Semiconductor wafer, semiconductor device, and method for producing semiconductor device

A semiconductor device comprising:

• a silicon carbide substrate having a first carrier concentration which is uniform in a thickness direction;
• a carrier concentration transition layer provided on the silicon carbide substrate;
• an epitaxial layer provided on the carrier concentration transition layer, the epitaxial layer having a second carrier concentration which is uniform in the thickness direction and the second carrier concentration being lower than the first carrier concentration;
• a surface structure provided on a surface of the epitaxial layer, the surface structure including at least one of a transistor and a Schottky barrier diode, and
• a rear side electrode provided on a rear side of the silicon carbide substrate,
• wherein
• the carrier concentration of the carrier concentration transition layer has a concentration gradient in the thickness direction,
• the concentration gradient is such a gradient that the carrier concentration decreases continuously as a distance along the thickness direction from an interface increases, the interface being provided between a layer directly below the carrier concentration transition layer and the carrier concentration transition layer, and the carrier concentration decreases at a lower rate of decrease as the distance from the interface along the thickness direction in the carrier concentration transition layer increases,
• X is a film thickness ratio in the carrier concentration transition layer,
• the film thickness ratio is obtained by dividing a position in the thickness direction of the carrier concentration transition layer by a film thickness of the carrier concentration transition layer,
• X is a variable having a domain of 0≤X≤1,
• Y is a carrier concentration ratio in the carrier concentration transition layer,
• the carrier concentration ratio is obtained by dividing a carrier concentration of the carrier concentration transition layer in a range of 0<X≤1 by a carrier concentration of the carrier concentration transition layer when X=0, and
• when a concentration range lying between a following equation (b1) and equation (b2) is defined in advance,
• Y
• =
• 1.05
• 1.74
• ×
• 10
• -
• 3
• +
• 1.00
• ×
• X
• -
• 1.04
• (
• b
• ⁢
• ⁢
• 1
• )
• Y
• =
• 1.95
• 1.11
• ×
• 10
• -
• 1
• +
• 0.89
• ×
• X
• -
• 1.50
• (
• b2
• )
• the carrier concentration of the carrier concentration transition layer includes a concentration gradient that falls within the concentration range.

A method for producing a semiconductor device, comprising:

• a first step of preparing a silicon carbide substrate having a first carrier concentration which is uniform in a thickness direction;
• a second step of providing a carrier concentration transition layer provided on the silicon carbide substrate by supplying a growth gas and a dopant gas;
• and
• a third step of providing an epitaxial layer provided on the carrier concentration transition layer, the epitaxial layer having a second carrier concentration which is uniform in the thickness direction and the second carrier concentration being lower than the first carrier concentration, wherein
• the second step is configured to control flow rates of the growth gas and the dopant gas so that the carrier concentration of the carrier concentration transition layer has a concentration gradient in the thickness direction,
• the concentration gradient is such a gradient that the carrier concentration decreases continuously as a distance along the thickness direction from an interface increases, the interface being provided between a layer directly below the carrier concentration transition layer and the carrier concentration transition layer, and the carrier concentration decreases at a lower rate of decrease as the distance from the interface along the thickness direction in the carrier concentration transition layer increases,
• X is a film thickness ratio in the carrier concentration transition layer,
• the film thickness ratio is obtained by dividing a thickness of the carrier concentration transition layer in a middle of growth after the carrier concentration transition layer starts to grow by a film thickness design value of the carrier concentration transition layer,
• X is a variable having a domain of 0≤X≤1,
• Y is a carrier concentration ratio in the carrier concentration transition layer,
• the carrier concentration ratio is obtained by dividing a carrier concentration of the carrier concentration transition layer in a range of 0<X≤1 by a carrier concentration of the carrier concentration transition layer when X=0, and
• when a concentration range lying between a following equation (c1) and equation (c2) is defined in advance,
• Y
• =
• 1.05
• 1.74
• ×
• 10
• -
• 3
• +
• 1.00
• ×
• X
• -
• 1.04
• (
• c
• ⁢
• ⁢
• 1
• )
• Y
• =
• 1.95
• 1.11
• ×
• 10
• -
• 1
• +
• 0.89
• ×
• X
• -
• 1.50
• (
• c2
• )
• the second step is configured to control the flow rates of the growth gas and the dopant gas so that the carrier concentration of the carrier concentration transition layer includes a concentration gradient that falls within the concentration range.