Method for manufacturing an insulated gate bipolar transistor

Abstract

Method for manufacturing an insulated gate bipolar transistor, which includes a drift layer of a first conductivity type between an emitter side, at which a gate and emitter electrode are arranged, and a collector side, at which a collector electrode is arranged including steps: providing a substrate of a second conductivity type, applying a dopant of the first conductivity type on the first side, creating a drift layer of the first conductivity type on the first layer, diffusing the ions such that a buffer layer is created, having a higher doping concentration than the drift layer, creating a base layer of the second conductivity type on the drift layer, creating an emitter layer of the first conductivity type on the base layer, thinning the substrate on the second side such that the remaining part of the substrate forms a collector layer.

Claims

1. A method for manufacturing an insulated gate bipolar transistor, which includes a drift layer of a first conductivity type between an emitter side, at which a gate electrode and an emitter electrode are arranged, and a collector side opposite to the emitter side, at which a collector electrode is arranged, wherein the manufacturing method comprises manufacturing steps in the following order: providing a substrate of a second conductivity type, which is opposite to the first conductivity type, the substrate of the second conductivity type having a first side and a second side opposite to the first side, and the substrate of the second conductivity type having a doping concentration of 5*10.sup.15 to 1*10.sup.17 cm.sup.−3, creating a first layer of the first conductivity type on the first side by applying a dopant of the first conductivity type by epitaxial growth or deposition, resulting in the first layer having a first layer thickness between 0.5 and 2 μm, creating a drift layer of the first conductivity type on the first layer, which has a low doping concentration, diffusing the dopant such that a buffer layer is created, the buffer layer having a higher doping concentration than the drift layer, wherein in a direction perpendicular to the second side, the buffer layer does not comprise an area of constant doping concentration, creating a base layer of the second conductivity type on the drift layer, creating an emitter layer of the first conductivity type on the base layer, thinning the substrate on the second side such that the remaining part of the substrate forms a collector layer having the collector side to which the collector electrode is formed.

2. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the substrate has a substrate thickness of at least 300 μm.

3. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the dopant is applied by implantation, in particular with a dose of 1*10.sup.12 to 5*10.sup.13 cm.sup.−2.

4. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the first layer has at least one of a first layer thickness between 0.5 and 1 μm, or a doping concentration of 1*10.sup.16 to 5*10.sup.17 cm.sup.−3.

5. The method for manufacturing an insulated gate bipolar transistor according to claim 4, characterized in that the step of diffusing comprises diffusing the first layer to at least 5 or at least 10 times the first layer thickness.

6. The method for manufacturing an insulated gate bipolar transistor according to claim 4, characterized in that a buffer layer thickness of the buffer layer is 5 to 30 μm.

7. The method for manufacturing an insulated gate bipolar transistor according to claim 4, characterized in that the buffer layer has a maximum doping concentration between 1*10.sup.15 to 5*10.sup.16 cm.sup.−3.

8. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the step of diffusing comprises diffusing the first layer to at least 5 or at least 10 times the first layer thickness.

9. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that a buffer layer thickness of the buffer layer is 5 to 30 μm.

10. The method for manufacturing an insulated gate bipolar transistor according to claim 9, characterized in that the buffer layer thickness of the buffer layer is 10 to 30 μm.

11. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the buffer layer has the same or a higher maximum doping concentration than the collector layer.

12. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the buffer layer has a lower maximum doping concentration than the collector layer.

13. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the buffer layer has a maximum doping concentration between 1*10.sup.15 and 5*10.sup.16 cm.sup.−3.

14. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the collector layer has a collector layer thickness of 3 to 30 μm.

15. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that creating the drift layer is done by epitaxial growth.

16. The method for manufacturing an insulated gate bipolar transistor according to claim 1, characterized in that the step of diffusing comprises diffusing the dopant so that the doping concentration of the buffer layer decreases steadily without keeping a constant part of a doping concentration from the original first layer.

