JPH08264490A - Fabrication of semiconductor device - Google Patents

Abstract

PURPOSE: To eliminate dissolution of etch-cut portion into chemicals used to isolate a photoresist masking the rear surface of element in the case of etch- cutting by covering such an etch cut portion at the surface of a wafer where elements are formed with the photoresist resistive to the chemicals in order to prevent isolation of element from a glass plate during the process. CONSTITUTION: A part 13a to be etched cut on the surface 12a where an element 12 is formed of a semiconductor wafer 11 is covered with a negative resist 13 which is resistive to chemicals in the width wider than the width thereof. The entire part thereof is coated with a positive resist 14 and the surface is attached to a glass plate 15 and the rear surface is polished. Thereafter, the opposite surface of the semiconductor wafer 11 is covered with a positive resist 17, except for the part to be etched and the etch-cut is performed by the dry etching method from the opposite surface of the semiconductor wafer 11. The positive resist 17 is removed with the chemicals to dissolve the negative resist 13. Thereafter, PHS is formed under the condition that the semiconductor wafer 11 is attached to the glass plate 15. Then, an element 12 is isolated from the glass plate 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for dividing a compound semiconductor device having a PHS structure by etching.

[0002]

2. Description of the Related Art Etch cut is used as one of the element dividing methods for a semiconductor device. Conventional PHS (Pla
Power ME with ted heat sink) structure
A method of manufacturing the SFET will be described with reference to FIG.
FIG. 3 is a wafer cross-sectional view showing the flow of the etch cutting process in the order of steps. A plurality of elements 2 are formed on one surface of the semiconductor wafer 1 (Fig. 3a). Next, the first negative resist 3 is formed on the device forming surface 2a (wafer surface) of the wafer 1.
Is uniformly applied, and predetermined heat treatment such as drying and baking is performed (FIG. 3b). A second negative resist 5 (may be the same as the first negative resist) on a transparent glass plate 4 which is a holding plate.
Is evenly applied, and a predetermined heat treatment is applied to the wafer 1
The first negative resist 3 coated surface of the wafer 1 and the second negative resist 5 coated surface of the glass plate 4 are bonded so that the glass plate 4 and the glass plate 4 are parallel to each other. At this time, the glass plate 4 is heated in order to make the adhesion easy and strong.

The negative resist is used for the wafer surface 2a and the glass plate because it does not dissolve when the positive resist is etched by the cover and then the positive resist is removed with a release agent as described later. Is. In this specification, "photoresist resistant to chemicals"
The term "coating agent resistant to chemicals" is used, but this does not mean that it is stronger than the absolute standard. When "a photoresist" is selected as the etch-cut cover and "a chemical solution that removes it" is selected, a photoresist or coating agent that substantially withstands the chemical solution is a "chemical-resistant photoresist" or "Please note that it is a coating agent that is resistant to chemicals (Fig. 3c).

Next, the wafer 1 is made to have a predetermined thickness by mechanical polishing and chemical polishing (FIG. 3d). Next, the positive resist 6 is selectively left on the back surface of the element 2 using a positive resist and a double-sided aligning machine. Next, the positive resist is used as a cover to perform an etch cut by wet or dry etching to divide the element 2 into individual elements 2. However, the element 2 is still attached to the glass plate 4. Although not shown, no positive resist is left in the via hole forming portion. At this time, at the same time, a via hole (not shown) for passing heat or electricity on the surface of the element 2 to the back surface is penetrated (3e). Next element 2
The positive resist on the back surface is removed with a positive resist release agent that does not dissolve the first negative resist. Next, a metal (not shown) is formed on the first negative resist 3 exposed by etching and removing the entire surface of the element 2 on the glass plate 4 and the wafer, as an electrical connection for plating the back surface of the element 2 which has been etched off. Are sputtered (not shown).

