Substrate for semiconductor device and method for producing same

Abstract

To provide a substrate for a semiconductor device that can impart good electrical characteristics to the device, and a simple manufacturing method for such the substrate.SOLUTION: A substrate for a semiconductor device includes a high-resistivity silicon single-crystal substrate with a resistivity of 100 Ω cm or higher, a first buffer layer consisting of an AlN layer formed on the high-resistivity silicon single-crystal substrate, and a nitride semiconductor layer provided on the first buffer layer, and there is no low-resistivity portion on the surface of the high-resistivity silicon single-crystal substrate whose resistivity is relatively lower than that of the entire substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a substrate for a semiconductor device and a method for manufacturing the same. [Background technology]

[0002] Epitaxial substrates using nitride semiconductors are used in power devices that operate at high frequencies and high output, etc. In particular, high electron mobility transistors (HEMTs) are known as devices suitable for amplifying high frequency bands such as microwaves, quasi-millimeter waves, and millimeter waves.

[0003] An epitaxial substrate used in such HEMTs and the like is disclosed, for example, in Patent Document 1. The epitaxial substrate is composed of, for example, a buffer layer made of an AlN layer, an AlGaN layer, and a superlattice structure in which GaN layers and AlN layers are alternately stacked on a silicon substrate, and a device active layer formed thereon in the form of a channel layer made of GaN, a barrier layer made of AlGaN, and a cap layer made of GaN. A semiconductor element (for example, a HEMT) can be obtained by providing a source electrode, a drain electrode, and a gate electrode on the epitaxial substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-225703 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in an epitaxial substrate with the above structure, if the silicon substrate is a high-resistivity silicon substrate, diffusion of Al from the AlN layer into the high-resistivity silicon substrate will cause a low-resistivity layer to form in the high-resistivity silicon substrate, and current will flow laterally through this portion as a leak path, degrading the electrical characteristics of the device.

[0006] The present invention has been made to solve the above problems, and an object of the present invention is to provide a substrate for a semiconductor device that can impart good electrical characteristics to the device, and a simple method for producing such a substrate. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides High-resistivity silicon single crystal substrate with resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on the high-resistivity silicon single crystal substrate; and a nitride semiconductor layer provided on the first buffer layer; A substrate for a semiconductor device comprising: The present invention provides a substrate for semiconductor devices, the surface of which is free of low resistivity portions having a resistivity relatively lower than the resistivity of the entire high resistivity silicon single crystal substrate.

[0008] In this way, if a semiconductor device substrate is a high resistivity silicon substrate with a resistivity of 100 Ω·cm or more and no low resistivity portions are present, semiconductor devices with excellent high frequency characteristics can be manufactured.

[0009] The nitride semiconductor layer provided on the first buffer layer is a second buffer layer formed on the first buffer layer and made of a nitride semiconductor layer; and a device active layer formed of a nitride semiconductor layer on the second buffer layer; It is preferable that:

[0010] In the present invention, it is particularly preferable to use such a structure as a substrate for a semiconductor device.

[0011] The present invention also provides a method for producing a substrate for a semiconductor device, comprising the steps of: (1) preparing a laminated substrate including a high-resistivity silicon single crystal substrate having a resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on a surface of the high-resistivity silicon single crystal substrate, and a nitride semiconductor layer provided on the first buffer layer; (2) irradiating the laminated substrate with an electron beam from the back surface side of the high-resistivity silicon single crystal substrate to eliminate a low-resistivity portion formed on the front surface of the high-resistivity silicon single crystal substrate, the low-resistivity portion having a resistivity relatively lower than the resistivity of the entire high-resistivity silicon single crystal substrate; The present invention provides a method for producing a substrate for a semiconductor device, comprising the steps of:

[0012] With such a manufacturing method, it is possible to relatively easily eliminate the low resistivity portion formed on the surface of a high resistivity silicon single crystal substrate, and it is possible to manufacture a substrate for semiconductor devices that can be used to manufacture semiconductor devices with excellent high frequency characteristics.

