Method and apparatus for removing polysilicon sacrificial gates in a gate-last process

Abstract

The application discloses a method and device for removing polycrystalline silicon sacrificial gate in a back gate process, and belongs to the technical field of semiconductors. The method solves the problem of polycrystalline silicon residue at the bottom of a gate groove in the prior art. The method for removing polycrystalline silicon sacrificial gate adopts a polycrystalline silicon etchant to perform wet etching on polycrystalline silicon to form a groove without polycrystalline silicon residue, and the polycrystalline silicon etchant contains isopropyl alcohol. The polycrystalline silicon etchant containing isopropyl alcohol can obviously reduce surface tension, so that the polycrystalline silicon etchant can fully contact with the polycrystalline silicon residue at the bottom of the gate groove and strengthen the reaction, thereby solving the problem of polycrystalline silicon residue.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of semiconductor, and particularly relates to a method and device for removing polysilicon sacrificial gate in a gate-last process. BACKGROUND

[0002] The main device in integrated circuits, especially in very large scale integrated circuits, is metal-oxide-semiconductor (MOS) field effect transistor, simply referred to as MOS transistor. Since the MOS transistor was invented, its geometric size has been continuously reduced. In this case, various practical and fundamental limitations and technical challenges begin to appear, and further reduction of device size is becoming increasingly difficult. In the process of reducing the transistor device, the higher gate leakage current caused by the reduction of the gate oxide layer thickness. For this reason, the solution that has been proposed is to replace the traditional heavily doped polysilicon gate and silicon dioxide (or silicon oxynitride) gate dielectric layer with a metal gate and a high dielectric constant (K) gate dielectric layer.

[0003] In the gate-last semiconductor process, in the process of replacing the polysilicon gate with a metal gate to improve the performance of the device, the dummy polysilicon gate needs to be removed first, and then the metal gate is replaced.

[0004] However, in the existing dummy polysilicon gate removal process using alkaline solution for wet etching, the problem of polysilicon residue at the bottom of the gate trench occurs, as shown in FIG. 1, which affects the conductivity of the semiconductor device. Even if the time of the dummy polysilicon gate removal process is increased, this problem cannot be effectively reduced, and even the problem of over-etching of the gate oxide layer may occur. Figure 1 SUMMARY

[0005] In view of the above analysis, the present application aims to provide a method and device for removing polysilicon sacrificial gate in a gate-last process, which solves the problem of polysilicon residue at the bottom of the gate trench in the prior art.

[0006] The main purpose of the present application is achieved by the following technical solutions:

[0007] The present application provides a method for removing polysilicon sacrificial gate in a gate-last process, which uses a polysilicon etchant to wet etch the polysilicon to form a trench without polysilicon residue. The polysilicon etchant contains isopropyl alcohol.

[0008] In one possible design, the polysilicon etchant also contains an alkaline solution, which is ammonia or tetramethylammonium hydroxide, and the alkaline solution is diluted with deionized water.

[0009] In one possible design, the alkaline solution, isopropyl alcohol and deionized water are mixed uniformly in a chemical medicine mixing tank and then enter the etchant supply line. ​

[0010] In a possible design, the alkali solution and the deionized water are added into the chemical mixture tank, mixed uniformly, and then enter the etchant supply line, and isopropanol is added into the etchant supply line.

[0011] In a possible design, the chemicals in the chemical mixture tank are sequentially added into the heater and the filter through the circulating pump, and then circulated to the chemical mixture tank.

[0012] In a possible design, the volume ratio of the alkali solution to the deionized water is 1:2-1:10, and the volume of the isopropanol is 0.5%-5% of the volume of the mixed solution of the alkali solution and the water.

[0013] In a possible design, the etching temperature of the etchant is 30-80 DEG C.

[0014] In a possible design, the flow rate of the etchant is 600-2500 ml / min.

[0015] The application also provides a device for removing the polysilicon sacrificial gate in the back gate process, which comprises a chemical mixture tank, a chemical supply line, a chemical heating and filtering circulation pipeline, and an etchant supply line.

