JP4304498B2 - Semiconductor device and semiconductor module - Google Patents

Description

  The present invention relates to a semiconductor device and a semiconductor module having an isolation structure. In particular, the present invention relates to a high-frequency signal isolation structure in a high-frequency semiconductor integrated circuit chip operating in the millimeter wave band.

  In a semiconductor chip, a high-frequency signal leaked from a certain circuit on the chip to the inside of the semiconductor chip propagates over the long distance without much attenuation, and interferes with other circuits on the same chip. There is a problem that the original function is impaired. The above problem is particularly remarkable in a semiconductor chip that operates in a millimeter wave band of 30 GHz or more.

  In addition, the above problem becomes significant even in a semiconductor chip in which a via is formed and a conductor layer is formed on the back surface of the wafer, and a countermeasure for blocking a high-frequency signal propagating inside the semiconductor chip is not taken. Here, the via formation means that a hole penetrating the front and back surfaces of the semiconductor chip is formed, and a conductive material is embedded in the hole, or a conductive film is formed on the inner wall of the hole.

  Even at frequencies sufficiently lower than 30 GHz, there is an interference problem similar to the above problem, but the cause is mainly due to capacitive coupling, unlike the problem in the millimeter wave band. Therefore, there is a need for an isolation technique that is particularly effective in the millimeter wave band, that is, a technique for preventing high-frequency signal interference through a semiconductor chip.

Here, interference through the semiconductor chip in the millimeter wave band will be described in detail. A semiconductor chip is generally a dielectric, and the material used for the semiconductor chip has a relative dielectric constant such as Si: 11.7, GaAs: 12.0, InP: 12.1, and the like. There are many things to have. On the other hand, if the semiconductor chip is regarded as one rectangular waveguide made of a dielectric, the cutoff frequency of the TE ₁₀ mode (fundamental mode) having the lowest cutoff frequency propagating inside the waveguide is:
f _c = c / 2a (1)
It is expressed. Here, c = (εμ) ^−0.5 , ε is the dielectric constant of the semiconductor, μ is the magnetic permeability of the semiconductor, and a is the length of the longer side of the rectangular waveguide. Substituting the value of a typical semiconductor chip on a formula that represents the f _c, approximately 20GHz~40GHz becomes cutoff frequency.

  Next, compound semiconductors such as GaAs and InP are often used for semiconductor chips operating at 30 GHz or higher. Since these semiconductor chips use a semi-insulating substrate, tan δ representing the loss of high-frequency signals inside the semiconductor chip is usually sufficiently smaller than 0.01. That is, in a semiconductor chip manufactured by a compound semiconductor, a high frequency signal of several tens of GHz or more can be easily propagated through the substrate and is transmitted without attenuating a long distance because of a small loss.

Since a high-frequency signal can propagate inside the semiconductor chip, an interference problem becomes apparent when a high-frequency signal leaks from the circuit on the semiconductor chip into the semiconductor. Usually, a high-frequency signal propagating through a coplanar line (CPW) used in a semiconductor integrated circuit propagates in a pseudo TEM mode, and the efficiency of directly exciting the TE ₁₀ mode that can propagate through the semiconductor chip is low. However, since the TEM mode is disturbed in the bent portion of the coplanar line, the TE ₁₀ mode inside the semiconductor chip can be excited. Further, the TEM mode disturbance becomes more prominent as the width of the coplanar line becomes wider. In an actual circuit, in order to suppress transmission loss, a wide coplanar line is used everywhere, and the coplanar line has a very large bent portion. In addition, when a semiconductor chip is mounted, imperfections during assembly, line subjectivity of the structure itself, or characteristic impedance disturbance at the connection point between the external circuit and the semiconductor chip that transmits high-frequency signals For example, unnecessary electromagnetic wave radiation is likely to occur. In a semiconductor chip having a plurality of ports for high-frequency signals, high isolation between the ports is required, so that there is often a problem of inter-port interference due to propagation inside the semiconductor chip.

  In order to prevent the interference problem, there is a method using a radio wave absorber as a prior art, and various radio wave absorbers are commercially available (for example, see Non-Patent Document 1). In the above method, a radio wave absorber that absorbs electromagnetic waves in a target frequency band is disposed so as to be close to the front surface, back surface, or side surface of the semiconductor chip, and electromagnetic waves leaking from the semiconductor chip are absorbed and converted to Joule heat. By doing so, interference is suppressed.

