JP2668528B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device in which a capacitor, a bipolar transistor, and the like using a nitride film as a dielectric are formed on a semiconductor substrate. 2. Description of the Related Art A semiconductor device of this type is manufactured by including a process of forming a capacitor using a nitride film (Si ₃ N ₄ layer) as a dielectric in a series of processes for forming a bipolar transistor or the like.
However, if a nitride film serving as a capacitance dielectric is laminated before the step of fabricating a bipolar transistor or the like, an oxide film may be formed on the upper surface of the nitride film by etching or heat treatment performed in a subsequent step. Alternatively, impurities may enter the nitride film, so that the capacitance value of the capacitor, which should be originally determined only by the thickness of the laminated nitride film, changes from an expected value. In order to prevent such a situation from occurring, a nitride film serving as a dielectric of a capacitor is formed after a series of steps of fabricating a bipolar transistor or the like, specifically, between an emitter diffusion step and a contact hole forming step. It was supposed to be laminated. Problems to be Solved by the Invention However, according to the above conventional method, a nitride film is formed on a semiconductor substrate many times as a passivation film, an interlayer insulating film or an antioxidant film for selective oxidation until the emitter diffusion step is completed. Nevertheless, after the emitter diffusion step is completed, a nitride film serving as a dielectric of the capacitor must be further formed, resulting in a disadvantage that the cost is increased. However, a nitride film serving as a dielectric of a capacitor is stacked in a stage prior to a process of fabricating a bipolar transistor or the like, and a nitride film is formed for the purpose of protecting the nitride film when performing etching or heat treatment in a subsequent process. It is only necessary to mask the top, but this increases the number of steps and increases the cost. The present invention has been created under the above background,
It is an object of the invention to provide a method of manufacturing a semiconductor device without the above-mentioned drawbacks. Means for Solving the Problems A method for manufacturing a semiconductor device according to the present invention is a method for manufacturing a semiconductor device in which a capacitor having a nitride film as a dielectric and a bipolar transistor are formed on a semiconductor substrate. In order to solve the problem, after forming a base region of a transistor on a semiconductor substrate, a nitride film is stacked on the semiconductor substrate, contact holes for an emitter and a collector electrode of the transistor are formed, and a conductive layer is formed on the nitride film. After covering with a crystalline silicon layer and patterning the conductive polycrystalline silicon layer, an emitter region of the transistor is formed by heat treatment, and thereafter, electrodes of the capacitor and the transistor are formed. Example Hereinafter, an example of a method for manufacturing a semiconductor device of the present invention will be described with reference to the drawings. FIG. 1 is a process sectional view of a method for manufacturing a semiconductor device. Here, an example will be described in which a nitride film serving as a dielectric of a capacitor is used as a passivation film in a transistor formation region that is a circuit element other than the capacitor. In the stage of FIG. 1 (a), an oxide film 3 is opened on the side 2b of the silicon epitaxial layers 2a and 2b partitioned by the isolation layer 1, and then a P-type impurity is diffused to form a base region 4. Has been done. From this state, as shown in FIG. 1 (b), the oxide film 3 on the surface of the epitaxial layer 2a is removed to diffuse and form the N ⁺ -type impurity region 5 serving as one conductor of the capacitor. Grow. Subsequently, a part of the oxide film 3 'covering the impurity region 5 is removed to expose the impurity region 5 to form a dielectric attachment region.
The layers are laminated by a CVD method (FIG. 1 (c)). Then the first
Proceeding to the stage of FIG. 4D, the oxide film 3 and the nitride film 6 covering a part of the surface of the base region 4 and a part of the epitaxial layer 2b outside the base region 4 are removed, and a thickness of several hundreds to several thousand degrees is removed. A polycrystalline silicon layer 7 doped with N-type impurities is formed to protect the nitride film 6. Next, the polycrystalline silicon layer 7 is patterned and subjected to heat treatment to become the other conductor of the capacitor and protect the nitride film of the dielectric portion, together with the emitter electrode layer 7b, the collector electrode layer 7c and the emitter electrode layer 7c. The layer 8 is formed (FIG. 1E). Then, as shown in FIG. 1 (f), through a contact hole forming step, aluminum deposition and patterning are performed to form capacitor electrodes 9a and 9b, an emitter electrode 10a, a base electrode 10b, and a collector electrode 10c. In this embodiment, the polycrystalline silicon layer 7 is heat-treated while the nitride film 6 serving as the dielectric of the capacitor is protected by the polycrystalline silicon layer 7a, and the impurities contained therein are diffused into the base region 4. The emitter region 8 is formed. Therefore, an oxide film is not formed on the upper surface of the nitride film 6 serving as a dielectric of the capacitor, and impurities do not enter the nitride film 6, and the capacitance value of the capacitor is reduced.
Of the film thickness. Further, when the emitter region 8 is formed, the impurities contained in the polycrystalline silicon layer 7 tend to diffuse into regions other than the emitter region 8. Performance can be improved. Further, the polycrystalline silicon layer 7 serves as a metal stopper for preventing aluminum spikes in the emitter electrode 10a.
Also used as 7b. As described above, the nitride film 6 is used not only as a dielectric of the capacitor but also as a passivation film for preventing a contamination source to the transistor region, while the polycrystalline silicon layer 7 is used.
Is used not only to protect the nitride film 6 but also as a metal stopper for preventing aluminum spikes. Since the nitride film 6 and the polycrystalline silicon layer 7 have a plurality of functions as described above, the number of steps as a whole can be reduced and the cost can be reduced accordingly. As described above, in the case of the method for manufacturing a semiconductor device according to the present invention, the capacitance value of the capacitor is determined only by the thickness of the nitride film. In addition, the nitride film and the polycrystalline silicon layer can have various functions, and the number of steps as a whole can be reduced, which is also advantageous in terms of cost reduction.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) to 1 (f) are process sectional views of a method for manufacturing a semiconductor device according to an embodiment of the present invention. 2a ... Epitaxial layer serving as a capacitor forming region 2b ... Epitaxial layer serving as another circuit element forming region 5 ... Impurity layer 6 serving as one conductor of a capacitor ... Nitride film 7 ... Polycrystalline silicon layer

Claims (1)

(57) [Claims] In a method of manufacturing a semiconductor device in which a capacitor and a bipolar transistor having a nitride film as a dielectric formed on a semiconductor substrate, after forming a base region of the transistor on the semiconductor substrate, a nitride film is stacked on the semiconductor substrate. After forming contact holes for the emitter and collector electrodes of the transistor, cover the nitride film with a conductive polycrystalline silicon layer, pattern the conductive polycrystalline silicon layer, and then form a transistor emitter region by heat treatment. Then, a method of manufacturing a semiconductor device, characterized in that electrodes of a capacitor and a transistor are formed thereafter.