Next, a negative resist film (not shown) is formed on the portion excluding the portion to be plated with gold (that is, the back surface and the side surface of the element 2). Next, gold 7 is attached by plating to the back surface, side surfaces and inside of via holes (not shown) of the element 2. Next, the negative resist is removed with a negative resist remover. Here, when gold 7 plating is performed on the back surface of the element 2 and the deep hole of the via hole on the back surface of the element 2, it is necessary to remove the photoresist in this portion by development. At this time, in order to remove the photoresist of the hole which is hard to be exposed to light, a negative resist which does not cure the portion not exposed to light is suitable. Also, when stripping the negative resist after gold 7 plating,
There is sputtered metal on the first negative resist 3,
The negative resist stripping solution does not dissolve the first negative resist 3. Next, the metal between the elements 2 is removed by wet or dry etching using gold 7 as a mask to divide each element 2 into individual elements 2 (FIG. 3f). Next, the element 2 is peeled from the glass plate 4 with a negative resist peeling agent. Next element 2
Is washed with an organic solvent (Fig. 3g).

[0006]

According to this etching method, the first negative resist 3 on the surface of the element 2 (for example, the product of Co., Ltd.) is used.
OMR83 manufactured by Tokyo Ohka Co., Ltd.) The first step is performed by applying heat (application of wafer 1 to glass substrate 4, dry etching step, metal sputtering step, other photoresist baking step after application, etc.) after application. Of the negative resist 3 of FIG.
Is difficult to remove with a negative resist remover (for example, OMR83 remover manufactured by Tokyo Ohka Co., Ltd.). If it is attempted to remove the negative resist that cannot be removed with another chemical solution, the constituent material of the element 2 will be adversely affected and cannot be used. As a result, there is a problem in that a defective appearance occurs due to the adhesion of the first resist 3 to the surface of the element 2 and the yield decreases.

If a positive resist (for example, a novolac type) is used instead of coating the first negative resist 3 on the surface of the element 2, even if the positive resist adheres to the surface of the element 2, it adheres to the surface of the element 2 in a later step. The quality of the positive resist changed,
The removal of the positive resist does not become difficult with a positive resist stripper (eg methyl ethyl ketone). However, when the positive resist on the back surface at the time of etching is removed with a positive resist stripper, the positive resist between the elements 2 is dissolved,
Subsequently, the positive resist on the surface of the element 2 is dissolved. Also,
When the negative resist is coated on the back surface of the element 2 at the time of etching, the positive resist is dissolved in the negative resist remover when removing the negative resist on the back surface. Therefore, there is a problem that the element 2 is separated from the glass plate 4 and cannot be used in the subsequent steps.

[0008]

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems, and selectively etches a portion of a semiconductor wafer on which an element is formed, which is to be etched, wider than its width. A first step of coating with a photoresist that is strong against chemicals, a second step of applying a coating agent that easily dissolves in the chemicals even when heat is applied to it, and a third step of attaching the surface to a holding plate. Step, a fourth step of covering the opposite surface of the semiconductor wafer with a photoresist except for a portion to be etched, a fifth step of etching cut from the opposite surface of the semiconductor wafer, and dissolving a photoresist resistant to the chemical solution. A sixth step of removing the photoresist coated in the fourth step with a chemical solution that does not include, and a seventh step of processing the semiconductor wafer in a state where the semiconductor wafer is attached to the holding plate, and And a eighth step of peeling off from the holding plate an element, and to provide a method of manufacturing a semiconductor device characterized by having a process of the semiconductor wafer to the Izure of step is heated. Specifically, the part to be etched on the surface of the semiconductor wafer where the elements are formed is
Wider than that width, a first step of selectively coating with a negative resist, a second step of applying a positive resist on the entire surface, and a third step of attaching the surface to a holding plate, A fourth step of covering the opposite surface of the semiconductor wafer with a positive resist except for a portion to be etched, a fifth step of etching and cutting from the opposite surface of the semiconductor wafer, and a positive resist stripping that does not dissolve the negative resist A sixth step of removing the positive resist coated in the fourth step with an agent, a seventh step of treating the semiconductor wafer in a state of being attached to the holding plate thereafter, and the element from the holding plate. An eighth step of stripping, and a method of manufacturing a semiconductor device, characterized in that the semiconductor wafer is heated in any one of the above steps. Further, on the surface of the semiconductor wafer on which the elements are formed, the element surface is made narrower than that, and the first step of coating with a photoresist that easily dissolves in the chemical solution even when heat is selectively applied, and the chemical solution on it The second step of applying a strong coating agent to the entire surface, the third step of sticking the surface to the holding plate, and the fourth surface of the opposite surface of the semiconductor wafer, excluding the planned etching portion, with photoresist. Process,
A fifth step of etching-cut from the opposite surface of the semiconductor wafer, a sixth step of removing the photoresist of the fourth step with a chemical solution that does not dissolve a coating agent that is strong in the chemical solution, and then the semiconductor wafer is retained. There is a seventh step of treating in a state of being attached to a plate, and an eighth step of peeling the element from the holding plate, and a treatment of heating the semiconductor wafer in any of the above steps. A method for manufacturing a semiconductor device is provided. Specifically, the first step of selectively covering the element surface of the surface of the semiconductor wafer on which the elements are formed with a positive resist, and the second step of coating the entire surface with a negative resist. And a third step of attaching the surface to a holding plate, a fourth step of covering the opposite surface of the semiconductor wafer with a positive resist except for a portion to be etched, and a fifth step of etching cut from the opposite surface. And a sixth step of removing the positive resist coated in the fourth step with a polyresist release agent that does not dissolve the negative resist,
After that, there is a seventh step of processing the wafer in a state of being attached to the holding plate, and an eighth step of peeling the element from the holding plate, and a treatment in which the wafer is heated in any of the above steps. Provided is a method for manufacturing a semiconductor device having the above.

