CN105817991A - Chemical mechanical grinding method - Google Patents

Abstract

A chemical mechanical polishing method, comprising: providing a wafer to be ground; placing the wafer to be ground on a first grinding pad, and using a first grinding liquid to perform first grinding on the grinding wafer, wherein the first grinding liquid has The first pH value; the wafer to be ground is separated from the first grinding pad, and the first cleaning liquid is sprayed on the surface of the wafer to be ground to perform the first cleaning, the first cleaning liquid has a second pH value, and the second pH value is the same as the first pH value. The absolute value of the difference between a pH value is less than or equal to 1; after the first cleaning, the wafer to be ground is placed on the second polishing pad, and the second grinding liquid is used to perform the second grinding on the wafer to be ground, and the second grinding liquid has the first Three pH values, and the absolute value of the difference between the third pH value and the second pH value is less than or equal to 1. The invention avoids acid-base conflicts on the surface of the wafer to be ground, thereby preventing a large number of microscopic particles from appearing on the surface of the wafer to be ground, and avoiding scratches on the surface of the wafer to be ground by the microscopic particles during the second grinding process.

Description

chemical mechanical polishing method

technical field

The invention relates to the technology in the field of semiconductor manufacturing, in particular to a chemical mechanical polishing method.

Background technique

With the rapid development of ultra-large-scale integrated circuits, the manufacturing process of integrated circuits has become more and more complex and surprising. In order to improve integration and reduce manufacturing costs, the size of semiconductor devices is decreasing day by day, and planar wiring has been difficult to meet the high-density distribution of semiconductor devices. It has become one of the development trends to use multi-layer wiring technology to increase the integration density of semiconductor devices. Among them, chemical mechanical polishing (CMP, Chemical Mechanical Polishing) technology can realize the flattening of the entire wafer, which is an important process in the semiconductor manufacturing process. one of the steps.

The equipment used in chemical mechanical polishing mainly includes a polishing head (head) and a polishing table (platen), and a polishing pad (pad) is arranged on the polishing table. During the chemical mechanical polishing process, the wafer to be chemically mechanically polished is fixed on the grinding table with its surface to be polished downward, and the grinding head is pressed down on the back of the wafer to be polished. The grinding head and the grinding table rotate separately for grinding. During the grinding process, it is necessary to continuously add slurry (slurry). With the relative movement between the polishing pad and the wafer to be polished and the continuous addition of slurry, the grinding of the wafer to be polished is realized and a flat surface is formed. During chemical mechanical polishing, the grinding rate is mainly adjusted by adjusting the down-force of the grinding head and the selectivity of the grinding liquid.

However, in the prior art, after chemical mechanical polishing of the wafer to be ground, the surface of the wafer to be ground has poor morphology and many defects, for example, the surface of the wafer to be ground has scratches, particles and slurry residues (slurry residues).

Among them, the particles and slurry on the surface of the wafer to be polished remain in the subsequent cleaning process, which is relatively easy to clean and remove, while the scratches on the surface of the wafer to be polished are difficult to remove, so scratches on the surface of the wafer to be polished are the cause of One of the main reasons for the reduction of production yield.

Contents of the invention

The problem solved by the invention is the problem of scratches on the surface of the wafer to be polished after chemical mechanical polishing in the prior art.

In order to solve the above problems, the present invention provides a chemical mechanical polishing method, comprising: providing a wafer to be polished; placing the wafer to be polished on a first polishing pad, and using a first polishing liquid to perform a second grinding process on the wafer to be polished; A grinding, wherein the first grinding liquid has a first pH value; after the first grinding, the wafer to be ground is separated from the first grinding pad, and the first cleaning liquid is sprayed on the surface of the wafer to be ground performing the first cleaning, wherein the first cleaning liquid has a second pH value, and the absolute value of the difference between the second pH value and the first pH value is less than or equal to 1; after the first cleaning, the The wafer to be ground is placed on a second grinding pad, and the wafer to be ground is subjected to second grinding using a second grinding liquid, wherein the second grinding liquid has a third pH value, and the third pH value The absolute value of the difference from the second pH value is less than or equal to 1.

Optionally, a grinder table is provided, and the input area of the machine table to be grinded is cleaned before grinding with a pre-grinding cleaning liquid, and the absolute value of the difference between the pH value of the pre-grinding cleaning liquid and the first pH value is less than is equal to 1; before placing the surface of the wafer to be ground on the first polishing pad, place the wafer to be ground on the input area of the grinding machine table.

Optionally, the first grinding is chemical mechanical grinding; the second grinding is chemical mechanical grinding; and the grinding rate of the first grinding is greater than the grinding rate of the second grinding; the grinding rate of the first grinding pad is The hardness is greater than that of the second polishing pad.

Optionally, the first pH value is 3-4; the second pH value is 3-4; and the third pH value is 3-4.

Optionally, the first cleaning solution is a first grinding solution without abrasive particles; or, the first cleaning solution is a first grinding solution without abrasive particles added with hydrogen peroxide.

Optionally, the first cleaning solution is oxalic acid solution or oxalic acid solution.

Optionally, the first pH value is 9 to 11; the second pH value is 9 to 11; and the third pH value is 9 to 11.

Optionally, while the first cleaning is performed on the surface of the wafer to be polished, the first cleaning is performed on the surface of the first polishing pad.

Optionally, the duration of the first cleaning is less than or equal to 5 seconds.

