Laser Annealing Method for Back-Illuminated Image Sensor

Abstract

The present invention provides a laser annealing method for a back-illuminated image sensor, comprising providing a substrate, thinning the back surface of the substrate, and then performing wet cleaning on the substrate; forming a first silicon dioxide layer on the front surface of the substrate; doping the substrate to generate a doped layer at the top of the substrate; annealing the substrate with high-energy laser so that the first silicon dioxide layer is converted into a silicon layer. Before laser annealing of the substrate in the present invention, a silicon dioxide layer is deposited, reducing the tunneling effect during the arsenic ion implantation process; protecting silicon during the laser annealing process to prevent local areas of the substrate from melting under the high temperature generated by the laser annealing; silicon dioxide has the effect of increasing the laser transmittance, and the annealing effect is better; silicon dioxide will react with carbon and be transformed into pure silicon in the enhanced laser annealing, without the need for wet protection of the front surface.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly to a laser annealing method for a back-illuminated image sensor. Background Art

[0002] X-ray silicon detectors are mainly divided into two categories: amorphous flat-panel X-ray detectors and high-end silicon-based X-ray detectors. The domestic technology of amorphous flat-panel X-ray detectors is relatively mature at present, with certain international market competitiveness, and the process manufacturing is not compatible with the FAB process. Silicon-based X-ray detectors have developed two generations so far. The first-generation products are front-illuminated processes, which are compatible with the FAB process and do not require the backside process of silicon wafers, and the process complexity is relatively low. The second-generation products are back-illuminated processes, which add the backside process of silicon wafers on the basis of the first-generation process, with higher accuracy and more flexible applications.

[0003] Figure 2 It is the so-called FSI silicon detector, that is, X-rays are converted into light by a scintillator and then incident on the silicon detector from the front. The silicon PIN / array needs to be side-bonded to the PCB. In this way, such a detector module can only be made one-dimensional. Figure 3 It is a back-illuminated silicon detector. X-rays are converted into light by a scintillator and then incident on the silicon detector from the back. The generated photoelectrons need to diffuse to the front active region before they can be collected as electrical signals. Here, the silicon diode / array is directly flip-chip bonded to the PCB through the flip-chip technology. In this way, a two-dimensional detection system can be realized.

[0004] In the current back-illuminated silicon detectors, the following problems exist:

[0005] When laser annealing the substrate, local regions of the substrate melt at the high temperature generated by the laser annealing;

[0006] The back-illuminated silicon detector does not have a tool to remove the silicon dioxide layer on the substrate, and the removal of the silicon dioxide layer is rather troublesome. Summary of the Invention

[0007] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a laser annealing method for a back-illuminated image sensor, which is used to solve the problems that when laser annealing the substrate in the prior art, local regions of the substrate melt at the high temperature generated by the laser annealing; the back-illuminated silicon detector does not have a tool to remove the silicon dioxide layer on the substrate, and the removal of the silicon dioxide layer is rather troublesome.

[0008] To achieve the above object and other related objects, the present invention provides a laser annealing method for a back-illuminated image sensor, including:

[0009] Step 1: Provide a substrate, thin the back surface of the substrate, and then perform wet cleaning on the substrate;

[0010] Step 2: Form a first silicon dioxide layer on the front surface of the substrate;

[0011] Step 3: Dope the substrate, and generate a doped layer on the front surface layer of the substrate below the first dioxide layer;

[0012] Step 4: Anneal the substrate using high-energy laser, so that the first silicon dioxide layer is converted into a silicon layer.

[0013] Preferably, in Step 1, the back surface of the substrate is soldered to the PCB board through the bump process technology.

[0014] Preferably, the substrate in Step 1 is an N-type substrate.

[0015] Preferably, the ions doped in Step 3 are arsenic ions. Preferably, in Step 1, the Taiko process is used to thin the back surface of the substrate.

[0016] Preferably, the thinning thickness of the back surface of the substrate in Step 1 is 100 microns.

[0017] Preferably, the resistivity of the substrate in Step 1 is 700 Ω.cm.

[0018] Preferably, the power of the high-energy laser in Step 4 is 1.2 J / CM^2 to 3.6 J / CM^2.