17. The method for manufacturing an insulated gate bipolar transistor according to claim 16, characterized in that the doping concentration of the buffer layer increases on a side of the buffer layer towards the substrate to a maximum value, from which the doping concentration steadily decreases to the doping concentration of the drift layer, wherein the doping concentration of the drift layer is constant.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter of the invention will be explained in more detail in the following text with reference to the attached drawings, in which:

(2) FIGS. 1 to 9 show different manufacturing steps according to the invention for the manufacturing of an IGBT;

(3) FIG. 10 shows an IGBT manufactured according to the inventive manufacturing method;

(4) FIG. 11 shows different manufacturing steps according to the invention for the manufacturing of an IGBT; and

(5) FIGS. 12 to 18 show the doping profiles during various steps of the manufacturing method.

DETAILED DESCRIPTION OF THE INVENTION

(6) For manufacturing an inventive insulated gate bipolar transistor (IGBT) 10 the manufacturing steps are performed in the following order: providing a p doped substrate 1 having a first and a second side 12, 14 opposite to the first side (FIG. 1), creating an n type first layer 25 on the first side 12 by applying an n dopant (FIG. 2), creating an (n−) doped drift layer 3 on the first layer 25, which has a low doping concentration, exemplarily by epitaxial growth (FIG. 3), diffusing the dopant introduced in layer 25 such that a buffer layer 2 having a buffer layer thickness 22 is created (FIG. 4), wherein the buffer layer 2 has a higher doping concentration than the drift layer 3, creating a p doped base layer 5 on the drift layer 3 (FIG. 6), creating an (n+) doped emitter layer 6 on the base layer 5 (FIG. 7), thinning 48 the substrate 1 on the second side 14 such that the remaining part of the substrate forms a collector layer 4 (FIG. 8 showing the thinning and FIG. 9 showing the resulting collector layer 45).

(7) At any appropriate manufacturing step, a gate electrode 7, which is attached to the base layer 5 and the emitter layer 6, and an emitter electrode 8, which is in contact to the base layer 5 and the emitter layer 6 at an emitter contact area, are created.

(8) Exemplarily, the gate electrode 7 is created after the creation of the buffer layer 2 and before creation of the emitter layer 6, base layer 5 and thinning 48 of the substrate (FIG. 5). The gate electrode 7 is created at the side opposite to the second side (i.e. on the emitter side 65). On the second side 14, a collector electrode 9 is created. The collector electrode 9, which is in contact to the collector layer 4, is created after the thinning of the substrate 1. The emitter electrode 8 is created after the gate electrode 7 and may be created before the thinning 48 of the substrate 1 (FIG. 11) or after the thinning 48 of the substrate 1, exemplarily it is created together with the collector electrode 9 (FIG. 10).

(9) The FIGS. 12 to 18 show the doping concentrations of the layers during the manufacturing process. In these figures, the manufacturing is exemplarily shown for a P substrate 1.

(10) Exemplarily, the substrate has a doping concentration of (5*10.sup.15 to 1*10.sup.17) cm.sup.−3 (FIG. 12). The doping concentration is so high that the collector layer 4 resulting as the remaining part of the substrate after thinning can provide a controlled injection.

(11) The substrate thickness is chosen to be so thick that the substrate can be handled in the following manufacturing steps without a danger of cracks. Exemplarily, the substrate thickness is at least 300 μm.

(12) The first layer 25 may be created by applying ions on the first side, e.g. by implantation of a dopant (FIG. 13). Exemplary, the implantation dose may be (1*10.sup.12 to 5*10.sup.13) cm.sup.−2.