Optionally, after performing the first cleaning on the first grinding pad, further include the step of: spraying a second cleaning liquid on the first grinding pad to perform second cleaning, wherein the second cleaning liquid has a fourth pH value, and the absolute value of the difference between the fourth pH value and the second pH value is less than or equal to 1.

Optionally, further comprising the step of: after the second grinding, separating the wafer to be ground from the second grinding pad, spraying a third cleaning solution on the surface of the wafer to be ground to perform a third cleaning, wherein, The third cleaning solution has a fifth pH value, and the absolute value of the difference between the fifth pH value and the third pH value is less than or equal to 1; after the third cleaning, the wafer to be ground is placed in On the third polishing pad, the third grinding liquid is used to perform the third grinding on the wafer to be ground, wherein the third grinding liquid has a sixth pH value, and the difference between the sixth pH value and the fifth pH value The absolute value of is less than or equal to 1.

Optionally, the first pH value, the third pH value and the sixth pH value are the same.

Optionally, while performing the third cleaning on the surface of the wafer to be polished, the third cleaning is performed on the second polishing pad.

Optionally, after performing the third cleaning on the second grinding pad, further comprising the step of: spraying a fourth cleaning liquid on the second grinding pad to perform fourth cleaning, wherein the fourth cleaning liquid has the seventh pH value, and the absolute value of the difference between the seventh pH value and the fifth pH value is less than or equal to 1.

Optionally, after the third grinding, the wafer to be ground is separated from the third grinding pad, and the fifth cleaning solution is sprayed on the surface of the wafer to be ground, and the wafer to be ground and the second The third polishing pad performs fifth cleaning, wherein the fifth cleaning solution has an eighth pH value, and the absolute value of the difference between the eighth pH value and the sixth pH value is less than or equal to 1.

Optionally, a grinding machine table is provided, and the output area of the grinding machine table is subjected to post-grinding treatment with a cleaning liquid after grinding, and the absolute value of the difference between the pH value of the cleaning liquid after grinding and the eighth pH value is less than or equal to 1. After performing the fifth cleaning, placing the wafer to be ground in the output area of the grinder table.

Optionally, the method further includes the step of: brushing the surface of the wafer to be polished with a scrubbing solution, and the absolute value of the difference between the pH value of the scrubbing solution and the pH value of the cleaning solution after grinding is less than or equal to 1.

Optionally, the wafer to be ground includes: a substrate and a dielectric layer on the surface of the substrate, a groove is formed in the dielectric layer; a gate film that fills the groove and covers the surface of the dielectric layer, and the The top of the gate film is higher than the surface of the dielectric layer.

Optionally, the first grinding removes a part of the thickness of the gate film; the second grinding removes the gate film higher than the surface of the dielectric layer to form a gate layer located in the trench; the third grinding Partial thickness of the dielectric layer and the gate layer are removed.

Compared with the prior art, the technical solution of the present invention has the following advantages:

In the technical solution of the chemical mechanical polishing method provided by the present invention, the wafer to be ground is placed on a first grinding pad, and the first grinding liquid is used to perform the first grinding on the grinding wafer, wherein the first grinding The liquid has a first pH value; after the first grinding, the wafer to be ground is separated from the first grinding pad, and the first cleaning liquid is sprayed on the surface of the wafer to be ground to perform the first cleaning, wherein the first A cleaning solution has a second pH value, and the absolute value of the difference between the second pH value and the first pH value is less than or equal to 1. When there is a solution on the surface of the wafer to be ground, there are microscopic particles in the solution itself, and the microscopic particles repel or attract each other to form a charged layer, so a zeta potential layer is formed on the surface of the wafer to be ground accordingly; because the surface of the wafer to be ground Therefore, the zeta potential layer on the surface of the wafer to be ground can be prevented from becoming thicker, the microscopic particles on the surface of the wafer to be ground can be prevented from increasing significantly, and the microscopic particles can be avoided in the subsequent second grinding process of the wafer to be ground. Round surfaces cause scratches.

At the same time, after the first cleaning, the wafer to be ground is placed on a second grinding pad, and the wafer to be ground is subjected to a second grinding using a second grinding liquid, wherein the second grinding liquid It has a third pH value, and the absolute value of the difference between the third pH value and the second pH value is less than or equal to 1. In the same way, prevent the sudden change of the pH value of the surface of the wafer to be ground during the second grinding, prevent the surface of the wafer to be ground from producing a large amount of microscopic particles, and prevent the microscopic particles from scratching the surface of the wafer to be ground during the second grinding process . Therefore, the present invention can improve the problem of scratches on the surface of the wafer to be polished during the chemical mechanical polishing process, and improve the interface quality of the surface of the wafer to be polished after grinding.

Further, a grinding machine table is provided, and the input area of the machine table to be ground is cleaned before grinding using a pre-grinding cleaning liquid, and the absolute value of the difference between the pH value of the pre-grinding cleaning liquid and the first pH value is less than or equal to 1 . Similarly, acid-base conflicts on the surface of the wafer to be ground can be prevented, and a large number of microscopic particles can be avoided on the surface of the wafer to be ground.

Further, after performing the first cleaning on the first polishing pad, it also includes the step of: spraying a second cleaning solution on the first polishing pad to perform the second cleaning, wherein the second cleaning solution has a fourth pH value, and The absolute value of the difference between the fourth pH value and the second pH value is less than or equal to 1. Similarly, the present invention can avoid acid-base conflicts on the surface of the first polishing pad, prevent a large number of microscopic particles from being generated on the surface of the first polishing pad, and avoid damage to other wafers when other wafers are ground on the first polishing pad.