[0019] Preferably, it further includes Step 5: Deposit a silicon nitride layer on the silicon layer; and then deposit a second oxide layer on the silicon nitride layer.

[0020] Preferably, the thickness of the silicon nitride layer is 500 Å to 800 Å.

[0021] Preferably, the thickness of the second silicon dioxide layer is 5000 Å to 7000 Å.

[0022] As described above, the laser annealing method for the back-illuminated image sensor of the present invention has the following beneficial effects:

[0023] Before laser annealing of the substrate in the present invention, a silicon dioxide layer is deposited, which reduces the tunneling effect during the arsenic ion implantation process; protects the silicon during the laser annealing process, preventing the local area of the substrate from melting under the high temperature generated by the laser annealing; silicon dioxide has the effect of laser antireflection, and the annealing effect is better; silicon dioxide will react with carbon and be converted into pure silicon in the enhanced laser annealing, without the need for wet protection of the front surface. Description of the Drawings

[0024] Figure 1Shown is a schematic process flow diagram of the present invention;

[0025] Figure 2 Shown is a schematic diagram of a front-illuminated silicon detector in the prior art;

[0026] Figure 3 Shown is a schematic diagram of a back-illuminated silicon detector in the prior art;

[0027] Figure 4 Shown is a schematic diagram of the substrate of the present invention;

[0028] Figure 5 Shown is a schematic diagram of forming the first oxide layer of the present invention;

[0029] Figure 6 Shown is a doping schematic diagram of the present invention;

[0030] Figure 7 Shown is a schematic diagram of forming the doped layer of the present invention;

[0031] Figure 8 Shown is an annealing schematic diagram of the present invention;

[0032] Figure 9 Shown is a schematic diagram of forming the silicon layer of the present invention;

[0033] Figure 10 Shown is a schematic diagram of the subsequent process of the present invention.

[0034] Explanation of reference numerals:

[0035] Substrate - 10

[0036] First silicon dioxide layer - 11

[0037] Doped layer - 12

[0038] Silicon layer - 13

[0039] Silicon nitride layer - 14

[0040] Second silicon dioxide layer - 15 Detailed implementation manners

[0041] The following illustrates the implementation manners of the present invention through specific specific examples. 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 implementation manners, 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.

[0042] Please refer to Figure 1 , the present invention provides a laser annealing method for a back-illuminated image sensor, including:

[0043] Step 1: Provide a substrate 10 as shown in Figure 4 . Then, thin the back side of the substrate 10. The wafer substrate 10 can be thinned by thinning or grinding to improve the chip heat dissipation effect. At the same time, thinning to a certain thickness is beneficial to the subsequent packaging process. After that, wet wash the substrate 10 to remove the by-products during thinning;

[0044] In a possible implementation manner, in Step 1, the back side of the substrate 10 is soldered to the PCB board through the bump process technology.

[0045] In a possible implementation manner, the substrate 10 in Step 1 is an N-type substrate 10 or a P-type substrate 10, and its N-type substrate 10 or P-type substrate 10 can be formed by ion implantation. The type of the substrate 10 is determined according to the actual product type, and no specific limitation is made here.

[0046] In a possible implementation manner, the Taiko process is a wafer back grinding technology in the prior art. This technology is different from the previous back grinding. When grinding the wafer, the edge part (about 3 mm) of the wafer periphery will be retained, and only the inside of the circle is ground and thinned. By introducing this technology, the effect of reducing the handling risk of the thin wafer and reducing warping can be achieved. The thinning method in Step 1 is preferably the Taiko process.

[0047] In a possible implementation manner, the thickness of thinning in Step 1 is 100 microns.

[0048] In a possible implementation manner, the resistivity of the substrate 10 in Step 1 is 700 Ω·cm.

[0049] Step 2: Refer to Figure 5 . The first silicon dioxide layer 11 can be formed on the front side of the substrate 10 by thermal growth or deposition. Here, the first silicon dioxide layer 11 is used to reduce the tunneling effect during the ion implantation process;

[0050] Step 3: Refer to Figure 6 . Dope the substrate 10, and a doped layer 12 as shown in Figure 7 is generated at the top of the front side of the substrate 10;

[0051] In a possible implementation manner, the ion type of doping in Step 3 is opposite to the type of the substrate 10. If the substrate 10 is P-type, the ion type of doping is N-type. If the substrate 10 is N-type, the ion type of doping is P-type.