[0009]

According to the above means, since the etch-cut portion of the surface of the wafer on which the elements are formed is covered with the photoresist resistant to the chemical or the coating agent resistant to the chemical, the photoresist masking the back surface of the element during the etching is removed. Does not dissolve in chemicals. Therefore, the element is not peeled off during the sixth step. Also, the surface of the element, where the rest of the resist or coating agent causes a poor appearance, is coated with a photoresist that easily dissolves in a chemical solution even when heat is applied, or a coating agent that easily dissolves in a chemical solution when heat is applied. Even if there is a heat treatment after coating or coating the photoresist, the coating agent or the photoresist does not remain on the surface of the pellet and the appearance is not deteriorated.

[0010]

Embodiment 1 An example in which the manufacturing method according to claims 1 and 2 of the present invention is applied to the manufacture of a power MESFET having a PHS structure will be described with reference to FIG. FIG. 1 is a wafer cross-sectional view showing the flow of the etch-cut process of the present invention in the order of flow. A plurality of elements 12 are formed on the semiconductor wafer 11 (FIG. 1a). The next step is a feature of the present invention.
A negative resist (for example, a cyclized rubber-based OMR83 (stock) is used as an example of a photoresist that is wider and wider than the portion 13a between the elements 12 on the element forming surface 12a (wafer surface) of the wafer 11 and is selectively resistant to chemicals. ) A film made by Tokyo Ohka Co., Ltd. is formed (hereinafter referred to as the first negative resist 13) (FIG. 1b).

Next, a positive resist 14 (for example, novolac-based O) is formed on the element 12 and the first negative resist film 13 as a coating agent that easily dissolves even when heat is applied by a chemical solution.
FPR-800C (manufactured by Tokyo Ohka Co., Ltd.) is uniformly applied to the entire surface (FIG. 1c). Next, on the transparent glass plate 15 which is a holding plate, a second negative resist 16 is formed in order to maintain the adhesive strength.
(For example, OMR83) is applied uniformly, and the positive resist 14 coated surface of the wafer 11 and the second negative resist 16 coated surface of the glass plate 15 are bonded so that the wafer 11 and the glass plate 15 are parallel to each other. However, positive resist 14
If the adhesive strength to the glass plate 15 is obtained in step 1, the negative resist 16 is unnecessary. At this time, the glass plate 15 and the wafer 11 are heated for easy and strong adhesion (FIG. 1d). Next, the wafer 11 is made to have a predetermined thickness by mechanical polishing and chemical polishing (FIG. 1e).

