Power MOS device having an integrated current sensor and manufacturing process thereof

Abstract

Power MOS device, in which a power MOS transistor has a drain terminal that is coupled to a power supply node, a gate terminal that is coupled to a drive node and a source terminal that is coupled to a load node. A detection MOS transistor has a drain terminal that is coupled to a detection node, a gate terminal that is coupled to the drive node and a source terminal that is coupled to the load node. A detection resistor has a first terminal coupled to the power supply node and a second terminal coupled to the detection node.

Claims

1. A power MOS device comprising: a semiconductor body having a first conductivity type, a first surface and a second surface, the semiconductor body including a first region, having the first conductivity type and a first doping level, and a drift region having the first conductivity type and a second doping level greater than the first doping level, the drift region being arranged between the first surface and the second surface; a power MOS transistor having a first conduction terminal, a gate terminal and a second conduction terminal, the first conduction terminal of the power MOS transistor being directly electrically and physically connected to a reference-potential node, the gate terminal of the power MOS transistor being directly electrically and physically connected to a drive node and the second conduction terminal of the power MOS transistor being directly electrically and physically connected to a load node, a detection MOS transistor having a first conduction terminal, a gate terminal and a second conduction terminal, the first conduction terminal of the detection MOS transistor being directly electrically and physically connected to a detection node, the gate terminal of the detection MOS transistor being directly electrically and physically connected to the drive node and the second conduction terminal of the detection MOS transistor being directly electrically and physically connected to the load node, a detection resistor having first and second terminals, the first terminal being directly electrically and physically connected to the reference-potential node, a switch directly electrically and physically connected to the second terminal of the detection resistor and configured to selectively electrically couple the detection resistor to the detection node, wherein: the power MOS transistor includes: first and second insulated gate regions arranged inside the drift region and extending into the semiconductor body from the first surface; a first channel region having a second conductivity type, arranged in the drift region laterally between the first insulated gate region and the second insulated gate region; and a first source region having the first conductivity type and being arranged between the first channel region and the first surface of the semiconductor body, the first source region abutting the first and the second insulated gate regions and extending laterally from the first insulated gate region toward the second insulated gate region, the second conduction terminal of the power MOS transistor including the first source region; the detection MOS transistor includes: third and fourth insulated gate regions arranged inside the first region of the semiconductor body from the first surface; a second channel region having the second conductivity type, arranged in the first region of the semiconductor body between the third insulated gate region and the fourth insulated gate region; and a second source region having the first conductivity type and being arranged between the second channel region and the first surface of the semiconductor body, the second conduction terminal of the detection MOS transistor including the second source region; the switch includes: a third channel region having the second conductivity type, arranged in the first region of the semiconductor body and adjacent to the third insulated gate region; and a third source region having the first conductivity type and being arranged between the third channel region and the first surface of the semiconductor body; and the detection resistor includes a resistive detection portion of the first region of the semiconductor body arranged beneath the second and third channel regions.

2. The device according to claim 1, wherein the switch includes a control terminal electrical coupled to a control node that is different from, and independent of, the drive node.

3. The device according to claim 1, wherein the switch includes a connection MOS transistor having a first conduction terminal, a control terminal and a second conduction terminal, the first conduction terminal of the connection MOS transistor being electrically coupled to the detection node, the control terminal of the connection MOS transistor being configured to receive a drive signal, the second conduction terminal of the connection MOS transistor forming a detection terminal, and the third source region being coupled to the second conduction terminal.

4. The device according to claim 3, wherein the control terminal of the connection MOS transistor is electrically coupled to the drive node.

5. The device according claim 1, including: a fifth insulated gate region arranged inside the semiconductor body from the first surface; a coupling portion of the semiconductor body arranged beneath the first surface of the semiconductor body and between the third insulated gate region and the fifth insulated gate region; and a first contact region extending from the first surface into the coupling portion and forming the detection node.

6. The device according to claim 5, wherein a portion of the drift region arranged between the second gate region and the fifth gate region forming an inactive portion.

7. The device according to claim 5, further including: a second contact region and a third contact region extending from the first surface into the body, the second contact region passing through the first source region and the first channel region, the third contact region passing through the second source region and the second channel region; a source metallization region extending above the first surface and being in electrical contact with the second contact region and the third contact region; and a detection metallization region in electrical contact with the first contact region; the source metallization region and the detection metallization region being formed on a same metallization level.

