CN1787171A - Method for Improving Capacitance Performance of Metal-Dielectric-Metal Structure - Google Patents

Abstract

The invention relates to the technical field of semiconductor devices, in particular to a method for improving the quality of a metal-dielectric-metal (MIM) capacitor in a semiconductor passive element manufacturing process. The method comprises the following steps: step 1: photoetching and forming a capacitor lower plate pattern on a substrate; step 2: sequentially evaporating titanium/gold/titanium to form a lower capacitor plate; and step 3: depositing a dielectric layer; and 4, step 4: manufacturing an air bridge; and 5: and photoetching the upper electrode plate pattern, and forming the upper electrode plate by adopting an electroplating method. The method has the advantages of simple process, low cost and good repeatability, and the characteristics of the obtained capacitor device are greatly improved compared with the traditional process.

Description

Methods for Improving Capacitive Performance of Metal-Dielectric-Metal Structures

technical field

The invention relates to the technical field of semiconductor devices, and relates to a method for improving the quality of metal-medium-metal (MIM) capacitors in the manufacturing process of semiconductor passive components. New process methods formed in the process of devices and circuits.

Background technique

In Microwave Monolithic Integrated Circuit (MMIC), a large number of passive devices and active devices will be integrated on the same chip, which is one of the important signs that Microwave Monolithic Integrated Circuit (MMIC) is different from traditional integrated circuits. In microwave monolithic integrated circuit (MMIC) design, passive devices are often used in various sub-circuits such as matching networks, DC bias networks, phase conversion and filters, and the quality of capacitors in passive devices will directly affect It affects the reliability of the entire microwave monolithic integrated circuit (MMIC). In the microwave field, capacitors mostly use covered capacitors, that is, metal-dielectric-metal structures. This structure has a large capacitance per unit area and can effectively reduce the chip area. It is widely used in low-impedance matching in microwave monolithic integrated circuits (MMICs). circuit, bypass and DC blocking circuit.

In the current domestic process flow, the main process flow for making metal-dielectric-metal capacitors is as follows:

1. Glue coating, photolithography out of the lower plate.

2. Evaporate the lower plate metal gold.

3. The dielectric layer is grown by plasma enhanced chemical vapor deposition (PECVD).

4. Apply glue, photolithographically cut out the openings, and use dry/wet methods to remove the dielectric layer at the holes.

5. Apply glue and photo-etch the bridge deck.

6. Coating by sputtering.

7. Glue coating, photolithography out of the upper plate.

8. Electroplating completes the air bridge and the upper plate.

9. Remove the plating layer.

However, there are some defects in this method: first, a dielectric layer is directly deposited on the metal gold of the lower plate, because the adhesion between the gold and the dielectric is not good, which affects the surface condition of the metal lower plate, and the dielectric is directly deposited on the lower plate. Such a surface will affect the growth of the dielectric layer, thereby reducing the compactness of the dielectric, reducing the quality of the dielectric layer, resulting in a large leakage of the capacitor, a decrease in the quality factor Q value, and a low breakdown voltage. Secondly, in order to improve the quality of capacitance, people generally use methods to improve the dielectric layer, such as thickening the dielectric layer and using different deposition methods, but thickening the dielectric layer will reduce the unit capacitance value and increase the chip area. The method of depositing a dielectric will greatly increase the chip manufacturing cost and increase the complexity of the process.

Contents of the invention

The present invention proposes a new method for making the lower metal plate of a capacitor, the main purpose of which is: 1. improve the adhesion of the capacitor dielectric layer and the lower metal plate; Growth quality; 3. Improve a series of problems such as metal-dielectric-metal capacitance DC and microwave characteristics.

In order to achieve the above object, the technical solution of the present invention is to provide a method for improving the capacitance performance of the metal-dielectric-metal structure, which is applied in the metal-dielectric-metal (MIM) covering capacitance manufacturing process of semiconductor passive devices, including the following Steps (as shown in Figure 10):

Step 1: On the substrate, photolithography forms the lower plate pattern of the capacitor;

Step 2: Evaporate titanium/gold/titanium in sequence to form the lower plate of the capacitor;

Step 3: depositing a dielectric layer;

Step 4: Make the air bridge;

Step 5: Photolithographically engraving the pattern of the upper plate, and forming the upper plate by electroplating.

