JP2012004444A - Method of manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device in which electrical characteristics can be measured with high precision.SOLUTION: A method of manufacturing a semiconductor device of the present invention includes the successive steps of: forming a protective film 22 on a rear surface 10b of a substrate 10, the protective film 22 composed of an insulator and having a thickness of 1 μm or less; growing a GaN-based semiconductor layer on a front surface 10a of the substrate 10 using metal organic chemical vapor deposition (MOCVD) technique; and measuring electrical characteristics of the GaN-based semiconductor layer.

Description

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

  Gallium nitride (GaN) -based semiconductors are used in electronic devices such as field effect transistors (FETs) and optical devices such as light emitting diodes and laser diodes. The GaN-based semiconductor layer is formed by growing an epitaxial layer on the substrate.

  Patent Document 1 discloses a technique for reducing the warpage of a wafer by adjusting the composition ratio of the AlGaN layer.

JP 2008-166349 A

  In the manufacturing process of a semiconductor device, it is required to appropriately manage the electrical characteristics of the functional portion on the surface side of the substrate on which the semiconductor element is formed. However, in the conventional manufacturing method, when the functional portion is formed, an electrically active layer is also formed on the back surface of the substrate, so that the accuracy of measurement of electrical characteristics may be lowered.

  In view of the above problems, an object of the present invention is to provide a method for manufacturing a semiconductor device capable of measuring electrical characteristics with high accuracy.

  In the present invention, after the step of forming a protective film made of an insulator on the back surface of the substrate and having a thickness of 1 μm or less, and the step of providing the protective film, the surface of the substrate is subjected to GaN using MOCVD. And a step of measuring electrical characteristics of the GaN-based semiconductor layer after the step of growing the GaN-based semiconductor layer and the step of growing the GaN-based semiconductor layer. According to the present invention, it is possible to measure electrical characteristics with high accuracy.

  In the above configuration, the step of measuring the electrical characteristics may be a step of measuring at least one of sheet resistance, electron mobility, or carrier concentration of the GaN-based semiconductor layer. According to this configuration, sheet resistance, electron mobility, or carrier concentration can be measured with high accuracy.

  The said structure WHEREIN: The process of measuring the said electrical characteristic can be set as the structure which is a process of measuring the sheet resistance of the said GaN-type semiconductor layer by performing an eddy current measurement or a four-point probe method.

  The said structure WHEREIN: It can be set as the structure which has the process of removing the said protective film after the process of growing the said GaN-type semiconductor layer.

  In the above structure, the substrate may be formed of any one of silicon, silicon nitride, or gallium nitride. According to this configuration, it is possible to measure the electrical characteristics with high accuracy.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the semiconductor device which can measure an electrical property with high precision can be provided.

1A and 1B are cross-sectional views illustrating a method for manufacturing a semiconductor device according to a comparative example. FIG. 2A to FIG. 2C are cross-sectional views illustrating the method for manufacturing the semiconductor device according to the first embodiment. FIG. 3A and FIG. 3B are cross-sectional views illustrating a method for manufacturing a semiconductor device according to the second embodiment.

  Embodiments of the present invention will be described with reference to the drawings.

  First, a comparative example will be described. 1A and 1B are cross-sectional views illustrating a method for manufacturing a semiconductor device according to a comparative example.

  As shown in FIG. 1A, for example, a substrate 10 made of Si is prepared. The surface of the substrate 10 is a front surface 10a, and the back surface opposite to the front surface 10a is a back surface 10b.

  As shown in FIG. 1B, a GaN-based semiconductor layer is grown on the surface 10 a of the substrate 10 by using an MOCVD method (Metal Organic Chemical Vapor Deposition). Specifically, an AlN (aluminum nitride) layer 12 is formed on the surface 10 a, and an AlGaN (aluminum gallium nitride) layer 14 is formed on the AlN layer 12. Further, a GaN (gallium nitride) layer 16 is formed on the AlGaN layer 14, and an AlGaN layer 18 is formed on the GaN layer 16.

  In the step of FIG. 1B, for example, the substrate 10 is placed on the susceptor with the back surface 10b facing down and then heated. A source gas serving as a raw material for the GaN-based semiconductor layer (epitaxial layer) is introduced to grow a GaN-based semiconductor layer on the surface 10a. When there is a finite gap between the substrate 10 and the susceptor, the source gas wraps around the back surface 10b, and the back surface growth layer 20 containing Al, Ga, In, etc. contained in the source gas is formed on the back surface 10b. There is. In addition, since the growth temperature is several hundred degrees or more, impurities such as Al, Ga, and In may diffuse from the back growth layer 20 to the substrate 10. The diffused impurity may become a dopant to form a conductive doping layer 21 on the substrate 10 (see the broken line in the figure).

