JP2013080936A - Silicon carbide substrate, semiconductor device and wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that an electronic element cannot be mounted practically on a silicon carbide when mounting a device such as an electronic element because a high-frequency loss of the silicon carbide substrate is large.SOLUTION: Because it is found that an electronic element can be mounted and sufficiently operated when a silicon nitride substrate has a high-frequency loss under 20 GHz of 2.0 dB/mm and under, the silicon carbide substrate having a high frequency loss of 2.0 dB/mm and over is heated at 2000°C and over. According to this heat treatment, a high frequency loss under 20 GHz can be made 2.0 dB/mm and under. Further, by manufacturing the silicon nitride substrate by CVD without flowing nitride to a heater, the high frequency loss can be made 2.0 dB/mm and under.

Description

  The present invention relates to a silicon carbide (SiC) substrate, a semiconductor device including the silicon carbide substrate, and a wiring substrate.

  In general, since a silicon carbide substrate is excellent in corrosion resistance to chemicals such as acid and alkali, for example, as shown in Patent Document 1, a polishing pad used in CMP (chemical mechanical polishing) is processed and adjusted. Is used.

  On the other hand, as disclosed in Patent Document 2, the silicon carbide substrate is less likely to crack than a silicon substrate or the like, and has high thermal conductivity, so that it is intended to be used as a substrate for SOI (Semiconductor On Insulator). ing. In this case, silicon carbide may be used as a base material for the SOI substrate, and a silicon substrate may be formed on the silicon carbide base via an insulating film. That is, in an SOI substrate, silicon carbide is often used as a support member, and silicon is often used as an element formation region for forming a semiconductor element.

  In addition, as disclosed in Patent Document 3, it is also proposed to form a low-loss high-frequency wiring board using ceramics containing silicon carbide.

JP 2006-95637 A Japanese Patent Application No. 2007-184896 JP 2000-228461 A

  As described in Patent Documents 2 and 3, not only using a silicon carbide substrate as a support substrate and a wiring substrate, but recently mounting various electronic elements such as a semiconductor device on the silicon carbide substrate, or It is also considered to form an electronic element in a silicon carbide substrate. Thus, when an electronic element is directly attached to a silicon carbide substrate, the silicon carbide substrate proposed so far cannot be used as it is.

  For example, a silicon carbide substrate used for an electronic device used in a high frequency band such as the GHz band is required to have a small loss at a high frequency. However, the silicon carbide substrate that has been proposed in the past has insufficient electrical characteristics such as a large high-frequency loss. Therefore, the actual situation is that an example of a silicon carbide substrate on which an electronic device is actually mounted has not been proposed. .

  An object of the present invention is to provide a silicon carbide substrate with low high-frequency loss.

  Another object of the present invention is to provide a semiconductor device, a wiring board, and the like including a silicon carbide substrate with low high-frequency loss.

  According to the first aspect of the present invention, there is obtained a silicon carbide substrate characterized in that loss at a frequency of 20 GHz is 2 dB / mm or less.

  According to the second aspect of the present invention, there is obtained a silicon carbide substrate characterized in that it is formed of polycrystalline silicon carbide in the first aspect.

  According to the third aspect of the present invention, there is obtained a semiconductor device including a substrate formed of polycrystalline silicon carbide having a loss at a frequency of 20 GHz of 2 dB / mm or less.

  According to the fourth aspect of the present invention, there is obtained a wiring board including a silicon carbide substrate formed of polycrystalline silicon carbide having a loss at a frequency of 20 GHz of 2 dB / mm or less.

  According to the present invention, a silicon carbide substrate in which high-frequency loss at 20 GHz is reduced to 2 dB / mm or less can be obtained. Furthermore, the high frequency loss could be reduced to 2 dB / mm or less by heating the silicon carbide substrate obtained by a normal manufacturing method to 2000 ° C. or higher.

(A), (b), (c), and (d) is process drawing explaining the manufacturing method of the preliminary | backup SiC substrate used for producing the SiC substrate which concerns on this invention. It is a figure explaining the heat treatment furnace used when manufacturing the SiC substrate which concerns on this invention. It is a figure which shows the heat processing process in the heat processing furnace shown by FIG. It is a graph which shows the high frequency loss characteristic of the SiC substrate obtained by the heat treatment process shown by FIG.2 and FIG.3. It is a graph which shows the high frequency loss characteristic of the other SiC substrate obtained by the heat treatment process shown by FIG.2 and FIG.3. It is a figure explaining the measuring method which measures the high frequency loss characteristic of a SiC substrate.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments to which the present invention is applied will be described in detail with reference to the drawings.