“Solid-type radio wave shield absorber μect PP3100 Technical Information”, Kyocera Corporation

  In the method using the radio wave absorber, in order to efficiently absorb the leaked electromagnetic wave, it is necessary to dispose the radio wave absorber as close to the semiconductor chip as possible. However, if the circuit is arranged so as to be in contact with the surface of the semiconductor chip on which the circuit is formed, the circuit characteristics deteriorate, so that it is difficult to make it approach too much. The arrangement is often used not for improving the isolation of the semiconductor chip but for the purpose of preventing resonance of electromagnetic waves due to the space (cavity) inside the module in which the semiconductor chip is mounted.

  In addition, when the radio wave absorber is disposed in contact with the back surface of the semiconductor chip, the contact area between the semiconductor chip and the radio wave absorber can be sufficiently large, and electromagnetic waves can be efficiently absorbed. There is a problem that the heat dissipation characteristics of the semiconductor chip deteriorate due to the thermal resistance of the radio wave absorber. Although the material of the commercially available radio wave absorber has not been clarified accurately, a rubber-like or resin-like material added with a necessary additive to have a radio wave absorption function, or ceramics, There are materials that have the effect of absorbing radio waves by adding necessary additives, and all materials have high thermal resistance, and the heat dissipation effect of the semiconductor chip deteriorates. For this reason, it is difficult to use a method using a radio wave absorber for a semiconductor chip that requires low thermal resistance, such as a power amplifier. In addition, it is difficult to control the thickness and flatness of the radio wave absorber made of the above material, and when the radio wave absorber is disposed in contact with the back surface of the semiconductor chip, accurate alignment of the semiconductor chip becomes difficult. Problems are likely to occur in processes such as wire bonding.

  Furthermore, when the radio wave absorber is disposed in contact with the side surface of the semiconductor chip, good contact cannot be obtained because the contact area is small. The method is used as a supplementary means in combination with other isolation techniques.

  Another problem of the method using the radio wave absorber is that it is difficult to optimize the radio wave absorber according to the use conditions. Depending on the given external conditions, there are dielectric constant, magnetic permeability, resistivity, dielectric loss, etc. that the wave absorber absorbs electromagnetic waves most efficiently, but the types of wave absorbers that are actually available are limited Yes. It is particularly effective in the millimeter wave band, and it is particularly difficult to obtain a radio wave absorber optimized for the purpose of improving the isolation of the semiconductor chip. Further, the cost of the radio wave absorber is high, and the manufacturing cost of the high frequency module is reduced. This is the cause of the increase.

  Therefore, the present invention has a structure that strongly suppresses interference between circuits and / or lines on a semiconductor chip, that is, enables high isolation without causing deterioration of heat dissipation characteristics of the semiconductor chip. An object is to provide a semiconductor device and a semiconductor module.

  It is another object of the present invention to provide a semiconductor device and a semiconductor module that have a structure that can be manufactured at a low cost and can be easily adjusted in accordance with use conditions while enabling high isolation.

According to the semiconductor device and the semiconductor module of the present invention,
A semiconductor chip and a resistor substrate having a resistivity of 0.2 Ωcm or more and 10 Ωcm or less, the semiconductor chip has an electromagnetic wave propagation mode capable of propagating inside the semiconductor chip, and The resistor substrate is any one of a single crystal Si substrate, a GaAs substrate, and an InP substrate , and has a structure in which the resistor substrate is disposed in contact with a surface where the circuit of the semiconductor chip is not formed.

Also, according to another embodiment of the present invention,
The electromagnetic wave that can propagate through the semiconductor chip is preferably 30 GHz or more.

Furthermore, according to another embodiment of the present invention,
The semiconductor chip preferably has a coplanar line.

  By using the structure according to the present invention, it is possible to achieve high isolation of the semiconductor chip while maintaining good heat dissipation characteristics, high frequency characteristics, and thermal stability. In addition, since it can be easily adjusted according to use conditions and can be easily mounted, the performance and cost reduction of the semiconductor device or module using the isolation structure according to the present invention can be achieved.

  The best mode for carrying out the present invention will be described in detail below with reference to the drawings.