Next, a positive resist (for example, OFPR-8) is used.
00C) and a double-sided aligning machine, the positive resist 17 is left except for the planned etching portion 13a on the back surface of the semiconductor wafer 11 and the planned etching portion such as a via hole formation planned portion (not shown). Next, the positive resist 17 is used as a cover to perform an etch cut by dry etching to divide the element 12 into individual elements 12. At this time, at the same time, the surface of the element 12 is penetrated through a via hole (not shown) that allows heat and electricity to pass through to the back surface (FIG. 1f). Next, the positive resist 17 on the back surface of the element 12 is removed with a positive resist remover (for example, methyl ethyl ketone). At this time, the first negative resist 13 does not dissolve in methyl ethyl ketone, so that the element 12 does not peel off. Next, as an electrical connection for plating the back surface of the element 12 that has been cut off by etching, the entire back surface of the element 12 attached to the glass plate 15 and the first negative resist 13 exposed by etching and removing the metal (see FIG. Sputter (not shown). Next, a negative resist film (not shown) is formed on the portion to be plated with gold, that is, the portion other than the back surface and the side surface of the element 12. Next, gold 18 is applied by plating to the back surface, side surfaces and via holes (not shown) of the element 12. Next, the negative resist is removed with a negative resist remover. Next, the metal (not shown) between the elements 12 is etched by using the gold 18 as a mask to divide the elements 12 into individual elements 12 (FIG. 1g).

Next, the element 12 is stripped from the glass plate 15 with a negative resist stripping agent (eg, OMR-710 stripping solution manufactured by Tokyo Ohka Co., Ltd.). Next, the element 12 is washed with an organic solvent (FIG. 1h). In this embodiment, if the negative resist 13 remains on the surface of the element 12, the positive resist is brought into contact with a portion having a poor appearance, and the negative resist is used in a portion brought into contact with the positive resist peeling agent. The positive resist 13 on the surface of the element 12 is subjected to heat treatment in the step after coating on the surface of the element 12 (step of attaching the wafer 11 to the glass plate 15,
Dry etching process, sputtering process, positive resist 1
Even after the 3 coating process, the photoresist baking-fastening process, etc.) does not cause deterioration and difficulty in removal. For this reason, the PR process of FIG. 1B is increased once, but there is an effect of further lowering the pellet unit price due to the reduction of the appearance defect due to the resist adhesion. Further, there is the first negative resist film 13 in a portion where the positive resist release agent contacts between the elements 12,
The element 12 does not peel off.

In the present embodiment, a positive resist is used as a coating agent that easily dissolves in a chemical solution even when heat is applied. The positive resist is used for the element 12 and the glass plate 15.
It is convenient that the first negative resist 13 can be simultaneously removed by a negative resist remover that removes the first negative resist 13 when peeling it from. However, the “coating agent which can be easily dissolved in a chemical solution even when heat is applied” which can be used in the present invention is not limited to the positive resist. It can be selected from commercially available coating agents such as waxes. Withstand the heat applied in the process,
Lastly, any material that can be easily removed with a chemical solution such as an organic solvent may be used. If it is not possible at the same time by a chemical solution (for example, a negative resist stripper or the like) that removes the photoresist (first negative resist 13 in the present embodiment) that is resistant to the chemical solution, the coating agent after removing the photoresist that is resistant to the chemical solution. May be treated again with a removable chemical solution. A photoresist that is strong against chemicals and a photoresist that serves as a cover for etch cut, and a combination of a chemical that removes the latter and does not dissolve the former can be selected from commercially available photoresists, their strippers, and commercially available organic solvents. As a conventional photoresist, a negative resist can be used as a photoresist resistant to a chemical solution, a positive resist can be used as a photoresist for an etch-cut cover, and a ketone can be used as a chemical solution for removing the latter.

[0015]

Second Embodiment A manufacturing method according to claims 3 and 4 of the present invention, which is different from the first embodiment, will be described with reference to FIG. FIG. 2 is a wafer cross-sectional view showing the flow of the etch cutting process of the present invention in the order of flow. A plurality of elements 22 are formed on one surface of the semiconductor wafer 21 (Fig. 2a). The following are the features of the present invention. A positive resist film 23 (for example, a novolac OFPR-) is used as an example of a photoresist which is narrower than the element 22 on the element forming surface 22a (wafer surface) of the wafer 21 and is easily melted even when heat is applied to the chemical solution.
800C made by Tokyo Ohka Co., Ltd.) (hereinafter referred to as the first positive resist film 23) (FIG. 2b).