8. A power MOS device, comprising: a semiconductor body having a first conductivity type, a first surface, a second surface, a first region, having the first conductivity type and a first doping level, and a drift region having the first conductivity type and a second doping level greater than the first doping level, the drift region being arranged between the first surface and the second surface; first, second, third, fourth, and fifth insulated gate regions arranged inside the semiconductor body from the first surface, the first and second insulated gate regions being arranged in the drift region and extending into the semiconductor body from the first surface, the third and fourth insulated gate regions being arranged in the first region; a first channel region having a second conductivity type, arranged in the drift region and laterally between the first insulated gate region and the second insulated gate region, which are adjacent to one another; a second channel region having the second conductivity type, arranged inside the first region and between the third insulated gate region and the fourth insulated gate region, which are adjacent to one another; a third channel region having the second conductivity type, arranged inside the first region and between the third insulated gate region and the fifth insulated gate region, which are adjacent to one another; an inactive pseudo-channel region having the second conductivity type, arranged inside the drift region and between the second insulated gate region and the fifth insulated gate region, which are adjacent to one another, the inactive pseudo-channel region being devoid of any source regions; a first source region having the first conductivity type and being arranged between the first channel region and the first surface of the semiconductor body, the first source region abutting the first and the second insulated gate regions and extending laterally from the first insulated gate region toward the second insulated gate region, the first source region, the first channel region, the first insulated gate region and the second insulated gate region being part of a power MOS transistor; a second source region having the first conductivity type and being arranged between the second channel region and the first surface of the semiconductor body, the second source region, the second channel region, the third insulated gate region and the fourth insulated gate region being part of a detection MOS transistor; a third source region having the first conductivity type and being arranged between the third channel region and the first surface of the semiconductor body, the third source region, the third channel region, the third insulated gate region, and the fifth insulated gate region being part of a connection MOS transistor; a first contact region extending from the first surface into the third channel region; and a resistive detection portion of the semiconductor body arranged beneath the second and third channel regions and forming a detection resistor.

9. The device according to claim 8, wherein the drift region is delimited laterally in part by the fifth insulated gate region.

10. The device according to claim 8, further including: a second contact region and a third contact region extending from the first surface into the body, the second contact region passing through the first source region and the first channel region, the third contact region passing through the second source region and the second channel region; a source metallization region extending above the first surface in electrical contact with the second contact region and the third contact region; and a detection metallization region in electrical contact with the first contact region; the source metallization region and the detection metallization region being formed on a same metallization level.

11. The device according to claim 8, wherein: the connection MOS transistor is a switch electrically coupled to the detection resistor and configured to selectively electrically couple the detection resistor to a detection terminal.

12. The device according to claim 11, wherein the third and fourth insulated gate regions are configured to receive a drive signal.

13. A power MOS device, comprising: a power MOS transistor formed in a drift region of semiconductor body having a first surface and a second surface, the power MOS transistor having a first conduction region, a gate region and a second conduction region, the first conduction region of the power MOS transistor being directly electrically and physically connected to a reference-potential node, the second conduction region of the power MOS transistor being directly electrically and physically connected to a load node and the gate region of the power MOS transistor being directly electrically and physically connected to a drive node, wherein the power MOS transistor includes: first and second insulated gate regions arranged inside the drift region and extending into the semiconductor body from the first surface; a first channel region having a second conductivity type, arranged in the drift region laterally between the first insulated gate region and the second insulated gate region; and a first source region having the first conductivity type and being arranged between the first channel region and the first surface of the semiconductor body, the first source region abutting the first and the second insulated gate regions and extending laterally from the first insulated gate region toward the second insulated gate region, the second conduction terminal of the power MOS transistor including, the first source region; a detection MOS transistor formed in a first region of the semiconductor body and including a first conduction region, a gate region and a second conduction region, the first conduction region of the detection MOS transistor being directly electrically and physically connected to a detection node, the second conduction region of the detection MOS transistor being directly electrically and physically connected to the load node and the gate region of the detection MOS transistor being directly electrically and physically connected to the drive node, the first region having a first conductivity type and a first doping level, the drift region having the first conductivity type and a second doping level greater than the first doping level, the drift region being arranged between the first surface and the second surface; a connection MOS transistor formed in the first region of the semiconductor body and including a first conduction region, a gate region and a second conduction region, the first conduction region of the connection MOS transistor being directly electrically and physically connected to the detection node; a detection resistor formed in the first region semiconductor body and extending between the reference-potential node and the detection node; a first metallization region on the first surface and in electrical contact with the second conduction region of the power MOS transistor and the second conduction region of the detection MOS transistor; a detection metallization region on the first surface and in electrical contact with the second conduction region of the connection MOS transistor; and a second metallization region on the second surface and in electrical contact with the first conduction region of the power MOS transistor and electrically coupled to the reference-potential node.

