTT, vol. MTT-33, pp586-592, No. 7, July 1985)
(Reference 1) and "RoundRobin Test on a Dielectric Res
onator Method for Measuring Complex Permittivity a
t Microwave Frequency "(IEICE Trans. ELECTRON.,
E77-C, 6, pp. 882-887, June 1994) and are also disclosed in the JIS standard "JIS R 1627".

FIG. 7 shows a set of dielectric resonators for conductivity measurement described in JIS R 1627, each having the same relative permittivity and dielectric loss tangent, and having different heights by integral multiples. A pair of conductor plates 32 is provided on both end surfaces of the dielectric cylinders 31a and 31b.
Is attached. From the resonance frequency f ₀ of each resonator and the measured values of no-load Q and Qu, the conductor plate 32
Can be calculated.

[0007]

However, the methods disclosed in the above-mentioned documents and JIS standards are applied only when measuring the conductivity of the surface of the conductor plate 32. At present, there is no known method for measuring the conductivity at the interface between the substrate and the dielectric substrate.

Further, research and development in the millimeter wave region of 60 GHz or 77 GHz have recently been carried out in order to realize an on-vehicle radar or a millimeter wave wireless LAN. Has been
It is not known at all what measurement system should be used.

Accordingly, an object of the present invention is to provide a novel measurement method capable of measuring the conductivity at the interface between a metal layer and a dielectric substrate in the microwave to millimeter wave region, that is, at the metal layer interface. It is assumed that.

[0010]

Means for Solving the Problems As a result of repeated studies on the above problems, the present inventors have found that both ends or one of the two end surfaces of a dielectric cylinder made of a dielectric material having a known relative dielectric constant and dielectric loss tangent are known. By forming a dielectric resonator by attaching a dielectric substrate having a metal layer adhered to an end face in a predetermined relationship, an interface between the metal layer and the dielectric substrate, that is, a conductive layer at the metal layer interface is formed. Rate can be measured,
The present invention has been reached.

That is, the method for measuring the conductivity of the interface of a metal layer according to the present invention comprises the steps of: measuring the conductivity of the interface between the metal layer and the dielectric substrate in an object to be measured comprising a dielectric substrate having a metal layer adhered to the surface; A method of measuring the dielectric constant, wherein the dielectric substrate of which the relative dielectric constant and the dielectric loss tangent are known is sandwiched so that the dielectric substrate of the device to be measured faces the dielectric cylinder, or Forming a dielectric resonator in which one end face of the body cylinder is opposed to the dielectric substrate of the object to be measured, and the other end face is sandwiched by being opposed to a conductive plate having a known conductivity; The resonance frequency f ₀ and the no-load Q and Qu are measured from the resonance waveform of the TE _0mn mode (m = 1, 2, 3,..., N = 1, 2, 3 _,. Based on the resonance frequency and the no-load Q, the metal layer and the It is characterized in that to calculate the high frequency conductivity of the interface between the dielectric substrate.

In addition, the input and output of the signal to the above-mentioned dielectric resonator are performed by using a non-radiation device composed of a coaxial cable having a loop antenna formed at the tip or a dielectric strip and conductor plates disposed above and below the dielectric strip. A dielectric line (hereinafter simply referred to as N
It is called RD guide. ) Makes it possible to measure the conductivity in the microwave to millimeter-wave range.

[0013]

FIG. 1 is a block diagram showing an embodiment of a basic configuration of a measuring system in a measuring method according to the present invention. According to FIG. 1, a microwave signal output from a synthesized sweeper 1 is divided into two, and one is input to a network analyzer 2 as a reference. The other is configured to be input to the dielectric resonator 3 for measuring the interface conductivity and to transmit the transmitted signal to the network analyzer 2.

Next, the method of measuring the interface conductivity and the principle thereof according to the present invention will be described. The measuring method of the present invention is based on a method in which a dielectric plate having a predetermined dimensional ratio (height t / diameter d) is provided on both end surfaces with a conductor plate (usually, the diameter of the dielectric cylinder is large enough so that the edge effect can be ignored). When a field plate having a diameter D about three times as large as d is provided in parallel and sandwiched therebetween, a high-frequency current flowing through the plate in the TE 0 _mn resonance mode is short-circuited, that is, a dielectric and a conductor. It is based on the basic principle that it is distributed only at the interface with.

That is, according to the present invention, the dielectric substrate 5 on which the metal layer 4 is adhered is used as an object to be measured. As shown in FIG. A dielectric cylinder 6 made of a dielectric material having a known dielectric loss tangent and having a predetermined dimensional ratio (height t / diameter d) is formed such that the dielectric substrate 5 of the object to be measured faces the end face of the dielectric cylinder 6. Thus, the dielectric resonator A is sandwiched from both ends.