Further, after the second grinding, the wafer to be polished is separated from the second grinding pad, and a third cleaning solution is sprayed on the surface of the wafer to be polished to perform a third cleaning, wherein the third cleaning solution having a fifth pH value, and the absolute value of the difference between the fifth pH value and the third pH value is less than or equal to 1; after the third cleaning, placing the wafer to be polished on a third polishing pad, using The third grinding liquid performs the third grinding on the wafer to be ground, wherein the third grinding liquid has a sixth pH value, and the absolute value of the difference between the sixth pH value and the fifth pH value is less than or equal to 1 . The invention provides a three-step grinding process, and avoids producing a large amount of microscopic particles on the surface of the wafer to be ground when the wafer to be ground is subjected to the third grinding, improves the surface quality of the wafer to be ground after the third grinding, and prevents the microscopic particles from being produced in the third grinding process. 3. During the grinding process, the surface of the wafer to be ground is scratched.

Furthermore, after the third grinding, it also includes the step of: brushing the surface of the wafer to be ground with a scrubbing solution, and the absolute value of the difference between the pH value of the scrubbing solution and the pH value of the cleaning solution after grinding is less than is equal to 1. The invention can further avoid damage to the surface of the wafer to be polished during the scrubbing process.

Description of drawings

1 to 8 are schematic diagrams of the semiconductor structure of the chemical mechanical polishing process provided by an embodiment of the present invention.

detailed description

It can be seen from the background art that in the prior art, after chemical mechanical polishing is performed on the wafer to be polished, there are scratches on the surface of the wafer to be polished, and the scratches lead to a low production yield of the semiconductor structure.

It has been found through research that common grinding liquids include abrasives, reactants and deionized water, and the abrasives are generally silica or alumina. Microscopic particles (microscopic particles) can be produced in the grinding liquid itself. When the particulate matter is suspended in the grinding liquid, the particles repel or attract each other, so that a charged layer is formed in the grinding liquid, so that the wafer to be ground The surface develops a zeta potential, which is either positive or negative.

When the wafer to be ground is ground, at least the following steps are included: step S1, the surface of the wafer to be ground is first ground, and the pH value (hydrogen ion concentration index, HydrogenIonConcentration) of the first grinding liquid is 3 to 4 or 9 to 11 ; Step S2, after performing the first grinding, perform the first cleaning on the surface of the wafer to be ground, the first cleaning solution is deionized water, the pH value of the deionized water is about 6; step S3, after performing the first After cleaning, a second grinding is performed on the surface of the wafer to be ground, and the pH value of the second grinding liquid is 3 to 4 or 9 to 11.

In other embodiments, the wafer to be polished is even subjected to three-step grinding, and after the second grinding and before the third grinding, the surface of the wafer to be polished is cleaned for the second time, and the second cleaning liquid is deionized water.

Carrying out micro-topography analysis on the wafer surface to be ground finds that after the second grinding, the scratches (scratches) on the surface of the wafer to be ground are significantly more than the scratches on the surface of the wafer to be ground before the second grinding; and when using During the three-step grinding process, after the third grinding, the scratches on the surface of the wafer to be ground are obviously more than the scratches on the surface of the wafer to be ground after the second grinding.

Research has found that the reason for this problem is that the pH value of the surface of the wafer to be ground is constantly changing, and in different process steps, the pH value of the surface of the wafer to be ground varies greatly; When the pH value of the round surface changes greatly, an acid-base conflict (pHShock) occurs on the surface of the wafer to be polished. When the surface of the wafer to be polished has a grinding liquid or cleaning liquid, the zeta potential layer on the surface of the wafer to be polished will become thicker. , correspondingly, the number of microscopic particles on the surface of the wafer to be ground increases significantly. During the second grinding process, due to the significant increase in the number of microscopic particles on the surface of the wafer to be polished, the microscopic particles will cause serious scratches on the surface of the wafer to be polished, affecting the surface quality of the wafer to be ground after grinding.

Further studies have found that when the pH value of the surface of the wafer to be ground changes by less than or equal to 1, and when the surface of the wafer to be ground has a grinding liquid or a cleaning liquid, the thickness of the zeta potential layer on the surface of the wafer to be ground remains almost constant. Therefore, it is possible to avoid the generation of a large number of microscopic particles on the surface of the wafer to be ground.

To this end, the present invention provides a chemical mechanical polishing method, providing a wafer to be ground; placing the wafer to be ground on a first grinding pad, and using a first grinding liquid to perform first grinding on the ground wafer, wherein , the first grinding liquid has a first pH value; after the first grinding, the wafer to be ground is separated from the first grinding pad, and the first cleaning liquid is sprayed on the surface of the wafer to be ground to perform the first cleaning , wherein, the first cleaning solution has a second pH value, and the absolute value of the difference between the second pH value and the first pH value is less than or equal to 1; after the first cleaning, the crystal to be ground The circle is placed on the second grinding pad, and the second grinding liquid is used to perform the second grinding on the wafer to be ground, wherein the second grinding liquid has a third pH value, and the third pH value is the same as the second pH value The absolute value of the difference between the values is less than or equal to 1. The invention avoids the acid-base conflict on the surface of the wafer to be ground, thereby preventing the increase of microscopic particles on the surface of the wafer to be ground due to the acid-base conflict, thereby avoiding scratches on the wafer to be ground by the second grinding process.

In order to make the above objects, features and advantages of the present invention more comprehensible, specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

1 to 8 are schematic diagrams of the semiconductor structure of the chemical mechanical polishing process provided by an embodiment of the present invention.

