Semiconductor element, semiconductor device, and power converter

A semiconductor element comprising a metal-insulator-semiconductor field effect transistor,

• wherein the metal-insulator-semiconductor field effect transistor comprises:
• a semiconductor substrate of a first conductivity type;
• a first silicon carbide semiconductor layer of the first conductivity type, which is arranged on the principal surface of the semiconductor substrate;
• a body region of a second conductivity type, which is defined in the first silicon carbide semiconductor layer;
• a source region of the first conductivity type, which is defined in the body region;
• a second silicon carbide semiconductor layer of the first conductivity type, which is arranged on the first silicon carbide semiconductor layer so as to be at least partially in contact with the body region and the source region;
• a gate insulating film, which is arranged on the second silicon carbide semiconductor layer;
• a gate electrode, which is arranged on the gate insulating film;
• a source electrode, which contacts with the source region;
• and
• a drain electrode, which is arranged on the back surface of the semiconductor substrate, and
• wherein the second silicon carbide semiconductor layer has been grown epitaxially on the first silicon carbide semiconductor layer, and
• wherein supposing the potential of the drain electrode with respect to the potential of the source electrode is identified by Vds,
• the potential of the gate electrode with respect to the potential of the source electrode is identified by Vgs,
• the gate threshold voltage of the metal-insulator-semiconductor field effect transistor is identified by Vth,
• the direction of a current flowing from the drain electrode toward the source electrode is defined to be a forward direction, and
• the direction of a current flowing from the source electrode toward the drain electrode is defined to be a reverse direction,
• Vth is equal to or higher than 2 V at room temperature,
• if Vgs≧Vth is satisfied,
• then the metal-insulator-semiconductor field effect transistor makes the drain electrode and the source electrode electrically conductive with each other through the second silicon carbide semiconductor layer, and
• if 0 V≦Vgs<Vth is satisfied,
• then the metal-insulator-semiconductor field effect transistor does not make a current flow in the forward direction but functions as a diode that makes a current flow in the reverse direction from the source electrode toward the drain electrode through the second silicon carbide semiconductor layer when Vds<0 V, and
• wherein the absolute value of a turn-on voltage of the diode is smaller than the absolute value of a turn-on voltage of a body diode that is formed by the body region and the first silicon carbide semiconductor layer, and
• wherein the difference in the absolute value of the turn-on voltage between the diode and the body diode is 0.7 V or more, and
• wherein the absolute value of the turn-on voltage of the diode is less than 1.0 V at room temperature.

A semiconductor device comprising

• a semiconductor element including a metal-insulator-semiconductor field effect transistor, and
• a potential setting section for setting a potential at the semiconductor element,
• wherein the metal-insulator-semiconductor field effect transistor includes:
• a semiconductor substrate of a first conductivity type;
• a first silicon carbide semiconductor layer of the first conductivity type, which is arranged on the principal surface of the semiconductor substrate;
• a body region of a second conductivity type, which is arranged on the first silicon carbide semiconductor layer;
• a source region of the first conductivity type, which is arranged on the body region;
• a recess, which extends through the body region and the source region to reach the first silicon carbide semiconductor layer;
• a second silicon carbide semiconductor layer of the first conductivity type, which defines the side surface of the recess and which is arranged so as to be at least partially in contact with the body region and the source region;
• a gate insulating film, which is arranged on the second silicon carbide semiconductor layer;
• a gate electrode, which is arranged on the gate insulating film;
• a source electrode, which contacts with the source region;
• and
• a drain electrode, which is arranged on the back surface of the semiconductor substrate, and
• wherein the second silicon carbide semiconductor layer has been grown epitaxially on the first silicon carbide semiconductor layer, and
• wherein supposing the potential of the drain electrode with respect to the potential of the source electrode is identified by Vds,
• the potential of the gate electrode with respect to the potential of the source electrode is identified by Vgs,
• the gate threshold voltage of the metal-insulator-semiconductor field effect transistor is identified by Vth,
• the direction of a current flowing from the drain electrode toward the source electrode is defined to be a forward direction, and
• the direction of a current flowing from the source electrode toward the drain electrode is defined to be a reverse direction,
• Vth is equal to or higher than 2 V at room temperature, and
• in a transistor turned-ON mode, the potential setting section raises the potential Vgs of the gate electrode with respect to the potential of the source electrode to a level that is equal to or higher than the gate threshold voltage Vth, thereby making the drain electrode and the source electrode electrically conductive with each other through the second silicon carbide semiconductor layer, and
• in a transistor turned-OFF mode, the potential setting section sets the potential Vgs of the gate electrode with respect to the potential of the source electrode to be equal to or higher than zero volts but less than the gate threshold voltage Vth, thereby making the metal-insulator-semiconductor field effect transistor function as a diode that makes a current flow in the reverse direction from the source electrode toward the drain electrode through the second silicon carbide semiconductor layer, and
• wherein the absolute value of a turn-on voltage of the diode is smaller than the absolute value of a turn-on voltage of a body diode that is formed by the body region and the first silicon carbide semiconductor layer, and
• wherein the difference in the absolute value of the turn-on voltage between the diode and the body diode is 0.7 V or more, and
• wherein the absolute value of the turn-on voltage of the diode is less than 1.0 V at room temperature.