  In the manufacturing process of a semiconductor device, a process of measuring electrical characteristics of a GaN-based semiconductor layer, such as sheet resistance, may be performed. In the comparative example, the back surface growth layer 20, the doping layer 21 and the like have conductivity. Therefore, the measurement accuracy of the electrical characteristics of the GaN-based semiconductor layer may be reduced.

  In order to improve the measurement accuracy, it may be considered to remove the back growth layer 20 and the doping layer 21. However, a process such as etching or polishing is added for the removal, which complicates the process. For example, even when etching, polishing, or the like is performed to reduce the thickness, it is difficult to measure the electrical characteristics of the GaN-based semiconductor layer until these steps are completed. As a result, it becomes difficult to remove defective semiconductor devices until the electrical characteristics are measured, which may increase the cost of the semiconductor devices.

  Next, Example 1 will be described. FIG. 2A to FIG. 2C are cross-sectional views illustrating the method for manufacturing the semiconductor device according to the first embodiment.

  As shown in FIG. 2A, for example, a process of forming a protective film 22 on the back surface 10b of the substrate 10 made of, for example, Si (silicon) is performed using, for example, a sputtering method. The protective film 22 is made of an insulator such as silicon oxide, silicon nitride, or silicon oxynitride, and has a thickness of 100 nm, for example.

  As shown in FIG. 2B, after the step of forming the protective film 22, the AlN layer 12, the AlGaN layer 14, the GaN layer 16, and the AlGaN are formed on the surface 10a of the substrate 10 in order from the bottom using the MOCVD method. Layer 18 is grown. That is, a step of growing a GaN-based semiconductor layer on the surface 10a is performed.

  In this step, as in the step already described with reference to FIG. 1B, the source gas may wrap around the back surface 10b. However, since the protective film 22 is formed on the back surface 10b, the back surface growth layer 20 grows in contact with the protective film 22, and contact with the substrate 10 is prevented. For this reason, the diffusion of impurities from the back surface growth layer 20 to the substrate 10 is also suppressed. In other words, the protective film 22 insulates the substrate 10 and the back surface growth layer 20.

  After the step of growing the GaN-based semiconductor layer, a step of measuring electrical characteristics of the GaN-based semiconductor layer is performed. The electrical characteristic is, for example, sheet resistance. The sheet resistance is measured by, for example, eddy current measurement or the four-probe method.

  As shown in FIG. 2C, after the step of growing the GaN-based semiconductor layer, a step of removing the protective film 22 is performed. For example, the protective film 22 can be selectively removed by etching using HF (hydrogen fluoride), BHF (buffered hydrofluoric acid), or the like as an etchant. Further, in order to reduce the thickness, the protective film 22 can also be removed by polishing the back surface 10b. Note that the protective film 22 and the back surface growth layer 20 have little influence on the electrical characteristics of the GaN-based semiconductor layer. Therefore, the protective film 22 removal step may be performed before or after the measurement of the electrical characteristics. Further, the protective film 22 may be left without being removed. Thus, the semiconductor device according to Example 1 is completed.

  Next, the sheet resistance measurement results are compared between the semiconductor device according to the comparative example and the semiconductor device according to the first embodiment. First, sample generation conditions will be described. First, the MOCVD method will be described.

First, the substrate 10 made of silicon was introduced into the reactor of the MOCVD apparatus, and the temperature of the substrate 10 was raised to 1050 ° C. The surface of the substrate 10 is thermally cleaned by raising the temperature. Using H ₂ as a carrier gas, TMA (trimethylaluminum) and NH ₃ (ammonia) were supplied into the reactor, and the pressure in the reactor was increased to 100 Torr (13.3 MPa). Thereby, an AlN layer 12 having a thickness of about 250 nm was grown on the surface 10a of the substrate 10. By raising the temperature of the substrate 10 to 1050 ° C., the AlN layer 12 was almost lattice-relaxed. Next, the temperature of the substrate 10 was raised to 1100 ° C., TMA, NH ₃ and TMG (trimethylgallium) were supplied into the reactor, and the pressure was maintained at 13.3 MPa. As a result, an AlGaN layer 14 having a thickness of about 25 nm was grown on the AlN layer 12.

Further, the temperature of the substrate 10 was raised to 1150 ° C., TMG and NH ₃ were supplied, and the pressure was maintained at 13.3 MPa. As a result, a GaN layer 16 having a thickness of about 1 μm was grown on the AlGaN layer 14. Next, the temperature of the substrate 10 was lowered to 1050 ° C., TMA, NH ₃ and TMG were supplied, and the pressure was maintained at 13.3 MPa. As a result, an AlGaN layer 18 having a thickness of about 30 nm and an Al composition ratio of 0.25 was grown on the GaN layer 16.