Referring to FIG. 1 , a wafer to be ground is provided.

In this embodiment, the gate of the semiconductor structure is formed after chemical mechanical polishing as an example.

The corresponding wafer to be ground includes: a substrate 100 and a dielectric layer 101 located on the surface of the substrate 100, a groove is formed in the dielectric layer 101; a work function film 102 is formed on the surface of the dielectric layer 101, the groove bottom and the sidewall surface A gate film 103 is formed on the surface of the work function film 102, the gate film 103 fills the trench and the top of the gate film 103 is higher than the surface of the dielectric layer 101;

In other embodiments, the wafer to be ground may not include the work function film 102 .

Wherein, the material of the substrate 100 is silicon, germanium, silicon germanium, silicon carbide, gallium arsenide or indium gallium; the substrate 100 can also be a silicon-on-insulator substrate or a germanium-on-insulator substrate; The material of the dielectric layer 101 is silicon oxide, silicon nitride or silicon oxynitride; the material of the work function film 102 is Ti, Ta, TiN, TaN or WN; the material of the gate film 103 is polysilicon, copper, aluminum or tungsten.

In this embodiment, the material of the substrate 100 is silicon, the material of the dielectric layer 101 is silicon oxide, the material of the work function film 102 is tungsten nitride (WN), and the material of the gate film 103 is aluminum.

Referring to FIG. 2 , the wafer to be polished is placed on a first polishing pad, and the wafer to be polished is subjected to first grinding with a first polishing liquid, wherein the first polishing liquid has a first pH value.

The first polishing process is chemical mechanical polishing, and the first polishing pad is a hard pad.

The first grinding process is a rough grinding stage. Specifically, the first grinding process in this embodiment grinds and removes a part of the thickness of the gate film 103 so that the thickness of the remaining gate film 103 is relatively thin. The first grinding process has a higher grinding rate for the gate film 103 , so that the gate film 103 with a larger thickness can be quickly removed by grinding, and the efficiency of chemical mechanical grinding can be improved.

In a specific embodiment, after the first grinding, the thickness of the gate film 103 higher than the dielectric layer 101 is 500 angstroms to 5000 angstroms.

The first grinding solution includes deionized water, chemical additives and first grinding particles, and the first grinding solution may be an acidic solution or an alkaline solution.

In this embodiment, the first grinding liquid has a first pH value of 3 to 4, and the corresponding chemical additives include one or more of carbon dioxide, citric acid or oxalic acid.

In another embodiment, the first grinding liquid has a first pH value of 9 to 11, and the corresponding chemical additives include one or more of potassium hydroxide, sodium hydroxide, lithium hydroxide or ammonia water.

In this embodiment, before moving the wafer to be polished to the first polishing pad, the wafer to be polished will be placed in the input area of the grinding machine table, and then the wafer to be polished will be moved onto the first polishing pad.

For this reason, in this embodiment, before the wafer to be ground is placed in the input area of the grinding machine table, the input area of the grinding machine table is cleaned with a pre-grinding cleaning liquid, and the pH value of the pre-grinding cleaning liquid is The absolute value of the difference from the first pH value is less than or equal to 1. In this embodiment, the first pH value is 3 to 4, corresponding to the pH value of the cleaning solution before grinding is 3 to 4; in another embodiment, the first pH value is 9 to 11, corresponding to the pH value of the cleaning solution before grinding Values are 9 to 11.

Before the wafer to be ground is moved to the first polishing pad from the grinder table, the pH value of the surface solution of the wafer to be ground is almost the same as the pH value of the cleaning solution before grinding; when the wafer to be ground is moved to the first On the polishing pad, after the first polishing solution is sprayed on the wafer to be polished, the pH value of the surface of the wafer to be polished is the same as the first pH value.

Since the absolute value of the difference between the pH value of the cleaning solution before grinding and the first pH value is less than or equal to 1, it can prevent the acid-base conflict on the surface of the wafer to be ground, and prevent the occurrence of acid-base conflict on the surface of the wafer to be ground. The amount of microscopic particles (microscopic particles) in the solution on the surface of the polished wafer is increased, so as to avoid excessive microscopic particles appearing in the first grinding process and causing scratches on the surface of the wafer to be polished.

Please refer to FIG. 3 , after the first grinding, the wafer to be ground is separated from the first grinding pad, and the wafer to be ground is sprayed with a first cleaning liquid to perform the first cleaning 10, wherein the first cleaning The liquid has a second pH value, and the absolute value of the difference between the second pH value and the first pH value is less than or equal to 1.

Specifically, in this embodiment, the first cleaning liquid is sprayed on the surface of the gate film 103 after the first polishing to perform the first cleaning 10 . Since there are grinding residues on the surface of the gate film 103 after the first grinding, if the grinding residues are not removed, in the subsequent second grinding process, the grinding residues will cause adverse effects on the subsequent second grinding. Therefore, in this embodiment, before the second grinding, the surface of the wafer to be ground is cleaned 10 to remove the grinding residue.

Since before the first cleaning 10, the pH value of the surface of the gate film 103 is the same as the first pH value, if the second pH value is greatly different from the first pH value, the acid-base conflict problem will occur on the surface of the gate film 103 , causing more microscopic particles to be generated on the surface of the gate film 103, and the microscopic particles will cause scratches on the surface of the wafer to be polished during the subsequent second grinding process.

