Planarization polishing method for controlling large-size wafer by using magnetorheological elastomer
Technical Field
The invention relates to the technical field of ultra-precise polishing of semiconductor wafers, in particular to a method for controlling planarization and polishing of large-size wafers by utilizing a magnetorheological elastomer.
Background
With the development of electronic information technology, semiconductor wafers are made of single crystal silicon of a first generation semiconductor material, gallium arsenide, indium phosphide and the current third generation semiconductor silicon carbide, gallium nitride and the like, and meanwhile, the sizes of the wafers are continuously increased, such as 12 inches, 14 inches, 15 inches and the like, and in CMP of the wafers, the uniformity of the polishing thickness of the wafers is an important parameter for measuring the processing quality, the uniformity of the wafers directly influences the utilization of subsequent devices, the qualification rate of the wafers is determined, and the manufacturing cost of chips is directly influenced.
Because the wafer is affected by the polishing pressure nonuniformity, the polishing speed nonuniformity, the polishing liquid nonuniformity, the wafer deformation and other factors, the polished wafer thickness uniformity is poor, so that how to realize the planarization polishing of the wafer becomes an important problem to be solved.
The magnetorheological elastomer is a magnetic control intelligent material formed by distributing magnetic particles in a high molecular polymer, and the hardness change of the magnetorheological elastomer can be controlled according to the intensity of an external magnetic field; referring to the prior patent, no method for realizing planarization and polishing of large-size wafers by utilizing magneto-rheological elastomer magneto-control mechanical characteristics exists at present.
Patent CN107195547a discloses a method for improving the flatness of a wafer on line, which utilizes the polishing pressure of each partition to change the material removal rate of the corresponding partition, thereby realizing the flatness polishing of the wafer. But the non-uniformity of the wafer tends to be continuous and the pressure in each zone is uniform, which makes it difficult to accurately control the continuous pressure profile of the wafer to achieve continuous control of die material removal. Furthermore, the method is not particularly concerned with utilizing the controllable mechanical properties of magnetorheological elastomers to achieve control of wafer polishing pressure.
Patent CN111906683a discloses a composite polishing method and device, and the method uses the characteristic that the magnetorheological elastomer has magnetic control rigidity as a polishing pad, and controls the rigidity gradient of the magnetorheological elastomer through the magnitude of current to realize polishing integrated processing of a workpiece. The polishing method can realize the polishing of magnetic field control, but cannot realize the uniform polishing of the wafer, because the uniform polishing of the wafer involves the pressure distribution of the polishing head, the flow distribution of the polishing liquid, the rotation speed distribution of the polishing disk, the deformation of the wafer itself, and the like.
Patent CN113290426B discloses a method for improving uniformity of polishing thickness of a wafer, which determines pressure distribution of different positions of a polishing head according to thickness data of different positions of a test wafer, further determines shape of a correction pad, and adjusts uniformity of pressure of the polishing head by adding the correction pad. By adding the correction pad, the method has great human and mechanical errors, is difficult to realize uniformity of TTV=1μm, and has complex polishing correction flow, thus greatly reducing polishing efficiency.
Patent CN114227525a discloses a method for improving the uniformity of the thickness of a wafer by polishing, which measures the thickness of the polished wafer, uses a place with a larger local thickness as a correction area, and adds a trimming pad to the correction area to continue polishing until a qualified target wafer is obtained. The method needs to be corrected by adding a correction pad, and also has larger human and mechanical errors, and has complex polishing flow and low polishing efficiency.
Patent CN102328272B discloses a chemical mechanical polishing method, which measures the pre-film thickness value of a wafer before polishing, measures the post-film thickness value of the wafer after polishing, and uses an end point detection device to determine whether the wafer is polished uniformly, if not, performs chemical mechanical polishing according to the difference between the pre-film thickness value and the post-film thickness value until the wafer surface is polished uniformly. However, this method does not specifically describe how to control the wafer surface to achieve uniform polishing.
Therefore, a planarization polishing method for controlling a large-size wafer by using a magnetorheological elastomer is provided.
Disclosure of Invention
According to the defects of the prior art, the invention provides a planarization polishing method for controlling a large-size wafer by using a magnetorheological elastomer, so as to solve the planarization polishing problem of the large-size wafer in chemical mechanical polishing.
In order to achieve the above object, the present invention provides a wafer planarization polishing method using a magneto-rheological elastomer polishing head, the method comprising the steps of:
s1: adsorbing a large-size wafer on a polishing head with a magneto-rheological elastomer of a rotary CMP device;
s2: performing first-step polishing on a high-precision large-size wafer made of the same material, and acquiring thickness distribution data of the large-size wafer after the first-step polishing;
s3: adjusting the magnetic field distribution and the intensity according to the thickness distribution data, controlling the magnetorheological elastomer to polish the large-size wafer in the second step, and repeatedly optimizing the magnetic field distribution and the magnetic field intensity to planarize and polish the polished large-size wafer in the second step;
s4: and establishing the magnetic control polishing process of the large-size wafer through the magnetic control polishing parameters of the second step of polishing.