  1A and 1B are diagrams showing an embodiment of an isolation structure used in a semiconductor device and a semiconductor module according to the present invention, wherein FIG. 1A is a top view and FIG. 1B is a side view. According to FIG. 1, a single crystal Si substrate 2 is disposed in contact with the back surface of the semiconductor chip 1, and the module housing is disposed on the surface of the single crystal Si substrate 2 opposite to the surface bonded to the semiconductor chip 1. The body 3 is bonded. Here, the surface on which the circuit of the semiconductor chip is formed is referred to as the front surface, and the surface opposite to the surface on which the circuit is formed is referred to as the back surface.

  The semiconductor chip 1 includes a coplanar line as a wiring means, and high-frequency electromagnetic waves can propagate through the inside. As already described, if the semiconductor chip 1 is regarded as a single rectangular waveguide made of a dielectric, an electromagnetic wave having a cutoff frequency or higher expressed by the equation (1) propagates through the semiconductor chip 1. Exists.

  FIG. 2 is a diagram illustrating an example of a circuit formed on the semiconductor chip 1. A coplanar line 7 is connected to the amplifier circuit 6. In the example of FIG. 2, the semiconductor chip 1 has two connection points 8 with the outside.

  The structure for isolation according to the present invention is characterized by using a single crystal Si substrate 2 as shown in FIG. 1 instead of a rubber-like, resin-like or ceramic-like wave absorber.

  The thermal conductivity of Si is 148 W / m ° C., which is an extremely high value compared to the thermal conductivity 0.1 to 40 W / m ° C. of conventional wave absorbers. Therefore, the heat dissipation efficiency of the semiconductor chip 1 is hardly deteriorated, and it has characteristics suitable for application to a power amplifier having a large heat generation amount. Further, the relative permittivity of the conventional wave absorber has various values, but the relative permittivity of the single-crystal Si substrate 2 is 11.7, which is the relative permittivity of GaAs of 12.0 and InP. When the semiconductor chip 1 is made of a Si substrate, a GaAs substrate, or an InP substrate, the relative dielectric constant is approximately the same as 12.1, without changing the characteristic impedance of the coplanar line formed on the semiconductor chip. Isolation is possible.

Furthermore, the thermal expansion coefficient of the single crystal Si is 2.6 × 10 ⁶ / K, which is close to the thermal expansion coefficient of 4 to 6 × 10 ⁶ / K of GaAs or InP. There is also an advantage that the semiconductor chip is not easily peeled off or cracked. In addition, many of the conventional wave absorbers are thermally unstable materials, whereas single crystal Si is a material that is stable even at a high temperature of 500 ° C. or higher. A change in characteristics and failure of the semiconductor chip due to outgas from the radio wave absorber are not a problem.

  Further, the single crystal Si substrate 2 can be a wafer for manufacturing Si devices. Therefore, the single crystal Si substrate 2 having uniform thickness, flatness, electrical characteristics, etc. can be obtained easily and inexpensively. Therefore, the problem that it is difficult to accurately align the semiconductor chip, which may occur when a conventional radio wave absorber is used, is also solved.

  Next, the relationship between the resistivity of the single crystal Si substrate and the isolation effect will be described. The undoped single crystal Si substrate 2 has a low high-frequency loss, and the highly doped single crystal Si substrate 2 has a function similar to that of a conductor substrate. The isolation effect also varies depending on the resistivity of the crystalline Si substrate.

  FIG. 3 is a diagram showing the relationship between the resistivity of the single crystal Si substrate and the isolation effect. The attenuation amount in FIG. 3 indicates the attenuation amount of the electromagnetic wave when the electromagnetic wave of 30 GHz or more is propagated between the opposing side surfaces 4-5 of the semiconductor chip in FIG. In FIG. 3, the wavelength of the electromagnetic wave is λ (= c / f), the lengths L1, L2, L3, and L4 of each side of the semiconductor chip 1 and the single crystal Si substrate 2 are all 2λ, and the semiconductor chip 1 The thickness d of λ / 10 was λ / 10, and the thickness e of the single crystal Si substrate 2 was 0.6λ. Therefore, the following description is valid without depending on the frequency at 30 GHz or more. As a specific example, at 100 GHz, when the dielectric constant ε of the semiconductor is 12, λ is about 1.2 mm, and the length of each side of the semiconductor chip 1 and the single crystal Si substrate 2 is about 2.4 mm. The thickness d of the semiconductor chip 1 is about 0.12 mm.