14. The device according to claim 13, wherein: the semiconductor body has the first conductivity type; the first insulated gate region and the second insulated gate region are positioned on opposite sides of the second conduction region of the power MOS transistor; the gate region of the detection MOS transistor includes a third insulated gate region and a fourth insulated gate region positioned on opposite sides of the second conduction region of the detection MOS transistor; and the gate region of the connection MOS transistor includes the third insulated gate region and a fifth insulated gate region positioned on opposite sides of the second conduction region of the detection MOS transistor.

15. The device according to claim 13, wherein: the connection MOS transistor is a switch electrically coupled to the detection resistor and configured to selectively electrically couple the detection resistor to a detection terminal.

16. The device according to claim 14, wherein the gate region of the connection MOS transistor is electrically coupled to the drive node.

17. The device according to claim 14, wherein the connection MOS transistor includes a connection channel region having a second conductivity type, the connection channel region being arranged inside the first region of the semiconductor body.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) For a better understanding of the present disclosure preferred embodiments thereof will be described, purely as non-limiting examples, with reference to the attached drawings, in which:

(2) FIG. 1 shows the electric diagram of a known power MOS device with an integrated current sensor,

(3) FIG. 2 shows the electric diagram of the present power MOS device,

(4) FIG. 3 shows a cross section of a portion of a possible implementation of the power MOS device of FIG. 2,

(5) FIG. 4 is a top view of the power MOS device of FIG. 3,

(6) FIG. 5 shows the behaviour of characteristic quantities of the power MOS device of FIG. 2,

(7) FIG. 6 shows the behaviour of electrical quantities of the power MOS device of FIG. 2,

(8) FIGS. 7-15 are cross sections of a silicon die in successive manufacturing steps of the power MOS device of FIG. 3,

(9) FIG. 16 is an electric diagram of another embodiment of the present power MOS device,

(10) FIG. 17 is a cross section of the power MOS device of FIG. 16, and

(11) FIG. 18 is a electric diagram of an alternative embodiment of the present power MOS device.

DETAILED DESCRIPTION

(12) FIG. 2 shows a power MOS device 10 including a power MOS transistor 12 and a detection MOS transistor 13.

(13) The power MOS transistor 12 has a gate terminal that is coupled to a drive node 16, a drain terminal that is coupled to a power supply node 17 and a source terminal forming a load node 11. FIG. 2 also shows a load 15 (typically outside the power MOS device 10) that is designed to be coupled between the load node 11 and a reference-potential line (ground).

(14) The detection MOS transistor 13 has a gate terminal that is coupled to the drive node 16, a drain terminal forming a detection node 18 and a source terminal coupled to the load node 11.

(15) A detection resistor 14 has a first terminal coupled to the power supply node 17 and a second terminal coupled to the detection node 18.

(16) In use, the power supply node 17 receives a power supply voltage V.sub.S and the drive node 16 receives a drive signal D.sub.S, in a known manner.

(17) Furthermore, the detection MOS transistor 13 and the detection resistor 14 detect the current supplied by the power MOS transistor 12 to the load 15.

(18) Indeed, the power MOS transistor 12 and the detection MOS transistor 13 have the same voltage drop V.sub.GS between the gate and source terminals, and are therefore under the same biasing conditions. The power MOS transistor 12 and the detection MOS transistor 13 therefore conduct respective currents I.sub.1, I.sub.2 that are proportional to one another according to the equation (1).

