JP2008066515A - Semiconductor device and method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor device which can be improved in performance by heating a specific portion without causing thermal deterioration in performance of the semiconductor layer, and a method of manufacturing the semiconductor device. <P>SOLUTION: The semiconductor device is configured in such a way that GaN is deposited as a semiconductor substrate layer 2 on a substrate 1 made of Al<SB>2</SB>O<SB>3</SB>or SiC, AlGaN is epitaxially grown as a semiconductor epitaxial layer 3 thereon, a metal laminate Ti/Al/Ni/Au is formed as an ohmic electrode 5 on a predetermined position of the semiconductor epitaxial layer 3, and an uppermost layer 6 made of a carbon (C) is formed on the ohmic electrode 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.

A nitride semiconductor is a compound of at least one element among group III elements such as A1, Ga, and In and nitrogen that is a group V element. For example, the nitride semiconductor has a general formula of Al _1-ab Ga _a In. _b N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1). Nitride semiconductors are of direct transition type and have a wide band gap from a maximum of 6.2 eV to 0.8 eV depending on the composition. In addition, a composition having a wide band gap has a large thermal stability, breakdown electric field, and saturation electron velocity. The above characteristics are expected to be applied to light-receiving / light-emitting devices in the far-infrared to ultraviolet region and electronic devices such as high-temperature / high-power / high-frequency transistors using nitride semiconductors. Yes.

  In the use of electronic devices, development of heterostructure field effect transistors (HFETs) is in progress. In order to improve the characteristics of the HFET, it is necessary to reduce the sheet resistance or the contact resistance of the semiconductor epitaxial wafer for HFET. These lead to improvements in the high frequency characteristics, output characteristics, and power efficiency of the HFET.

  In order to reduce the sheet resistance, it is necessary to optimize the structure of the semiconductor epitaxial wafer. For example, it is necessary to increase the concentration of the two-dimensional electron gas (2DEG) induced in the channel by increasing the thickness of the AlGaN barrier layer, increasing the Al composition, or increasing the modulation doping.

  In order to reduce the contact resistance, it is necessary to optimize the structure of the semiconductor epitaxial wafer and the process conditions. The contact resistance can be reduced by reducing the thickness of the barrier layer of the semiconductor epitaxial wafer and increasing the 2DEG concentration and the modulation doping concentration. Further, the contact resistance can be reduced by the structure of the ohmic metal and the subsequent heat treatment temperature.

  However, the structure of these semiconductor epitaxial wafers affects other transistor characteristics. For example, an increase in the modulation doping concentration causes an increase in gate leakage. Although increasing the thickness of the barrier layer or increasing the Al composition is effective in reducing the sheet resistance, the contact resistance increases. Further, since the internal stress with the buffer layer is increased, the crystallinity may be deteriorated.

  There is a report that a heat treatment at 830 ° C. or higher is necessary in the process for reducing the contact resistance (see, for example, Non-Patent Document 1 below). In the conventional technique, after a predetermined ohmic electrode (for example, Ti / Al / Ni / Au) is deposited, a sample is placed on Si or C, and lamp heating is performed. The wavelength of the high-intensity light emitted by the lamp is 1500 nm to 5000 nm.

FIG. 11 is a schematic diagram showing a heat treatment technique for reducing the contact resistance of the ohmic electrode in the prior art. In the figure, GaN is deposited as a semiconductor substrate layer 2 on a substrate 1 (Al ₂ O ₃ , SiC), and AlGaN is epitaxially grown as a semiconductor epitaxial layer 3 thereon. The substrate 1, the semiconductor substrate layer 2 and the semiconductor epitaxial layer 3 constitute a semiconductor epitaxial wafer 4. On the semiconductor epitaxial layer 3, a metal stack: Ti / Al / Ni / Au is formed as an ohmic electrode 5. The lamp heating for reducing the contact resistance of the ohmic electrode 5 is performed with a contact heating plate 7 made of a material that absorbs infrared rays such as C or Si underneath so that the semiconductor epitaxial wafer 4 transmits infrared rays. . C or Si of the contact heating plate 7 is lamp-heated, and the semiconductor epitaxial wafer 4 is contact-heated by the heat. Therefore, the entire semiconductor epitaxial wafer 4 and ohmic electrode 5 are heated.