  With reference to FIG. 1, a method of manufacturing a silicon carbide substrate (referred to as a preliminary silicon carbide substrate) at a pretreatment stage used when manufacturing a silicon carbide (SiC) substrate according to the present invention will be described.

  First, as shown to Fig.1 (a), the graphite base material 10 is prepared. Here, a disc-shaped graphite base material having a predetermined size made of high-purity graphite matched to the size of the SiC substrate to be produced was prepared. Thereafter, the disk-shaped graphite substrate 10 is introduced into a CVD apparatus, and silicon carbide 12 is grown to a predetermined thickness on the upper surface, the lower surface, and the peripheral surface of the graphite substrate 10 by CVD as shown in FIG. Let The grown silicon carbide 12 had a 3C—SiC crystal structure. Specifically, as a CVD apparatus, a CVD furnace equipped with a reaction part and a heater part was used, and a device capable of flowing a gas (for example, nitrogen gas) into the heater part was used. The disc-shaped graphite base material 10 was grown in the above CVD apparatus by heating and holding at a predetermined temperature (for example, 1000 to 1600 ° C.) in a hydrogen atmosphere.

In addition, the pressure in a CVD apparatus was 1.3 kPa, for example. In this state, together with hydrogen gas (H ₂ ) as a carrier gas, 5 to 20% by volume of SiCl ₄ , C ₃ H ₈ or the like as a raw material for SiC is supplied. SiC raw material combinations include SiH ₄ / CH ₄ , SiH ₄ / C ₂ H ₄ , SiH ₄ / C ₃ H ₈ , SiCl ₄ / CCl ₄ , SiCl ₄ / CH ₄ , CH ₃ SiCl ₃ , (CH ₃ ) ₂ SiCl ₂ may be used. By supplying these gases, a 3C-SiC crystal body 12 as a SiC layer was formed on the surface of the graphite substrate 10 by a desired thickness (for example, 0.5 to 1 mm).

  Here, two types of SiC substrates were manufactured: a SiC substrate manufactured without flowing nitrogen to prevent the heater from being consumed, and a SiC substrate manufactured with nitrogen flowing.

  Next, the graphite base material 10 on which the 3C—SiC crystal was grown was mechanically polished, and the SiC on the peripheral surface was removed by grinding as shown in FIG. The mechanical polishing was performed using, for example, diamond abrasive grains.

  Subsequently, the graphite substrate 10 whose upper and lower surfaces are covered with 3C—SiC is heated at 900 to 1400 ° C. in an oxygen atmosphere, so that the graphite substrate 10 is removed by burning and desorbing. Two 3C-SiC substrates 14 were obtained (FIG. 1 (d)).

  Thereafter, the 3C-SiC substrate 14 was mechanically polished, and finally the wafer edge portion was chamfered and cleaned, and then a predetermined inspection was performed to manufacture a high-purity SiC substrate. The 3C—SiC substrate thus obtained was formed of 3C—SiC crystal (polycrystalline SiC), which is one of polytypes of SiC crystal. In addition, although the example of the SiC substrate of 3C-SiC was demonstrated in this example, the polytype of the SiC substrate for high frequency use of this invention may be 4H-SiC, for example, and it is a polycrystal of silicon carbide (SiC). The structure is not particularly limited. Here, a SiC substrate manufactured by CVD or the like is referred to as a preliminary silicon carbide (SiC) substrate.

  With reference to FIG. 2, a method for improving the high-frequency loss of silicon carbide substrate (preliminary silicon carbide (SiC) substrate) 14 obtained in FIG. 1 (d) will be described. It has been found that the high frequency loss of the preliminary silicon carbide substrate 14 can be improved by heat treatment in the heat treatment furnace shown in FIG.

  The heat treatment furnace shown in FIG. 2 has a stainless steel furnace body 20, and the furnace includes a heat treatment part (reaction part) 21 and a heater part 22. The heat treatment part 21 and the heater part 22 are graphite members. Or it is divided by the partition 24 covered with silicon carbide or a material containing these. Further, a rare gas such as argon or helium and nitrogen can be selectively flowed into the heat treatment section 21 in the furnace, and the inside of the furnace can be evacuated by a vacuum pump.

