JP2008218785A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a semiconductor device which contains a good quality SiN surface protection film having a small gate leak current and small current collapse. <P>SOLUTION: In the manufacturing method of the semiconductor device, at least one thin film layer is formed on a substrate while a semiconductor element layer is formed, and the surface protection film made of SiN is formed on the semiconductor element layer by a CVD method. At the step of forming the SiN surface protection film, reaction gases SiH<SB>4</SB>and NH<SB>3</SB>are supplied by a carrier gas N<SB>2</SB>, and under the condition of SiH<SB>4</SB>/NH<SB>3</SB>≥5 and N<SB>2</SB>/SiH<SB>4</SB>≥75 as an abundance ratio of each gas, the SiH<SB>4</SB>gas is supplied to the reaction chamber at a flow rate of 20 sccm or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  In the recent advanced information society, high-speed communication and large-capacity recording media are indispensable. In order to achieve higher-speed communication, technology using high electron mobility transistors has been actively developed. High electron mobility transistors are generally made of compound semiconductors, and types thereof include gallium arsenide (GaAs), indium phosphide (InP), gallium nitride (GaN), and silicon germanium (SiGe).

  Recently, among the types of high electron mobility transistors described above, GaN-based nitride semiconductors have attracted particular attention. As a semiconductor forming the nitride semiconductor device, there are types such as aluminum nitride (AlN) and indium nitride (InN) in addition to GaN. Nitride semiconductors typified by these are wide gap semiconductors having a larger band gap than conventional semiconductors, and the band gap can be greatly changed by changing the concentration of gallium. Therefore, it is possible to change the emission wavelength from ultraviolet to red, and development has been carried out as a material for light emitting / receiving devices for visible light. As an example of the achievement of the optical device, there is an achievement such as practical application of a blue light emitting diode.

  Nitride semiconductors have also been developed as high-power / high-frequency electronic devices because of their features such as high saturation drift velocity, large breakdown electric field, good thermal conductivity, and heterojunction characteristics. Nitride semiconductors are also noted for their characteristics such as being stable at high temperatures of 500 ° C. and higher, being physically strong, and not using toxic substances such as arsenic. ing.

  In nitride semiconductor devices, problems such as gate leakage current and current collapse related to the surface have conventionally existed. As a countermeasure against these problems, it has been conventionally known to use a silicon nitride (SiN) film as a surface protective film. Although the SiN surface protective film can reduce current collapse to some extent, it has not been able to sufficiently meet the demand for higher voltage and higher power density of nitride semiconductor devices.

As a countermeasure against the above problems, it is known that the hydrogen content of the SiN surface protective film is made 15% or less. The SiN surface protective film having a hydrogen content of 15% or less suppresses the change in the surface state of the nitride semiconductor device and the charged state of the surface defect level, thereby reducing the gate leakage current and current collapse. (See Patent Document 1). In the method of manufacturing a semiconductor device described in Patent Document 1, a P-CVD (Plasma enhanced Chemical Vapor Deposition) method is used, and (SiH ₄ reactive gas): (SiH ₄ + N ₂ carrier gas + rare gas) ≦ 1 : SiN surface protective film having a hydrogen content of 15% or less can be formed under the conditions of 200, RF power density of 0.02 to 0.1 W / cm ² , and substrate temperature of 250 to 400 ° C.
JP 2005-286135 A

  However, since the rare gas is used as the carrier gas in the formation conditions to reduce the hydrogen content of the SiN surface protective film, the stoichiometry of Si and N is reduced, and a high-quality SiN surface protective film is formed. As a result, it has been found that there is a problem that the nitride semiconductor device does not operate correctly.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to provide a method for manufacturing a semiconductor device including a high-quality SiN surface protective film with a small gate leakage current and a small current collapse.

In order to solve the above-described problems, according to the present invention, a preparation step of preparing a substrate in a reaction chamber, and a semiconductor device for forming a semiconductor device layer while forming at least one thin film layer on the substrate A layer forming step, a protective film forming step of forming a surface protective film made of SiN on the semiconductor element layer by a CVD method, an electrode forming step of forming an electrode connected to the semiconductor element in the semiconductor element layer, In the protective film forming step, the reactive gases SiH ₄ and NH ₃ are supplied by the carrier gas N ₂ , and the abundance ratio of each gas is SiH ₄ / NH ₃ ≦ 5 and N _A method of manufacturing a semiconductor device is provided, wherein SiH ₄ gas is supplied to the reaction chamber at a flow rate of 20 sccm or less under the condition of ₂ / SiH ₄ ≧ 75.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
(Example 1)
FIG. 1 is a cross-sectional view showing a configuration of a nitride semiconductor high electron mobility transistor 10 that can be manufactured according to the present invention. The nitride semiconductor high electron mobility transistor 10 is formed on a SiC (silicon carbide) substrate 11 by metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy: The buffer layer 12, the i-GaN layer 13, and the i-AlGaN layer 14 formed by MBE method, etc. are sequentially stacked on the SiN surface protective film 15, the gate electrode 16 for bias, and the ohmic electrode 17a. , 17b are provided.