For this reason, in this embodiment, the absolute value of the difference between the second pH value and the first pH value is less than or equal to 1, so as to avoid acid-base conflicts on the surface of the gate film 103, thereby preventing microscopic particles.

In this embodiment, the first pH value is 3 to 4, and the second pH value is 3 to 4, for example, the second pH value is 3.3, 3.5 or 3.8. The first cleaning liquid can be the first grinding liquid not containing the first grinding particles, the first grinding liquid not containing the first grinding particles and added with hydrogen peroxide, or other suitable chemical solutions, for example, the first cleaning liquid can be Oxalic acid solution or oxalic acid solution

In other embodiments, the first pH value is 9 to 11, and the second pH value is 9 to 11, for example, the second pH value is 9.5, 10 or 10.5.

While carrying out the first cleaning 10 to the surface of the wafer to be ground, the first cleaning 10 is carried out to the first grinding pad to remove the grinding residue on the surface of the first grinding pad and prevent subsequent grinding of other grinding pads on the first grinding pad. When the wafer is damaged, other wafers to be ground are damaged.

The duration of the first cleaning 10 is less than or equal to 5 seconds. Since the first cleaning 10 has a limited cleaning effect on the first grinding pad, after the first cleaning 10 is carried out to the first grinding pad, it may also include the step of: spraying the second cleaning liquid to the first grinding pad for the second cleaning. Cleaning, wherein the second cleaning solution has a fourth pH value, and the absolute value of the difference between the fourth pH value and the second pH value is less than or equal to 1.

Since the absolute value of the difference between the fourth pH value and the second pH value is less than or equal to 1, it is possible to prevent acid-base conflicts on the surface of the first polishing pad, and correspondingly avoid the generation of microscopic particles on the surface of the first polishing pad, thereby preventing subsequent grinding in the first grinding pad. scratches other wafers to be polished while grinding on the pad.

Referring to FIG. 4 , after the first cleaning of the wafer to be ground, the wafer to be ground is placed on a second polishing pad, and the wafer to be ground is subjected to a second grinding using a second grinding liquid, wherein the The second grinding liquid has a third pH value, and the absolute value of the difference between the third pH value and the second pH value is less than or equal to 1.

The second grinding is chemical mechanical grinding, and the grinding rate of the second grinding is less than that of the first grinding, the second grinding pad is a soft grinding pad (softpad), and the hardness of the second grinding pad is less than the hardness of the first grinding pad .

Specifically, the second grinding process in this embodiment grinds and removes the gate film 103 (refer to FIG. 3 ) and the work function film 102 (refer to FIG. 3 ) higher than the surface of the dielectric layer 101 to form a The work function layer 112, the gate layer 113 located on the surface of the work function layer 112, and the gate layer 113 fills the trench. Since the grinding rate of the second grinding is smaller, the planarization effect of the second grinding process is better than that of the first grinding process.

The second grinding liquid includes deionized water, chemical additives and second grinding particles. During the second grinding process, the surface of the wafer to be ground is covered by the second grinding liquid. Since the second grinding liquid itself has microscopic particles, the microscopic particles repel or attract each other, so that a charged layer is formed in the second grinding liquid, thereby forming a zeta potential layer on the surface of the wafer to be ground, and the zeta potential layer Potential is positive or negative.

If there is an acid-base conflict problem in the surface environment of the wafer to be ground, under the influence of the acid-base conflict, the zeta potential layer on the surface of the wafer to be ground will become thicker, that is, the number of microscopic particulate matter on the surface of the wafer to be ground will increase; During the second grinding process, the microscopic particulate matter will scratch the surface of the wafer to be ground. Specifically in this embodiment, if acid-base conflict occurs on the surface of the gate film 103 during the second grinding process, more microscopic particles will be generated on the surface of the gate film 103 , thereby causing scratches on the surface of the gate film 103 .

Because before the second grinding, the pH value of the surface of the gate film 103 is close to the second pH value, for this reason, in order to avoid the increase of the thickness of the zeta potential layer on the surface of the gate film 103, prevent the microscopic particulate matter on the surface of the gate film 103 As the content increases, the absolute value of the difference between the third pH value and the second pH value in this embodiment is less than or equal to 1.

In one embodiment, when the second pH value is 3 to 4, the third pH value is 3 to 4, for example, the third pH value is 3.2, 3.5 or 3.8. In another embodiment, when the second pH value is 9 to 11, the third pH value is 9 to 11, for example, the third pH value is 9.5, 10 or 10.5.

In this embodiment, the pH value of the second grinding liquid is the same as that of the first grinding liquid, that is, the third pH value is the same as the first pH value.

Referring to FIG. 5 , after the second grinding, the wafer to be ground is separated from the second grinding pad, and a third cleaning solution is sprayed on the wafer to be ground to perform a third cleaning 30, wherein the third The cleaning solution has a fifth pH value, and the absolute value of the difference between the fifth pH value and the third pH value is less than or equal to 1.

The third cleaning 30 is used to clean and remove the grinding residue on the surface of the gate film 103 and the dielectric layer 101 after the second grinding, so as to prevent the grinding residue from causing damage to the surface of the gate film 103 during the subsequent grinding process. .

Similarly, in order to prevent acid-base conflicts on the surface of the wafer to be ground and avoid microscopic particles on the surface of the wafer to be ground, the absolute value of the difference between the fifth pH value and the third pH value is less than or equal to 1. In one embodiment, when the third pH value is 3 to 4, the fifth pH value is 3 to 4, for example, the fifth pH value is 3.3, 3.5 or 3.8. In another embodiment, when the third pH value is 9 to 11, the fifth pH value is 9 to 11, for example, the fifth pH value is 9.5, 10 or 10.5.