[0052] In a possible implementation manner, the substrate 10 is N-type and the doped ion is arsenic ion.

[0053] Step 4: Refer toFigure 8 , high-energy laser is used to anneal the substrate 10, so that the first silicon dioxide layer 11 reacts with carbon at high temperature and is transformed into a silicon layer 13 as shown in Figure 9 . The silicon layer 13 here protects the substrate 10 during the laser annealing process, preventing the local area of the substrate 10 from melting under the high temperature generated by the laser annealing, and can also play a role in increasing the laser transmission, resulting in a better annealing effect.

[0054] In a possible implementation manner, the power of the high-energy laser in step four is 1.2 J / CM^2 to 3.6 J / CM^2.

[0055] In a possible implementation manner, please refer to Figure 10 . It further includes step five, depositing a silicon nitride layer 14 on the silicon layer 13; and then depositing a second silicon dioxide layer 15 on the silicon nitride layer 14; which can protect the substrate 10, and then the substrate 10 is removed and fixed.

[0056] In a possible implementation manner, the thickness of the silicon nitride layer 14 is 500 angstroms to 800 angstroms.

[0057] In a possible implementation manner, the thickness of the second silicon dioxide layer 15 is 5000 angstroms to 7000 angstroms.

[0058] It should be noted that the illustrations provided in this embodiment only schematically illustrate the basic concept of the present invention. Therefore, only the components related to the present invention are shown in the drawings, rather than being drawn according to the number, shape and size of the components in actual implementation. The types, quantities and proportions of the components in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0059] In summary, before laser annealing of the substrate in the present invention, a silicon dioxide layer is deposited to reduce the tunneling effect during the arsenic ion implantation process; protect silicon during the laser annealing process to prevent the local area of the substrate from melting under the high temperature generated by the laser annealing; the silicon dioxide has the effect of increasing the laser transmission, and the annealing effect is better; the silicon dioxide will react with carbon and be transformed into pure silicon in the enhanced laser annealing, without the need for wet protection of the front surface. Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0060] The above embodiments only illustratively explain the principles and effects of the present invention, rather than limiting the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A laser annealing method for a back-illuminated image sensor, characterized in that, it at least includes: Step 1: Provide a substrate, then thin the back surface of the substrate, and then perform wet cleaning on the substrate; Step 2: Form a first silicon dioxide layer on the front surface of the substrate; Step 3: Dope the substrate to generate a doped layer at the top of the front surface of the substrate; Step 4: Anneal the substrate with high-energy laser, so that the first silicon dioxide layer reacts with carbon at high temperature to be converted into a silicon layer. The silicon layer is used to protect the substrate during the laser annealing process, prevent the local area of the substrate from melting at the high temperature generated by the laser annealing, and play a role in laser antireflection to enhance the annealing effect.

2. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The back surface of the substrate in Step 1 is welded to the PCB board through a bump process technology.

3. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The substrate in Step 1 is an N-type substrate or a P-type substrate.

4. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The ion type of the doping in Step 3 is opposite to the type of the substrate.

5. The laser annealing method for a back-illuminated image sensor according to claim 4, characterized in that: The doped ion is an arsenic ion.

6. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The thinning method in Step 1 is the Taiko process.

7. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The thickness of the thinning in Step 1 is 100 microns.

8. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The resistivity of the substrate in Step 1 is 700 Ω·cm.

9. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The power of the high-energy laser in Step 4 is 1.2 J / cm² to 3.6 J / cm².

10. The laser annealing method for a back-illuminated image sensor according to claim 1, characterized in that: The annealing process further includes depositing a silicon nitride layer on the silicon layer; and then depositing a second silicon dioxide layer on the silicon nitride layer.

11. The laser annealing method for a back-illuminated image sensor according to claim 10, characterized in that: The thickness of the silicon nitride layer is 500 Å to 800 Å.

12. The laser annealing method for a back-illuminated image sensor according to claim 10, characterized in that: The thickness of the second silicon dioxide layer is 5000 Å to 7000 Å.

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