JP4857458B2 - High voltage semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a planar high-voltage semiconductor device and mainly relates to a resistive field plate structure.
[0002]
[Prior art]
A resistive field plate is one of the withstand voltage structures of planar semiconductor elements such as power MOSFETs, IGBTs, and diodes. In this method, the high-resistance conductive film generally located in the breakdown voltage structure has an annular simple pattern, which is easy to design and has the advantage that the area occupied by the breakdown voltage structure can be reduced. The effect is the same for both vertical and horizontal elements. Japanese Patent Laid-Open No. 7-326775 is an example in which a simple pattern is improved. The simple pattern states that the leakage current increases remarkably in a high-temperature environment, which may cause thermal runaway, hindering practical use. Japanese Patent Application Laid-Open No. 7-326775 discloses that the strip-shaped high-resistance conductive film 73 is spirally formed as a resistive field plate in order to increase the resistance value of the resistive field plate and suppress the leakage current (FIG. 6).
[0003]
FIG. 7 is a schematic plan view of a breakdown voltage structure of a conventional semiconductor device. A breakdown voltage structure 60 is provided so as to cover the exposed pn junction formed by p diffusion layer 52 and n ⁻ layer 51. The breakdown voltage structure 60 has a function of expanding the depletion layer formed in the n ⁻ layer 51 in the lateral direction and reducing the electric field strength in the n ⁻ layer 51.
FIG. 8 is an enlarged detail view of an E portion in FIG. 7, in which FIG. 8A is a plan view, and FIG. 8B is a cross-sectional view taken along lines AA and BB. The structure of FIG. 8 is a breakdown voltage structure of a resistive field plate. On the surface layer of one semiconductor substrate (n ⁻ layer 51), a field plate electrode 54 that is in good electrical contact with the p diffusion layer 52 and an end plate electrode 55 that is opposed to the field plate electrode 55 with a certain distance are disposed. The n ⁻ layer 51 is in electrical contact. A field oxide film 53 is formed on the p diffusion layer 52 and the n ⁻ layer 51, and the electrodes 54 and 55 are formed so as to protrude from the field oxide film 53. A high resistance conductive film 56 is formed on field oxide film 53 in contact with both electrodes 54 and 55. The locations a to i in FIG. 10A match the locations a to i in FIG. a is the inner edge of the field plate electrode, b is the inner edge of the high-resistance conductive film, c is the inner edge of the field oxide film, d is the pn junction, e is the outer edge of the field plate electrode, f is the inner edge of the end plate electrode, and g is the field The outer end of the oxide film, h is the outer end of the high-resistance conductive film, and i is the outer end of the end plate electrode.
[0004]
In the case of the vertical MOSFET, a source electrode and a gate electrode are arranged in another region (not shown) of the p diffusion layer 52, and a drain electrode (not shown) is arranged on the back surface of the n ⁻ layer 51, that is, on the back surface of the semiconductor substrate. Is done. In the case of a lateral IGBT, the end plate electrode 55 is in contact with a p diffusion layer (not shown) formed separately and serves as a collector electrode.
[0005]
Between the field plate electrode 54 and the end plate electrode 55 is a high resistance conductive film 56 capable of passing a weak current, and a field oxide film 53 is disposed below the high resistance conductive film 56. In the off state, when a potential higher the potential of the end plate electrode 55 relative to the field plate electrode 54, p diffusion layer 52 and n in the semiconductor substrate ^- a voltage is applied between the layers 51, mainly n ^- depletion in a layer The layer spreads and a potential distribution is created inside the semiconductor substrate. This potential distribution also affects the breakdown voltage structure on the surface of the semiconductor substrate and interacts with the high-resistance conductive film 56. As a result, a weak current is applied to the high-resistance conductive film 56 between the field plate electrode 54 and the end plate electrode 55. It is possible to stabilize the withstand voltage by flowing and making the potential distribution uniform.
[0006]
As described above, in the high resistance conductive film 56 which is a resistive field plate, the potential distribution generated by passing a weak current through the semi-insulating film acts on the potential of the semiconductor substrate surface portion, resulting in a breakdown voltage structure. It has the function of making the spread potential distribution uniform (homogenizing the electric field strength). Therefore, by adopting the high resistance conductive film 56, it becomes possible to easily obtain a high breakdown voltage semiconductor device.
[0007]
[Problems to be solved by the invention]
However, in a conventional withstand voltage structure using a high-resistance conductive film with a simple pattern, the potential distribution is non-uniform at the curved portion, and this non-uniform potential distribution causes a significant increase in leakage current and may cause thermal runaway. is there.