Further, in step S1, the large-size wafer material includes any one of a silicon wafer, a sapphire wafer, a silicon carbide wafer, a gallium nitride wafer, and a gallium arsenide wafer, and the wafer size is 4 inches or more.
Further, in step 2, the first polishing step is a preliminary experimental step performed to obtain a large-sized wafer planarization polishing process.
Further, in step S2, the high-precision large-size wafer made of the same material is a large-size wafer made of the same material obtained by the same previous processing step, and has a stable processing effect.
Further, in step S2, the thickness distribution data of the large-size wafer is distributed on circles with different radii of the large-size wafer; wherein the number of the thickness distribution data is adapted to the wafer size, and the larger the wafer size is, the larger the number of the thickness distribution data is.
Further, in step S3, the second polishing is also an early experimental step performed to obtain a large-sized wafer planarization polishing process.
Further, in step S3, the magnetic field distribution is determined by the thickness distribution data of the large-sized wafer, and the distribution area with a large thickness corresponds to the existing magnetic field distribution.
Further, in step S3, the magnetic field strength is determined by the thickness distribution data of the large-sized wafer, and the magnetic field is larger as the thickness of the large-sized wafer is larger.
Further, in step S3, the magnetic field is used to control the magnetorheological elastomer to polish the large-sized wafer;
the hardness of the magnetorheological elastomer is controlled by the magnetic field, so that the polishing pressure of the large-size wafer is controlled, and the material removal of the large-size wafer is controlled.
Further, in step S3, the larger the magnetic field intensity of the region with magnetic field distribution is, the larger the hardness of the magnetorheological elastomer is, the larger the polishing pressure of the region with large wafer thickness is, and the larger the material removal rate is.
Furthermore, the magnetorheological elastomer can realize hardness change under magnetic field control, and the magnetorheological effect of the magnetorheological elastomer is 0-500%. The beneficial effects of the invention are as follows:
the invention utilizes the magnetic field mechanical controllable characteristic of the magnetorheological elastomer to regulate and control the hardness distribution of the magnetorheological elastomer, thereby controlling the polishing pressure distribution of the wafer, realizing large wafer thickness and large material removal rate and finally obtaining the polishing surface with uniform wafer thickness distribution.
The invention can obtain the wafer surface with uniform thickness on the large-size wafer production line, establishes the magnetic control polishing process, reduces the procedures of re-disassembling the wafer to adjust the wafer pressure, and the like, and can greatly improve the polishing efficiency and the polishing precision.
Drawings
FIG. 1 is a schematic diagram of the steps of the method of the present invention.
FIG. 2 is a schematic diagram of a magnetorheological elastomer to control planarization and polishing of a large-sized wafer.
Fig. 3 is a schematic view of a single large-sized wafer.
FIG. 4 is a schematic diagram of controlling the planarization and polishing of a large-sized wafer by gradually decreasing the magnetic field strength along the radial direction from the center of the wafer.
Fig. 5 is a layout of a plurality of wafer rings.
In the figure: 1. a large-sized wafer; 2. a non-magnetic conductive sheet; 3. a magnetorheological elastomer; 4. a polishing head support; 5. a magnetic field.
Detailed Description
The following detailed description of the invention, taken in conjunction with the accompanying drawings, is to be understood that the detailed description is presented by way of illustration and example only, and not by way of limitation.
Examples:
a method for controlling planarization and polishing of a large-sized wafer using a magnetorheological elastomer according to an embodiment of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a flow chart of a method for controlling planarization and polishing of a large-sized wafer using a magnetorheological elastomer in accordance with an embodiment of the present invention. The polishing method of the invention can be applied to rotary CMP equipment, which mainly comprises a polishing head with magnetorheological elastomer, a magnetic field control system thereof, a trimmer, a polishing liquid conveying device, a polishing disk and the like, wherein the polishing head with magnetorheological elastomer and the magnetic field control system are one of the most critical components, and are a core and a foundation for realizing wafer uniformity polishing.
As shown in fig. 1, a 12-inch single crystal SiC wafer is adsorbed on the magnetorheological elastomer polishing head, and the wafer uniformity polishing method is controlled as follows:
s1, mounting a large-size wafer on a magnetorheological elastomer polishing head of a rotary CMP polishing machine.
In connection with the magnetorheological elastomer control wafer planarization polishing schematic of fig. 2, a 12 inch single crystal SiC wafer was mounted on the polishing head with the magnetorheological elastomer and the C-face of the SiC wafer was subjected to chemical mechanical polishing.
The polishing head fixes the SiC wafer in an adsorption mode.
S2, performing first-step polishing on the 12-inch monocrystalline SiC wafer, and acquiring thickness distribution data of the wafer after the first-step polishing.
Setting polishing parameters of CMP to polish the monocrystalline SiC wafer in the first step; thickness data of a 12-inch SiC wafer from the center to the radial direction was detected by an end point detecting device after polishing, as shown in fig. 3.