  FIG. 12 is a schematic view when the above-mentioned semiconductor epitaxial wafer 4 is lamp-heated to reduce the contact resistance of the ohmic electrode. The semiconductor epitaxial wafer 4 is an Si heating plate 7 in the annealing furnace casing. It is placed on the plate and heated by contact with the heat of the lamp absorbed by the Si plate.

However, it has been reported that heat treatment at a high temperature by the above method causes an increase in sheet resistance and an increase in current collapse (see Non-Patent Documents 2 and 3 below). Such deterioration due to heat treatment is considered to be caused by changes in the surface state due to heat, changes in the channel potential state, and a decrease in the carrier activation rate of the modulation doped layer.
T. Nakayama et al., Appl. Phys. Lett. 85 (2004) 3775. K. Shiojima et al., Jpn. J. Appl. Phys. 43 (2004) 100. T. Hashizumeet al., Appl. Surface Sci. 234 (2004) 387.

  As described above, in the nitride semiconductor HFET, heat treatment at a high temperature is required to reduce the contact resistance. However, the heat treatment at a high temperature degrades the surface state of the semiconductor epitaxial wafer and causes an increase in sheet resistance and an increase in current collapse.

  The present invention has been devised to solve the above problems, and the problem to be solved by the present invention is to improve the performance by heating a specific portion without causing thermal degradation of the performance of the semiconductor layer. A semiconductor device and a method for manufacturing the semiconductor device are provided.

In order to solve the above problems, in the present invention, as described in claim 1,
In a semiconductor device including a semiconductor layer as a constituent element, the semiconductor device includes a deposit having an infrared absorbing substance having an infrared absorption coefficient larger than the infrared absorption coefficient of the semiconductor layer as a constituent element at a predetermined position on the semiconductor layer. A characteristic semiconductor device is formed.

In the present invention, as described in claim 2,
2. The semiconductor device according to claim 1, wherein the semiconductor layer is a nitride semiconductor layer.

In the present invention, as described in claim 3,
3. The semiconductor device according to claim 1, wherein the infrared absorbing material is carbon, silicon, or polyimide resin.

In the present invention, as described in claim 4,
4. The laminated body is a laminated body, the uppermost layer of the laminated body is made of the infrared absorbing material, and the layers of the laminated body excluding the uppermost layer are made of metal. The semiconductor device is configured.

In the present invention, as described in claim 5,
A method for manufacturing a semiconductor device comprises the step of lamp heating the semiconductor device according to claim 1, 2, 3 or 4.

  By using the present invention, it is possible to heat only a specific portion of a semiconductor device, and the performance of the semiconductor device can be improved by heating the specific portion without causing thermal deterioration of the performance of the semiconductor layer. Law can be provided.

  If the present invention is applied to improve the performance of the ohmic electrode of the semiconductor epitaxial wafer, when the ohmic electrode of the semiconductor epitaxial wafer is heated, only the ohmic electrode is heated, and the contact resistance of the electrode is reduced. The effect of preventing deterioration of the surface due to heat appears.

  The semiconductor device according to the present invention is characterized in that a semiconductor layer is a constituent element, and an infrared absorbing material having an infrared absorption coefficient larger than that of the semiconductor layer at a predetermined position on the semiconductor layer is a constituent element. The semiconductor device manufacturing method according to the present invention is characterized by having a step of lamp heating the semiconductor device according to the present invention.

  In the following description, the semiconductor layer is a nitride semiconductor layer, the infrared absorbing material is carbon, silicon, or polyimide resin, the deposited body is a laminate, and the uppermost layer of the laminate is the infrared absorbing layer. Although the case where the layer of the laminate excluding the uppermost layer is made of a metal and is further limited will be described, the present invention is not limited to this.