(19) The current I.sub.2 flowing through the detection MOS transistor 13 also flows through the detection resistor 14 and may be determined from the voltage drop on the detection resistor 14 itself, detecting the potential on the detection node 18.

(20) The power MOS device 10 addresses the problem of electrical misalignment between the power MOS transistor 12 and the detection MOS transistor 13, since they are biased in exactly the same manner, as previously specified. The power MOS device 10 is therefore not affected by the electrical misalignment and systematic error of the known power device in FIG. 1.

(21) In the power MOS device 10, both the current I.sub.1 (flowing through the power MOS transistor 12) and the current I.sub.2 (flowing through the detection MOS transistor 13) are supplied to the load 15. Consequently, the power MOS device 10 has a high efficiency and enables a very wide choice of the area ratio between the MOS transistors 12 and 13.

(22) FIGS. 3 and 4 show a possible implementation of the power MOS device 10 in FIG. 2. In particular, FIG. 3 is a cross section of just one portion of the structure in FIG. 4 and the entire structure is obtained by flipping FIG. 3 about the right-hand edge of same and continuing on both sides.

(23) The power MOS device 10 is integrated in a die 100 made of semiconductor material including a semiconductor body 19 (made for example of silicon), having a first conductivity type (for example N) and first and second surfaces 19A, 19B.

(24) The semiconductor body 19 includes a substrate 21 and an epitaxial layer 23 arranged on top of one another and respectively forming the second and first surfaces 19B, 19A. The substrate 21 has a doping level that is much greater than the doping level of the epitaxial layer 23 (for example, the substrate 21 has a doping level that is greater than 10.sup.19 atoms/cm.sup.3 and the epitaxial layer 23 has a doping level of between 10.sup.14 and 10.sup.15 atoms/cm.sup.3).

(25) The epitaxial layer 23 includes a drift region 22 having the same conductivity type as the epitaxial layer, but a doping level that is higher and suited to the breakdown voltage to be sustained (for example greater than 10.sup.16 atoms/cm.sup.3). The drift region 22 extends between the first surface 19A and the substrate 21 through the entire thickness of the epitaxial layer 23 and, in plan view (FIG. 4), is frame-shaped and is arranged close to the periphery of the die 100.

(26) The epitaxial layer 23 also accommodates a plurality of insulated gate regions 37A-37E, hereinafter referred to as active, inactive and detection gate regions. As shown in FIG. 3, the insulated gate regions 37A-37E extend from the first surface 19A towards the substrate 21 and, in the top view of FIG. 4, parallel to one another and to an axis Y of a Cartesian coordinate system XYZ. Each of the insulated gate regions 37A-37E includes a conductive trench gate region 26, for example made of polysilicon, surrounded by an insulating gate layer 27, for example made of silicon oxide. The trench gate regions 26 are all coupled together electrically.

(27) Pairs of adjacent insulated gate regions 37A-37E define respective portions of the epitaxial layer 23 extending parallel to the axis Y. In particular, in the present embodiment, the pairs of insulated gate regions 37A-37E delimit two coupling portions 40 (only one shown in FIG. 3), a plurality of active portions 41 (only one shown in FIG. 3), two inactive portions 42 (only one shown in FIG. 3), and two detection portions 43 (only one shown in FIG. 3).

(28) The active portions 41 and the inactive portions 42 are within the drift region 22. In particular, FIG. 3 shows an active portion 41 arranged between a first and a second active gate regions 37A, 37B and an inactive portion 42 arranged between the second active gate region 37B and an inactive gate region 37C. As shown in FIG. 3, the inactive gate region 42 extends approximately along the longitudinal internal edge (parallel to the axis Y) of the drift region 22.

(29) The coupling portions 40 and the detection portions 43 are arranged in the zone of the epitaxial layer 23 surrounded by the drift region 22. In particular, FIG. 3 shows a coupling portion 40 arranged between the inactive gate region 37C and a first detection gate region 37D, and a detection portion 43 arranged between the first detection gate region 37D and a second detection gate region 37E.