FIG. 9 shows an example in which the potential distribution between the outer end of the field plate electrode and the inner end of the end plate electrode is calculated using a conventional high-resistance conductive film having a simple pattern. III is a straight portion (A-A line in FIG. 8) of the field plate electrode and the end plate electrode, and II is a curved portion (BB line in FIG. 8). In the straight line portion, the potential distribution is constant and ideal, whereas in the curved portion, the potential distribution from the field plate electrode changes abruptly. For this reason, the function of expanding the potential distribution inside the semiconductor substrate is weakened by that amount, the design margin is small, and even a slight dimensional variation causes a large variation in breakdown voltage. In addition, the high resistance conductive film in the curved portion consumes a relatively large amount of power because current is concentrated and voltage drop is large. As a result, the curved portion is easily broken.
[0008]
Further, in the pattern in which the strip-like high resistance conductive film disclosed in Japanese Patent Application Laid-Open No. 7-326775 which is prevented from this harmful effect is spiral, there is a problem that the area occupied by the withstand voltage structure increases.
SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor device that solves the above-mentioned problems and has a simple pattern of resistive field plate withstand voltage structure, uniformizing the potential distribution at the curved portion and ensuring stable withstand voltage. is there.
[0009]
[Means for Solving the Problems]
In order to achieve the above-described object, a first field electrode, which is a field plate electrode formed above a pn junction, is opposed to the first electrode in a withstand voltage structure of a resistive field plate formed on the surface of a semiconductor substrate. A high-voltage semiconductor having a second electrode, which is an end plate electrode, and a resistive conductive film that is in contact with the first electrode and the second electrode and is formed between the first electrode and the second electrode In the device
A curved portion having a different peripheral length between the first electrode end and the second electrode end facing each other, a second electrode having a long peripheral length, and a portion where the second electrode end and the resistive conductive film are not selectively in contact with each other It is set as the structure to provide.
[0010]
Moreover, it is good to provide the said non-contact location by providing an insulating film between the said 2nd electrode and this 2nd electrode end, and the said resistive conductive film.
Further, it is preferable to provide a portion which is not the contact by providing an opening in the resistive electro-conductive film on the upper second electrode and the second electrode end.
In addition, a resistive field plate withstand voltage structure formed on the surface of the semiconductor substrate, a first electrode that is a field plate electrode formed above the pn junction, and an end plate electrode that is disposed to face the first electrode In a high withstand voltage semiconductor device having a certain second electrode and a resistive conductive film formed between the first electrode and the second electrode in contact with the first electrode and the second electrode,
In the different sweeps perimeter opposite the first electrode and the second electrode, when a configuration in which Ru with a plurality of openings in the first electrode and the resistive conductive film in the region sandwiched between the second electrode Good.
[0011]
The resistive conductive film sandwiched between the openings may have the same width on the first electrode side and the second electrode side.
The opening may reach the second electrode.
The opening may reach the first electrode and the second electrode.
In addition, it is effective that the resistive conductive film sandwiched between the openings has a stripe shape.
[0012]
As described above, the current flowing through the resistive conductive film at the curved portion by preventing the contact between the end plate electrode having a large curvature radius of the curved portion and the resistive conductive film or by partially removing the resistive conductive film. Is made uniform on the side with a large curvature and the side with a small curvature to make the potential gradient constant. By making the current density uniform, thermal runaway at the curved portion can be prevented.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
1A and 1B show a high voltage semiconductor device according to a first embodiment of the present invention. FIG. 1A is a plan view of an essential part, and FIG. 1B is a cross-sectional view taken along line AA in FIG. FIG. 2C is a partial cross-sectional view taken along the line BB. The difference from FIG. 8 is that a part of the insulating film 7 is disposed between the end plate electrode 5 and the high resistance conductive film 6.
[0014]
In FIG. 1, p diffusion layer 2 is formed on the surface layer of n ⁻ layer 1 (semiconductor substrate), and field oxide film 3 is formed on p diffusion layer 2 and n ⁻ layer 1. Field plate electrode 4 is formed on p diffusion layer 2 and field oxide film 3, and end plate electrode 5 is formed on n ⁻ layer 1 and field oxide film 3. The field plate electrode 4 and the end plate electrode 5 face each other, and the distance between them is constant. A high resistance conductive film 6 is formed on the field plate electrode 4, the end plate electrode 5, and the field oxide film 3 sandwiched between the electrodes 4 and 5. In forming the high-resistance conductive film 6, an insulating film 7 is selectively formed on the end plate electrode 5 and the field oxide film 3 at a portion where the electrodes 4 and 5 are curved (curved portion D). The high resistance conductive film 6 is formed through the insulating film 7 (FIG. 3C). In addition, ai in a figure is the same as FIG. Further, j represents an end portion on the fan-shaped end plate electrode inner end f side, and k represents an end portion on the end plate electrode outer end h side.