[0013] The nitride semiconductor layer provided on the first buffer layer is a second buffer layer formed on the first buffer layer and made of a nitride semiconductor layer; and a device active layer formed of a nitride semiconductor layer on the second buffer layer; It is preferable to set the above.

[0014] In the present invention, it is particularly preferable to use such a structure as a substrate for a semiconductor device. Effect of the Invention

[0015] As described above, the present invention can provide a substrate for semiconductor devices that can impart good electrical characteristics to the device by eliminating low resistivity portions formed on the surface of a high resistivity silicon single crystal substrate, and a simple method for manufacturing such a substrate. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing an example of a method for producing a substrate for a semiconductor device according to the present invention. [Diagram 2] 1 is a photograph of an electrode of a CPW formed on a substrate for a semiconductor device in an embodiment. [Diagram 3] 1 shows the results of SNDM measurement of cross sections of semiconductor device substrates produced in Examples and Comparative Examples. [Figure 4] 1 shows the results of measuring the diffusion state of Al into a Si wafer in a semiconductor device substrate produced in a comparative example by backside SIMS. [Diagram 5] 1 shows the results of measuring second harmonics of semiconductor device substrates produced in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] As mentioned above, epitaxial substrates with HEMT structure have a problem in that Al in the first buffer layer made of AlN layer diffuses into the surface of the high-resistance silicon substrate to form a low-resistance layer, which deteriorates the electrical characteristics of the device. For example, when an n-type silicon single crystal substrate is used as the high-resistance silicon substrate, Al in the first buffer layer made of AlN layer diffuses into the surface of the n-type silicon single crystal substrate to form a P channel, which deteriorates the electrical characteristics of the device.

[0018] As a result of extensive investigations into solving the above problems, the inventors found that a P channel generated by diffusion of Al can be eliminated by irradiating an n-type silicon single crystal substrate, which has an AlN layer laminated on the front surface of the n-type silicon single crystal substrate, with an electron beam from the back surface of the n-type silicon single crystal substrate, and thus completed the present invention.

[0019] That is, the present invention is a substrate for a semiconductor device including a high-resistivity silicon single crystal substrate having a resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on the high-resistivity silicon single crystal substrate, and a nitride semiconductor layer provided on the first buffer layer, wherein the surface of the high-resistivity silicon single crystal substrate does not include a low-resistivity portion having a resistivity relatively lower than the resistivity of the entire high-resistivity silicon single crystal substrate.

[0020] The present invention also provides a method for manufacturing a substrate for a semiconductor device, comprising the steps of: (1) preparing a laminated substrate including a high-resistivity silicon single crystal substrate having a resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on a surface of the high-resistivity silicon single crystal substrate, and a nitride semiconductor layer provided on the first buffer layer; and (2) irradiating the laminated substrate with an electron beam from a back surface side of the high-resistivity silicon single crystal substrate to eliminate a low-resistivity portion formed on the surface of the high-resistivity silicon single crystal substrate, the low-resistivity portion having a resistivity relatively lower than the resistivity of the entire high-resistivity silicon single crystal substrate.

[0021] The present invention will be described in detail below, but the present invention is not limited thereto.

[0022] [Substrates for semiconductor devices] The substrate for a semiconductor device of the present invention includes a high-resistivity silicon single crystal substrate having a resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on the high-resistivity silicon single crystal substrate, and a nitride semiconductor layer provided on the first buffer layer, wherein the high-resistivity silicon single crystal substrate does not have a low-resistivity portion.

[0023] The nitride semiconductor layer provided on the first buffer layer is not particularly limited, but for example, it is preferable to have a second buffer layer made of a nitride semiconductor layer provided on the first buffer layer and a device active layer made of a nitride semiconductor layer provided on the second buffer layer.