  As a heat treatment method, first, a preliminary SiC substrate 14 (which may be SiC 12 with a graphite base material from which the graphite base material has not been removed) is prepared and set in the reaction section 21 in the furnace 20. When setting, it is desirable to set using a graphite jig, but the preliminary SiC substrate 14 may be directly stacked and set. After setting the SiC substrate 14, the heat treatment shown in FIG. 3 is performed. In this example, when SiC is grown by a CVD apparatus, a preliminary SiC substrate (referred to as “A substrate”) manufactured without flowing nitrogen through the heater portion and a preliminary SiC substrate (referred to as “B substrate”) manufactured while flowing nitrogen are used. And both were subjected to heat treatment using the heat treatment furnace shown in FIG.

  As shown in FIG. 3, first, after setting the preliminary SiC substrate 14, the pressure in the furnace is reduced to -90 kPa, and then the atmosphere in the furnace is replaced with nitrogen. Repeat this twice. This process is for replacing the air in the furnace with nitrogen. This replacement step may be performed twice or more. In addition to nitrogen, a rare gas such as argon or helium may be used. After replacing the air in the furnace with nitrogen, the temperature is raised to 800 ° C. in a nitrogen atmosphere. When the temperature reaches 800 ° C., the atmosphere in the furnace is replaced from a nitrogen atmosphere to an argon atmosphere. This replacement takes about 30 minutes. Up to 800 ° C., temperature is measured using a thermocouple.

  Subsequently, the temperature is raised from 800 ° C. to a treatment temperature (2000 ° C. to 2300 ° C.) in an argon atmosphere, and the heat treatment temperature is maintained for about 1 hour. From 800 ° C. to the processing temperature (2000 ° C. to 2300 ° C.), since a temperature of 1700 ° C. or higher cannot be measured with a thermocouple, temperature measurement is performed using a radiation thermometer. In this heat treatment furnace, a thermocouple and a radiation thermometer are used. However, if there is another measuring device that can measure, it may be used. According to experiments, it has been found that a high heat treatment temperature such as 2300 ° C. is preferable. In the experiment, the processing time was 1 hour, but the processing time may be adjusted so that the high-frequency loss is reduced.

  After the heat treatment, the temperature is lowered to room temperature in about 20 hours. The surface of the SiC substrate after the heat treatment is polished and washed to obtain a silicon carbide (SiC) substrate according to the present invention.

  Referring to FIG. 4, the high-frequency loss characteristic of the SiC substrate obtained by heat-treating the A substrate is shown. In FIG. 4, the horizontal axis indicates the frequency in the GHz band, and the vertical axis indicates the high-frequency loss (RF-loss (dB / mm)). As is clear from the curve C1 in FIG. 4, the SiC substrate (that is, the A substrate) in which the nitrogen gas was not flowed in the CVD apparatus, even if the substrate was not heat-treated, had a very high frequency loss of 1.4 dB / mm at 20 GHz. It turns out that it is low.

  According to the knowledge of the present inventors, it has been found that a SiC substrate showing a high frequency loss of 2.0 dB / mm or less at 20 GHz has no practical problem in mounting an electronic element. Therefore, it can be seen that the SiC substrate manufactured without flowing nitrogen gas has sufficient high-frequency loss characteristics.

  Further, the high-frequency loss characteristics of the SiC substrate subjected to the heat treatment of FIG. 3 at 2000 ° C., 2150 ° C., and 2300 ° C. with respect to the above-described unheated A substrate are shown by curves C2, C3, and C4, respectively. As is apparent from comparison of curves 2 to C4, it can be seen that the high-frequency loss can be reduced by performing the heat treatment as compared with the unheated SiC substrate, and the higher the heat-treatment temperature, the lower the high-frequency loss.

  In fact, the SiC substrate heat-treated at 2300 ° C. has a high-frequency loss at 20 GHz lower than 1 dB / mm, whereas the SiC substrate heat-treated at 2000 ° C. and 2150 ° C. has a high-frequency loss at 20 GHz of about 1 dB / mm. Furthermore, the high frequency loss at 40 GHz of the SiC substrate heat treated at 2000 ° C. and 2150 ° C. is about 2 dB / mm, while the SiC substrate heat treated at 2300 ° C. has a high frequency loss at 40 GHz of about 1.5 dB / mm.

  As described above, it can be seen that the SiC substrate that has been subjected to the heat treatment at 2000 ° C. or higher sufficiently withstands high frequency loss at 40 GHz.

  Referring to FIG. 5, the high-frequency loss characteristic when the B substrate is heat-treated is shown. As is clear from FIG. 5, the high-frequency loss characteristic of the B substrate in the unheated state, the high-frequency loss characteristic of the SiC substrate that has been subjected to the heat treatment at 2000 ° C., and the high-frequency loss characteristic of the SiC substrate that has been subjected to the heat treatment at 2300 ° C. Curves C5, C6, and C7 are shown.