[0015]
Further details will be described. The curved portion D has a radius of curvature of 90 ° (one quarter of a circle), an inner diameter of the field plate electrode outer end e of 50 μm, and an inner diameter of the end end of the electrode plate electrode f of 110 μm. The impurity concentration of the semiconductor substrate (n ⁻ layer 1) is 5 × 10 ¹⁶ cm ⁻³ (specific resistance = 60 Ω · cm). The thickness of the field oxide film 3 having a breakdown voltage structure is 0.7 μm. The distance between the field plate electrode outer end e and the pn junction portion d inside the semiconductor substrate is 15 μm. An SiN film, which is an insulating film, is formed to a thickness of 0.3 μm so as to cover the field plate electrode 4, the field oxide film 3, and the end plate electrode 5, and then on the end plate electrode 5 located in the curved portion D The insulating film 7 is left only on a part of the insulating film 7 and the field oxide film 3 in the vicinity thereof, and the insulating film in other portions is removed. The shape of the insulating film 7 is such that the width W along the inner end f of the end plate electrode is 12 μm, the length L1 protruding from the electrode 5 on the field plate oxide film 3 is 10 μm, and is formed in a later process. The protruding length L2 from the outer peripheral edge h of the high-resistance conductive film has a fan shape of 10 μm. This fan-shaped insulating film 7 selectively covers the end plate electrode 5. Here, three insulating films 7 are equally arranged. Next, as shown in the figure, the high resistance conductive film 6 is formed by a-Si plasma CVD with a thickness of about 0.06 μm so as to cover the electrodes 4 and 5 and the field oxide film 3 and the insulating film 7. Formed.
[0016]
In the case of this embodiment, the length of the inner end b of the high resistance conductive film in contact with the field plate electrode 4 of the curved portion D is about 78 μm, whereas the length of the outer end h of the high resistance conductive film in contact with the end plate electrode 5 is set. The thickness was about 121 μm. By using these lengths, the potential distribution in the curved portion D is made uniform as compared with the conventional case without the insulating film 7. The shape, number, and arrangement of the insulating film 7 shown here may be changed.
[0017]
When the distance between the field plate electrode 4 and the end plate electrode 5 is the same as that of the conventional element, the maximum value of the element breakdown voltage is 650 V, which is the same as the conventional element breakdown voltage, but the minimum value is 550 V in the conventional element. As a result, the variation of about 15% in the conventional device was improved to 6%.
In addition, as a reliability test, when 500 V was applied at 150 ° C. and left as it was, the conventional product showed an abnormality in the breakdown voltage of 3 out of 50 pieces by 600 hours. I found that there was no problem.
[0018]
FIG. 2 is an example in which the potential distribution of the high resistance conductive film is calculated. I is the calculation result at the curved portion D in the present invention. Since it is not in direct contact with the end plate electrode 5, the potential gradient is made uniform compared to the potential distribution of the curved portion D in the conventional element II, so that the field plate electrode 4 and the end plate electrode 5 of the straight portion C The potential distribution is approaching. As a result, the effect of expanding the depletion layer in the semiconductor substrate (n ⁻ layer 1) is enhanced, and since current concentration is relaxed, power consumption is suppressed, and further element breakdown can be prevented.
[0019]
3A and 3B show a high voltage semiconductor device according to a second embodiment of the present invention. FIG. 3A is a plan view of the main part, and FIG. 3B is a cross-sectional view taken along line AA in FIG. FIG. 2C is a partial cross-sectional view taken along the line BB.
In FIG. 3, n ^- p-diffusion layer 2 is formed on the surface layer of the layer 1, p diffusion layer 2 on and the n ^- to form a field oxide film 3 is formed on the layer 1. Field plate electrode 4 is formed on p diffusion layer 2 and field oxide film 3, and end plate electrode 5 is formed on n ⁻ layer 1 and field oxide film 3. The field plate electrode 4 and the end plate electrode 5 face each other, and the distance between them is constant. A high resistance conductive film 6 is formed on the field plate electrode 4, the end plate electrode 5, and the field oxide film 3 sandwiched between the electrodes 4 and 5. In the high resistance conductive film 6, an opening 8 is selectively formed on the end plate electrode 5 and the field oxide film 3 in the curved portion D where both the electrodes 4 and 5 are curved ((c) in the figure). .