Second, conditions for forming the protective film 22 will be described. As a method, an RF (Radio Frequency: high frequency) sputtering method was used. First, the substrate 10 was introduced into a sputtering apparatus. As the sputtering target, SiO ₂ (silicon dioxide) was used, and sputtering was performed in an Ar gas atmosphere. The gas flow rate was 20 sccm (3.38 × 10 ⁻² Pa · m ³ / s), the gas pressure was 0.2 Pa, the RF power was 0.3 kW, and pre-sputtering was performed for 10 minutes. After pre-sputtering, while maintaining the gas flow rate and gas pressure, the RF power was increased to 0.6 kW, the shutter between the target and the substrate 10 was opened, and sputtering was performed for 10 minutes. As a result, a protective film 22 made of SiO ₂ and having a thickness of 100 nm was formed on the back surface 10 b of the substrate 10.

Sheet resistance was measured by measuring eddy current. Table 1 shows the sheet resistance in each of the comparative example, the comparative example after polishing the back surface 10b, and the example 1. The back surface 10b was polished in the state of FIG. 1B until the back surface growth layer 20 and the doping layer 21 were removed.

  As shown in Table 1, the sheet resistance of the semiconductor device according to the comparative example was 630Ω / □. On the other hand, the sheet resistance of the semiconductor device according to Example 1 was 700Ω / □. In addition, the sheet resistance after polishing of the semiconductor device according to the comparative example was 700Ω / □, which was the same as the sheet resistance of Example 1. After polishing, the back growth layer 20 and the doping layer 21 are removed, so that the sheet resistance is measured with high accuracy. The sheet resistance of the semiconductor device according to Example 1 showed the same value as the sheet resistance of the semiconductor device after polishing. In other words, according to Example 1, by forming the protective film 22, the sheet resistance could be measured with high accuracy as after the back surface growth layer 20 and the doping layer 21 were removed.

  According to Example 1, by forming the protective film 22, the influence of the back surface growth layer 20 and the formation of the doping layer 21 can be suppressed, and the electrical characteristics of the GaN-based semiconductor layer can be measured with high accuracy. Become. That is, the protective film 22 functions as an insulating film between the substrate 10 and the back surface growth layer 20 and a diffusion prevention film. Since the growth of the GaN-based semiconductor layer is performed by the MOCVD method, even when a GaN-based semiconductor layer with good crystallinity is formed and the source gas wraps around the back surface 10b, the electrical characteristics can be measured with high accuracy. it can. In addition, a process for measuring electrical characteristics can be performed after the growth process of the GaN-based semiconductor layer, so that defective products can be found quickly. Therefore, the cost of the semiconductor device can be reduced.

  Although the thickness of the protective film 22 is 100 nm, it is preferably 1 nm or more in order to suppress the diffusion of impurities from the back surface growth layer 20 to the substrate 10. Further, as described above, in the step of removing the protective film 22, wet etching for selectively removing the protective film 22 may be performed without etching the GaN-based semiconductor layer. In order to perform etching selectively, the thickness of the protective film 22 is preferably 10 nm or more, and more preferably 50 nm or more. By setting the thickness of the protective film 22 to 10 nm or more, etching of the protective film 22 for removing the back surface growth layer 20 becomes easy. Further, the thickness of the protective film 22 may be larger than 100 nm. However, if the protective film 22 is too thick, the trouble of forming the protective film increases. Further, the warp of the wafer may increase due to the stress generated in the protective film 22. For this reason, it is preferable that the thickness of the protective film 22 is 1 μm or less. By setting the thickness to 1 μm or less, the protective film 22 can be easily formed and warpage can be suppressed. More preferably, the thickness can be 800 nm or less, or 500 nm or less. For the above reasons, the thickness of the protective film 22 can be in the range of 1 nm to 1 μm, preferably 10 nm to 800 nm, and more preferably 50 nm to 500 nm.

  The protective film 22 is not limited to a silicon compound such as silicon oxide, silicon nitride, and silicon oxynitride, and may be made of other materials. Although the protective film 22 is formed by the RF sputtering method, a sputtering method other than the RF sputtering method may be used. For example, a vacuum deposition method, an ALD (Atomic Layer Deposition) method, a CVD (Chemical Vapor Deposition) method, a PLD (Pulse) method may be used. (Laser Deposition) method, ion plating method or the like. By the above method, the protective film 22 can be formed with high accuracy.