  In the present invention, for example, a material that transmits infrared rays and desirably has a forbidden band width of 2 eV or more is used as a substrate of a semiconductor epitaxial wafer. Further, as an ohmic electrode that is a constituent element of the deposited body, for example, after depositing a plurality of layers of metal, and as an uppermost layer made of the infrared absorbing material, for example, after depositing silicon or carbon in layers Take the means of heating it with a lamp.

FIG. 1 is a schematic view showing an example of a semiconductor device according to the present invention. As shown in the drawing, for example, Al ₂ O ₃ or SiC is used as the substrate 1 of the semiconductor epitaxial wafer 4. However, even when a material that transmits infrared rays and preferably has a forbidden band width of 2 eV or more is used as the substrate 1, the effects of the present invention are similarly exhibited.

  In FIG. 1, GaN is deposited as a semiconductor substrate layer 2 on a substrate 1, and an AlGaN layer as a nitride semiconductor layer is epitaxially grown thereon as a semiconductor epitaxial layer 3 as the semiconductor layer. The substrate 1, the semiconductor substrate layer 2 and the semiconductor epitaxial layer 3 constitute a semiconductor epitaxial wafer 4.

  Further, in FIG. 1, the deposit is a laminate, and a metal laminate: Ti / Al / Ni / Au is formed at a predetermined position of the semiconductor epitaxial layer 3 as an ohmic electrode 5 which is a constituent element. . However, the type of metal material, the number of layers, and the film thickness of each layer do not affect the effects of the present invention. The uppermost layer 6 made of the infrared absorbing material, which is a constituent element of the deposited body, is a layer made of carbon (C). However, even if this infrared absorbing material is silicon (Si), the effect is equivalent. Further, the infrared absorbing material only needs to have an infrared absorption coefficient larger than the infrared absorption coefficient of the semiconductor epitaxial layer 3 as the semiconductor layer in the wavelength region: 1500 nm to 5000 nm. The greater the difference in the infrared absorption coefficient, the more remarkable the effect.

  FIG. 2 is a schematic diagram showing a heat treatment technique for reducing the contact resistance of the ohmic electrode 5 as heat treatment by lamp heating in the method for manufacturing a semiconductor device according to the present invention. In the figure, the semiconductor device shown in FIG. 1 is irradiated with infrared rays emitted from a lamp. The electrode part is heated because carbon or silicon of the uppermost layer 6 absorbs infrared rays. On the other hand, since the semiconductor epitaxial wafer 4 transmits infrared rays, it is not heated. Therefore, in this method, since only the electrode portion is locally heated, deterioration of the surface state of the semiconductor epitaxial wafer 4 can be suppressed.

  Note that C or Si in the present invention may be any crystallinity such as single crystal, microcrystal, and amorphous.

[Embodiment 1]
First, a resist is applied to the AlGaInN surface (epi surface) of the semiconductor epitaxial wafer 4, and a portion where the ohmic electrode 5 is deposited is removed by exposure and development. Next, the ohmic electrode 5 was deposited by electron beam evaporation (EB evaporation) to obtain the state shown in FIG.

  Next, C or Si was deposited as the uppermost layer 6 by a sputtering method using Ar plasma to obtain the state shown in FIG. The film thickness of C or Si to be deposited is 2 μm. The same effect can be obtained when the film thickness of C or Si to be deposited is 0.1 to 5 μm.

  Thereafter, lift-off was performed with an organic solvent, and the ohmic electrode 5 and the uppermost layer 6 on the resist were removed together with the resist to obtain the state shown in FIG. The state shown in FIG. 5 is the same as the state shown in FIG.

  As an example of the lamp heating step in the method for manufacturing a semiconductor device according to the present invention, the semiconductor device according to the present invention (shown in FIGS. 1 and 5) manufactured as described above is heated by lamp heating to contact resistance of the ohmic electrode 5. Reduced.