(13) Alternatively, the first layer 25 may be created by epitaxially growing or depositing the first layer 25, exemplarily with a first layer thickness 27 between 0.5 . . . 2 μm, exemplarily 0.5 . . . 1 μm and/or a doping concentration of 1*10.sup.16 . . . 5*10.sup.17 cm.sup.−3. The epitaxial first layer 25 comprises an n dopant, which is diffused in the later diffusion step such that the doping concentration decreases steadily without keeping a constant part of the doping concentration from the original epitaxial first layer 25. The dopant of the epitaxial layer diffuses into the substrate 1 as well as into the drift layer 3 so that the doping concentration of the buffer layer 2 increases on its side towards the substrate 1 to a maximum value, from which it steadily drops to the constant doping concentration of the drift layer 3. Thus, the epitaxial first layer 25 is so thin and the dopant is diffused such that the final diffused buffer layer 2 does not comprise any part of constant high doping concentration (i.e. from the doping concentration of the original first layer) in a direction perpendicular to the second side 14 (depth direction). That means that the doping concentration of the buffer layer changes steadily without keeping the same value in different depths.

(14) For an epitaxial or deposited layer, the dopant of the epitaxial layer may be deeply diffused to at least 5 times the epitaxial first layer thickness, exemplarily to at least 10 times. The thickness of the layers is measured in depth direction (i.e. in a direction perpendicular to the first side 12 as the extension of the layer in the depth direction.

(15) After the creation of the first layer 25, the drift layer 3 is created by epitaxial growth (FIG. 14). Then the buffer layer 2 is created by diffusing the dopant such that the diffused ions spread in an area of (5 to 30) μm (in depth direction, i.e. in a direction perpendicular to the second side 14, which corresponds to the collector side 45). The dopant diffuses into the drift layer 3 (FIG. 15). The buffer layer thickness 22 is, thus, 5 . . . 30 μm exemplarily 10 . . . 30 μm. The drift layer 3 in the finalized IGBT shall be the layer of unamended doping concentration by the diffusion step, i.e. of the doping concentration achieved by the epitaxial growth for the drift layer 3. Exemplarily, the drift layer 3 has a constantly low doping concentration. Therein, the substantially constant doping concentration of the drift layer 3 means that the doping concentration is substantially homogeneous throughout the drift layer 3, however without excluding that fluctuations in the doping concentration within the drift layer being in the order of a factor of one to five may be possibly present due to e.g. a fluctuations in the epitaxial growth process. The final drift layer thickness 32 and doping concentration is chosen due to the application needs. An exemplary doping concentration of the drift layer 5 is between 5*10.sup.12 cm.sup.−3 and 5*10.sup.14 cm.sup.−3.

(16) The buffer layer 2 corresponds to the area, into which the dopant diffuses in the drift layer 3. On the side towards the substrate (collector layer 4), the buffer layer 2 extends to such area, in which the charge from the n doped dopant overbalances the charge from the p substrate.

(17) The buffer layer 2 may have the same or a higher maximum doping concentration than the collector layer 4, i.e. the maximum doping concentration of the buffer layer may be at least as high as from the collector layer 4 (i.e. p substrate 1). In another alternative, the maximum doping concentration of the buffer layer 2 is lower than the doping concentration of the collector layer 4 (p substrate 1). As the substrate 1/p collector layer 4 is uniformly doped the maximum doping concentration of the p collector layer 4/p substrate 1 corresponds to the (local) doping concentration, whereas in the buffer layer 2 the doping concentration drops beyond the maximum doping concentration to greater depths, i.e. towards the emitter side 65, in the IGBT.

(18) The maximum doping concentration of the buffer layer 2 may be between 1*10.sup.15 to 5*10.sup.16 cm.sup.−3.

(19) A sheet carrier concentration, which corresponds to an integral of the doping concentration (impurity ions) over the depth, is 1*10.sup.12 5*10.sup.13 cm.sup.−2 for an implanted layer and 2*10.sup.12 . . . 1*10.sup.14 cm.sup.−2 for an epitaxial or deposited layer having a thickness in the range of 0.5 . . . 2 μm, or 2*10.sup.12 . . . 5*10.sup.13 cm.sup.−2 for an epitaxial or deposited layer having a thickness in the range of 0.5 . . . 1 μm.

(20) An exemplarily collector layer thickness 42 is (3 to 30) μm and the doping concentration may have a value in a range of (5*10.sup.15 to 1*10.sup.17) cm.sup.−3.