  From FIG. 3, it can be seen that a very large attenuation is exhibited around a resistivity of 1 Ωcm. In addition, when a preferable attenuation of 20 dB is used as a threshold value, a single crystal Si substrate 2 having a resistivity between 0.2 Ωcm and 10 Ωcm can be used. Unlike the conventional wave absorber, in the single crystal Si substrate 2, the isolation effect can be easily optimized by changing the doping amount of the Si substrate. Even if a high-frequency signal leaks from the coplanar line included in the semiconductor chip 1 to the inside of the semiconductor chip, it is attenuated in the process of propagating inside the semiconductor chip, and interference with other circuits on the same semiconductor chip is effective. Is suppressed.

  FIG. 4 is a diagram showing the relationship between the thickness of the single crystal Si substrate and the isolation effect. 1 shows the relationship between the thickness e of the single-crystal Si substrate 2 in the structure of FIG. 1 and the attenuation of electromagnetic waves of 30 GHz or more between the opposing side surfaces 4-5 of the semiconductor chip. In FIG. 4, the resistivity of the single crystal Si substrate 2 is 1 Ωcm, and other conditions are the same as in FIG. Considering that the isolation effect is best when all the electromagnetic waves radiated from the semiconductor chip 1 to the single crystal Si substrate 2 are absorbed by the single crystal Si substrate 2 and do not return by reflection or the like, the single crystal The Si substrate 2 is preferably as thick as possible. In order to ensure an attenuation of 20 dB or more under the optimum condition of a resistivity of 1 Ωcm, the thickness e needs to be 0.33λ or more. Further, considering that the change in attenuation is small when the thickness e is λ or more, a preferable range of the thickness e is 0.3λ to λ.

  FIG. 5 is a diagram showing the relationship between the side length of the single crystal Si substrate and the isolation effect. 1 shows the relationship between the length of each side and the attenuation of electromagnetic waves of 30 GHz or more between the opposing side surfaces 4-5 of the semiconductor chip with the sides L3 and L4 of the single crystal Si substrate 2 being the same. It is a thing. In FIG. 5, the resistivity of the single crystal Si substrate 2 is 1 Ωcm, and other conditions are the same as those in FIG. As shown in FIG. 5, when the lengths L3 and L4 are longer than the lengths L1 and L2 of the semiconductor chip, good isolation characteristics can be obtained.

  Although the example using a single crystal Si substrate has been described, a resistor substrate in which impurities are doped into GaAs, InP, etc., instead of the single crystal Si, to have the same resistivity as Si. By using this, it is possible to obtain an isolation effect even though it cannot be expected to have a thermal resistance as low as Si and cost reduction.

It is a figure which shows embodiment of the isolation structure which the semiconductor device and semiconductor module by this invention have. It is a figure which shows the example of the circuit formed on a semiconductor chip. It is a figure which shows the relationship between the resistivity of a single crystal Si substrate, and the isolation effect. It is a figure which shows the relationship between the thickness of a single crystal Si substrate, and the isolation effect. It is a figure which shows the relationship between the length of the side of a single crystal Si substrate, and the isolation effect.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor chip 2 Single crystal Si substrate 3 Module housing | casing 4, 5 Side surface of semiconductor chip 6 Amplifying circuit 7 Coplanar line 8 Connection

Claims (4)

Having a semiconductor chip and a resistor substrate having a resistivity of 0.2 Ωcm or more and 10 Ωcm or less,
The semiconductor chip has a propagation mode of electromagnetic waves that can propagate inside the semiconductor chip,
2. The semiconductor device according to claim 1, wherein the resistor substrate is any one of a single crystal Si substrate, a GaAs substrate, and an InP substrate , and has a structure disposed in contact with a surface of the semiconductor chip where a circuit is not formed. The semiconductor device according to claim 1, wherein an electromagnetic wave capable of propagating through the semiconductor chip is 30 GHz or more. The semiconductor chip is the semiconductor device according to claim 1 or 2, characterized in that it has a coplanar line. Having a semiconductor chip and a resistor substrate having a resistivity of 0.2 Ωcm or more and 10 Ωcm or less,
The semiconductor chip has a propagation mode of electromagnetic waves that can propagate inside the semiconductor chip,
2. The semiconductor module according to claim 1, wherein the resistor substrate is any one of a single crystal Si substrate, a GaAs substrate, and an InP substrate , and has a structure arranged in contact with a surface on which the circuit of the semiconductor chip is not formed.

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