  Further, the i-GaN layer 13 and the i-AlGaN layer 14 have an element isolation region 18 formed by ion implantation. The SiC substrate 11 may be a silicon or sapphire substrate.

  As an example of the basic operation of the nitride semiconductor high electron mobility transistor 10, the ohmic electrode 17a is set as a ground potential, the ohmic electrode 17b is set as a drain electrode, a positive potential is applied, and a negative potential is applied to the gate electrode 16. Apply. By changing the negative potential applied to the gate electrode, it is possible to control electrons traveling in a two-dimensional electron gas layer (not shown) included in the i-GaN layer 13.

  Next, an embodiment of a method for manufacturing the nitride semiconductor high electron mobility transistor 10 will be described with reference to FIG.

  First, a SiC substrate 11 processed to an appropriate size is prepared in a reaction chamber for manufacturing a semiconductor device. A buffer layer 12, an i-GaN layer 13, and an i-AlGaN layer 14 are sequentially formed on the SiC substrate 11 by MOCVD. A cross-sectional view after the formation of the i-AlGaN layer 14 is shown in FIG.

Thereafter, a SiN surface protective film 15 is formed on the i-AlGaN layer 14 by P-CVD. In the formation process of the SiN surface protection film 15, the reaction gases SiH ₄ (silane) and NH ₃ (ammonia) are supplied by the carrier gas N ₂ . The abundance ratio of each gas at this time is set to SiH ₄ / NH ₃ ≦ 5 and N ₂ / SiH ₄ ≧ 75. While satisfying these conditions, SiH ₄ gas is further supplied at a flow rate of 20 sccm or less. For example, when the flow rate of SiH ₄ gas is 20 sccm, the N ₂ gas flow rate may be 1500 sccm or more and the NH ₃ gas flow rate may be 4 sccm or more. The temperature in the atmosphere may be 300 ° C. to 350 ° C. FIG. 2B shows a cross-sectional view after the formation of the SiN surface protective film 15 is completed. The method for forming the SiN surface protective film 15 is not limited to the P-CVD method, and may be a thermal CVD method or a catalytic-CVD method.

In the P-CVD method for forming the SiN surface protection film 15, the RF (high frequency) frequency for generating plasma is set to 13.56 MHz, but the RF frequency may be set to 40 MHz or more. By making the RF frequency 40 MHz or more, it is possible to increase the decomposition efficiency of SiH ₄ . Therefore, increasing the RF frequency has the same effect as reducing the flow rate of SiH ₄ and does not reduce the flow rate of SiH 4 (ie, does not reduce the formation speed of the SiN surface protection film 15). -It is possible to reduce damage on the surface of the AlGaN layer 14.

After the SiN surface protection film 15 is formed, an element isolation region 18 is generated in the i-GaN layer 13 and the i-AlGaN layer 14 by ion implantation. Further, a part of the SiN surface protection film 15 is removed by etching, and a gate electrode 16 and ohmic electrodes 17a and 17b are formed in the removed part. Note that the etching may be dry etching with sulfur hexafluoride (SF ₆ ) and the etching rate may be 300 Å / min or less. FIG. 2 (c) shows a cross-sectional view after completion of electrode formation.

  The SiN surface protective film 15 formed under the above conditions has a low hydrogen content (for example, 15% or less), and the stoichiometry of Si and N is improved. Hereinafter, it will be described that the SiN surface protective film 15 has a low hydrogen content and good stoichiometry.

FIG. 3 shows a SiN surface protective film (shown by curve 3A) included in a nitride semiconductor high electron mobility transistor manufactured according to an embodiment of the present invention and a SiN surface protective film included in a conventional nitride semiconductor high electron mobility transistor. It is a graph which compares an infrared absorption spectrum with (shown by curve 3B). As can be seen from FIG. 3, the Si—H bond peak intensity of the SiN surface protective film according to the embodiment of the present invention (Ip1) compared to the Si—H bond (near 2160 cm ⁻¹ ) peak intensity (Ip1) of the conventional SiN surface protective film ( Ip2) is clearly decreasing. Therefore, the SiN surface protective film according to the embodiment of the present invention has a significantly reduced hydrogen content than the conventional SiN surface protective film. Further, the bond peak seen in the vicinity of 3350 cm ⁻¹ is an NH bond peak. The NH bond peak intensity of the conventional SiN surface protective film is denoted by Ip3, and the NH bond peak intensity of the SiN surface protective film according to the embodiment of the present invention is denoted by Ip4.