The second grinding liquid includes deionized water, chemical additives and second grinding particles. The third cleaning solution may be the second grinding solution without the second grinding particles, or the second grinding solution without the second grinding particles and added with hydrogen peroxide, or other suitable chemical solutions. For example, when the fifth pH value is 3 to 4, the third cleaning solution may be an oxalic acid solution or a citric acid solution.

In this embodiment, while the third cleaning 30 is performed on the surface of the wafer to be polished, the third cleaning 30 is performed on the second polishing pad to remove the grinding residue on the surface of the second polishing pad and prevent the second polishing pad from Acid-base conflict occurs on the surface to produce too many microscopic particles, so it can avoid scratching other wafers when the second polishing pad is used to polish other wafers.

And because the time of the third cleaning 30 is usually shorter, the duration of the third cleaning 30 is usually less than 5 seconds, so the cleaning ability of the third cleaning 30 to the second grinding pad is limited, for this reason the third cleaning is performed on the second grinding pad After 30, the method may further include a step of: spraying a fourth cleaning solution on the second polishing pad to perform fourth cleaning, wherein the fourth cleaning solution has a seventh pH value. Likewise, in order to avoid acid-base conflicts on the surface of the second polishing pad, the absolute value of the difference between the seventh pH value and the fifth pH value is less than or equal to 1.

In one embodiment, when the fifth pH value is 3-4, the seventh pH value is 3-4. In another embodiment, when the fifth pH value is 9-11, the seventh pH value is 9-11.

Referring to FIG. 6, after the third cleaning, the wafer to be ground is placed on a third grinding pad, and a third grinding liquid is used to perform a third grinding on the wafer to be ground, wherein the third grinding The liquid has a sixth pH value, and the absolute value of the difference between the sixth pH value and the fifth pH value is less than or equal to 1.

The third polishing is chemical mechanical polishing, the hardness of the third polishing pad is smaller than that of the second polishing pad, and the polishing rate of the third polishing is smaller than that of the second polishing. The third grinding is used to further modify the topography of the surface of the wafer to be ground after the second grinding.

Specifically in this embodiment, the third grinding process grinds and removes a partial thickness of the dielectric layer 101, work function layer 112 and gate layer 113, so that the top surfaces of the remaining dielectric layer 101, work function layer 112 and gate layer 113 Flatness is further improved.

Similarly, in the third grinding process, there are suspended microscopic particles in the third grinding liquid, so that the surface of the dielectric layer 101 , the surface of the work function layer 112 and the surface of the gate layer 113 have a zeta potential layer. In order to prevent the zeta potential layer from becoming thicker and avoid the increase in the number of microscopic particles on the surface of the dielectric layer 101, the surface of the work function layer 112, and the surface of the gate layer 113, the absolute value of the difference between the sixth pH value and the fifth pH value in this embodiment is less than is equal to 1.

In one embodiment, the fifth pH value is 3 to 4, and the corresponding sixth pH value is 3 to 4, for example, the sixth pH value is 3.2, 3.5 or 3.8. In another embodiment, when the fifth pH value is 9 to 11, the corresponding sixth pH value is 9 to 11, for example, the sixth pH value is 9.5, 10 or 10.5.

In this embodiment, the pH values of the first grinding liquid, the second grinding liquid and the third grinding liquid are the same, that is, the first pH value, the third pH value and the sixth pH value are the same.

Referring to FIG. 7 , after performing the third grinding, the wafer to be ground is separated from the third grinding pad, the surface of the wafer to be ground is sprayed with the fifth cleaning solution, and the wafer to be ground is subjected to the first grinding process. Fifth cleaning 50, wherein the fifth cleaning solution has an eighth pH value, and the absolute value of the difference between the eighth pH value and the sixth pH value is less than or equal to 1.

The fifth cleaning 50 removes the grinding residue left on the surface of the wafer to be polished by the third grinding. Specifically, in this embodiment, the grinding residue on the surface of the dielectric layer 101, the surface of the work function layer 112, and the surface of the gate layer 113 is removed. . In this embodiment, in order to prevent acid-base conflicts on the surface of the dielectric layer 101 , the surface of the work function layer 112 and the surface of the gate layer 113 , the absolute value of the difference between the eighth pH value and the sixth pH value is less than or equal to 1.

In one embodiment, when the sixth pH value is 3-4, the eighth pH value is 3-4. In another embodiment, when the sixth pH value is 9-11, the eighth pH value is 9-11.

In this embodiment, the fifth cleaning 50 is performed on the wafer to be polished, and the fifth cleaning is performed on the third polishing pad to remove the grinding residue on the surface of the fifth polishing pad and avoid acid-base conflicts on the surface of the fifth polishing pad. .

The duration of the fifth cleaning 50 is shorter, generally less than 5 seconds, so in order to thoroughly remove the grinding residue on the surface of the third grinding pad, after the fifth cleaning 50, the step can also be included: spraying the surface of the third grinding pad The sixth cleaning solution is to perform sixth cleaning on the third polishing pad, the sixth cleaning solution has a ninth pH value, similarly, the absolute value of the difference between the ninth pH value and the eighth pH value is less than is equal to 1.

