JP5106008B2 - Manufacturing method of semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a wide gap semiconductor element including silicon carbide, and more particularly to a method for manufacturing a semiconductor element having an electrode contact to a p-type semiconductor layer.

  In wide gap semiconductors such as silicon carbide semiconductors, it is difficult to obtain a p-type semiconductor layer having a low resistance compared to an n-type semiconductor layer. In addition, it is difficult to obtain the contact resistance of the electrode contact, which is an important factor for reducing the resistance, with a low contact resistance as compared with the n-type semiconductor layer.

In order to obtain a low-resistance semiconductor element, AlTi is used as the electrode metal, and the carrier concentration of the p-type layer is set to 10 ¹⁸ / cm ³ or more, so that low contact resistance of 10 ⁻⁶ Ωcm ² or 10 ⁻⁷ Ωcm ² The following Patent Document 1 shows that the above can be obtained.

  As another configuration, Patent Document 2 below discloses that the contact resistance is reduced by setting the contact resistivity between the electrode and the semiconductor region and the sheet resistance of the semiconductor region within a predetermined range.

JP 2002-75909 A JP 2002-76022 A

However, in the semiconductor device described in Patent Document 1, in order to set the carrier concentration of the p-type semiconductor layer to 10 ¹⁸ / cm ³ , the acceptor doping concentration N _{A is set} to about 10 ¹⁹ / cm ³ or higher. There is a problem that it is difficult to reduce the cost because it is necessary to go through a complicated process such as ion implantation at a high temperature.

  Further, since the sheet resistance value is determined by the doping concentration, carrier concentration, and mobility of the semiconductor layer, the doping concentration and carrier concentration of the semiconductor layer may be different even with the same sheet resistance value. In particular, when the electrode is formed and the doping concentration on the surface of the semiconductor layer that greatly affects the contact resistance is different, the semiconductor element described in Patent Document 2 does not necessarily have a low contact resistance even if the sheet resistance value is as set. There was a problem that could not get.

In addition, when the contact resistance is not reduced to 10 ⁻⁶ Ωcm ² or 10 ⁻⁷ Ωcm ² , the current / voltage characteristics include a non-linear component that is not linear. The impact is not considered much. In addition, there is a problem that it is not known how low the contact resistance should be in order to prevent the element resistance from being affected.

  Accordingly, the present invention has been made to solve such a problem, and a low-resistance semiconductor element that does not increase the element operating voltage is a non-ohmic component whose current / voltage characteristics at the contact with the p-type semiconductor region are not linear. It aims at realizing | achieving in the electrode in which.

A method for manufacturing a semiconductor device according to the present invention is a method for manufacturing a semiconductor device comprising a p-type SiC semiconductor region and a metal electrode formed on the p-type SiC semiconductor region . The acceptor doping concentration N _A (/ cm ³ ) and the barrier height φ (eV) obtained by subtracting the work function of the metal of the electrode from the Fermi level of the p-type SiC semiconductor region is 0.043 LN _A metal material satisfying (N _A ) −1.63 <φ <0.052LN (N _A ) −1.85 is selected, and the metal electrode made of the metal material is formed on the p-type SiC semiconductor region. The contact resistance including a non-ohmic component between the p-type SiC semiconductor region and the electrode is set to 10 ⁻⁶ Ωcm ² to 10 ⁻⁴ Ωcm ² .

According to the semiconductor device of the present invention, the acceptor concentration of the p-type semiconductor layer region where the electrode is formed and the barrier height between the p-type semiconductor region and the metal of the electrode are set in a range that does not significantly affect the device resistance. Thus, a low resistance element can be obtained. Moreover, since it is an electrode having current / voltage characteristics including a non-ohmic component without a low contact resistance such as 10 ⁻⁶ Ωcm ² or 10 ⁻⁷ Ωcm ² , the p-type semiconductor layer has a high value of 10 ¹⁸ / cm ³ or more. The carrier concentration is not essential, and it is not necessary to go through a complicated process such as ion implantation at a high temperature, so that the cost can be reduced.