[0020]
In the first embodiment, there is an insulating film 7 between the end plate electrode 5 and the high-resistance conductive film 6, and the number of steps is increased to form this. In the second embodiment, an opening 8 is formed in the high resistance conductive film 6 in place of the insulating film 7 so that the end plate electrode 5 and the high resistance conductive film 6 are not selectively in contact with each other. The opening 8 has a length of 12 μm along the inner end f of the end plate electrode, a length L1 protruding from the inner end f of the electrode on the field plate oxide film 3 of 10 μm, and a high resistance conductive film. It has a fan-like shape that is several μm inside from the outer peripheral edge h. Three openings 8 were arranged uniformly. Since the opening 8 can be formed simultaneously in the patterning step and the etching step of the high resistance conductive film 6, it can be carried out without increasing the number of steps as shown in FIG. The effect is the same as that of the first embodiment. In the drawing, m represents an end portion on the fan-shaped end plate electrode inner end f side, and n represents an end portion on the end plate electrode outer end h side.
[0021]
4A and 4B show a high voltage semiconductor device according to a third embodiment of the present invention. FIG. 4A is a plan view of the main part, and FIG. 4B is a cross-sectional view taken along line AA in FIG. FIG. 2C is a partial cross-sectional view taken along the line BB. This embodiment has a structure in which a part of the high resistance conductive film 6 in the curved portion D of the withstand voltage structure is removed. Unlike the second embodiment, the end plate electrode 5 is not in contact with the field oxidation in the vicinity of the electrode 5. The opening 9 is provided in the film 3. This is effective when the distance between the field plate electrode 4 and the end plate electrode 5 is relatively long.
[0022]
In this third embodiment, since the width L of the high resistance conductive film 6 sandwiched between the openings 9 is substantially equal toward the field plate electrode 4 side, the density of the current flowing through this portion is the end plate electrode 5 side. And the field plate electrode 4 side are substantially equal, and the potential distribution at the curved portion D is made uniform.
4 shows the case where the length of the end plate electrode 5 is longer than the length of the field plate electrode 4 at the curved portion D, but conversely, the length of the field plate electrode is longer than the length of the end plate electrode. That is, even when the field plate electrode 4 and the end plate electrode 5 in FIG. 4 are interchanged, it is effective to provide the opening 9 as shown in FIG. In this case, the position of the outer end e of the field plate electrode in FIG. 4 is the position of the outer end of the end plate electrode in the case of replacement, and the position of the inner end f of the end plate electrode in FIG. The position of the inner end of the field plate electrode in this case. Naturally, the pn junction comes under the field plate electrode when it is replaced.
[0023]
5A and 5B show a high voltage semiconductor device according to a fourth embodiment of the present invention. FIG. 5A is a plan view of the main part, and FIG. 5B is a cross-sectional view taken along line AA in FIG. FIG. 2C is a partial cross-sectional view taken along the line BB. In this embodiment, the method of the third embodiment is further advanced so that the shape of the high-resistance conductive film 6 at the curved portion D is made into a large number of stripes, and the width w of each stripe-shaped high-resistance conductive film 6 is ended. The plate electrode 5 side and the field plate electrode 4 side are made equal. By doing so, the density of the current flowing through the striped high-resistance conductive film 11 becomes constant from the end plate electrode 5 side to the field plate electrode 4 side, and the potential distribution is made uniform along the straight line portion C. Further, in order to make the potential distribution uniform with the adjacent stripe-shaped high-resistance conductive film 11, when the adjacent stripe-shaped high-resistance conductive films 11 are connected by a bridge 12 (bridge) as shown by a dotted line. Good.
[0024]
Further, by providing the opening 10 so as not to come into contact with the outer end e of the field plate electrode, the depletion layer extending in the n ⁻ layer 1 at this point can be elongated. Even when the opening 10 is brought into contact with the outer edge e of the field plate electrode, it is preferable to shorten the contact length as much as possible (in the figure, as indicated by the tip of the arrow F, the vertex of the triangle indicated by the dotted line is outside the field plate electrode. Touches end e).
[0025]
In addition, when the field plate electrode 4 and the end plate electrode 5 in FIG. 5 are interchanged, the opening 10 should not be in contact with the inner end of the field plate electrode when interchanged, or the contact length should be as short as possible. To do. Doing so improves the growth of the depletion layer.