  As is apparent from the curve C5, the unheated B substrate exhibits a high-frequency loss of about 2.5 dB / mm at 20 GHz, and is insufficient for mounting an electronic device or the like. However, the SiC substrate obtained by heat-treating the B substrate at 2000 ° C. and 2300 ° C. has a high-frequency loss at 20 GHz of 2.0 dB / mm or less as shown by the curves C6 and C7. Can be used as a substrate.

  Next, a method for measuring the high frequency loss (dB / mm) shown in FIGS. 4 and 5 will be described.

  Referring to FIG. 6, a wiring diagram for high frequency loss measurement is shown. As shown in the drawing, a signal conductor line 30 having a line width S is arranged at the center of the surface of the SiC substrate 14, and ground conductor lines 32 are arranged on both sides of the signal conductor line 30 with a gap W therebetween. Has been. Here, the characteristic impedance is adjusted to 50Ω by changing the interval W and the signal conductor line width S between the signal conductor line 30 and the ground conductor line 32. In this case, the length of the signal conductor wire 30 is 1 mm.

  For the signal conductor line 30 and the ground conductor line 32, about 1 μm of Al is vapor-deposited on the SiC substrate 14 by a vapor deposition method, and a coplanar line pattern composed of the signal conductor line 30 and the ground conductor line 32 is formed of a photoresist. In this example, the signal conductor wire 30 and the ground conductor wire 32 are both formed by vapor deposition. However, the conductor wires 30 and 32 may be formed by using a sputtering method, a CVD method, a plating method, or the like in addition to the vapor deposition method. It may be formed. Further, in the illustrated example, Al is used for the conductor wires 30 and 32, but a metal such as Cu or Au may be used.

  A signal was incident from one terminal of the conductor wires 30 and 32, and a signal transmitted through the other terminal was measured using a network analyzer. In this case, transmission characteristics with a signal frequency from 10 MHz to 50 GHz were measured.

In the measurement results shown in FIG. 4 and FIG. 5, the value of the operation transmission matrix (S ₂₁ ) of the signal passing characteristic in the signal of 1, 5, 10, 20, 30, 40 GHz is shown as dB / mm. .

  In the embodiment described above, the SiC substrate on which the electronic element is mounted and mounted has been described. However, the SiC substrate according to the present invention is not limited to this, and is used for wiring substrates, for polishing pad adjustment, or for supporting SOI. It can also be used as a substrate. As a SiC substrate on which an electronic element is mounted and mounted, for example, there is one in which a Si layer or other semiconductor layer is formed on a SiC substrate, and this semiconductor layer is used as at least a part of the electronic element. Or there exists what mounted the electronic element produced separately on the SiC substrate. As an SOI support substrate, for example, there is an SOI configuration in which an insulating layer is provided on a SiC substrate and a semiconductor layer such as Si is provided thereon. Examples of the wiring board include a structure in which a wiring layer having a predetermined pattern is provided directly on the surface of the SiC substrate or via another insulating layer.

10 Graphite base material 12 SiC
14 SiC substrate 20 Furnace body of heat treatment furnace 22 Heater 24 Graphite member

Claims (4)

  It is composed of polycrystalline silicon carbide by CVD, and is heat-treated so that the transmission loss at a frequency of 20 GHz represented by the operation transmission matrix (S21) of signal transmission characteristics is 2 dB / mm or less. Silicon carbide substrate.   A polycrystalline silicon carbide substrate formed by CVD and heat-treated so that the transmission loss at a frequency of 20 GHz represented by the operation transmission matrix (S21) of the signal passing characteristic is 2 dB / mm or less, and formed on the substrate A semiconductor device comprising a semiconductor layer or an electronic element.   A polycrystalline silicon carbide substrate formed by CVD and heat-treated so that the transmission loss at a frequency of 20 GHz represented by the operation transmission matrix (S21) of the signal passing characteristic is 2 dB / mm or less, and formed on the substrate A semiconductor device including an insulator layer and a semiconductor layer or an electronic element provided over the insulator layer.   It includes a silicon carbide substrate formed of polycrystalline silicon carbide by a CVD method, heat-treated so that the transmission loss at a frequency of 20 GHz represented by the operation transmission matrix (S21) of the signal passing characteristic is 2 dB / mm or less. A wiring board characterized by that.

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