(30) The active portion 41 contains an N-type active source region 50 (for example with a doping level greater than 10.sup.19 atoms/cm.sup.3), a P-type active channel region 53, a first P-type active enriched region 54 with a doping level greater than the active channel region 53 (for example with a doping level greater than 5.Math.10.sup.17 atoms/cm.sup.3), and a second P-type active enriched region 70 with a doping level greater than the first active enriched region 54. More specifically, the active source region 50 extends from the first surface 19A, the active channel region 53 extends beneath the active source region 50, the first active enriched region 54 lies inside the active channel region 53, and the second active enriched region 70 lies above the first active enriched region 54, straddling the interface between the active source region 50 and the active channel region 53.

(31) Similarly, the detection portion 43 accommodates a P-type detection channel region 57, a first P-type enriched detection region 58 with a doping level greater than the detection channel region 57, a second P-type enriched detection region 73 with a doping level greater than the first enriched detection region 58, and an N-type detection source region 52. The detection source region 52 extends from the first surface 19A, the detection channel region 57 extends beneath the detection source region 52, the first enriched detection region 58 extends inside the detection channel region 57, and the second enriched detection region 73 extends above the first enriched detection region 58, at the interface between the detection source region 52 and the detection channel region 57.

(32) The inactive portion 42 accommodates a P-type pseudo-channel region 55, a first P-type inactive enriched region 56 with a doping level greater than the pseudo-channel region 55, and a second P-type inactive enriched region 71 with a doping level greater than the first inactive enriched region 56. The pseudo-channel region 55 extends from the first surface 19A, the first inactive enriched region 56 extends inside the pseudo-channel region 55, and the second inactive enriched region 71 extends above the first inactive enriched region 56.

(33) An upper portion of the coupling portion 40 accommodates an N-type enrichment region 51 with a high doping level (for example equal to the doping level of the active source and detection source regions 50, 52), extending from the first surface 19A. Furthermore, the coupling portion 40 accommodates an enriched coupling region 72 approximately beneath the enrichment region 51.

(34) In practice, the drift region 22 and the regions contained therein form the power MOS transistor 12 of FIG. 2, and the detection portion 43 and the regions contained therein form the detection MOS transistor 13 in FIG. 2. As explained in greater detail below, the portion of the epitaxial layer beneath the coupling portion 40 and the detection portion 43 define a resistive detection portion 44. This forms the detection resistor 14 in FIG. 2, represented here by three resistive elements R.sub.1, R.sub.2 and R.sub.3, in which R.sub.1 is connected in series to the parallel circuit formed by R.sub.2 and R.sub.3.

(35) Furthermore and as shown in the top view in FIG. 4, the area of the power MOS transistor 12 (which approximately matches the area of the drift region 22) is much greater than the area of the detection MOS transistor 13 (which approximately matches the area of the detection portions 43, only one of which is shown in FIG. 3).

(36) A drain metallization layer 20 (for example comprising three superposed layers of titanium, nickel and gold) is arranged beneath the second surface 19B and form the drain terminal of the power MOS transistor 12 and of the detection MOS transistor 13, as well as the power supply node 17 in FIG. 2.

(37) Furthermore, an insulating layer 24, for example of silicon oxide (SiO.sub.2) extends above the first surface 19A. First and second contact regions 28A, 28B of conductive material (such as tungsten and/or titanium) extend through the insulating layer 24 as well as in the epitaxial layer 23. Each first contact region 28A extends vertically (in a direction Z of the Cartesian coordinate system XYZ) inside a respective portion 41-43 of the epitaxial layer 23, through the channel regions 53, 55, 57 into the second enriched regions 70, 71, 73. Each contact region 28B (only one of which is shown in FIG. 3) extends vertically (in direction Z) inside a respective portion 40 of the epitaxial layer 23, through the enrichment region 51 into the enriched region 72.

(38) A source metallization layer 25 made of conductive material (such as aluminum) is arranged above the insulating layer 24 and forms (see in particular FIG. 4) a source metallization region 30 and a detection metallization region 31. As shown in particular in FIG. 4, the source metallization region 30 is trident-shaped, having two outer arms 60, an inner arm 62 and a base 61. The outer arms 60 extend parallel to the axis Y, substantially above the drift region 22; the base 61 extends parallel to the axis X above the drift region 22; and the inner arm 62 extends parallel to the axis Y, substantially above the detection portion 43. The detection metallization region 31 is U-shaped, substantially complementary to the shape of the source metallization region 30 and has two arms 64 extending above the coupling portions 40 and between the arms 61, 62 of the source metallization region 30. The arms 64 of the source metallization region 30 are connected to a pad 65. The die 100 also accommodates bias and connection structures of the trench gate region 26 and a pad for the source metallization region 30, not shown.