[0024] Conventionally, in a semiconductor device substrate in which an AlN layer is laminated on a high-resistivity silicon single crystal substrate, there exists a low resistivity portion on the surface of the high-resistivity silicon single crystal substrate, which is caused by Al diffused from the AlN layer. For example, when the high-resistivity silicon single crystal substrate is an n-type silicon single crystal substrate, the diffused Al forms a P channel on the surface of the n-type silicon single crystal substrate, which does not exist in reality, and the resistivity of the surface decreases. Even when the high-resistivity silicon single crystal substrate is a p-type silicon single crystal substrate, the diffused Al increases the p-type dopant on the surface of the p-type silicon single crystal substrate, which decreases the resistivity of the surface. Thus, conventional semiconductor device substrates have a problem that the electrical characteristics of the device deteriorate due to the P channel caused by Al diffused from the AlN layer.

[0025] On the other hand, in the substrate for semiconductor devices of the present invention, since there is no low resistivity portion having a resistivity relatively lower than the resistivity of the entire high resistivity silicon single crystal substrate on the surface of the high resistivity silicon single crystal substrate, it is possible to impart good electrical characteristics to the device. In the substrate for semiconductor devices of the present invention, the high resistivity silicon single crystal substrate may be either n-type or p-type.

[0026] In the present invention, the high-resistivity silicon single crystal substrate has a "front surface" and a "back surface," and the "front surface" refers to the surface on which a first buffer layer made of an AlN layer is formed, and the "back surface" refers to the surface opposite to the surface on which the first buffer layer is formed.

[0027] [Method of manufacturing substrate for semiconductor device] The substrate for semiconductor devices of the present invention can be easily manufactured by the method for manufacturing a substrate for semiconductor devices of the present invention. (1) preparing a laminated substrate including a high-resistivity silicon single crystal substrate having a resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on a surface of the high-resistivity silicon single crystal substrate, and a nitride semiconductor layer provided on the first buffer layer; (2) A step of irradiating the laminated substrate with an electron beam from the back surface side of the high-resistivity silicon single crystal substrate to eliminate a low-resistivity portion formed on the surface of the high-resistivity silicon single crystal substrate, the low-resistivity portion having a resistivity relatively lower than the resistivity of the entire high-resistivity silicon single crystal substrate. Includes.

[0028] The method for manufacturing a substrate for a semiconductor device of the present invention will be specifically described below with reference to Fig. 1, taking as an example a case where the high-resistance silicon single crystal substrate is an n-type silicon single crystal substrate, but the method for manufacturing a substrate for a semiconductor device of the present invention can also be carried out in the same manner in the case where a p-type silicon single crystal substrate is used. Note that the structure of the substrate for a semiconductor device described below is an example, and is not limited thereto.

[0029] <Process (1)> First, an n-type silicon single crystal substrate 1 is prepared. The substrate to be prepared is not particularly limited as long as it is an n-type silicon single crystal substrate with a high resistance of 100 Ω·cm or more. For example, the substrate may be a substrate with a diameter of 100 to 300 mm, doped with P, Sb, or As, FZ single crystal, and oriented in the direction perpendicular to the substrate. <111> In the case of a p-type silicon single crystal substrate, the dopant may be, for example, B, Al, or Ga.

[0030] Next, a first buffer layer 10 made of an AlN layer 2 is formed on the surface 1a of the n-type silicon single crystal substrate 1. The thickness of the AlN layer 2 is not particularly limited, but can be, for example, 20 to 500 nm, more preferably 50 to 300 nm, further preferably 100 to 200 nm, and particularly preferably 150 nm.

[0031] Next, a nitride semiconductor layer is formed on the first buffer layer 10. The nitride semiconductor layer is not particularly limited, but for example, a second buffer layer 20 made of a nitride semiconductor layer provided on the first buffer layer 10, and a device active layer 30 made of a nitride semiconductor layer provided on the second buffer layer 20 are preferable.

[0032] As the second buffer layer 20 to be formed on the first buffer layer 10, for example, an AlGaN layer 3 having a thickness of 20 to 500 nm, more preferably 50 to 300 nm, even more preferably 100 to 200 nm, and particularly preferably 160 nm, can be formed, and further, on the AlGaN layer 3, a superlattice layer (SLs(GaN / AlN)) 4 can be formed in which GaN layers and AlN layers are alternately stacked in, for example, 10 to 120 pairs, preferably 50 to 100 pairs, and particularly 70 pairs.