[0016] The upper part of the chemical mixture tank is provided with all or part of the chemical supply line.

[0017] The side of the chemical mixture tank is provided with the chemical heating and filtering circulation pipeline, which is used for heating and filtering the chemicals required by the polysilicon etchant; along the circulation direction, the circulation pump, the heater and the filter are sequentially arranged on the chemical heating and filtering circulation pipeline.

[0018] The bottom of the chemical mixture tank is provided with the etchant supply line, which is used for supplying the etchant; when part of the chemical supply line is arranged on the upper part of the chemical mixture tank, the remaining chemical supply line is arranged on the etchant supply line.

[0019] In a possible design, the chemical supply line comprises a deionized water supply line, an alkali solution supply line and an isopropanol supply line; the deionized water supply line, the alkali solution supply line and the isopropanol supply line are arranged on the upper part of the chemical mixture tank.

[0020] In a possible design, the chemical supply line comprises a deionized water supply line, an alkali solution supply line and an isopropanol supply line; the deionized water supply line and the alkali solution supply line are arranged on the upper part of the chemical mixture tank, and the isopropanol supply line is arranged on the etchant supply line.

[0021] Compared with the prior art, the application can at least achieve one of the following technical effects:

[0022] 1) The wet etching method of the present application uses isopropyl alcohol (IPA) in the polysilicon etchant, which can significantly reduce the surface tension of the polysilicon etchant, so that it can fully contact with the residual polysilicon at the bottom of the gate trench, strengthen the reaction, and thus solve the problem of residual polysilicon. And it will not cause the reduction of the thickness of the gate oxide layer because of the need to extend the etching time.

[0023] 2) The upper part of the chemical tank is provided with all or part of the medicine supply line; the isopropyl alcohol supply line is arranged on the etchant supply line, when the etching process does not need IPA, only need to stop the supply of IPA, do not need to replace the solution in the chemical tank as a whole; or the isopropyl alcohol supply line is arranged on the upper part of the chemical tank, the chemical tank can make the medicine mixing more uniform, the addition of IPA dosage control is more accurate, and the structure of the polysilicon removal device is simple and the cost is low.

[0024] 3) The chemical tank is provided with a medicine heating and filtering circulation pipeline on one side; along the circulation direction, a circulating pump, a heater and a filter are sequentially arranged on the medicine heating and filtering circulation pipeline. The heater heats the etchant to achieve the ideal reaction rate, so as to achieve the ideal etching effect; the filter can filter the particles in the etchant to prevent impurities from blocking the etchant supply line during etching.

[0025] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be achieved and obtained by the structure specifically pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0026] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings:

[0027] Figure 1 Effect diagram of removing polysilicon for prior art;

[0028] Figure 2 Effect diagram of removing polysilicon for the present application;

[0029] Figure 3 Schematic diagram of removing polysilicon device for the present application Figure 1 ;

[0030] Figure 4 Schematic diagram of removing polysilicon device for the present application Figure 2 ;

[0031] Figure 5 Schematic diagram of removing polysilicon device for comparative example 1.

[0032] Reference signs

[0033] 1-Semiconductor substrate; 2-Interface layer; 3-Sacrificial gate; 4-Dielectric layer; 5-Sidewall; 6-Chemical mixing tank; 7-Deionized water supply line; 8-Alkali supply line; 9-Isopropanol supply line; 10-Etching agent supply line; 11-Circulation pump; 12-Heater; 13-Filter. Detailed Implementation

[0034] Embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0035] The accompanying drawings illustrate various structural schematics according to embodiments of the present disclosure. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0036] In the context of this disclosure, when a layer / element is referred to as being "above" another layer / element, the layer / element may be directly above the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "above" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.

[0037] The embodiments of this application are applied to the removal of polysilicon sacrificial gates in post-gate processes. The following will describe how to remove the sacrificial gate using the technical solution of this invention, according to an embodiment of the present invention.

[0038] like Figure 1 , Figure 2 As shown, the sacrificial gate and source / drain formation in the replacement gate process have been completed on the semiconductor substrate 1. An interface layer 2 is formed on the semiconductor substrate 1, and in some embodiments, a gate dielectric layer (not shown) may also be formed. A sacrificial gate 3, sidewalls 5 surrounding the sacrificial gate 3, and a dielectric layer 4 are located on the interface layer 2. In addition, source / drain regions are also formed on the semiconductor substrate 1, which are not shown in the figure.

[0039] Figure 2The formation of the transistor components in the semiconductor substrate 1 can be performed according to conventional techniques. For example, a gate dielectric layer and a sacrificial gate layer can be formed on the semiconductor substrate 1, the sacrificial gate layer can be etched to form a sacrificial gate, a sidewall can be formed outside the sacrificial gate, and a source / drain region can be formed. Finally, an interlayer dielectric layer can be deposited on the entire semiconductor substrate and CMP can be performed to expose the top of the sacrificial gate. The embodiments of the present application are not limited in this regard.

[0040] The sacrificial gate 3 of the present application is a polysilicon sacrificial gate. In order to remove the residual polysilicon in the bottom region of the gate trench, the wettability of the polysilicon etchant in the wet etching process needs to be improved. Wettability refers to the ability or tendency of a liquid to spread on a solid surface. The contact angle θ is the minimum 0° and the maximum 180°. The smaller the contact angle, the better the wettability. When θ = 0, the liquid completely wets the solid surface, the liquid spreads on the solid surface, and the smaller the surface tension of the liquid, the better the wettability, the larger the contact area between the liquid and the solid, and the more complete the reaction. Microstructuring a surface will amplify the surface tension. A hydrophobic surface (with a contact angle greater than 90°) will become more hydrophobic after microstructuring, and its new contact angle will be larger than the original. However, a hydrophilic surface (with a contact angle less than 90°) will become more hydrophilic after microstructuring, and its new contact angle will be smaller than the original. Polysilicon itself is hydrophobic, and the residual polysilicon in the bottom of the gate trench is more hydrophobic after microstructuring, making it more difficult to contact and react with the polysilicon etchant.

[0041] The polysilicon etchant used in the wet etching process of the present application contains isopropyl alcohol (IPA). IPA can significantly reduce the surface tension of the polysilicon etchant, allowing it to fully contact and react with the residual polysilicon in the bottom of the gate trench, thereby solving the problem of residual polysilicon, as shown in FIG. 2. Figure 2

[0042] The polysilicon etchant also includes a lye, which is ammonia or tetramethylammonium hydroxide (TMAH), and the lye is diluted with deionized water.

[0043] Specifically, the volume ratio of lye to deionized water is 1:2 to 1:10, such as 1:4, 1:6, 1:8, etc.; isopropyl alcohol is 0.5% to 5% (volume fraction) of the mixture of lye and water, such as 1%, 3%, etc. If the proportion of lye is too low, etching cannot be performed, and if it is too high, etching consistency will be poor. If the content of isopropyl alcohol is too low, it will not achieve the effect of adding isopropyl alcohol, and if it is too high, it will cause the etching ability to decrease and the cost to be too high.

[0044] ​The temperature of the polysilicon etchant is 30-80°C. If the temperature is too low, the process time will be increased and the production capacity will be reduced. If the temperature is too high, the consistency will be poor. The flow rate of the polysilicon etchant is 600-2500 ml / min. If the flow rate is too low, the consistency will be poor and the process time will be increased when processing the whole wafer. If the flow rate is too high, the cost will be increased and the control effect of the valves and other parts will be different, which will cause poor uniformity.

[0045] The isopropyl alcohol is added by directly adding the lye, isopropyl alcohol and deionized water into the chemical mixing tank 6 and mixing uniformly. The chemical mixing tank 6 can make the mixing of chemicals more uniform, the dosage of IPA added more accurate, and the structure of the polysilicon removal device simpler and the cost lower. However, when the liquid is changed, the whole solution in the chemical mixing tank 6 needs to be replaced, i.e. when the process does not need IPA, the whole solution in the chemical mixing tank 6 needs to be replaced.

[0046] Another method of adding isopropyl alcohol is to first add the lye and deionized water into the chemical mixing tank 6 and mix uniformly, then connect the isopropyl alcohol supply line to the etchant supply line 10, and mix in real time during etching. The real-time mixing of IPA into the etchant supply line 10 requires a separate flow meter or a quantitative valve to control the supply amount of IPA and cooperate with the etchant, and the system is relatively complex. However, when the etching process does not need IPA, only the supply of IPA needs to be stopped, and the whole solution in the chemical mixing tank 6 does not need to be replaced.

[0047] After the etching of the sacrificial gate is completed, a metal gate can be formed in the gate trench by conventional techniques, thereby completing the replacement gate process. For example, the metal gate can be formed by directly filling metal at the original position of the dummy gate and removing the excess metal by CMP. According to some embodiments of the present application, a gate dielectric layer, a work function metal layer and a gate conductor layer can also be formed in the gate trench first.

[0048] The present application also discloses a device for removing polysilicon, which can be used in the gate replacement process to remove polysilicon, as shown in Figure 3 、 Figure 4 The device for removing polysilicon includes a chemical mixing tank 6, chemical supply lines and an etchant supply line 10. The chemical mixing tank 6 is used for processing chemicals used by the polysilicon etchant. Each chemical supply line is used for inputting one kind of chemical into the chemical mixing tank 6 or the etchant supply line 10. The etchant supply line 10 is used for outputting the etchant.

[0049] The chemical supply lines include a deionized water supply line 7, a lye supply line 8 and an isopropyl alcohol supply line 9. The deionized water supply line 7 and the lye supply line 8 are arranged on the chemical mixing tank 6. The isopropyl alcohol supply line 9 has two arrangement methods: one is arranged on the chemical mixing tank 6, and the other is arranged on the etchant supply line 10.

[0050] The chemical medicine mixing tank 6 is provided with a medicine heating and filtering circulation pipeline, which is sequentially provided with a circulation pump 11, a heater 12 and a filter 13 from top to bottom. The circulation pump 11 is used to pump the liquid in the chemical medicine mixing tank 6 from the bottom and flow into the tank from the top, which is used to promote the mixing of the chemical medicine used for etchant and to pump the etchant from the chemical medicine mixing tank 6 into the circulation pipeline to filter and heat the etchant. The etchant is filtered to prevent the existence of insoluble impurities in the chemical medicine, which can block the etchant supply line 10 during etching. If the etchant is recycled, it is necessary to filter even multiple times to remove the particles in the solution. The etchant is heated to a set temperature to make the etching reach the ideal reaction rate and etching effect. The chemical reaction is related to temperature. Generally, the higher the temperature, the faster the reaction. However, in the semiconductor process, it is not necessary to make the reaction rate faster. The temperature needs to be controlled at a suitable temperature. The temperature of the polysilicon etchant in the present application is controlled at 30-80℃. If the temperature is too low, the process time will be increased and the production capacity will be reduced. If the temperature is too high, the consistency will be poor. The heater can control the heating temperature with an accuracy of ±0.5, and the filter can filter particles above 0.2um.

[0051] When the isopropyl alcohol supply line 9 is arranged on the etchant supply line 10, a second heater is arranged on the isopropyl alcohol supply line 9 to prevent the addition of isopropyl alcohol from reducing the temperature of the etchant and thus affecting the reaction rate. At this time, a quantitative valve or flow meter is arranged on the isopropyl alcohol supply line 9 to adjust the amount of IPA added into the etchant supply line 10. The amount of IPA injection is controlled by the quantitative valve or flow meter.

[0052] Example 1

[0053] The polysilicon etchant includes isopropyl alcohol, ammonia and deionized water. The isopropyl alcohol is added from the top of the chemical medicine mixing tank 6. The volume ratio of the lye to the deionized water is 1:2. The isopropyl alcohol accounts for 5% (volume fraction) of the mixed solution of the lye and water. The temperature of the polysilicon etchant is 30℃, and the etchant flow rate during etching is 1000ml / min.

[0054] In the pseudo-polysilicon gate removal process of wet etching, there is no polysilicon residue in the etching of the gate trench bottom area, and there is no problem of over-etching of the gate oxide layer.

[0055] Example 2

[0056] The polysilicon etchant includes isopropyl alcohol, ammonia and deionized water, the isopropyl alcohol is added from the etchant supply line 10, the volume ratio of the alkali solution to the deionized water is 1:10, the isopropyl alcohol is 0.5% (volume fraction) of the mixed solution of the alkali solution and water, the temperature of the polysilicon etchant is 80°C, and the etchant flow rate is 2000 ml / min during etching.

[0057] In the pseudo-polysilicon gate removal process of wet etching, there is no polysilicon residue in the etching of the bottom area of the gate trench, and there is no problem of over-etching of the gate oxide layer.

[0058] Example 3

[0059] The polysilicon etchant includes isopropyl alcohol, TMAH and deionized water, the isopropyl alcohol is added from above the chemical mixing tank 6, the volume ratio of the alkali solution to the deionized water is 1:5, the isopropyl alcohol is 3% (volume fraction) of the mixed solution of the alkali solution and water, the temperature of the polysilicon etchant is 50°C, and the etchant flow rate is 1500 ml / min during etching.

[0060] In the pseudo-polysilicon gate removal process of wet etching, there is no polysilicon residue in the etching of the bottom area of the gate trench, and there is no problem of over-etching of the gate oxide layer.

[0061] Example 4

[0062] The volume ratio of the alkali solution to the deionized water is 1:8, and the isopropyl alcohol is 2% (volume fraction) of the mixed solution of the alkali solution and water. The isopropyl alcohol, ammonia and deionized water are added into the chemical mixing tank in proportion from the isopropyl alcohol supply line, the alkali solution supply line and the deionized water supply line respectively. The liquid in the chemical mixing tank is pumped out from the bottom, heated and filtered, and then reenters the chemical mixing tank. The polysilicon etchant in the chemical mixing tank is mixed uniformly and heated to 60°C.

[0063] During etching, the polysilicon etchant is sent from the etchant supply line to the top of the polysilicon to be etched. The etchant flow rate is 1800 ml / min during etching.

[0064] In the pseudo-polysilicon gate removal process of wet etching, there is no polysilicon residue in the etching of the bottom area of the gate trench, and there is no problem of over-etching of the gate oxide layer.

[0065] In the above description, the technical details of the patterning of each layer, etching, etc. are not described in detail. However, those skilled in the art should understand that various technical means can be used to form layers, regions, etc. of the desired shape. In addition, those skilled in the art can also design methods that are not exactly the same as the methods described above in order to form the same structure. In addition, although each embodiment is described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination.

[0066] The above description is only the preferred embodiment of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method for removing a polysilicon sacrificial gate in a post-gate process, characterized in that, The polycrystalline silicon is etched by a polycrystalline silicon etchant to form a trench without polycrystalline silicon residue, the polycrystalline silicon etchant contains isopropyl alcohol, and the isopropyl alcohol reduces the surface tension of the polycrystalline silicon etchant; the polycrystalline silicon etchant also contains lye, and the lye is diluted by deionized water; the volume ratio of the lye to the deionized water is 1:2-1:10, and the volume of the isopropyl alcohol is 0.5%-5% of the volume of the mixed solution of the lye and the water; The etching temperature of the etchant is 30°C or 80°C, and the flow rate of the etchant is 600-2500 ml / min; The method for removing the polycrystalline silicon sacrificial gate in the back gate process is realized by a device for removing the polycrystalline silicon sacrificial gate in the back gate process, and the device comprises a chemical medicine mixing tank, medicine supply lines, a medicine heating and filtering circulation pipeline and an etchant supply line; The upper part of the chemical medicine mixing tank is provided with all or part of the medicine supply lines; The side of the chemical medicine mixing tank is provided with the medicine heating and filtering circulation pipeline, which is used for heating and filtering the chemical medicines required by the polycrystalline silicon etchant; along the circulation direction, the medicine heating and filtering circulation pipeline is sequentially provided with a circulation pump, a heater and a filter; the heater controls the heating temperature accuracy to be ±0.5, and the filter filters particles above 0.2 μm; The bottom of the chemical medicine mixing tank is provided with the etchant supply line for supplying the etchant; when part of the medicine supply lines are arranged at the upper part of the chemical medicine mixing tank, the remaining medicine supply lines are arranged on the etchant supply line; The medicine supply lines comprise deionized water supply lines, lye supply lines and isopropyl alcohol supply lines; The deionized water supply lines and the lye supply lines are arranged at the upper part of the chemical medicine mixing tank, and the isopropyl alcohol supply lines are arranged on the etchant supply line; a second heater is arranged on the isopropyl alcohol supply line; The wet etching is performed, and there is no polycrystalline silicon residue in the etching of the bottom area of the gate trench, and no over-etching of the gate oxide layer is caused.