  The N—H / Si—H peak ratio (ie, Ip3 / Ip1) obtained by dividing the N—H bond peak intensity of the conventional SiN surface protective film by the Si—H bond peak intensity is 1 to 2. In contrast, the N—H / SiH peak ratio (ie, Ip4 / Ip2) of the SiN surface protective film according to the embodiment of the present invention is 19 or more. Since the stoichiometry of Si and N is said to be better as the NH / SiH peak ratio is larger, the SiN surface protective film according to the embodiment of the present invention has an excellent stoichiometry compared to the conventional SiN surface protective film. It will be ikiometori.

  FIG. 4 is a graph showing the breakdown voltage of a nitride semiconductor high electron mobility transistor (shown by curve 4A) and a conventional nitride semiconductor high electron mobility transistor (shown by curve 4B) manufactured according to an embodiment of the present invention. is there. In the measurement in FIG. 4, the ohmic electrode 17a is set as a drain electrode, and the ohmic electrode 17b is set as a source electrode. After that, by applying a reverse gate voltage (Vgs) that is about 1 V larger than the threshold voltage of the nitride semiconductor high electron mobility transistor, the drain current is pinched off, and then the drain voltage (Vds) is applied. Measure the breakdown voltage. In the graph of FIG. 4, the horizontal axis represents the drain voltage, and the vertical axis represents the drain leakage current (Ids).

  As can be seen from FIG. 4, the drain leakage current of the conventional nitride semiconductor high electron mobility transistor is 7 μA when the drain voltage is 120 V, whereas the nitride semiconductor high electron mobility manufactured according to the embodiment of the present invention. When the transistor has a drain voltage of 120 V, the drain leakage current is 0.3 μA. Therefore, the drain leakage current of the nitride semiconductor high electron mobility transistor manufactured according to the embodiment of the present invention is reduced to about 1/20 as compared with the conventional one, and the breakdown voltage is greatly improved.

  FIG. 5 shows the leakage between the gate and drain of a nitride semiconductor high electron mobility transistor (shown by curve 5A) and a conventional nitride semiconductor high electron mobility transistor (shown by curve 5B) manufactured according to an embodiment of the present invention. It is a graph which compares an electric current (Igd). In the measurement in FIG. 5, the gate drain voltage (Vgd) is changed from 0 V to −40 V, and the leakage current between the gate and drain at each gate drain voltage is measured. In the graph of FIG. 5, the horizontal axis represents the gate drain voltage (V), and the vertical axis represents the leakage current (A) between the gate and drain. The vertical axis of the graph is a logarithmic memory.

As can be seen from FIG. 5, in the conventional nitride semiconductor high electron mobility transistor, the leakage current gradually increases by changing the gate drain voltage from 0V to -40V, and the leakage current increases when the gate drain voltage is -40V. The current has reached about 4.0 × 10 ⁻⁶ A. In contrast, the nitride semiconductor high electron mobility transistor manufactured according to the embodiment of the present invention has a leakage current of about 1.0 × 10 ⁻⁸ A when the gate drain voltage is −40 V, which is compared with the conventional product. It will be reduced to about 1/400.

  FIG. 6 is a graph showing current collapse characteristics. FIG. 6 (a) is a current collapse characteristic of a conventional nitride semiconductor high electron mobility transistor, and FIG. 6 (b) is a nitride manufactured according to an embodiment of the present invention. 2 shows current collapse characteristics of a physical semiconductor high electron mobility transistor. In the graph of FIG. 6, the horizontal axis represents the drain voltage (V) and the vertical axis represents the drain current (A). This current collapse characteristic is measured in a state where the gate voltage is changed in 1V increments. In each graph, the gate voltage is changed to + 1V, +/- 0V, -1V, -2V from above. The results are shown. In each gate voltage, the measurement results (shown by curves A1 to A4) with the drain voltage + 40V and gate voltage -5V applied each time one point is measured on the lower side, and the stress voltage on the upper side. It is a measurement result (shown by curves B1 to B4) in a state where no voltage is applied. Since current collapse is likely to occur when a stress voltage is applied, a measurement result without a stress voltage is shown above, and a measurement result with a stress voltage is shown below.