[0033] As the device active layer 30 formed on the second buffer layer 20, for example, a GaN layer 5 having a thickness of 100 to 2000 nm, preferably 400 to 1200 nm, more preferably 600 to 1000 nm, and particularly 800 nm may be formed, on which an AlGaN layer 6 having a thickness of, for example, 5 to 100 nm, preferably 10 to 50 nm, more preferably 20 to 30 nm, and particularly 25 nm may be formed, and on which an GaN layer 7 having a thickness of, for example, 1 to 10 nm, preferably 1 to 5 nm, and particularly 3 nm may be formed.

[0034] Furthermore, an electrode 8 may be formed thereon.

[0035] In the manner described above, a laminated substrate 100 including an n-type silicon single crystal substrate 1, a first buffer layer 10 made of an AlN layer 2, and a nitride semiconductor layer (second buffer layer 20 and device active layer 30) is prepared. In the laminated substrate 100 prepared here, Al of the AlN layer 2 diffuses into the n-type silicon single crystal substrate 1, and a region (low resistivity portion) 1' where a P channel exists is formed in a region near the surface 1a of the n-type silicon single crystal substrate 1. When a p-type silicon single crystal substrate is used, the low resistivity portion becomes a region with a relatively high concentration of p-type dopant compared to the entire p-type silicon single crystal substrate.

[0036] <Process (2)> Next, the laminated substrate 100 prepared in step (1) is irradiated with an electron beam 9 from the back surface 1b side of the n-type silicon single crystal substrate 1 to eliminate the P channel formed on the front surface 1a of the n-type silicon single crystal substrate 1, thereby producing a substrate for a semiconductor device 101 of the present invention having no region 1' where a P channel exists. When a p-type silicon single crystal substrate is used, the substrate for a semiconductor device of the present invention is produced by eliminating the excess P channel in the low resistivity portion of the front surface by electron beam irradiation to make the P channel concentration of the front surface equal to or lower than that of the entire substrate.

[0037] The conditions for the electron beam irradiation may be appropriately selected. The irradiation energy may be, for example, 300 to 5000 KeV, preferably 1 to 3 MeV, and particularly 2 MeV. The dose may be, for example, 1×10 14 / cm 2 More than 1×10 16 / cm 2 Less than or equal to 5×10 14 / cm 2 5×10 or more 15 / cm 2 In particular, it can be set to 2 MeV 1×10 14 / cm 2 More than 1×10 16 / cm 2 The following irradiation conditions are preferred.

[0038] The method for confirming the presence or absence of a P channel on the surface 1a of the n-type silicon single crystal substrate 1 is not particularly limited, but for example, a scanning nonlinear dielectric microscope (SNDM) can be used.

[0039] That is, whether or not a low resistivity portion exists on the surface of a high-resistivity silicon single crystal substrate can be confirmed by SNDM measurement. For example, in the case of an n-type silicon single crystal substrate, if a low resistivity portion exists, a signal derived from the P channel appears on the substrate surface, and if no low resistivity portion exists, no signal derived from the P channel appears.

[0040] According to the method for producing a substrate for a semiconductor device of the present invention as described above, it is possible to produce a substrate for a semiconductor device that can provide a semiconductor device with good electrical characteristics by eliminating the low resistivity portion formed on the surface of a high resistivity silicon substrate in a simple manner. EXAMPLES

[0041] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0042] (Example) n-type silicon single crystal substrate (diameter 150 mm, FZ single crystal, P-doped, orientation <111> A 150-nm-thick AlN layer was formed on the surface of the GaN substrate (resistivity of 100 Ω·cm or more), and then a 160-nm-thick AlGaN layer was formed on top of that, and then a superlattice layer was formed in which 70 pairs of GaN and AlN layers were alternately stacked. Next, an 800-nm-thick GaN layer was formed, on which a 25-nm-thick AlGaN layer was formed, and then a 3-nm-thick GaN layer was formed. Next, the layered substrate epitaxially grown as described above was removed from the manufacturing equipment, and a CPW electrode (Al) was formed by a photolithography process as shown in Figure 2 (L = 2199 μm).