<Embodiment 1>
FIG. 1 is a cross sectional view showing a silicon carbide semiconductor device according to the first embodiment of the present invention, and the configuration of the silicon carbide semiconductor device will be described below. The silicon carbide semiconductor element includes an n-type low resistance SiC substrate 1 (hereinafter referred to as an n-type substrate 1), and an n-type SiC drift layer 2 (hereinafter referred to as an n-type drift layer) for maintaining a withstand voltage on the n-type substrate 1. 2) is epitaxially grown, and p-type SiC region 3 (hereinafter referred to as p-type region 3) and p-type SiC contact region 4 (hereinafter referred to as p-type contact region 4) are ion-implanted and activated in the n-type drift layer 2. It is formed by epitaxial growth on the n-type drift layer 2 by a process. An n-type electrode 5 is formed under the n-type substrate 1, and a p-type electrode 6 (hereinafter referred to as an electrode 6) is formed on the p-type contact region 4.

Here, the n-type drift layer 2 has a layer thickness of about 3 to 50 μm and a doping concentration of about 1 to 15 × 10 ¹⁵ / cm ³ . The p-type region 3 has a layer thickness of about 0.5 to 2 μm and a doping concentration of about 3 to 20 × 10 ¹⁷ / cm ³ . The p-type contact region 4 has a layer thickness of about 0.1 to 0.5 μm and a doping concentration of about 5 to 10 × 10 ¹⁸ / cm ³ .

  Next, referring to FIGS. 2 and 3, the silicon carbide semiconductor element according to the first embodiment of the present invention includes a non-ohmic component whose current / voltage characteristics at the contact between p-type contact region 4 and electrode 6 are not linear. A description will be given of the influence on the element resistance in the case of the above.

Figure 2 is a doping concentration of the current density 300A / cm ³ and 600A / cm ^3, p-type contact region 4 is shown a relationship between the contact resistance and the voltage value of the element in the range of 2~20 × 10 ¹⁸ / cm ³ It is a graph. Here, the n-type drift layer 2 has a layer thickness of 12 μm and a doping concentration of 1 × 10 ¹⁶ / cm ³ . Further, since the contact resistance includes a non-ohmic component and varies depending on the current density, a value at a current density of 100 A / cm ² often used for measurement of the contact resistance value was used.

3, the contact resistance is 10 in the range of ^-3 to 10 ^-6 [Omega] cm ^2, p-type and the doping concentration N _A of the contact region 4, the relationship between the barrier height φ of the metal of the p-type contact region 4 and the electrode 6 It is the graph which showed.

As shown in FIG. 2, it can be seen that if the contact resistance value is 10 ⁻⁴ Ωcm ² or less, the element voltage is not increased significantly. Contact with the doping concentration N _A of the resistance value gives a 10 ^-4 [Omega] cm ² as a p-type contact region 4, p-type contact region 4 of the Fermi level from the relation between the barrier minus the work function of the metal electrode height 6 phi Is given by Equation 1 below.

In addition, a feature of this embodiment is that an element that operates with a low resistance in a region including a non-ohmic component is obtained. If the contact resistance value is 10 ⁻⁶ Ωcm ² or less, the current / voltage characteristics are obtained. Is a linear ohmic component, and the conditions at this time are disclosed in Japanese Patent Application Laid-Open No. H10-228707, and thus the description thereof is omitted. Here, a doping concentration N _A of the p-type contact region 4 to give 10 ^-6 [Omega] cm ² as the contact resistance, the relationship of the barrier height φ of the metal of the p-type contact region 4 and the electrode 6 in the number of 2 or less Given.

Therefore, so as to satisfy the equation (3) above, and the doping concentration N _A of the p-type contact region 4, if the barrier height between the metal of the p-type contact region 4 and the electrode 6 phi, the current-voltage characteristics, It can be seen that a p-type contact that does not affect the element resistance can be obtained even when a non-linear non-ohmic component is included.