Next, a negative resist (for example, OMR83) is uniformly applied to the entire surface of the element 22 and the first positive resist film 23 as a coating agent resistant to chemicals (hereinafter referred to as the first negative resist) (FIG. 2c). . Next, a second negative resist 26 (for example, OMR83) is uniformly applied to the transparent glass plate 25, which is a holding plate, in order to maintain the adhesive strength, and the wafer 21 and the glass plate 25 are parallel to each other. The coated surface of the first negative resist 24 and the coated surface of the second negative resist 26 of the glass plate 25 are bonded together. However, if the first negative resist 24 has sufficient adhesive strength to the glass plate 25, the second negative resist 26 is unnecessary. At this time, the glass plate 24 and the wafer 21 are heated for easy and strong adhesion (FIG. 2d).
Next, wafer 2 is mechanically and chemically polished.
1 has a predetermined thickness (FIG. 2e).

Next, a positive resist (for example, OFPR-8) is used.
00C) and a double-sided aligner are used to leave the positive resist 27 on the back surface of the semiconductor wafer 21 except for the portion to be etched. However, although not shown, no positive resist is left in the via hole forming portion. Next, the positive resist is used as a cover to perform an etching cut by dry etching to divide the element 22 into individual elements 22. At this time, at the same time, the surface of the element 22 is penetrated through a via hole (not shown) for passing heat and electricity to the back surface (FIG. 2f). Next, remove the positive resist on the back surface of the element 22 with a positive resist remover (for example, methyl ethyl ketone).
To remove. At this time, the first negative resist 24 does not dissolve in methyl ethyl ketone, so the element 22 is not peeled off. Next, as an electrical connection for plating the back surface of the element 22 that has been etched off, the entire surface of the glass plate 25 on which the element 22 is attached and the first negative resist 24 exposed by etching and removing the metal (metal ( Sputter (not shown). Next, a negative resist film (not shown) is formed except for the portions (the back surface and the side surface of the element 22) to be plated with gold. Next, gold 28 is applied to the element 2 by plating.
Attached to the back surface, side surface and via hole (not shown) of No. 2.

Next, the negative resist is removed with a negative resist peeling material. Next, the metal (not shown) between the elements 22 is removed by dry etching using gold 28 as a mask to divide each element 22 into individual elements 22 (FIG. 2g). Next, element 22
A negative resist stripper (eg OMR-710 strip station)
Then, it is peeled off from the glass Ida 25. Next, the element 22 is washed with an organic solvent (FIG. 2h). In this embodiment, the positive resist is brought into contact with a portion of the surface of the element 22 where the negative resist 23 is left, and the negative resist 23 is brought into contact with the body resist stripping solution. The positive resist 23 on the surface of the element 22 is applied with heat after being applied to the surface of the element 22 (a step of attaching the wafer 21 to the glass plate 25, a dry etching step, a sputtering step, and a photoresist baking after the positive resist applying step). Even in the tightening process, etc.), there is no problem that the quality is changed and removal becomes difficult. For this reason,
Although the PR process of FIG. 2b is increased once, there is an effect of further lowering the pellet unit price due to the reduction of the appearance defect due to the adhesion of the resist. Further, the portion of the positive resist between the elements 22 which is in contact with the quenching agent has the first negative resist film 23, and the elements 22 are not peeled off.

Further, according to this embodiment, since the first negative resist film is formed around the wafer when the first negative resist film 23 is formed, the side surface of the bonded portion of the wafer 21 and the glass plate 25 does not become the positive resist 23. Therefore, the element 22 does not peel off from the side surface. Although a novolac-based positive resist is used as a photoresist that easily dissolves in a chemical solution even if heat is applied in the above-mentioned embodiments, the present invention is not limited to this. Since it does not come into contact with the chemical solution that removes the photoresist that serves as the etch-cut cover, it is sufficient to select from the commercially available photoresists that can withstand the heat and can be easily removed with the chemical solution at the end. Although a cyclized rubber-based negative resist is used as the coating liquid resistant to chemicals in the above embodiments, the present invention is not limited to this. The photoresist that will be the etch-cut cover is selected, the chemical that removes it is selected, and the one that does not dissolve in it should be selected. It can be selected from photoresist, other resins, waxes and the like.

[0020]

According to the present invention, since the etch-cut portion is not dissolved in the chemical solution that comes into contact during the etch-cut process, the element does not peel off during the process. In addition, since a coating agent that easily peels off after the process is used for the contact portion with the element surface, there is no deposit that is difficult to peel off on the element surface, and the appearance defect resulting from this is eliminated.