(39) The source metallization region 30 is in electrical contact with the contact regions 28A, so as to contact the source regions 53, 57 of the MOS transistors 12, 13. The detection metallization region 31 is in electrical contact with the contact regions 28B, so as to contact the coupling portions 40. In practice, the source metallization region 30 forms the load node 11 in FIG. 2 and the detection metallization region 31 forms the detection node 18.

(40) As shown in FIG. 4, the first contact regions 28A extend along practically the entire length (in direction Y) of the metallization layer 25, while the second contact regions 28B extend along a length (in direction Y) that is less than the length of the coupling and detection portions 40, 43 such as to end at a distance d (for example 6-10 m) from the transverse edge parallel to the axis X and close to the base 61 of the source metallization region 30 of the drift region 22.

(41) In use, the power supply voltage V.sub.S is supplied to the drain metallization layer 20 and the drive signal D.sub.S is supplied to the gate regions 37A-37E. Furthermore, the pad 65 (corresponding to the node 18 in FIG. 2) is connected to the detection circuit (not shown) for detecting the potential of same node. The current I.sub.1 supplied by the power MOS transistor 12 flows between the drain metallization layer 20 and the source regions 50, through the drift region 22 and the active channel regions 53.

(42) The presence of the inactive portion 42 on the edge of the drift region 22 between the active portion 41 and the coupling portion 40, as well as the distance d between the transverse edge (parallel to the axis X in FIG. 4) of the drift region 22 and the end of the second contact regions 28B prevent the current I.sub.1 from flowing towards the coupling region 40, causing a voltage drop on this latter and a detection error.

(43) The current I.sub.2 supplied by the detection transistor 13 flows between the drain metallization layer 20 and the source regions 52, passing through the resistive detection portion 44, the detection portions 43 and the detection channel regions 57.

(44) The voltage drop across the resistive detection portion 44 is detected via the coupling portion 40, the second contact 28B and the detection metallization region 31, enabling detection of the drop on the detection resistor 14 and therefore the current I.sub.2 as well as, using the known surface area ratio, the current I.sub.1+I.sub.2 supplied to the load.

(45) It can be seen that the coupling portion 40 does not contribute to the current I.sub.2, since the detection node 18 is coupled to an input of the detection circuit (not shown) that is normally high-impedance. Consequently, no current flows through the coupling portion 40 and therefore the resistivity of said coupling portion 40 does not affect the current I.sub.2.

(46) FIG. 5 shows the plot of the ratio between the surface areas of the MOS transistors 12, 13 (here defined as K.sub.S) as a function of the variation of the resistance value R.sub.S of the detection resistor 14 for the known MOS device 1 in FIG. 1, indicated in FIG. 5 using reference sign A, and for the power MOS device 10 in FIG. 2, indicated using reference sign B, on the basis of simulations carried out by the applicant. In particular, the curves A and B are obtained by varying the resistance R.sub.S of the detection resistor 4 in FIG. 1 and of the detection resistor 14 in FIG. 2 with respect to a target value defined as the value at which, when the current I.sub.2 flows in the detection resistor 4 and in the detection resistor 14, these resistors have a voltage drop V.sub.KS the value of which is correlated to the sensitivity of the detection circuit (not shown). The voltage drop V.sub.KS is compared to a constant threshold value by the detection circuit to generate an intervention signal. In general, the parameter K.sub.S has a near-constant value.

(47) In particular, the curve A (for the known device 1 in FIG. 1) shows that, by varying the resistance R.sub.S of the detection resistor 4 by 33% with respect to the target value, a variation in the parameter K.sub.s of 25% is obtained. Consequently, varying the resistance value R.sub.S of the detection resistor 4, and therefore the voltage drop V.sub.KS on same, the parameter K.sub.S, and therefore the ratio between the surface areas of the MOS transistors 2, 3, varies considerably and undesirably.