In the method for improving the capacitance performance of the metal-dielectric-metal structure, the substrate is an aluminum nitride substrate.

The method for improving the capacitance performance of the metal-dielectric-metal structure includes sequentially evaporating titanium/gold/titanium, wherein the thickness of the titanium layer is ≤200 Å, and the thickness of the gold layer is ≤1 μm.

In the method for improving the capacitance performance of the metal-medium-metal structure, the deposition of the dielectric layer is to grow the dielectric layer by plasma enhanced chemical vapor deposition, and the dielectric layer is a silicon nitride layer with a thickness of ≤3000 Å.

In the method for improving the capacitive performance of a metal-dielectric-metal structure, the upper plate is a single layer or a double layer; in the case of a single layer, it is a gold layer; in the case of a double layer, the lower layer is a titanium layer, and the upper layer is a gold layer.

The invention uses multi-layer metal to make the lower plate of the capacitor. When evaporating the lower plate, a titanium/gold/titanium multi-layer structure is used, and then a dielectric layer is deposited to improve the adhesion between the medium and the metal and optimize the metal lower plate. The surface condition of the plate is conducive to the growth of the dielectric layer, and the purpose of improving the microwave and DC performance of the metal-dielectric-metal structure capacitance.

The method for making the lower pole plate with multi-layer metal in the present invention effectively improves the adhesion between the metal of the lower pole plate and the medium by improving the manufacturing method of the metal of the lower pole plate, and at the same time optimizes the surface condition of the lower pole plate, which is more conducive to the medium The growth of the layer, thus effectively improving the quality of the medium, makes the capacitor greatly improved in terms of high voltage resistance, reduced leakage current, and Q value of the quality factor. The process method of the invention is simple, low in cost, and good in repeatability. The characteristics of the obtained capacitor device are greatly improved compared with the traditional process.

Description of drawings

Figure 1: a schematic top view of the metal-dielectric-metal capacitor of the present invention;

Figure 2: Cross-sectional view of a metal-dielectric-metal capacitor made by a traditional process;

Fig. 3: is the cross-sectional view of the metal-dielectric-metal capacitor A of the present invention in Fig. 1;

Figure 4: DC leakage comparison of 200×200μm ² capacitors;

Fig. 5: the metal-dielectric-metal capacitance test chart that the inventive process makes;

Figure 6: Metal-dielectric-metal capacitance test diagram made by traditional technology;

Fig. 7: the metal-dielectric-metal capacitance quality factor Q value test chart that the inventive process makes;

Fig. 8: the metal-dielectric-metal capacitance quality factor Q value test chart that the process of the present invention makes;

Fig. 9: the top view (optical photo) of the metal-dielectric-metal capacitor made by the process of the present invention;

Fig. 10: Process flow diagram of the metal-dielectric-metal capacitor of the present invention.

Detailed ways

See Figure 1, Figure 3, and Figure 10. Figure 1 is a schematic top view of the metal-dielectric-metal capacitor of the present invention, Figure 3 is a cross-sectional view of the metal-dielectric-metal capacitor of the present invention in Figure 1, and Figure 10 is a process flow chart of the metal-dielectric-metal capacitor of the present invention. As shown in FIG. 3 , the structure of the metal-dielectric-metal capacitor of the present invention is: on the surface of the substrate 1 , a titanium layer 2 , a gold layer 8 , and a titanium layer 2 are fixed in sequence, and the three layers constitute the lower plate 3 . The dielectric layer 4 is affixed to the titanium layer 2 on the upper surface of the central area of the lower plate 3, and the plating layer 5 is affixed to the upper surface of the peripheral area of the dielectric layer 4 and the middle gold layer 8, and the upper surface of the plating layer 5 is affixed to the upper plate 6 , The upper board 6 is made of metal material. The right end of the metal-dielectric-metal capacitor is provided with an air bridge 7 .