After the third grinding, the grinding of the wafer to be ground is completed. Specifically in this embodiment, the first grinding removes the gate film 103 of a partial thickness (refer to FIG. 1 ), and the second grinding removes For the work function film 102 (refer to FIG. 2 ) and the remaining gate film 103 , the third grinding further improves the flatness of the surface of the dielectric layer 101 , the surface of the work function layer 112 and the surface of the gate layer 113 .

After finishing the grinding of the wafer to be ground, the wafer to be ground is placed in the output area of the grinder table. Since the pH value of the surface of the wafer to be ground is the eighth pH value before the wafer to be ground is moved to the output area, for this reason, in this embodiment, before the wafer to be moved is moved to the output area, cleaning after grinding is adopted. The liquid pair performs post-grinding cleaning treatment on the output area of the grinding machine table, and the absolute value of the difference between the pH value of the cleaning solution in the post-grinding cleaning treatment and the eighth pH value is less than or equal to 1.

Referring to FIG. 8 , after the wafer to be ground is polished, a scrubbing liquid is sprayed on the wafer to be ground, and a grinding brush is used to brush 60 the surface of the wafer to be ground.

A grinding brush is used to further remove residues on the surface of the dielectric layer 101 , the surface of the work function layer 112 and the surface of the gate layer 113 .

In the same way, in order to prevent the surface of the wafer to be ground from producing a large amount of microscopic particles during the process of brushing 60 on the surface of the wafer to be ground, it is necessary to avoid the impact of the microscopic particles on the dielectric layer 101, the work function layer 112, and the grid during the brushing 60 process. The electrode 113 causes scratches, and the absolute value of the difference between the pH value of the scrubbing liquid and the eighth pH value is less than or equal to 1.

After scrubbing the wafer to be ground, the wafer to be ground is cleaned with deionized water.

It should be noted that after the first grinding, the second grinding and the third grinding, the wafer to be ground is different from the wafer to be ground before the first grinding, the second grinding and the third grinding. After the first grinding, the wafer to be ground includes: a substrate 100 and a dielectric layer 101 on the surface of the substrate 100; a groove in the dielectric layer 101; a work function film 102 on the surface of the dielectric layer 101, the bottom of the groove and the sidewall surface (referring to Fig. 2); Be positioned at the gate film 103 (referring to Fig. 2) that is positioned at the work function film 102 surface and fills the trench, and the gate film 103 top is higher than the dielectric layer 101 surface, and the gate film 103 top is flat The degree is higher than the flatness of the top of the first gate film 103 before polishing.

After the second grinding, the wafer to be ground includes: a substrate 100 and a dielectric layer 101 located on the surface of the substrate 100; a groove located in the dielectric layer 101; a work function layer 112 located at the bottom and sidewall surfaces of the groove; 113 surface and fills the gate layer 113 of the trench.

After the third grinding, the wafer to be ground includes: a substrate 100 and a dielectric layer 101 located on the surface of the substrate 100; a groove located in the dielectric layer 101; a work function layer 112 located at the bottom and sidewall surfaces of the groove; 113 surface and filled with the gate layer 113 of the trench, and compared with before the third grinding, the thickness of the dielectric layer 101 becomes smaller after the third grinding.

Because in this embodiment, in the first grinding process, the first cleaning process and the second grinding process of the wafer to be ground, no acid-base conflict occurs on the surface of the wafer to be ground, thereby preventing the surface of the wafer to be ground from A large number of microscopic particles avoid scratches on the surface of the wafer to be polished during the second grinding process due to the existence of the microscopic particles.

And, the surface of the first grinding pad, the second grinding pad and the third grinding pad has no acid-base conflict all the time, avoiding a large amount of microscopic particles on the surface of the first grinding pad, the second grinding pad and the third grinding pad.

At the same time, when the surface of the wafer to be ground is ground by a three-step grinding process, the wafer to be ground is processed in the first grinding process, the first cleaning process, the second grinding process, the third cleaning process, and the third grinding process. There is no acid-base conflict on the surface of the wafer, thereby preventing a large amount of microscopic particles from being produced on the surface of the wafer to be ground, and avoiding scratches on the surface of the wafer to be ground in the second grinding process and the third grinding process.

Again, after finishing the grinding of the wafer to be ground, during the brushing process of the surface of the wafer to be ground, no acid-base conflict has occurred on the surface of the wafer to be ground, thereby further scratching the surface of the wafer to be ground in the brushing process, and further Improve the interface properties of the dielectric layer 101 , the work function layer 112 and the surface of the gate layer 113 .

Finally, since the material of the gate layer 113 in this embodiment is aluminum, if an acid-base conflict occurs on the surface of the gate layer 113 , the material of the gate layer 113 will also be corroded. However, in this embodiment, the acid-base conflict on the surface of the gate layer 113 is always avoided, so the surface performance of the gate layer 113 formed after grinding is further improved.

Although the present invention is disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, so the protection scope of the present invention should be based on the scope defined in the claims.

Claims (19)

1. a chemical and mechanical grinding method, it is characterised in that including:

Wafer to be ground is provided；

Being placed on the first grinding pad by described wafer to be ground, use the first lapping liquid that described grinding crystal wafer carries out the first grinding, wherein, described first lapping liquid has the first pH value；

After described first grinds, make wafer to be ground and the first grinding pad separate, spray the first cleanout fluid to described crystal column surface to be ground and carry out the first cleaning, wherein, described first cleanout fluid has the second pH value, and the absolute value of the difference of described second pH value and the first pH value is less than or equal to 1；

After described first cleans, described wafer to be ground is placed on the second grinding pad, uses the second lapping liquid described wafer to be ground to be carried out the second grinding, wherein, described second lapping liquid has the 3rd pH value, and the absolute value of the difference of described 3rd pH value and the second pH value is less than or equal to 1.