Alternatively, as shown in FIG. 2 (b), the dielectric cylinder 6 is arranged such that the dielectric substrate 5 of the object to be measured faces one end face of the dielectric cylinder 6, and the other of the dielectric cylinder 6. The dielectric resonator B is sandwiched so that the end face faces the conductor plate 7.

In the above dielectric resonators A and B, T
E _0mn mode (m = 1, 2, 3,..., N = 1, 2, 2,
By using the fact that the high-frequency current flowing through the metal layer 4 is distributed only at the interface between the metal layer 4 and the dielectric substrate 5 according to (3,...), The interface conductivity can be measured.

More specifically, when the dielectric resonator A shown in FIG. 2A is formed, the measured TE 0 _mn mode (m = 1, 2, 3,..., N = 1) , 2,3, ...)
The resonance frequency f ₀ and unloaded Q, it is possible to calculate the interfacial conductivity sigma _{in t} by the following Equation 1 (1) from Qu.

[0019]

(Equation 1)

However, A, B ₁ and B ₂ are given by the following equation (2)
(3) Calculated by equation (4).

[0021]

(Equation 2)

Here, tan δ ₁ and tan δ in equation (1)
₂ is the dielectric tangent of the dielectric cylinder 6 and the dielectric substrate 5, respectively.
In the equation (2), μ is the magnetic permeability of the metal layer 4, ω is 2πf ₀ , ∬ |
H | ² dS magnetic field of the integration of the upper and lower metal layer interface, W ^e is the resonator of the field energy, (3) (4) of the W _d1 ^e and W
_d2 ^e is the electric field energy in the dielectric cylinder 6 and in the dielectric substrate 5.

[0023] _{^{Incidentally, W e, W d1 e,}} W d2 relative permittivity of the dielectric cylinder 6 and the dielectric substrate 5 necessary for the calculation of ^{e ε} _'1, ^ε' ₂ and tan [delta ₁ and tan [delta ₂ is the Document 1 And Kobayashi, Sato, et al., "Science Technique MW87."
-7 "(1987).

The dielectric resonator B shown in FIG.
Is constructed, the measured TE _0mn mode (m =
The interface conductivity σ _int is calculated from the resonance frequency f ₀ of 1, 2, 3,..., N = 1, 2, 3,. Can be.

[0025]

(Equation 3)

Here, A _top , A _bottom , B ₁ , and B ₂ are calculated by the following equations (6), (7), (8), and (9).

[0027]

(Equation 4)

Here, σ _{metal in} equation (5) is the conductivity of the conductive plate 7, μ _{top in} equation (6) is the magnetic permeability of the metal layer 4, and ω is 2
πf ₀ , ∬ | H | ² dS _top is the integral of the magnetic field at the interface of the metal layer 4, μ _{bottom in the} equation (7) is the magnetic permeability of the conductor plate 7, ∬ | H
| ² dS _bottom is the integral of the magnetic field at the opposing surface of the conductor plate 7 and the dielectric cylinder 6.

It should be _{^{noted, W e, W d1 e,}} W d2 dielectric constant ε _'1, ε' the dielectric cylinder 6 and the dielectric substrate 5 necessary for the calculation of ^e ₂ and tan [delta ₁ and tan [delta ₂ and the conductive plate 7 Conductivity σ _metal
Describes the dielectric cylinder resonator method disclosed in the above-mentioned document 1 and “Religion Technique MW87-7” by Kobayashi and Sato (1987).
The measurement is performed by the cavity resonator method disclosed in US Pat.

When the measurement is performed based on the above measurement principle, and the measurement frequency is 50 GHz or less, a coaxial cable 8 is provided for the dielectric resonator A as shown in FIG. By forming the loop antenna 9 at the end of the cable 8, signal input and output can be performed. In this case, the loop antenna 9 is arranged so that the loop surface is parallel to the device under test in the resonator A. The position of the loop antenna 9 is appropriately adjusted so that the measurement of the resonance frequency f ₀ and the no-load Q and Qu can be performed at an insertion loss of 20 to 30 dB.

However, in the millimeter wave region where the measurement frequency is 50 GHz or more, it is difficult to input and output signals with the loop antenna at the tip of the coaxial cable as shown in FIG. Therefore, when the measurement frequency exceeds 50 GHz, the input and output of the signal to the dielectric resonator are performed by the dielectric strip and the conductor plate disposed above and below the dielectric strip.
Performed by RD guide.