FIG. 6 shows a schematic diagram of the lamp heating process. When the lamp is heated, the uppermost layer 6 on the ohmic electrode 5 is heated by absorbing infrared rays from the lamp, and the ohmic electrode 5 has a high thermal conductivity, so that the contact portion between the ohmic electrode 5 and the semiconductor epitaxial wafer 4 is also heated. Thereby, the contact resistance of the ohmic electrode 5 is reduced. On the other hand, since the semiconductor epitaxial wafer 4 transmits infrared rays and is supported only at the peripheral edge portion thereof, it is hardly heated if the support body is transparent to infrared rays such as SiO ₂ . Therefore, according to the method for manufacturing a semiconductor device according to the present invention, since only the electrode portion is locally heated, it is possible to suppress the deterioration of the surface state of the semiconductor epitaxial wafer 4. As a matter of course, the contact heating plate used in the conventional method is not used in the lamp heating process. However, the support plate made of a material that transmits infrared (e.g., SiO _2), may support a semiconductor epitaxial wafer 4.

  FIG. 7 shows an example of a temperature distribution during lamp heating in the method of manufacturing a semiconductor device according to the present invention. The infrared ray emitted from the lamp is absorbed, and C or Si in the uppermost layer on the electrode is heated to 850 ° C. At that time, since the electrode metal portion has high thermal conductivity, the contact portion between the metal and the semiconductor becomes 830 ° C. Since the semiconductor portion has a lower thermal conductivity than the electrode metal, the temperature of the channel portion remains at about 300 ° C.

  On the other hand, an example of the temperature distribution during lamp heating in the conventional method is shown in FIG. Since the lower plate portion is first heated, the lower portion has the highest temperature of 950 ° C. The heat was conducted by contact heat transfer from the plate (contact heating plate 7), and the temperature of the contact portion between the metal and the semiconductor and the channel portion was 830 ° C.

  As described above, it can be seen that in the method for manufacturing a semiconductor device according to the present invention, the effect of suppressing the temperature rise of the channel portion (the portion sandwiched between the left and right ohmic electrodes 5) is remarkable.

  After lamp heating, after performing other processes, a resist is applied again, a certain area of resist on the uppermost layer 6 is removed by exposure and development, and C or Si of the uppermost layer 6 is removed by dry etching, The state shown in FIG. 9 was obtained. C can also be removed using plasma ashing by oxygen plasma irradiation.

  After vapor deposition using Au as a pad, lift-off was performed, and Au on the resist was removed together with the resist to obtain the state shown in FIG. In the figure, the pad is indicated by Au.

  Channel resistance is 450 Ω / sq. As a result of producing an ohmic electrode by the method of this embodiment, the contact resistance of the ohmic electrode is as good as 0.3Ω / mm, and the channel resistance is 450Ω / sq. Good characteristics were obtained without deterioration. (According to the conventional method, the contact resistance is good (0.3 Ω / mm), but the channel resistance is increased (deteriorated) to 570 Ω / sq.). This is probably because only the ohmic electrode was heated and the epitaxial wafer was not heated, so that deterioration of the quality of the epitaxial wafer was suppressed.

  In the present embodiment, C or Si to be heated has the same dimensions as the electrode and is formed immediately above the electrode. However, if the peripheral part including the ohmic electrode is heated, an effect can be obtained. Alternatively, Si may be formed so as to cover the electrode. Similarly, C or Si smaller than the electrode area may be formed on a part of the electrode surface.