[0043] Next, the back side of the n-type silicon single crystal substrate of the laminated substrate was irradiated with 2MeV 1×10 using Nissin Electric's equipment (NHV Corporation 3000kV machine). 15 / cm 2 The resultant substrate was irradiated with an electron beam of 1000 .mu.m to prepare a substrate for a semiconductor device.

[0044] (Comparative Example) A substrate for a semiconductor device was produced under the same conditions as in the example, except that the electron beam was not irradiated.

[0045] (Evaluation of the presence or absence of P-channel) For the semiconductor device substrates manufactured in the examples and comparative examples, chips were taken from parts of the samples with CPW electrodes, and the cross sections were visualized using a scanning nonlinear dielectric microscope (SNDM), as shown in Figure 3. Figure 3 (a) shows the results for the example, and (b) for the comparative example. Note that 2DEG in Figure 3 stands for two-dimensional electron gas, and the voltage-resistant layer is a high-resistance layer doped with carbon. This layer prevents the input signal from leaking to the substrate side.

[0046] In the example where electron beam irradiation was performed, only a weak signal (blue signal) originating from the n-type silicon single crystal substrate itself was observed at the location indicated by [1] in Fig. 3(a) (near the boundary between the n-type Si single crystal substrate and the buffer layer), and no signal (red signal) originating from the P channel was observed. From this, it was confirmed that in the present invention, the P channel (low resistivity portion) generated on the surface of the n-type Si single crystal substrate can be eliminated by electron beam irradiation.

[0047] In the comparative example where electron beam irradiation was not performed, a strong signal (red signal) originating from the P channel is seen at the location indicated by [1] in Figure 3(b). Furthermore, the results of investigating the diffusion of Al into the silicon single crystal substrate by backside SIMS are shown in Figure 4. As shown here, when electron beam irradiation is not performed, it is clear that a P channel (low resistivity area) exists on the surface of the silicon single crystal substrate.

[0048] (Evaluation of high frequency characteristics) The high frequency characteristics of the semiconductor device substrates manufactured in the examples and comparative examples were measured. The results are shown in Figure 5. As is clear from Figure 5, in the examples in which the P channel was eliminated by electron beam irradiation, the second harmonic was improved compared to the comparative example in which the P channel was present.

[0049] As described above, it has become clear that the present invention can provide good electrical characteristics to a device by eliminating low resistivity portions generated on the surface of a high resistivity silicon single crystal substrate for a semiconductor device by electron beam irradiation.

[0050] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0051] 1... n-type silicon single crystal substrate, 1'... region where a P channel exists, 1a... surface, 1b...back surface, 2...AlN layer, 3...AlGaN layer, 4...superlattice layer, 5...GaN layer, 6...AlGaN layer, 7...GaN layer, 8...electrode, 9...electron beam, 10...first buffer layer; 20...second buffer layer; 30...device active layer; 100...Laminated substrate, 101...Substrate for semiconductor device.

Claims

1. A method for manufacturing a substrate for a semiconductor device, comprising the steps of: (1) preparing a laminated substrate including a high-resistivity silicon single crystal substrate having a resistivity of 100 Ω cm or more, a first buffer layer made of an AlN layer formed on a surface of the high-resistivity silicon single crystal substrate, and a nitride semiconductor layer provided on the first buffer layer; (2) irradiating the laminated substrate with an electron beam from the back surface side of the high-resistivity silicon single crystal substrate to eliminate a low-resistivity portion formed on the front surface of the high-resistivity silicon single crystal substrate, the low-resistivity portion having a resistivity relatively lower than the resistivity of the entire high-resistivity silicon single crystal substrate; 2. A method for producing a substrate for a semiconductor device, comprising:

2. The nitride semiconductor layer provided on the first buffer layer, a second buffer layer formed on the first buffer layer and made of a nitride semiconductor layer; and a device active layer formed of a nitride semiconductor layer on the second buffer layer; 2. The method for producing a substrate for semiconductor devices according to claim 1,

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