(48) Conversely, the curve B (for the power device 10 in FIG. 2), for the same range of the resistance value of the detection resistor 14, shows a variation in the parameter K.sub.s of 1.3% in the resistance range shown, and therefore a low variability, as desired.

(49) In practice therefore, the designer has greater freedom to select the resistance value R.sub.S of the detection resistor 14, regardless of the desired surface-area ratio for the MOS transistors 12, 13.

(50) FIG. 6 shows the behavior of some electrical quantities as a function of the gate/source voltage V.sub.GS of the MOS transistors 12, 13, by biasing the power MOS transistor 12 so as to have a drain/source voltage (V.sub.DS) of 0.1 V, with a gate/source voltage (V.sub.GS) variable between 0 and 5 V. In particular, the curve C shows the plot of the drain current I.sub.D, and the curve D shows the plot of the voltage V.sub.KS detected on the detection node 18. The curves C and D have been measured by the applicant.

(51) More specifically, after the power MOS transistor 12 has been turned on, V.sub.GS2 V, the drain current I.sub.D increases and the voltage on the detection node 18 drops correspondingly, confirming the correct detection of the current in the power MOS transistor 12.

(52) FIGS. 7-15 show manufacturing steps of the power MOS device 10 shown in FIGS. 3 and 4, only for the active area of the device, and therefore omitting the edge areas and the external pads.

(53) With reference to FIG. 7, the epitaxial layer 23 is initially grown on the substrate 21, thereby forming the semiconductor body 19. The thickness and the doping concentration of the epitaxial layer 23 is such as to guarantee the desired output impedance and breakdown performance in the power MOS transistor 12, in a manner known to the person skilled in the art.

(54) Subsequently and as shown in FIG. 8, a first protective layer 80, for example made of silicon oxide (SiO.sub.2) is deposited or grown thermally on the first surface 19A. Subsequently, known photolithography and ion implantation and techniques, shown schematically by arrows 83, are to form an N-type implanted region 82 intended to form the drift region 22.

(55) Subsequently and as shown in FIG. 9, a heat treatment is performed to diffuse the ions of the implanted region 82, thereby obtaining the drift region 22.

(56) Subsequently and as shown in FIG. 10, the first protective layer 80 is removed and a plurality of gate trenches 90 is formed from the first surface 19A using known masked wet/dry etching techniques. The gate trenches 90 are then filled by thermally growing an insulating gate layer and depositing a filling layer, for example using polysilicon of the first conductivity type that is doped in situ. The portions of the insulating gate layer and of the filling layer on top of the first surface 19A are removed, for example using anisotropic dry etching, such as to form the trench gate regions 26 and the insulating gate layer 27. This creates the insulated gate regions 37A-37E delimiting the coupling portions 40, the active portions 41, the inactive portions 42 and the detection portions 43.

(57) Subsequently and as shown in FIG. 11, a second protective layer 97 made of insulating material is deposited on the first surface 19A and a first photoresist mask 91 is formed using known photolithography techniques. An ionic implantation process, indicated in FIG. 11 using a plurality of arrows 92, is used to implant P-type ionic dopant species, such as boron, thus forming the channel regions 53, 55, 57. The first photoresist mask 91 is then removed.

(58) As shown in FIG. 12, a second photoresist mask 93 is then used to perform a subsequent implantation of N-type ionic dopant species, such as arsenic, to form the source regions 50, 52 and the enrichment region 51, as shown by the arrow 94. The second photoresist mask 93 is then removed.

(59) A third photoresist mask 95, as shown in FIG. 13, is then used to perform a high-energy implantation of P-type ionic dopant species, such as boron, as shown by the arrows 96. The implantation parameters are in particular selected to form the enriched regions 54, 56, 58 at a distance of approximately 600 nm from the first surface 19A, in a known manner. More specifically, the enriched regions 54, 58 are formed beneath the source regions 50, 52. The third photoresist mask 95 is then removed.