[Embodiment 2]
The second embodiment is characterized in that a photosensitive polyimide resin is used as the infrared absorbing material. A polyimide resin is applied to the entire surface of the sample with a film thickness of 20 μm using a spin coater on the surface of the sample on which the electrode is formed (for example, the upper surface of the semiconductor device without the uppermost layer 6 in FIG. 1). The photosensitive polyimide resin is exposed by an exposure apparatus used in a normal semiconductor process and then developed, and is patterned so that the polyimide resin remains on the electrode and the polyimide resin other than the electrode is removed. . Thereby, for example, in FIG. 1, a state in which the uppermost layer 6 is made of polyimide resin is realized. Using this polyimide resin as an infrared absorbing material, lamp heating is performed as in the first embodiment. The subsequent removal of the polyimide resin is performed by reactive ion etching using oxygen gas. According to the method of the present embodiment, an infrared absorbing material can be formed more easily than in the first embodiment, and the same effect as in the first embodiment can be obtained.

  The above embodiment is merely an example, and the present invention is not limited to this. Generally, a semiconductor device has a layer of an infrared absorbing material that absorbs infrared light more strongly than a semiconductor layer in the semiconductor device as the uppermost layer on the electrode, and contacts the semiconductor device during lamp heating in the method of manufacturing the semiconductor device. As long as the contact heating plate to be heated is not used, the effect of the present invention appears.

  In the above embodiment, the infrared absorbing material is finally removed in the manufacturing process of the semiconductor device, but the same effect can be obtained when the infrared absorbing material is left on the electrode without being removed. . For example, a semiconductor device in which C, Si, polyimide resin or the like smaller than the electrode area is formed on a part of the electrode surface is manufactured, and a conductive wire is connected to the electrode surface portion on which no infrared absorbing material is formed. It is possible to operate by injecting current.

It is a schematic diagram which shows an example of the semiconductor device which concerns on this invention. It is a schematic diagram which shows the method of the heat processing for the contact resistance reduction of the ohmic electrode 5 as heat processing by the lamp heating in the manufacturing method of the semiconductor device which concerns on this invention. It is a schematic diagram which shows the method of forming the ohmic electrode in the semiconductor device which concerns on this invention. It is a schematic diagram which shows the method of forming the uppermost layer on an electrode in the semiconductor device which concerns on this invention. It is a schematic diagram which shows an example of the semiconductor device which concerns on this invention. It is a schematic diagram which shows the process of the lamp heating in the manufacturing method of the semiconductor device which concerns on this invention. It is a figure which shows an example of the temperature distribution at the time of lamp heating in the manufacturing method of the semiconductor device which concerns on this invention. It is a figure which shows an example of the temperature distribution at the time of lamp heating in the manufacturing method of the conventional semiconductor device. It is a schematic diagram which shows the state before forming a pad in the semiconductor device which concerns on this invention. It is a schematic diagram which shows the state which formed the pad in the semiconductor device which concerns on this invention. It is a schematic diagram which shows the method of the heat processing for the contact resistance reduction of the ohmic electrode in a prior art. It is a schematic diagram which shows the method of lamp heating when reducing the contact resistance of an ohmic electrode in the manufacturing method of the conventional semiconductor device.

Explanation of symbols

  1: substrate, 2: semiconductor substrate layer, 3: semiconductor epitaxial layer, 4: semiconductor epitaxial wafer, 5: ohmic electrode, 6: top layer, 7: contact heating plate.

Claims (5)

  In a semiconductor device including a semiconductor layer as a constituent element, the semiconductor device includes a deposit having an infrared absorbing substance having an infrared absorption coefficient larger than the infrared absorption coefficient of the semiconductor layer as a constituent element at a predetermined position on the semiconductor layer. A featured semiconductor device.   The semiconductor device according to claim 1, wherein the semiconductor layer is a nitride semiconductor layer.   3. The semiconductor device according to claim 1, wherein the infrared absorbing material is carbon, silicon, or polyimide resin.   4. The laminated body is a laminated body, the uppermost layer of the laminated body is made of the infrared absorbing material, and the layers of the laminated body excluding the uppermost layer are made of metal. Semiconductor device.   A method for manufacturing a semiconductor device, comprising the step of lamp heating the semiconductor device according to claim 1, 2, 3 or 4.

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