In particular, when the substrate 10 is made of Si, impurities such as In, Al, and Ga are easily diffused to become a dopant. The protective film 22 can measure the electrical characteristics with high accuracy even when Si, which easily diffuses impurities, is used as the substrate 10. In the case where the substrate 10 is made of Si, the rear surface 10b side of the substrate 10 is oxidized, it may be formed a protective film 22 made of SiO _2. Oxidation is performed by placing the substrate 10 in, for example, an oxidizing atmosphere and thermally oxidizing it. By forming the protective film 22 by oxidation, the process can be simplified. The substrate 10 may use SiC (silicon carbide) or GaN (gallium nitride) in addition to Si. In addition to the above, for example, TEG (triethylgallium) or TEA (triethylaluminum) may be used as the source gas in the growth process of the GaN-based semiconductor layer.

  The measurement of the sheet resistance is not limited to the method of measuring eddy current, and may be performed by, for example, a four-point probe method. The electrical characteristics to be measured are not limited to sheet resistance. According to the first embodiment, even when other electrical characteristics such as electron mobility and carrier concentration are measured, for example, by measuring the Hall effect, it is possible to measure with high accuracy. Further, the electrical characteristics to be measured are not limited to one, and a plurality of electrical characteristics may be measured.

  Example 2 is an application example to a HEMT (High Electron Mobility Transistor). FIG. 3A and FIG. 3B are cross-sectional views illustrating a method for manufacturing a semiconductor device according to the second embodiment. Since the steps shown in FIGS. 2A and 2B are the same in the second embodiment, description thereof is omitted. The process of measuring electrical characteristics such as sheet resistance of the GaN-based semiconductor layer after the GaN-based semiconductor layer is grown is also common.

  As shown in FIG. 3A, a step of forming an electrode is performed after the step of measuring electrical characteristics. That is, the source electrode 24, the drain electrode 26, and the gate electrode 28 are formed on the AlGaN layer 18 of the semiconductor device illustrated in FIG. The source electrode 24 and the drain electrode 26 are ohmic electrodes in which, for example, Ti / Al is laminated from the side closer to the AlGaN layer 18. The gate electrode 28 is formed by stacking, for example, Ni / Au from the side closer to the AlGaN layer 18. The AlGaN layer 18 functions as an electron supply layer.

  As shown in FIG. 3B, a step of removing the protective film 22 is performed. Through the above steps, the semiconductor device according to Example 2 is completed. As in the first embodiment, the step of measuring the electrical characteristics and the step of removing the protective film 22 may be switched in order. Further, the semiconductor device in the state of FIG. 3A may be completed without removing the protective film 22.

  According to the second embodiment, it is possible to realize a HEMT manufacturing method capable of measuring the electrical characteristics of the GaN-based semiconductor layer with high accuracy. Further, by setting the thickness of the protective film 22 to 1 μm or less, it is possible to suppress the warpage of the HEMT. The semiconductor device may be a transistor other than HEMT, or an optical semiconductor device such as a laser diode or a photodiode.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Board 10
Surface 10a
Back side 10b
AlN layer 12
AlGaN layer 14,18
GaN layer 16
Back growth layer 20
Doping layer 21
Protective film 22
Source electrode 24
Drain electrode 26
Gate electrode 28

Claims (9)

Forming a protective film made of an insulator and having a thickness of 1 μm or less on the back surface of the substrate;
After the step of providing the protective film, a step of growing a GaN-based semiconductor layer on the surface of the substrate using the MOCVD method;
And a step of measuring electrical characteristics of the GaN-based semiconductor layer after the step of growing the GaN-based semiconductor layer.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the step of measuring the electrical characteristics is a step of measuring at least one of sheet resistance, electron mobility, or carrier concentration of the GaN-based semiconductor layer. Method.   3. The step of measuring the electrical characteristics is a step of measuring a sheet resistance of the GaN-based semiconductor layer by measuring an eddy current or performing a four-point probe method. Semiconductor device manufacturing method.   4. The method of manufacturing a semiconductor device according to claim 1, further comprising a step of removing the protective film after the step of growing the GaN-based semiconductor layer. 5.   5. The method of manufacturing a semiconductor device according to claim 1, wherein the substrate is made of any one of silicon, silicon nitride, and gallium nitride.   The method for manufacturing a semiconductor device according to claim 1, wherein the protective film is made of any one of silicon oxide, silicon nitride, and silicon oxynitride.   The method for manufacturing a semiconductor device according to claim 1, wherein a thickness of the protective film is 1 nm or more.   The method for manufacturing a semiconductor device according to claim 1, wherein a thickness of the protective film is 10 nm or more and 800 nm or less.   9. The method of manufacturing a semiconductor device according to claim 1, wherein the protective film has a thickness of 50 nm to 500 nm.

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