Chemical and mechanical grinding method the most according to claim 1, it is characterized in that, grinder station is provided, uses the absolute value of the pH value of cleanout fluid before cleanout fluid is ground front cleaning, and described grinding to the input area of described board to be ground before grinding and the difference of the first pH value less than or equal to 1；Before being placed on the first grinding pad by described crystal column surface to be ground, described wafer to be ground is placed on the input area of grinder station.

Chemical and mechanical grinding method the most according to claim 1, it is characterised in that described first is ground to cmp；Described second is ground to cmp；And described first grind grinding rate more than described second grind grinding rate；The hardness of described first grinding pad is more than the hardness of described second grinding pad.

Chemical and mechanical grinding method the most according to claim 1, it is characterised in that described first pH value is 3 to 4；Described second pH value is 3 to 4；Described 3rd pH value is 3 to 4.

Chemical and mechanical grinding method the most according to claim 4, it is characterised in that described first cleanout fluid is the first lapping liquid without abrasive grains；Or, described first cleanout fluid is the first lapping liquid without abrasive grains that with the addition of hydrogen peroxide.

Chemical and mechanical grinding method the most according to claim 4, it is characterised in that described first cleanout fluid is ethanedioic acid solution or oxalic acid solution.

Chemical and mechanical grinding method the most according to claim 1, it is characterised in that described first pH value is 9 to 11；Described second pH value is 9 to 11；Described 3rd pH value is 9 to 11.

Chemical and mechanical grinding method the most according to claim 1, it is characterised in that while described crystal column surface to be ground is carried out the first cleaning, carries out the first cleaning to described first grinding pad surface.

Chemical and mechanical grinding method the most according to claim 8, it is characterised in that the described first duration cleaned was less than or equal to 5 seconds.

Chemical and mechanical grinding method the most according to claim 9, it is characterized in that, after described first grinding pad is carried out the first cleaning, further comprise the steps of: and spray the second cleanout fluid to described first grinding pad and carry out the second cleaning, wherein, described second cleanout fluid has the 4th pH value, and the absolute value of the difference of described 4th pH value and the second pH value is less than or equal to 1.

11. chemical and mechanical grinding methods according to claim 1, it is characterized in that, further comprise the steps of: after described second grinds, described wafer to be ground and the second grinding pad is made to separate, spray the 3rd cleanout fluid to described crystal column surface to be ground and carry out the 3rd cleaning, wherein, described 3rd cleanout fluid has the 5th pH value, and the absolute value of the difference of described 5th pH value and the 3rd pH value is less than or equal to 1；After the described 3rd cleans, described wafer to be ground is placed on the 3rd grinding pad, uses the 3rd lapping liquid described wafer to be ground to be carried out the 3rd grinding, wherein, described 3rd lapping liquid has the 6th pH value, and the absolute value of the difference of described 6th pH value and the 5th pH value is less than or equal to 1.

12. chemical and mechanical grinding methods according to claim 11, it is characterised in that described first pH value, the 3rd pH value and the 6th pH value are identical.

13. chemical and mechanical grinding methods according to claim 11, it is characterised in that while described crystal column surface to be ground is carried out the 3rd cleaning, described second grinding pad is carried out the 3rd cleaning.

14. chemical and mechanical grinding methods according to claim 13, it is characterized in that, after described second grinding pad is carried out the 3rd cleaning, further comprise the steps of: and carry out the 4th cleaning to described second grinding pad sprinkling the 4th cleanout fluid, wherein, described 4th cleanout fluid has the 7th pH value, and the absolute value of the difference of described 7th pH value and the 5th pH value is less than or equal to 1.

15. chemical and mechanical grinding methods according to claim 11, it is characterized in that, after carrying out the described 3rd and grinding, described wafer to be ground and the 3rd grinding pad is made to separate, spray the 5th cleanout fluid to described crystal column surface to be ground, described wafer to be ground and the 3rd grinding pad are carried out the 5th cleaning, wherein, described 5th cleanout fluid has the 8th pH value, and the absolute value of the difference of described 8th pH value and the 6th pH value is less than or equal to 1.

16. chemical and mechanical grinding methods according to claim 15, it is characterized in that, grinder station is provided, uses the absolute value of the pH value of cleanout fluid after cleanout fluid is ground post processing, and described grinding to the output area of described grinder station after grinding and the difference of the 8th pH value less than or equal to 1；After carrying out the described 5th and cleaning, described wafer to be ground is placed on the output area of grinder station.

17. chemical and mechanical grinding methods according to claim 16, it is characterized in that, further comprise the steps of: employing to scrub liquid described crystal column surface to be ground is scrubbed, and described in scrub the pH value of liquid and grind after the absolute value of difference of pH value of cleanout fluid less than or equal to 1.

18. chemical and mechanical grinding methods according to claim 11, it is characterised in that described wafer to be ground includes: substrate and be positioned at the dielectric layer of substrate surface, are formed with groove in described dielectric layer；Fill full described groove and be covered in the gate electrode film of dielectric layer surface, and described gate electrode film top is higher than dielectric layer surface.

19. chemical and mechanical grinding methods according to claim 18, it is characterised in that described first grinds the gate electrode film removing segment thickness；Described second grinds the removal gate electrode film higher than dielectric layer surface, forms the grid layer being positioned at described groove；Described 3rd grinds dielectric layer and the grid layer removing segment thickness.