If the obtained thickness distribution data gradually decreases from the center of the wafer to the radial direction, the larger the radius is, the larger the material removal rate is. I.e., the larger the radius of the large-sized wafer, the greater the material removal rate and the smaller the wafer thickness.
S3, determining and controlling the magnetic field distribution and strength of the magnetorheological elastomer according to the thickness distribution data of the 12-inch monocrystalline SiC wafer, polishing the large-size wafer in the second step, and repeatedly optimizing the magnetic field distribution and the magnetic field strength to enable the 12-inch monocrystalline SiC wafer polished in the second step to meet the planarization polishing requirement.
From the above data, it can be seen that the thickness of the wafer center is greatest and gradually decreases along the radial direction, and the system for controlling the magnetic field strength of the magnetorheological elastomer should include a data processor and a mechanical actuator or an electromagnetic control system.
The data processor receives the wafer thickness distribution data to determine the magnetic field distribution and the magnetic field intensity, and controls the mechanical executing mechanism or the electromagnetic control system to adjust the magnetic field distribution and the magnetic field intensity;
for example, as shown in fig. 4, the mechanical actuator is controlled to move the permanent magnet up and down to obtain different magnetic field distributions to control the hardness distribution of the magnetorheological elastomer, and further control the pressure distribution of the wafer; the magnetic field strength is gradually reduced from the center of the wafer to the radial direction, the hardness of the magnetorheological elastomer is gradually reduced from the center of the wafer to the radial direction, the polishing pressure distribution of the large-size wafer is gradually reduced from the center of the wafer to the radial direction, and the material removal rate of the large-size wafer is gradually reduced from the center of the wafer to the radial direction. In the polishing stage of the second step, the 12-inch SiC wafer is detected by the end point measuring device, and the magnetic field distribution and the magnetic field intensity of the second step of polishing are repeatedly adjusted and optimized, so that the 12-inch SiC wafer polished in the second step can stably meet the planarization requirement.
S4, establishing a flattening magnetic control polishing process of the 12-inch monocrystalline SiC wafer through the magnetic control polishing parameters of the second polishing step.
Through the first step and the second step of polishing, the magnetic control polishing parameters such as magnetic field distribution, magnetic field intensity and the like under the CMP polishing process are determined; further, a planarization magnetron polishing process of the 12-inch single crystal SiC wafer under the CMP polishing process can be established, that is, the magnetron polishing parameters are the same for the same 12-inch single crystal SiC wafer, and planarization can be achieved for the same 12-inch single crystal SiC wafer.
In the present example, the 12-inch SiC wafer thickness data is gradually reduced from the center of the wafer to the radial direction, but the present invention is not limited thereto; the magnetic field intensity can be gradually increased from the center of the wafer to the radial direction; the thickness data of the 12-inch SiC wafer can be firstly reduced and then increased or firstly increased and then reduced from the center of the wafer to the radial direction, and the magnetic field intensity is correspondingly reduced and then increased or firstly increased and then reduced.
In the present example, the 12-inch SiC wafer is subjected to magnetic control polishing, but the present invention is not limited to the 12-inch SiC wafer, and the wafer is 4-inch or more.
It should be noted that the present invention is not limited to the magnetorheological elastomer controlling the uniformity polishing of a single large-sized wafer, but may also be used for uniformly polishing a plurality of wafers arranged in a ring shape. As shown in fig. 5, a plurality of wafers arranged in a ring shape are subjected to magnetic control polishing by a flow shown in fig. 1 while obtaining thickness distribution data in a radial direction along the center of the polishing head.
The control concept of the magnetorheological elastomer is derived from a magnetic control compression model of the magnetorheological elastomer, and the model can be expressed as:
wherein ΔG is the magneto-compression modulus of the magnetorheological elastomer, H is the control magnetic field strength, μ0 is the vacuum permeability, μ1 is the magnetic particle permeability, R is the radius of the magnetic particle, and ε is the compression strain of the elastomer.
The above model shows that the magnetic field strength H is proportional to the modulus G of the magnetorheological elastomer, namely the magnetorheological elastomer has the characteristic of magnetic control rigidity.
It should be noted that, the material removal model concept of the magnetorheological elastomer polishing head for controlling wafer uniformity polishing is derived from Preston's equation, which describes the material removal rate of a wafer and can be expressed as:
R=kPV (2)
wherein R is the material removal rate of the wafer, k is the Preston coefficient, P is the polishing pressure of the wafer surface, and V is the relative speed between the wafer surface and the polishing pad.
The material removal rate of the wafer surface for different areas of the wafer can be expressed as:
R i =∑ i k i P i V i (3)
where Ri is the material removal rate for the i-position of the wafer surface radius, ki is the Preston coefficient for the i-position of the wafer surface radius, pi is the polishing pressure for the i-position of the wafer surface radius, vi is the relative speed of the i-position of the wafer surface radius to the polishing pad.
While illustrative embodiments of the invention have been described, it will be appreciated by those of ordinary skill in the art that: many variations and modifications may be made to the embodiment without departing substantially from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.