A semiconductor element comprising a metal-insulator-semiconductor field effect transistor,

• wherein the metal-insulator-semiconductor field effect transistor comprises:
• a semiconductor substrate of a first conductivity type;
• a first silicon carbide semiconductor layer of the first conductivity type, which is arranged on the principal surface of the semiconductor substrate;
• a body region of a second conductivity type, which is arranged on the first silicon carbide semiconductor layer;
• a source region of the first conductivity type, which is arranged on the body region;
• a recess, which extends through the body region and the source region to reach the first silicon carbide semiconductor layer;
• a second silicon carbide semiconductor layer of the first conductivity type, which defines the side surface of the recess and which is arranged so as to be at least partially in contact with the body region and the source region;
• a gate insulating film, which is arranged on the second silicon carbide semiconductor layer;
• a gate electrode, which is arranged on the gate insulating film;
• a source electrode, which contacts with the source region;
• and
• a drain electrode, which is arranged on the back surface of the semiconductor substrate, and
• wherein the second silicon carbide semiconductor layer has been grown epitaxially on the first silicon carbide semiconductor layer, and
• wherein supposing the potential of the drain electrode with respect to the potential of the source electrode is identified by Vds,
• the potential of the gate electrode with respect to the potential of the source electrode is identified by Vgs,
• the gate threshold voltage of the metal-insulator-semiconductor field effect transistor is identified by Vth,
• the direction of a current flowing from the drain electrode toward the source electrode is defined to be a forward direction, and
• the direction of a current flowing from the source electrode toward the drain electrode is defined to be a reverse direction,
• Vth is equal to or higher than 2 V at room temperature, and
• if Vgs≧Vth is satisfied,
• then the metal-insulator-semiconductor field effect transistor makes the drain electrode and the source electrode electrically conductive with each other through the second silicon carbide semiconductor layer, and
• if 0 V≦Vgs<Vth is satisfied,
• then the metal-insulator-semiconductor field effect transistor does not make a current flow in the forward direction but functions as a diode that makes a current flow in the reverse direction from the source electrode toward the drain electrode through the second silicon carbide semiconductor layer when Vds<0 V, and
• wherein the absolute value of a turn-on voltage of the diode is smaller than the absolute value of a turn-on voltage of a body diode that is formed by the body region and the first silicon carbide semiconductor layer, and
• wherein the difference in the absolute value of the turn-on voltage between the diode and the body diode is 0.7 V or more, and
• wherein the absolute value of the turn-on voltage of the diode is less than 1.0 V at room temperature.