Therefore, it is a block diagram showing one embodiment of the configuration of the measurement system when the measurement frequency is 50 GHz or more. According to FIG. 5, the synthesized sweeper 1
The microwave signal output from 1 is amplified by the microwave amplifier 12, and further amplified by the millimeter-wave module 13.
It is converted to a 75 GHz signal and further divided into two signals.
One is input to the network analyzer 15 via the detector R14 as a reference. On the other hand, a dielectric resonator 17 for measuring interface conductivity through an input NRD guide 16
And output NRD guide 18, detector A
19 is transmitted through the network analyzer 1
5 is input.

FIG. 6 is a schematic plan view (a) when the dielectric resonator A shown in FIG. 2 (a) is incorporated in a measurement system, and a schematic cross-sectional view (b). In this measurement system, a dielectric resonator A is provided at the center, and an NRD guide 16 for input to the dielectric resonator A and an NRD guide 18 for output are provided on both sides thereof. The NRD guides 16 and 18
Each of the NRD guides 16 and 18 is connected to a waveguide (not shown) at the ends of a dielectric strip 20 made of a square bar and upper and lower conductor plates 21 and 22 sandwiching the dielectric strip 20. Conversion units 23 and 24 are provided. Further, in order to stably arrange the device under test 25 composed of the dielectric substrate 5 and the metal layer 4 in the system,
Metal lids 26 and 27 are fitted so as to sandwich the dielectric resonator A and a part of the NRD guides 16 and 18.

In the above-described measurement system, the height of the dielectric cylinder 6 in the dielectric resonator A is equal to the height of the NRD guide 1.
The distance between the upper and lower conductive plates 21 and 22 is set to be the same as that of the upper and lower conductive plates 21 and 22.

Further, the thickness of the dielectric substrate 5 is set so that the distance between the metal layers 4 formed on the DUT 25 disposed above and below the dielectric cylinder 6 is equal to or less than a half wavelength of the resonance frequency. Set the This is because when the distance between the metal layers 4 is larger than a half wavelength of the resonance frequency, the electromagnetic field in the _TE0mn resonance mode is dissipated outside the dielectric resonator A.

Further, the dielectric strip 20 of the input / output NRD guide is protruded from the conductor plates 21 and 22 and disposed so as to be close to the tip of the dielectric strip 20 and the dielectric cylinder 6. Are arranged so as to be sandwiched by the 25 dielectric substrates 5 of the device under test. In this case, it is desirable that the distance between the projecting portion of the dielectric strip 20 and the dielectric cylinder 6 is adjusted to a position where the insertion loss becomes 20 to 30 dB. By adjusting the insertion loss to 20 to 30 dB, the resonance frequency f ₀ and the no-load Q and Qu can be measured with high accuracy.

The above measurement system is also applicable to the case where the measurement is performed using the dielectric resonator B shown in FIG.
The measurement can be performed in exactly the same manner by replacing the DUT 25 of the measurement system from the dielectric resonator A with the dielectric resonator B.

[0038]

EXAMPLES Example 1 Two types of 50 × 50 mm glass ceramics (No. 1,
No. 2) on a dielectric substrate made of Cr, a metal layer made of Cr having a thickness of 0.05 μm, and a metal layer made of Cu (thickness: 2 μm) further formed thereon by a sputtering method.
And a sample 2 (glass ceramic No. 2) having a 30 μm thick metal layer formed by simultaneous baking after applying a copper paste on the surface of a glass ceramic green sheet.
1), the specific conductivity σr (conductivity of copper σ ₀ = 5.8 × 10 ⁷ / Ω · m) at the interface between the metal layer and the dielectric substrate in the sample 3 (glass ceramic No. 2). Value)
Was measured by the dielectric resonator A of FIG. 2A using the measurement system of FIG. 4 using a coaxial cable having a loop antenna at the tip as an input / output line.

In addition, the specific conductivity σr of the surface of the metal layer in the sample to be measured was also measured. As shown in FIG. 3, the specific conductivity of the metal layer surface is such that a dielectric resonator C in which the dielectric cylinder 6 is sandwiched from both sides such that the metal layer 4 and the dielectric cylinder 6 face each other is formed. It was measured by applying JISR 1627.

It should be noted that sapphire having an end face perpendicular to the C axis (diameter d = 10000 m) is used as the dielectric cylinder 6 in FIG.
m, height t = 5.004 mm). Table 1 shows the dielectric properties of the sapphire cylinder and the two types of glass ceramics. The results of the measurement are shown in Table 2.