Then, comparing the calculation result with the current density of 300A / cm ² and 600A / cm ² in 10 ^-4 [Omega] cm ² or less as a contact resistance value shown in FIG. 2, the current density of 300A / cm ^2, p-type contact region 4 whereas smaller doping concentration ^{_{N a (2 × 10 18 /}} cm 3) is small element voltage, the current density is 600A / cm ^2, characteristic in the vicinity of the contact resistance 10 ^-4 Ωcm ² is reversed, larger doping concentration N _a of the p-type contact region ^{4 (2 × 10 19 / cm} 3) is smaller of the element voltage. Therefore, when the current density region using the element extensive as the doping concentration N _A of the p-type contact region 4, increase the range of the element voltage shown in Formula 4 which is an intermediate region near the region where characteristic is not reversed It is desirable as a range that does not.

Thus, the p-type contact region 4 doping concentration N _A that satisfies the number 3 and 4, by setting the barrier height between the metal of the p-type contact region 4 and the electrode 6 phi, in a wide range of current density An element that operates with low resistance can be obtained.

Further, as the doping concentration N _A of the p-type contact region 4 is shown by the number 4, since it does not require a high concentration exceeding 1 × 10 ¹⁹ / cm ^3, in the formation of p-type contact region 4, at high temperatures It is not necessary to go through a complicated process such as ion implantation, and the cost can be reduced.

<Embodiment 2>
FIG. 4 is a cross sectional view showing a silicon carbide semiconductor element in the second embodiment of the present invention. The difference from the first embodiment is that the p-type SiC contact region 14 (hereinafter, p-type contact region 14) has a doping concentration of about 1 to 5 × 10 ¹⁸ / cm ³ .

This embodiment assumes a current density of about 300 A / cm ² or less as the operating state of the element. In this case, as shown in FIG. 2, the smaller the doping concentration N _A of the p-type contact region 14, it is possible to lower the device voltage.

From FIG. 2, the silicon carbide semiconductor device of Patent Document 1, the carrier concentration of the p-type layer 10 ¹⁸ / cm ³ or more, that is, a doping concentration N _A of the acceptor 10 ¹⁹ / cm ³ units mid or more Thus, it is estimated that the barrier height when the contact resistance is 10 ⁻⁶ Ωcm ² or 10 ⁻⁷ Ωcm ² is 0.3 eV to 0.4 eV.

This value is considered as the lower limit when the surface state of the p-type contact region 14 is sufficiently cleaned. Accordingly, by the 1 × 10 ¹⁸ / cm ³ or more barriers is the value of the acceptor concentration N _A in the height 0.3eV in line to provide a contact resistance 10 ^-4 [Omega] cm ² in FIG. 3, does not significantly increase the device voltage The upper limit of the contact resistance of 10 ⁻⁴ Ωcm ² can be secured sufficiently. That is, at 1 × 10 ¹⁸ / cm ³ or less, a contact resistance of 10 ⁻⁴ Ωcm ² cannot be realized even at a barrier height of 0.3 eV.

Thus, as the doping concentration N _A of the p-type contact region 14, by a range shown in Equation 5, it is possible to obtain a device that operates at low resistance in the following current density of about 300A / cm ^2.

Further, as the doping concentration N _A of the p-type contact region 14 is indicated by the number 5, since it does not require a high concentration exceeding 1 × 10 ¹⁹ / cm ^3, in the formation of p-type contact region 14, at high temperatures It is not necessary to go through a complicated process such as ion implantation, and the cost can be reduced.

<Embodiment 3>
FIG. 5 is a cross sectional view showing a silicon carbide semiconductor element in the third embodiment of the present invention. The difference from the first embodiment is that the doping concentration of p-type SiC contact region 24 (hereinafter referred to as p-type contact region 24) is about 1 to 4 × 10 ¹⁹ / cm ³ .

This embodiment assumes a current density of about 600 A / cm ² or more as the operating state of the element. In this case, as shown in FIG. 2, the larger the doping concentration N _A of the p-type contact region 24, it is possible to lower the device voltage. Further, as shown in FIG. 2, it can be seen that in the region where the contact resistance is about 10 ⁻⁵ Ωcm ² or less, the device voltage does not decrease even if the contact resistance value is further reduced. That is, the upper limit of the contact resistance that does not increase the element voltage is 10 ⁻⁵ Ωcm ² .

As described above, from Figure 2, a silicon carbide semiconductor device of Patent Document 1, the carrier concentration of the p-type layer 10 ¹⁸ / cm ³ or more, that a doping concentration N _A of the acceptor 10 ¹⁹ / cm ³ units mid Alternatively, it is estimated that the barrier height is 0.3 eV to 0.4 eV when the contact resistance is 10 ⁻⁶ Ωcm ² or 10 ⁻⁷ Ωcm ² by making it higher.

This value is considered as the lower limit value when the surface state of the p-type contact region 24 is sufficiently cleaned. Therefore, by the contact resistance 10 ^-5 [Omega] cm ² is a value of the acceptor concentration N _A in the barrier height 0.4eV in line to provide a 4 × 10 ¹⁹ / cm ³ or less in FIG. 3, does not increase any element voltage The upper limit of the contact resistance of 10 ⁻⁵ Ωcm ² can be secured sufficiently. Therefore, as the doping concentration N _A of the p-type SiC contact region 24, by a range shown in Equation 6, it is possible to operate at lower voltage in the operation of 600A / cm ² of about or more current density. If it is 4 × 10 ¹⁹ / cm ³ or more, the contact resistance is 10 ⁻⁶ Ωcm ² even at a barrier height of 0.4 eV, so that it is not enough to secure 10 ⁻⁵ Ωcm ² .

Thus, as the doping concentration N _A of the p-type contact region 24, by a range shown in Equation 6, it is possible to obtain a device that operates at low resistance in the following current density of about 300A / cm ^2.

  In the above, a pn diode is taken as an example of a semiconductor element, and the contact to the p-type layer has been described. However, the element having a contact to the p-type layer is not limited to the pn diode, but the MPS (Merged pin and Schottky ) Diode, JBS (Junction Barrier Schottky) diode, electrostatic induction diode, MOSFET (Metal Oxide Semiconductor Field Effect Transistor), JFET (Junction FET), electrostatic induction transistor, IGBT (Insulated gate Bipolar Transistor), thyristor, p If the element has a contact to the mold layer, the operating voltage when a forward voltage is applied to the pn junction in the element can be lowered.

  In addition, although silicon carbide has been described as an example as a semiconductor, the physical constants of acceptor activation energy, effective mass, and dielectric breakdown electric field are similar to those of silicon carbide, and also in GaN, ZnO, and mixed crystals containing them. Similarly, the operating voltage when a forward voltage is applied to the pn junction in the element can be lowered.

It is sectional drawing which showed the silicon carbide semiconductor element in Embodiment 1 of this invention. . It is the graph which showed the relationship between the voltage value of an element and contact resistance in the silicon carbide semiconductor element of this invention. 4 is a graph showing the relationship between the doping concentration of the p-type contact region and the barrier height φ between the p-type contact region and the metal of the electrode 6 in the silicon carbide semiconductor device of the present invention. It is sectional drawing which showed the silicon carbide semiconductor element in Embodiment 2 of this invention. It is sectional drawing which showed the silicon carbide semiconductor element in Embodiment 3 of this invention.

Explanation of symbols

  1 n type substrate, 2 n type drift layer, 3 p type region, 4, 14, 24 p type contact region, 5 n type electrode, 6 p type electrode.

Claims (2)

a p-type SiC semiconductor region;
A metal electrode formed on the p-type SiC semiconductor region, comprising:
And the doping concentration of the acceptor to the p-type SiC semiconductor region N _A (/ cm ^3), the barrier height from the Fermi level of the p-type SiC semiconductor region minus the work function of the metal of the electrodes φ and (eV) Relationship
0.043 LN (N _A ) −1.63 <φ <0.052 LN (N _A ) −1.85
And selecting the metal material that satisfies the above, and forming the metal electrode made of the metal material on the p-type SiC semiconductor region,
A method for manufacturing a semiconductor device, wherein a contact resistance including a non-ohmic component between the p-type SiC semiconductor region and the electrode is set to 10 ⁻⁶ Ωcm ² to 10 ⁻⁴ Ωcm ² . The method according to claim 1, the doping concentration N _A of the acceptor to the p-type SiC semiconductor region are set so as to satisfy the ^{1 × 10 18 / cm 3 ~4} × 10 19 / cm 3.

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