[Brief description of drawings]

FIG. 1 is a wafer cross-sectional view showing a flow sequence of an etch cutting process according to an embodiment of the present invention.

FIG. 2 is a wafer cross-sectional view showing the flow sequence of an etch cutting process according to another embodiment of the present invention.

FIG. 3 is a wafer cross-sectional view of a conventional etch-cut manufacturing process flow.

[Explanation of symbols]

11, 21 Wafers 12, 22 Elements 12a, 22a Element formation surface 13 First negative resist (photoresist that is strong against chemicals) 13a, 23a Etched cut portion 14 Positive resist (coating that easily dissolves in chemicals even when heated) 15, 25 Glass plate (holding plate) 17, 27 Positive resist (photoresist) 23 First positive resist (photoresist that easily dissolves in chemical solution even when heat is applied) 24 First negative resist (coating agent strong against chemical solution)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H01L 29/812

Claims (4)

[Claims] 1. A surface of a semiconductor wafer on which elements are formed,
The first step is to make the etch cut area wider than its width and selectively coat it with a photoresist that is resistant to chemicals.The second step is to apply a coating agent that easily dissolves in the chemicals even if heat is applied on it. Step, a third step of attaching the surface to a holding plate, a fourth step of covering the opposite surface of the semiconductor wafer with a photoresist except for a portion to be etched, and an etch cut from the opposite surface of the semiconductor wafer A fifth step to do, a sixth step of removing the photoresist coated in the fourth step with a chemical solution that does not dissolve the photoresist strong in the chemical solution, and then in a state where the semiconductor wafer is attached to the holding plate. A seventh step of treating, and an eighth step of peeling the element from the holding plate,
A method of manufacturing a semiconductor device, characterized in that the semiconductor wafer is heated in any one of the steps. 2. A surface of a semiconductor wafer on which elements are formed,
The first step of selectively coating the portion to be etched with a width wider than its width with a negative resist, the second step of applying a positive resist on the entire surface, and the step of attaching the surface to the holding plate. Third step, excluding the intended etching portion of the opposite surface of the semiconductor wafer, a fourth step of covering with a positive resist, a fifth step of etching cut from the opposite surface of the semiconductor wafer, the negative resist A sixth step of removing the positive resist coated in the fourth step with a positive resist release agent that does not dissolve, a seventh step of processing the semiconductor wafer in a state of being attached to the holding plate thereafter, and the element And an eighth step of peeling the semiconductor wafer from the holding plate, and in any one of the above steps, the semiconductor wafer is heated. 3. A first step of coating the element surface of the semiconductor wafer, on which the elements are formed, with a photoresist that is narrower than the element surface and is easily dissolved by a chemical liquid even if heat is selectively applied, and Second step of applying a coating agent resistant to chemicals on the entire surface, a third step of attaching the surface to a holding plate, and the opposite surface of the semiconductor wafer is covered with a photoresist except for a portion to be etched. A fourth step, a fifth step of etching-cut from the opposite surface of the semiconductor wafer, a sixth step of removing the photoresist coated in the fourth step with a chemical solution that does not dissolve the coating agent strong in the chemical solution, Thereafter, there is a seventh step of processing the semiconductor wafer in a state of being attached to the holding plate, and an eighth step of peeling the element from the holding plate, and in any one of the above steps The method of manufacturing a semiconductor device characterized by having a process of serial semiconductor wafer is heated. 4. A first step of selectively covering the element surface of the semiconductor wafer on which the elements are formed with a positive resist with a narrower width, and a step of applying a negative resist on the entire surface. The second step, the third step of attaching the surface to the holding plate, the fourth step of covering the opposite surface of the semiconductor wafer with a positive resist, except for the planned etching portion, and the etch cut from the opposite surface. A fifth step of, and a sixth step of removing the positive resist coated in the fourth step with a positive resist release agent that does not dissolve the negative resist,
After that, there is a seventh step of processing the wafer in a state of being attached to the holding plate, and an eighth step of peeling the element from the holding plate, and a treatment in which the wafer is heated in any of the above steps. A method of manufacturing a semiconductor device, comprising: