A method of electroless copper plating

Abstract

The application provides a chemical copper electroplating method, which comprises the following steps: providing an intermediate structure, wherein the intermediate structure comprises a groove and a via; in a first electroplating preparation stage, providing a high-speed rotating speed to make the intermediate structure rotate at a high speed; in a second electroplating preparation stage, reducing the rotating speed of the intermediate structure to make the intermediate structure rotate at a low-speed rotating speed; in an electroplating immersion stage, providing an immersion voltage to the intermediate structure, and balancing the potential difference on the surface of the intermediate structure through the immersion voltage; and in an electroplating stage, providing an electroplating current to carry out electroplating growth until the electroplating is completed. The chemical copper electroplating method provided by the application can solve the problem that, in the existing copper electroplating process, the uneven surface of the surface to be electroplated leads to a potential difference, the copper layer grown by electroplating grows at an uneven speed, and holes exist on the growth surface.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing, and in particular to a method for chemically electroplating copper. Background Technology

[0002] As the density of integrated circuits increases, the number and density of conductor interconnects also increase. The resistance-capacitance delay (RC delay) caused by metal interconnects becomes more and more serious. The capacitance delay not only affects the speed of the chip, but also poses a serious threat to the reliability of the chip.

[0003] Compared to aluminum, copper has lower resistance, which effectively reduces capacitance delay. It has replaced aluminum as the interconnect material in advanced processes below 55nm. However, copper has the following drawbacks:

[0004] 1. During the etching process of trenches and vias (All in one, i.e., trend and via etch), sidewall uniformity issues are prone to occur (e.g.) Figure 13 (as shown), and will cause unevenness after subsequent metal seed layer filling;

[0005] 2. It is prone to galvanic cell effect, leading to copper wire corrosion;

[0006] 3. In the copper electroplating process, the plating solution is CuSO4. During this process, the metal seed layer will be corroded by the plating solution and become uneven. This phenomenon will be further aggravated during the CMP process.

[0007] 4. During the copper chemical mechanical polishing (CMP) process, the polishing slurry used can cause corrosion to the copper wires. Figure 12 As shown.

[0008] The industry mainly uses methods such as controlling the interval between processing steps and the humidity and acidity / alkalinity of the environment to effectively solve the galvanic cell effect. However, for the corrosion problem of copper wires by CMP polishing slurry, the main approach is to add triazole methylbenzene (BTA) corrosion inhibitor to the polishing slurry to reduce corrosion in copper wires. However, this cannot completely avoid corrosion and is costly.

[0009] Adding BTA cannot completely solve the corrosion problem in copper wires. The main reason is that there are tiny gaps in the copper wires, and the electroplating solution can corrode the internal metal of the copper layer through these gaps. Therefore, improving the filling quality of the tiny gaps in the copper wires is essential for the preparation of high-quality Cu interconnects. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a chemical electroplating copper method to solve the problem that in the existing copper electroplating process, the unevenness of the surface to be electroplated causes potential difference, resulting in uneven growth rate of the electroplated copper layer and the presence of holes on the growth surface.

[0011] To achieve the above and other related objectives, the present invention provides a method for chemical electroplating copper, the method comprising:

[0012] An intermediate structure is provided, the intermediate structure including trenches and vias;

[0013] In the first electroplating preparation stage, a high-speed rotational speed is provided to make the intermediate structure rotate at high speed.

[0014] In the second electroplating preparation stage, the rotation speed of the intermediate structure is reduced so that the intermediate structure is immersed in water at a low rotation speed.

[0015] During the electroplating water immersion stage, a water immersion voltage is provided to the intermediate structure to balance the potential difference on the surface of the intermediate structure.

[0016] During the electroplating stage, an electroplating current is provided to carry out electroplating growth until the electroplating is completed.

[0017] Optionally, the high-speed rotation speed is between 80 rpm and 170 rpm, and the low-speed rotation speed is between 10 rpm and 14 rpm.

[0018] Optionally, the duration of the first electroplating preparation stage is between 5s and 10s.

[0019] Optionally, the duration of the electroplating immersion stage is greater than or equal to 0.3s, and the immersion voltage is greater than or equal to 0.8V.

[0020] Optionally, the duration of the electroplating immersion stage is 0.5s, and the immersion voltage is 0.8V.

[0021] Optionally, the electroplating stage includes: a first electroplating stage, a second electroplating stage, and a third electroplating stage, wherein,

[0022] The electroplating current in the first electroplating stage is between 4.2A and 4.8A, the electroplating current in the second electroplating stage is between 6.4A and 7A, and the electroplating current in the third electroplating stage is between 37A and 43A.

[0023] Optionally, a metal seed layer is formed on the surface of the trench and the via, and the upper surface of the metal seed layer serves as the surface to be electroplated.

[0024] Optionally, the metal seed layer may be formed using a physical vapor deposition process.

[0025] Optionally, the method for preparing the intermediate structure includes:

[0026] A substrate is provided, and a patterned first mask layer is formed on the upper surface of the substrate;

[0027] The substrate is etched based on the first mask layer to form the trench;

[0028] A patterned second mask layer is formed on the upper surface of the substrate;

[0029] The substrate is etched based on the second mask layer to form the via;

[0030] The metal seed layer is formed on the surface of the trench and the via.

[0031] As described above, the chemical electroplating copper method of the present invention provides an initial water immersion voltage during the electroplating water immersion stage. The initial water immersion voltage can provide a high and stable potential for a certain period of time to the surface to be electroplated during the initial stage of electroplating, balance the potential difference caused by the unevenness of the sidewall surface in the trench and through hole, improve the compactness of copper grain growth, and thus obtain a flat and continuous copper growth interface. Attached Figure Description

[0032] Figure 1 The flowchart shown is a process for the chemical electroplating copper method described in this invention.

[0033] Figure 2 The diagram shown is a schematic representation of the structure after the first mask layer is formed, as described in the embodiment.

[0034] Figure 3 The diagram shown is a schematic representation of the structure after the trench is formed, as described in the embodiment.

[0035] Figure 4 The diagram shown is a schematic representation of the structure for removing the first mask layer as described in the embodiment.

[0036] Figure 5 The diagram shown is a schematic representation of the structure after the second mask layer is formed, as described in the embodiment.

[0037] Figure 6 The diagram shown is a schematic representation of the structure after the via is formed as described in the embodiment.

[0038] Figure 7 The diagram shown is a schematic representation of the structure after removing the first mask layer as described in the embodiment.

[0039] Figure 8 The diagram shown is a structural schematic of the intermediate structure described in the embodiment.

[0040] Figure 9 The diagram shows the structure after copper plating as described in the embodiment.

[0041] Figure 10 The diagram shows the structure after chemical mechanical grinding as described in the embodiment.

[0042] Figure 11 The diagram shows the surface potential distribution of the intermediate structure after it enters the electroplating solution.

[0043] Figure 12 The image shows the surface morphology of copper traces prepared using existing technology.

[0044] Figure 13 The image shows the morphology of the electroplated copper grown on the sidewall of the groove as described in the background art.

[0045] Figure 14 The image shows the surface morphology of copper traces prepared using the chemical electroplating copper method described in this invention.

[0046] Figure 15 The table displays the failure rate statistics under different water inlet voltage parameters.

[0047] Component labeling explanation

[0048] 10, intermediate structure; 11, trench; 12, via; 100, substrate; 110, first mask layer; 120, second mask layer; 130, metal seed layer. Detailed Implementation

[0049] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0050] Please see Figures 1 to 15 It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding and reading. They are not intended to limit the scope of the invention and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention's implementation.

[0051] For ease of description, spatial relative terms such as "above," "on top of," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of an institution or feature as shown in the figures to other institutions or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation beyond the orientation of the institution as described in the figures. For example, if the institution in the figures were inverted, an institution described as "above" or "on top of" other institutions or features would subsequently be positioned as "below" or "under" other institutions or features. Thus, the exemplary term "above" can include both "above" and "below." The institution may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0052] This embodiment provides a chemical electroplating method for copper, such as... Figure 1 As shown, the chemical electroplating copper method includes steps S1) to S5).

[0053] Step S1): Provide an intermediate structure 10, the intermediate structure 10 including a trench 11 and a via 12.

[0054] In this embodiment, as Figure 8 As shown, several trenches 11 and several vias 12 are formed within the intermediate structure 10. Copper is subsequently plated in the trenches 11 to form a copper trace layer, and copper is subsequently plated in the vias 12 to form an interconnection channel connecting the copper trace layer with other metal layers.

[0055] Specifically, the preparation method of the intermediate structure 10 includes steps S11 to S15.

[0056] Step S11): Provide a substrate 100, such as Figure 2 As shown, a patterned first mask layer 110 is formed on the upper surface of the substrate 100.

[0057] In this embodiment, the substrate 100 can be an N-type or P-type silicon substrate. The material of the substrate 100 includes one or more combinations of silicon, germanium, silicon germanide, silicon carbide, gallium arsenide, and indium gallium ionide. The semiconductor substrate 100 can also be a silicon-on-insulator semiconductor substrate or a germanium-on-insulator semiconductor substrate. The first mask layer 110 can be either a photoresist layer or a hard mask layer.

[0058] As one example, the first mask layer 110 is a photoresist layer, and the specific formation method includes: forming a photoresist material layer on the upper surface of the substrate 100 using a coating process, exposing and developing the photoresist material layer, and forming an opening pattern in the photoresist material layer that exposes the substrate 100, thereby obtaining the first mask layer 110.

[0059] As another example, the first mask layer 110 is a hard mask layer; the specific formation method includes: forming a hard mask material layer on the upper surface of the substrate 100, and forming a patterned photoresist layer on the upper surface of the hard mask material layer; etching the hard mask material layer based on the patterned photoresist layer to form an opening pattern in the hard mask material layer that exposes the substrate 100; and removing the patterned photoresist layer to obtain the first mask layer 110.

[0060] Step S12): As Figure 3 As shown, the trench 11 is formed by etching based on the first mask layer 110.

[0061] In this embodiment, a patterned first mask layer 110 is used as a mask, for example, by using a plasma etching process to etch the substrate 100 to form trenches 11, such as... Figure 4 As shown, after the trench 11 is formed, the first mask layer 110 is peeled off by a process such as ashing.

[0062] Step S13): As Figure 5 As shown, a patterned second mask layer 120 is formed on the upper surface of the substrate 100.

[0063] In this embodiment, the method described in step S11) is used to form a patterned second mask layer 120.

[0064] Step S14): As Figure 6 As shown, the via 12 is formed by etching based on the second mask layer 120.

[0065] In this embodiment, a patterned second mask layer 120 is used as a mask. For example, a plasma etching process is used to etch the substrate 100 to form vias 12. Figure 7 As shown, after forming the via 12, the second mask layer 120 is peeled off using an ashing process, for example.

[0066] Step S15): As Figure 8 As shown, the metal seed layer 130 is formed on the surface of the trench 11 and the via 12.

[0067] In this embodiment, for example, a physical sputtering deposition process is used to form a metal seed layer on the surface of the trench 11 and the via 12. The thin metal seed layer has a smooth surface, which can ensure that the copper layer grown by subsequent electroplating has a large grain size and a continuous growth interface. The metal seed layer can be a single-layer metal thin film or a multi-layer metal thin film, and the material of the metal seed layer can be titanium nitride (TiN), titanium (Ti), tantalum nitride (TaN), tantalum (Ta), etc.

[0068] Step S2): In the first electroplating preparation stage, a high-speed rotation speed is provided to make the intermediate structure 10 rotate at high speed.

[0069] In this embodiment, during the first electroplating preparation stage before the intermediate structure is immersed in water (before entering the electroplating solution), a rotating device (not shown) is used to provide the intermediate structure 10 with a pre-immersion rotation speed (between 80 rpm and 170 rpm). High-speed rotation can enhance the friction between the surface of the intermediate structure and the air, change the liquid wetting performance of the surface of the metal seed layer, and thus increase the contact ability between the electroplating solution and the surfaces to be electroplated in the trench 11 and the via 12, making the formed copper dielectric surface more uniform and improving defects (gap, hole, etc.) in the electroplating process.

[0070] Step S3): In the second electroplating preparation stage, reduce the rotation speed of the intermediate structure 10 so that the intermediate structure 10 enters the water at a low rotation speed.

[0071] In this embodiment, in the second electroplating preparation stage before the intermediate structure enters the water (before entering the electroplating solution), in order to prevent the electroplating solution from splashing when the intermediate structure enters the water due to excessive rotation speed, the rotation speed is first reduced, and then the intermediate structure is entered into the water at a low rotation speed (10 rpm to 14 rpm).

[0072] Step S4): During the electroplating water immersion stage, a water immersion voltage is provided to the intermediate structure 10 to balance the potential difference on the surface of the intermediate structure 10.

[0073] In this embodiment, the electroplating water immersion stage refers to the stage in which the intermediate structure is placed in the electroplating solution and enters the movement process of the set electroplating position. Figure 11 Displayed as Figure 8 The surface potential distribution of the structure within the dashed circle after entering the electroplating solution shows that the trench 11 and via 12 are not level with respect to the horizontal plane, and the depth of the trench 11 and the depth of the via 12 are also different. Furthermore, since the trench 11 and via 12 are formed using an etching process, as... Figure 11As shown, its etched sidewalls have high roughness and uneven surfaces. This unevenness creates a difference in surface potential. When the intermediate structure is immersed in water (meaning it enters the electroplating solution), the potential difference ΔU = Φconvex - Φconcave on the convex surface is greater than that on the concave surface. This results in Cu accumulating at the convex surface. 2+ More Cu than that that accumulates at the concave surface 2+ This results in a lower copper growth rate at the concave surface compared to the convex surface, leading to the formation of holes (such as) between the trench 11 and the via 12 during electroplating. Figure 13 As shown in the diagram, the copper growth interface is discontinuous and has gaps. Furthermore, the subsequent chemical mechanical polishing process after electroplating further exacerbates the interstitial corrosion, such as... Figure 12 As shown, this can lead to the copper interconnect linewidth failing to meet design standards or even copper interconnect line breakage.

[0074] By providing an initial water immersion voltage of ≥0.8V for ≥0.3s during the water immersion stage of the chemical electroplating process, a high and stable potential is achieved on the convex and concave surfaces of the trench 11 and via 12 to be electroplated during this stage. This stable potential balances the internal high and low potential difference ΔU caused by the unevenness of the sidewalls in the trench 11 and via 12, thereby affecting the electroplating growth rate on the convex and concave surfaces and ensuring that the growth rates are comparable. This avoids phenomena such as uneven sidewalls and holes (e.g., ...). Figure 14 (As shown).

[0075] It should be noted that, as Figure 15 The image shows the defect rate of the grown copper wire under different voltage values ​​and durations during the electroplating water immersion stage, based on image detection. Figure 15 The data shows that the water immersion voltage provided to the intermediate structure during the electroplating water immersion stage can effectively improve defects such as holes and copper wire breakage. Specifically, when the water immersion voltage is greater than 0.8V and the duration is greater than 0.5s, defects such as holes and copper wire breakage can be effectively avoided.

[0076] Step S5): In the electroplating stage, an electroplating current is provided to carry out electroplating growth until the electroplating is completed.

[0077] In this embodiment, the electroplating stage is divided into three stages: the first electroplating stage, the second electroplating stage, and the third electroplating stage. During electroplating growth, the electroplating rate is positively correlated with the magnitude of the electroplating current. However, if the electroplating current is continuously too high, it will lead to a rough surface of the electroplated copper layer and poor film density. Therefore, the electroplating current provided for the first electroplating stage is between 4.2A and 4.8A to obtain a continuous copper growth interface. Then, the electroplating current provided for the second electroplating stage is between 6.4A and 7A, and then it is increased to the third electroplating stage (electroplating current between 37A and 43A) until the electroplating is completed.

[0078] It should be noted that, as Figure 10 As shown, after electroplating, the copper layer formed by electroplating needs to be thinned using a chemical mechanical polishing process. After thinning, the polishing solution will corrode the copper material, exacerbating defects in the copper layer, such as… Figure 13 As shown, the copper layer prepared by the method described in this embodiment is continuous and has excellent density, which can effectively avoid corrosion in the CMP process.

[0079] In summary, the chemical electroplating copper method of the present invention provides an initial water immersion voltage during the electroplating water immersion stage. The initial water immersion voltage can provide a high and stable potential for a certain period of time to the surface to be electroplated during the initial stage of electroplating, balance the potential difference caused by the unevenness of the sidewall surface in the trench and through hole, improve the compactness of copper grain growth, and thus obtain a flat and continuous copper growth interface.

[0080] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for chemically electroplating copper, characterized in that, The chemical electroplating copper method includes: An intermediate structure is provided, the intermediate structure including trenches and vias; In the first electroplating preparation stage, a high-speed rotational speed is provided to make the intermediate structure rotate at high speed. In the second electroplating preparation stage, the rotation speed of the intermediate structure is reduced so that the intermediate structure is immersed in water at a low rotation speed. During the electroplating water immersion stage, an immersion voltage is provided to the intermediate structure to balance the potential difference caused by the unevenness of the sidewall surface in the trench and the through hole; the electroplating water immersion stage is the process in which the intermediate structure is placed into the electroplating solution and enters the set electroplating position. During the electroplating stage, an electroplating current is provided to carry out electroplating growth until the electroplating is completed.

2. The chemical electroplating copper method according to claim 1, characterized in that, The high-speed rotation speed is between 80 rpm and 170 rpm, and the low-speed rotation speed is between 10 rpm and 14 rpm.

3. The chemical electroplating copper method according to claim 1, characterized in that, The duration of the first electroplating preparation stage is between 5s and 10s.

4. The chemical electroplating copper method according to claim 1, characterized in that, The duration of the electroplating immersion stage is greater than or equal to 0.3s, and the immersion voltage is greater than or equal to 0.8V.

5. The chemical electroplating copper method according to claim 4, characterized in that, The duration of the electroplating immersion stage is 0.5s, and the immersion voltage is 0.8V.

6. The chemical electroplating copper method according to claim 1, characterized in that, The electroplating stage includes: a first electroplating stage, a second electroplating stage, and a third electroplating stage, wherein... The electroplating current in the first electroplating stage is between 4.2A and 4.8A, the electroplating current in the second electroplating stage is between 6.4A and 7A, and the electroplating current in the third electroplating stage is between 37A and 43A.

7. The chemical electroplating copper method according to claim 1, characterized in that, A metal seed layer is formed on the surface of the trench and the via, and the upper surface of the metal seed layer serves as the surface to be electroplated.

8. The chemical electroplating copper method according to claim 7, characterized in that, The metal seed layer is formed using a physical vapor deposition process.

9. The chemical electroplating copper method according to claim 7, characterized in that, The method for preparing the intermediate structure includes: A substrate is provided, and a patterned first mask layer is formed on the upper surface of the substrate; The substrate is etched based on the first mask layer to form the trench; A patterned second mask layer is formed on the upper surface of the substrate; The substrate is etched based on the second mask layer to form the via; The metal seed layer is formed on the surface of the trench and the via.

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