(60) Subsequently and as shown in FIG. 14, a dielectric layer 98, for example made of silicon oxide, is deposited to form the insulating layer 24 in FIG. 3 along with the second protective layer 97. Contact trenches 102 are then formed in the regions designed to contain the contact regions 28A and 28B. The second enriched regions 70-73 are then implanted. The contact trenches 102 are then filled with metal material (such as titanium and/or tungsten), thereby forming the plurality of contact regions 28A, 28B.

(61) Finally and as shown in FIG. 15, the source metallization layer 25 is deposited on the upper surface of the insulating layer 24. The source metallization region 30 and the detection metallization region 31 are defined using known selective photolithography and etching techniques. Furthermore, the drain metallization layer 20 is deposited on the second surface 19B, thus forming the MOS device 10 in FIG. 3.

(62) FIGS. 16-17 show a variant of the power MOS device 10. More specifically, FIGS. 16 and 17 show a power MOS device 210 including a connection MOS transistor 201. The general structure of the power MOS device 210 is similar to the structure of the power MOS device 10 in FIG. 2, and therefore the parts similar to those shown and described with reference to FIG. 2 are indicated in FIGS. 16 and 17 using reference signs increased by 200, and are not further described.

(63) The connection MOS transistor 201 is coupled to the detection node 218 and is controlled using the drive signal D.sub.S. More specifically, the connection MOS transistor 201 has a gate terminal coupled to the drive node 216, a drain terminal coupled to the detection resistor 214 via the detection node 218 and a source terminal coupled to the external circuitry (not shown) at a detection terminal 202.

(64) In use, the power MOS device 210 behaves in a manner similar to the manner described for the power MOS device 10 in FIG. 2.

(65) More specifically, the connection MOS transistor 201 enables the detection resistor 214 to be connected to and disconnected from the external circuitry connected to the detection node 218. In fact, when the power supply voltage V.sub.S is low, the connection MOS transistor 201 is turned off and disconnects the detection resistor 214 from the external circuitry.

(66) The power MOS device 210 in FIG. 16 may be implemented as shown in FIG. 17.

(67) As visible, the power MOS device 210 has a structure similar to the power MOS device 10 shown in FIG. 2, except for the fact that the coupling portion 240 accommodates a P-type connection channel region 259, which in turn accommodates a connection source region 251. The connection channel region 259 is similar to the channel regions 254-257 (and to the channel regions 54-57 in FIG. 3) and may be made at the same time as same, modifying the mask 91 in FIG. 11. The connection source region 251 is similar to the enrichment region 51 (FIG. 3) and is made in a similar manner (FIG. 12).

(68) FIG. 18 shows a variant of the power MOS device, indicated in this case using reference sign 310, including the connection MOS transistor 301. The structure of the power MOS device 310 is overall similar to the structure of the power MOS device 210 in FIG. 16 and only differs in that the gate terminal of the connection MOS transistor 301 is connected to a dedicated connection terminal 320 receiving a secondary drive signal D.sub.S2. In all other aspects, the power MOS device 310 is the same as the device in FIG. 16, and therefore similar parts are indicated in FIG. 18 using reference signs increased by 100, and are not further described.

(69) In use, the connection MOS transistor 301 has the same function as the connection MOS transistor 201 in FIG. 16, but can be controlled via the drive signal D.sub.S2, regardless of the voltages present in the power MOS device 310. Accordingly, connection of the detection node 318 to the external circuitry for monitoring the current supplied to the load 315 by the power MOS device 310 can be controlled, giving the user greater freedom when monitoring said current.

(70) The power device described herein provides numerous advantages. Indeed, by virtue of the positioning of the detection resistor 14; 214; 314 it is possible to prevent a systematic error and therefore any electrical misalignment between the power MOS transistor 12; 212; 312 and the detection MOS transistor 13; 213; 313, enabling them to operate under the same biasing conditions. Furthermore, the inactive portion 42; 242 between the coupling portion 40; 240 and the active portion 41; 241 provides a low-resistance current path and prevents the current to be measured from flowing towards the active portion 41; 241 instead of through the coupling portion 40; 240, and therefore towards the detection node 18; 218. This is also true of the circuit in FIG. 18, which is also implemented in the manner shown in FIG. 17.

(71) It is evident that modifications and variations may be made to the device and method described and illustrated without thereby departing from the scope of the present disclosure. For example, the conductivity types may be inverted.

(72) The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.