2. The method of removing a polysilicon sacrificial gate in a gate-last process of claim 1, wherein, The lye is ammonia water or tetramethylammonium hydroxide.

3. The method of removing a polysilicon sacrificial gate in a gate-last process of claim 2, wherein, After the lye and the deionized water are mixed uniformly in the chemical medicine mixing tank, the lye and the deionized water enter the etchant supply line, and the isopropyl alcohol is added to the etchant supply line.

4. The method of removing a polysilicon sacrificial gate in a gate-last process of claim 3, wherein, The medicines in the chemical medicine mixing tank enter the heater and the filter in sequence through the circulation pump and then are circulated to the chemical medicine mixing tank.

5. The method of removing polysilicon sacrificial gates in a gate-last process of claim 2, wherein, The volume ratio of the lye to the deionized water is 1:5-1:8, and the volume of the isopropyl alcohol is 2%-3% of the volume of the mixed solution of the lye and the water.

6. The method of removing a polysilicon sacrificial gate in a gate-last process of claim 2, wherein, The flow rate of the etchant is 1000-2000 ml / min.

7. An apparatus for removing polysilicon sacrificial gates in a gate-last process for the method of any one of claims 1 to 6, characterized in that, The device comprises a chemical medicine mixing tank, medicine supply lines, a medicine heating and filtering circulation pipeline and an etchant supply line; The upper part of the chemical medicine mixing tank is provided with all or part of the medicine supply lines; The side of the chemical medicine mixing tank is provided with the medicine heating and filtering circulation pipeline, which is used for heating and filtering the chemical medicines required by the polycrystalline silicon etchant; along the circulation direction, the medicine heating and filtering circulation pipeline is sequentially provided with a circulation pump, a heater and a filter; the heater controls the heating temperature accuracy to be ±0.5, and the filter filters particles above 0.2 μm; The chemical medicine mixing tank is provided with an etchant supply line at the bottom for supplying etchant containing isopropyl alcohol which reduces the surface tension of polysilicon etchant; the etchant also contains lye which is diluted with deionized water, the volume ratio of lye to deionized water being 1:2-1:10, the volume of isopropyl alcohol being 0.5%-5% of the volume of the mixed solution of lye and water, the etching temperature of the etchant being 30°C or 80°C, and the etchant flow being 600-2500ml / min; the upper part of the chemical medicine mixing tank is provided with some medicine supply lines, and the rest of the medicine supply lines are arranged on the etchant supply line; The medicine supply lines include deionized water supply lines, lye supply lines and isopropyl alcohol supply lines; The deionized water supply lines, lye supply lines and isopropyl alcohol supply lines are arranged on the upper part of the chemical medicine mixing tank respectively; Or the deionized water supply lines and lye supply lines are arranged on the upper part of the chemical medicine mixing tank respectively, and the isopropyl alcohol supply lines are arranged on the etchant supply line; a second heater is arranged on the isopropyl alcohol supply line.

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