[0026]
【Effect of the invention】
In this invention, a method of selectively sandwiching an insulating film between a field plate electrode and a high-resistance conductive film, a method of providing an opening in the high-resistance conductive film, and a high-resistance conductive film of a curved portion in a number of striped bands By using this method, the current density flowing through the resistive field plate at the curved portion can be made uniform with a simple pattern, and the potential distribution at the curved portion can be made uniform. As a result, the area occupied by the breakdown voltage structure of the high breakdown voltage semiconductor device can be reduced, and breakdown voltage breakdown at the curved portion can be prevented. In addition, the reliability of the breakdown voltage characteristic can be improved.
[Brief description of the drawings]
1A is a high voltage semiconductor device according to a first embodiment of the present invention; FIG. 1A is a plan view of a main part, FIG. 1B is a cross-sectional view of a main part taken along line AA in FIG. FIG. 2 is a potential distribution diagram of a high-resistance conductive film. FIG. 3 is a high voltage semiconductor device according to a second embodiment of the present invention, and FIG. FIG. 4B is a plan view of the main part cut along the line AA in FIG. 4A, and FIG. 4C is a cross-sectional view of the main part cut along the line BB in FIG. 1A is a plan view of a main part, FIG. 2B is a cross-sectional view of a main part cut along the line AA of FIG. 1A, and FIG. FIG. 5 is a high voltage semiconductor device according to a fourth embodiment of the present invention, wherein FIG. 5A is a plan view of the main part, and FIG. 5B is a main part cut along line AA in FIG. Cross-sectional view, (c) is a cross-sectional view of the main part cut along line BB. 6 is a diagram showing a breakdown voltage structure having a conventional belt-shaped high-resistance conductive film. FIG. 7 is a schematic plan view of a breakdown voltage structure of a conventional semiconductor device. FIG. 8 is an enlarged detail view of a portion E in FIG. FIG. 9B is a cross-sectional view taken along lines AA and BB. FIG. 9 is a conventional high-resistance conductive film having a simple pattern between the outer edge of the field plate electrode and the inner edge of the end plate electrode. Potential distribution chart [Explanation of symbols]
1 n ⁻ layer 2 p diffusion layer 3 field oxide film 4 field plate electrode 5 end plate electrode 6 high resistance conductive film 7 insulating films 8, 9, 10 opening 11 striped high resistance conductive film C linear portion D curved portion

Claims (8)

A resistive field plate withstand voltage structure formed on the surface of a semiconductor substrate, the first electrode being a field plate electrode formed above the pn junction intersecting the surface of the semiconductor substrate, and disposed opposite the first electrode A high-voltage semiconductor device having a second electrode, which is an end plate electrode, and a resistive conductive film in contact with the first electrode and the second electrode and between the first electrode and the second electrode ,
A curved portion having a different peripheral length between the first electrode end and the second electrode end facing each other, a second electrode having a long peripheral length, and a portion where the second electrode end and the resistive conductive film are not selectively in contact with each other A high withstand voltage semiconductor device characterized by being provided. The high breakdown voltage semiconductor device according to claim 1, wherein the non-contact portion is provided by providing an insulating film between the second electrode and the end of the second electrode and the resistive conductive film. The high breakdown voltage semiconductor device according to claim 1, wherein the non-contact portion is provided by providing an opening in the resistive conductive film on the second electrode and on the end of the second electrode. A resistive field plate withstand voltage structure formed on the surface of a semiconductor substrate, the first electrode being a field plate electrode formed above the pn junction intersecting the surface of the semiconductor substrate, and disposed opposite the first electrode High-voltage semiconductor device having a second electrode, which is an end plate electrode, and a resistive conductive film formed between the first electrode and the second electrode in contact with the first electrode and the second electrode In
A plurality of openings are provided in the resistive conductive film in a region sandwiched between the first electrode and the second electrode in curved portions having different peripheral lengths between the first electrode and the second electrode facing each other. High breakdown voltage semiconductor device. 5. The high voltage semiconductor device according to claim 4, wherein the width of the resistive conductive film sandwiched between the openings is equal on the first electrode side and the second electrode side. The high withstand voltage semiconductor device according to claim 4, wherein the opening reaches the second electrode. The high breakdown voltage semiconductor device according to claim 4, wherein the opening reaches the first electrode and the second electrode. 8. The high breakdown voltage semiconductor device according to claim 4, wherein a shape of the resistive conductive film sandwiched between the openings is a stripe shape.

Images