[0041]

[Table 1]

[0042]

[Table 2]

As is clear from the results in Table 2, the specific conductivity σr on the surface of the co-fired copper conductor layer is about 80%, while the specific conductivity σr at the interface with the dielectric substrate is 5%.
It shows a low value of about 0%, which indicates that the difference in conductivity between the surface and the interface can be clearly measured. Further, according to the measurement method of the present invention, the measurement error of the specific conductivity at the metallized interface was 3% or less, and a highly accurate measurement result could be obtained.

Example 2 The specific conductivity σr (conductivity of copper σ ₀ = 5.8 × 10) at the interface between the metal layer of the sample 3 to be measured and the dielectric substrate in Example 1 was used.
⁷ / Ω · m) was measured by the dielectric resonator A of FIG. 2A using the measurement system of FIG. 6 using an NRD guide as an input / output line.

As the dielectric cylinder 6 in FIG. 1, sapphire having an end face perpendicular to the C axis (diameter d = 3.103 m)
m, height H = 2.251 mm). Table 3 shows the dielectric characteristics of the sapphire cylinder and the glass ceramic No. 2 at 60 GHz. The results of the measurement are shown in Table 4.

[0046]

[Table 3]

[0047]

[Table 4]

As is clear from the results in Table 4, the specific conductivity σr on the surface of the co-fired copper metal layer is about 40%, while the specific conductivity σr at the interface with the dielectric substrate is 1%.
The value was as low as about 7%. Further, according to the measurement method of the present invention, the measurement error of the specific conductivity at the metallized interface was 1% or less, and a highly accurate measurement result was obtained.

[0049]

As described in detail above, according to the measuring method of the present invention, it is possible to accurately measure the relative conductivity of the interface between the metal layer and the dielectric substrate, which has been difficult to measure conventionally. This is effective in improving the transmission characteristics of a semiconductor element package or a high-frequency circuit board that handles high-frequency signals.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a conductivity measurement system for a metal layer interface according to the present invention.

FIGS. 2A and 2B are schematic diagrams showing the structure of a dielectric resonator used for measuring the conductivity of the metal layer interface according to the present invention, wherein FIG. 2A shows one example and FIG. 2B shows another example.

FIG. 3 is a schematic diagram showing the structure of a dielectric resonator used for measuring the conductivity of the surface of a metal layer.

FIG. 4 is a schematic cross-sectional view for explaining a measurement system at 50 GHz or less in the present invention.

FIG. 5 is a block diagram showing the overall configuration of a system for measuring the conductivity of a metal layer interface at 50 GHz or higher in the present invention.

FIG. 6 is a schematic plan view (a) and a schematic cross-sectional view (b) for describing a measurement system at 50 GHz or higher in the present invention.
It is.

FIG. 7 is a schematic diagram showing the structure of a set of dielectric resonators for measuring the conductivity of a metal plate described in JIS R 1627.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Synthesized sweeper 2 Network analyzer 3 Dielectric resonator 4 Metal layer 5 Dielectric substrate 6 Dielectric cylinder 7 Conductor plate

Continuing from the front page (72) Inventor Hiroshi Uchimura 3-5 Koikodai, Seika-cho, Soraku-gun, Kyoto Kyoto Inside the Central Research Laboratory, Sera Corporation (72) Inventor Ken Takeshita 3-5-kokodai, Seika-cho, Soraku-gun, Kyoto Kyoto Sera Corporation Central Research Laboratory

Claims (3)

[Claims] 1. A method for measuring the electrical conductivity of an interface between a metal layer and a dielectric substrate in an object to be measured comprising a dielectric substrate having a metal layer adhered to a surface thereof, comprising: Either the both ends of the dielectric cylinder whose dielectric loss tangent is known may be sandwiched so that the dielectric substrate of the device under test faces the dielectric cylinder, or one end surface of the dielectric cylinder may be in contact with the dielectric cylinder of the device under test. A dielectric resonator is formed in such a manner that the dielectric resonator is opposed to a body substrate and the other end face is sandwiched between a conductor plate having a known conductivity, and a TE _0mn mode (m = 1, 1) generated by the dielectric resonator is formed. , N = 1, 2, 3,...) To measure a resonance frequency and a no-load Q, and based on the resonance frequency and the no-load Q, Calculating a high-frequency conductivity at an interface with the dielectric substrate. A method for measuring the conductivity at the interface of the metal layer. 2. The method according to claim 1, wherein the input and output of signals to and from the dielectric resonator are performed by a coaxial cable having a loop antenna formed at the end. 3. An NRD guide (non-radiative dielectric line) comprising a dielectric strip and conductor plates disposed above and below the dielectric strip, for inputting and outputting signals to and from the dielectric resonator. The method for measuring conductivity at an interface of a metal layer according to claim 1.