  As can be seen from FIG. 6, in the conventional nitride semiconductor high electron mobility transistor, when the gate voltage is + 1V and the drain voltage is about 5V, the current drop due to current collapse is about 8% (that is, the rate of decrease of curve B1 with respect to curve A1). is there. In contrast, the nitride semiconductor high electron mobility transistor manufactured according to the embodiment of the present invention has a current drop of about 0.1% when the gate voltage is +1 V and the drain voltage is about 5 V, and the current collapse is reduced. Has been.

As described above, it is possible to reduce the gate leakage current and current collapse and improve the stoichiometry of Si and N by forming a high-quality SiN surface protective film by the method for manufacturing a semiconductor device of the present invention. .
(Example 2)
In addition, after forming the i-AlGaN layer, an SiN surface protective film may be formed after ion implantation into the i-GaN layer and the i-AlGaN layer and electrode formation on the i-AlGaN layer. An embodiment will be described with reference to FIG.

  The steps up to the formation of the i-AlGaN layer 14 are the same as those in Example 1 in FIG. FIG. 7A shows a cross-sectional view after the formation of the i-AlGaN layer 14 is completed.

  Thereafter, element isolation regions 18 are generated in the i-GaN layer 13 and the i-AlGaN layer 14 by ion implantation. Further, the gate electrode 16 and the ohmic electrodes 17a and 17b are formed on the i-AlGaN layer. FIG. 7B shows a cross-sectional view after the electrode formation is completed.

  Thereafter, the SiN surface protection film 15 is formed by the P-CVD method so as to cover the i-AlGaN layer 14, the gate electrode 16, and the ohmic electrodes 17a and 17b. Since the growth conditions of the SiN surface protection film 15 are the same as those in Example 1, they are omitted. FIG. 7C shows a cross-sectional view after the formation of the SiN surface protective film 15 is completed.

  Further, a part of the SiN surface protection film 15 is removed by etching to expose the gate electrode 16 and the ohmic electrodes 17a and 17b. FIG. 7D shows a cross-sectional view of the state in which the gate electrode 16 and the ohmic electrodes 17a and 17b are exposed.

  As described above, according to the method of manufacturing a semiconductor device of the embodiment of the present invention, the gate end is completely protected, so that current collapse caused by the surface level of the gate end can be suppressed.

It is sectional drawing which shows the structure of a nitride semiconductor high electron mobility transistor. It is sectional drawing of the production | generation part in each manufacturing process of the nitride semiconductor high electron mobility transistor. The graph which compares the infrared absorption spectrum of the SiN surface protective film formed by the Example of this invention, and the conventional SiN surface protective film. The graph which compares the pressure | voltage resistance of the nitride semiconductor high electron mobility transistor manufactured by the Example of this invention, and the nitride semiconductor high electron mobility transistor of a prior art example. 6 is a graph comparing the leakage current between the gate and drain of a nitride semiconductor high electron mobility transistor manufactured according to an embodiment of the present invention and a conventional nitride semiconductor high electron mobility transistor. The graph which compares the current collapse characteristic of the nitride semiconductor high electron mobility transistor manufactured by the Example of this invention, and the nitride semiconductor high electron mobility transistor of a prior art example. It is sectional drawing which shows the intermediate product of the nitride semiconductor high electron mobility transistor in each manufacturing process of another Example of this invention.

Explanation of symbols

10 Nitride semiconductor high electron mobility transistor
11 SiC substrate
12 Buffer layer
13 i-GaN layer
14 i-AlGaN layer
15 SiN surface protection film
16 Gate electrode
17a, 17b ohmic electrode
18 Element isolation region

Claims (4)

A preparation step of preparing a substrate in the reaction chamber;
A semiconductor element layer forming step of forming a semiconductor element layer while forming at least one thin film layer on the substrate;
A protective film forming step of forming a surface protective film made of SiN by a CVD method on the semiconductor element layer;
Forming an electrode connected to a semiconductor element in the semiconductor element layer, and a method of manufacturing a semiconductor device,
In the protective film forming step, the reactive gases SiH ₄ and NH ₃ are supplied by the carrier gas N ₂ , and the abundance ratio of each gas is under the conditions of SiH ₄ / NH ₃ ≧ 5 and N ₂ / SiH ₄ ≧ 75. A method of manufacturing a semiconductor device, wherein SiH ₄ gas is supplied to the reaction chamber at a flow rate of 20 sccm or less. The CVD method is a P-CVD method,
2. The method of manufacturing a semiconductor device according to claim 1, wherein an RF frequency for generating plasma in the P-CVD method is set to 40 MHz or more.   3. The method for manufacturing a semiconductor device according to claim 1, wherein the protective film forming step is performed after the electrode forming step.   4. The method of manufacturing a semiconductor device according to claim 1, wherein the semiconductor device is a nitride semiconductor high electron mobility transistor.

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