The present invention can be applied to the production of metal-medium-metal (MIM) structure capacitors on any substrate, and the present invention is described in detail below in conjunction with the production process, as shown in Figure 10:

1. To make the lower plate, since we use an aluminum nitride substrate with a flatness of ±150 Å, the adhesion between the substrate and the metal of the lower plate needs to be considered. This problem also exists on other substrates. The adhesion between the lower plate and the dielectric layer to be deposited also needs to be considered. At the same time, since the medium is directly deposited on the surface of the lower plate, a good surface condition is the guarantee of a high-quality growth medium. Based on these three points, the test A multilayer metal structure of titanium layer 2/gold layer 8/titanium layer 2 (200 Å/1 μm/200 Å) was selected to form the lower plate 3 of the metal-dielectric-metal capacitor by evaporation.

2. Deposition of dielectric layer The dielectric layer 4 is grown by plasma enhanced chemical vapor deposition (PECVD), and the dielectric layer 4 is silicon nitride (Si ₃ N ₄ ) with a thickness of 3000 Å. The medium is grown on the capacitor metal lower plate 3 of the new structure, and the compactness of the medium is improved due to the optimization of the surface condition.

3. The bridge surface 7 is photolithography, and the metal coating 5 is sputtered.

4. Make the upper pole plate 6, and the metal of the upper pole plate 6 is also closely connected with the dielectric layer 4. Here, titanium/gold is used as the metal of the upper pole plate 6 to improve the adhesion between the upper pole plate 6 and the medium of the capacitor.

5. Test analysis is shown in Table 1:

Table 1: Comparison table of microwave test results under different processes New Process Test Results Traditional craft test results Capacitance 3.1 picofarad (pF) (4GHz) 3.6 picofarads (pF) (4GHz) Quality factor Q value 41(6GHz) 12(6GHz) Dielectric constant 6.692(4GHz) 6.16(4GHz)

As can be seen from the DC test figure 4, the metal-dielectric-metal capacitor adopting the new process of the present invention has an order of magnitude lower leakage current at the same voltage than the traditional process, greatly improving the withstand voltage performance of the device, and the Q value of the quality factor Also there is obvious promotion in the whole frequency band (0.1GHz-15.1GHz), table 1 has listed the comparison of each parameter of capacitance performance, as shown in Figure 7, 8, under 6GHz, the capacitance quality factor Q value of the new technology of the present invention There are still 41, while the traditional craft pieces are down to 12. Can read capacitance value from Fig. 5, 6, the adopting of new technology of the present invention makes capacitance value drop to 3.1pF from 3.6pF, but also shows in Fig. 5, the sheet resonant frequency of new technology is raised to 14GHz, is more conducive to like this The application of the device in the microwave field also increases the dielectric constant from 6.16 to 6.69, indicating that the density of the medium is better and the quality is higher.

Fig. 9 is an optical photo of the metal-dielectric-metal capacitor produced by the process of the present invention.

Claims (5)

1. a method that improves metal-dielectric-metal structure capacitive property is applied to it is characterized in that in metal-dielectric-metal covering electric capacity manufacture craft of semiconductor passive device, comprises the steps:

Step 1: on substrate, photoetching forms electric capacity bottom crown figure;

Step 2: evaporate titanium/gold/titanium successively and form the electric capacity bottom crown;

Step 3: dielectric layer deposited;

Step 4: make air bridges;

Step 5: photoetching top crown figure, adopt electro-plating method to form top crown.

2. the method for raising metal-dielectric according to claim 1-metal structure capacitive property is characterized in that described substrate is an aluminium nitride substrate.

3. the method for raising metal-dielectric according to claim 1-metal structure capacitive property is characterized in that, the described titanium/gold/titanium that evaporates successively, and wherein, titanium layer is thick≤200 , golden bed thickness≤1 μ m.

4. the method for raising metal-dielectric according to claim 1-metal structure capacitive property is characterized in that, described dielectric layer deposited is that dielectric layer is silicon nitride layer, and is thick≤3000 with plasma reinforced chemical vapour deposition method somatomedin layer.

5. the method for raising metal-dielectric according to claim 1-metal structure capacitive property is characterized in that described top crown is individual layer or bilayer; During individual layer, be the gold layer, when double-deck, lower floor is a titanium layer, and the upper strata is the gold layer.

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