(21) FIG. 16 shows the half-finished device, in which the emitter sided processes have been done, exemplarily shown as the p doped base layer 5. FIG. 17 shows the half-finished device after the collector-sided thinning of the substrate 1, thus creating the collector layer 4. FIG. 18 shows for the final device the electric field, which is stopped within the buffer layer 2.

(22) The gate electrode 7 is created either as a planar or trench gate electrode. The gate electrode 7 is made by a method well known to persons skilled in the art.

(23) The finalized IGBT may have a planar gate electrode (as shown in FIG. 10), which comprises an electrically insulating layer 74 on top of the emitter side 65. An electrically conductive gate layer 72 is arranged on the insulating layer 74, thus insulated from any n or p doped layer in the IGBT. Thus, the insulating layer 74 insulates the gate layer 72 from any n or p doped layer in the IGBT extending to the emitter side 65 in an area below the gate layer 72. The gate layer 72 is exemplarily also covered by the insulating layer 74, by which insulating layer 74 the gate layer 72 is also insulated from the emitter electrode 8. Thus, exemplarily, the gate layer 72 is exemplarily completely embedded in the insulating layer 74. The gate layer 72 is exemplarily made of a heavily doped polysilicon or a metal like aluminum. The gate layer 72 is arranged on the emitter side 65 laterally to an emitter contact area. It extends to an area above the base layer 5, the emitter layer 6 as well as the drift layer 3. The at least one emitter layer 5, the gate layer 72 and the electrically insulating layer 74 are formed in such a way that an opening, which is the emitter contact area, is created above the base layer 5. The emitter contact area is surrounded by the emitter layer 5, the gate layer 72 and the electrically insulating layer 74.

(24) The emitter electrode 8 is arranged on the emitter side 65 and contacts the base layer 5 and the emitter layer 6 at the emitter contact area. The emitter electrode 8 exemplarily also covers the electrically insulating layer 74, but is separated and thus electrically insulated from the gate layer 72 by the insulating layer 74.

(25) Alternatively to the inventive IGBT with a planar gate electrode, the inventive IGBT may comprise a gate electrode formed as trench gate electrode. The trench gate electrode is arranged in the same plane as the base layer 5 in a recess in the semiconductor material and adjacent to the emitter layer 6, separated from each other by an insulating layer 74, which also separates the gate layer 72 from the drift layer 3. The insulating layer 74 is also arranged on top of the gate layer 72, thus insulating the trench gate layer 72 from the emitter electrode 8.

(26) The IGBT manufactured from the inventive method, may also comprise a highly p+ doped contact layer, which is arranged in between the emitter contact area and the p doped base layer 5 in order to have a highly doped interlayer at the contact to the emitter electrode 8. The p contact layer may be limited to the area at which a p doped layer is in contact to the emitter electrode 8, i.e. at the emitter contact area. The contact layer may have a maximum doping concentration between 5×10.sup.18/cm.sup.3 and 5×10.sup.19/cm.sup.3. The contact layer may also be formed as a diffused layer, i.e. as the p doped layers overlay each other, and the doping concentration of each layer decreases, but the contact layer is arranged up to a first depth, which is smaller than the of the base layer depth/thickness (measured from the emitter side 65). The contact layer and base layer 5 overlap such that at the cross point a discontinuous decrease of the doping concentration is present. The contact layer is created by applying p doped ions (either by implantation or deposition) and diffusing them into the device up to a depth, which is smaller than the depth of the base layer from the emitter side 65. It is about the thickness of the emitter layer 6.

(27) In another embodiment, the conductivity types are switched, i.e. all layers of the first conductivity type are p type (e.g. the drift layer 3) and all layers of the second conductivity type are n type (e.g. collector layer 4).

(28) It should be noted that the term “comprising” does not exclude other elements or steps and that the indefinite article “a” or “an” does not exclude the plural. Also elements described in association with different embodiments may be combined. It should also be noted that reference signs in the claims shall not be construed as limiting the scope of the claims.

(29) It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.