Ion implantation method

Abstract

This application provides an ion implantation method that uses an ion implanter to implant arsenic ions into a wafer to reduce the metal contamination content of the wafer. The method includes: generating an arsenic ion beam using the ion source of the ion implanter, the arsenic ion beam comprising multiple dopant ions with different mass-to-charge ratios, the dopant ions having different trajectories in a magnetic field; using a quality analyzer of the ion implanter to screen dopant ions that meet a standard based on their mass-to-charge ratio, the standard dopant ions including at least arsenic ions with a +2 valence; and implanting the standard dopant ions into the wafer using the implantation system of the ion implanter, wherein the implanted content of the +2 valence arsenic ions accounts for more than 99% of the total implanted dopant ions. This ion implantation method can reduce the metal contamination content during ion implantation.

Description

Technical Field

[0001] This application relates to the field of ion implantation, and more particularly to an ion implantation method. Background Technology

[0002] CMOS image sensors (CIS) have replaced CCDs as the mainstream image sensor chip due to their advantages of small size, low power consumption, and high integration. Because phosphorus (P) has a higher diffusion coefficient than arsenic (As) as the N-type implantation source in CIS chip photodiodes, the quantum mechanical tunneling effect increases the probability of phosphorus ion implantation leading to leakage current and the formation of white pixels. Therefore, in the most advanced image sensor chip manufacturing processes, As is used for ion implantation in the N-type regions of the photodiode.

[0003] However, when commonly used ion sources generate As ion beams, they are prone to mixing in metallic impurities (such as titanium, iron, chromium, molybdenum, tungsten, etc.) from silicon-based wafers, forming minority carrier recombination centers that lead to dark currents and cause white pixel defects in image sensor chips. Therefore, reducing the metal contamination content during ion implantation is crucial to the performance of CIS chips. Summary of the Invention

[0004] The technical problem to be solved by this application is to reduce the metal contamination content during ion implantation.

[0005] To address the aforementioned technical problems, this application provides an ion implantation method that uses an ion implanter to implant arsenic ions into a wafer to reduce the metal contamination content of the wafer. The method includes: generating an arsenic ion beam using the ion source of the ion implanter, the arsenic ion beam comprising multiple dopant ions with different mass-to-charge ratios, the dopant ions having different trajectories in a magnetic field; using the mass-to-charge ratio of the ion implanter's mass analyzer to screen for dopant ions that meet a standard, the dopant ions meeting the standard including at least arsenic ions with a +2 valence; and implanting the standard dopant ions into the wafer using the implantation system of the ion implanter, wherein the implanted content of the +2 valence arsenic ions accounts for more than 99% of the total implanted dopant ions.

[0006] In some embodiments of this application, the doped ions that meet the standard are doped ions with a mass-to-charge ratio between 34.5 and 40.5.

[0007] In some embodiments of this application, the mass analyzer of the ion implanter distinguishes the trajectories of doped ions with different mass-to-charge ratios in the magnetic field, thereby screening out doped ions that meet the criteria.

[0008] In some embodiments of this application, the ion source is a molybdenum metal ion source or a tungsten metal ion source.

[0009] In some embodiments of this application, the ion source gas includes arsine.

[0010] In some embodiments of this application, before implanting the standard-compliant doped ions into the wafer, the ion implantation method further includes: accelerating the standard-compliant doped ions using the accelerator of the ion implanter, wherein the acceleration method is radio frequency linear acceleration.

[0011] In some embodiments of this application, the accelerator includes at least eight radio frequency acceleration units, and each radio frequency acceleration unit is used to accelerate the standard-compliant doped ions.

[0012] In some embodiments of this application, the input power of the radio frequency acceleration unit is not less than 2kW.

[0013] In some embodiments of this application, the energy during implantation of the +2 valence arsenic ions is 100 keV to 5000 keV.

[0014] In some embodiments of this application, arsenic ions are implanted into the wafer to form the N-type region of the photodiode.

[0015] Compared with the prior art, the ion implantation method of this application has the following advantages:

[0016] Based on the requirements of image sensor chips for metal contamination levels, by comprehensively considering the mass-to-charge ratio range of common metal doped ions and combining the screening characteristics of the quality analyzer of the ion implanter, the valence state of the target arsenic ion beam is determined. This effectively reduces the metal contamination content introduced during arsenic ion beam implantation into wafers, improves chip yield, and is applicable to both molybdenum metal ion sources and tungsten metal ion sources. It also has the advantage of low cost.

[0017] The ion implantation method of this application has a large energy of implanted ions during ion implantation, which can meet the requirements for deep implantation of wafers. Attached Figure Description

[0018] The following accompanying drawings describe in detail the exemplary embodiments disclosed in this application. The same reference numerals denote similar structures in several views of the drawings. Those skilled in the art will understand that these embodiments are non-limiting and exemplary, and the drawings are for illustrative purposes only and are not intended to limit the scope of this application. Other embodiments may similarly fulfill the inventive intent of this application. It should be understood that the drawings are not drawn to scale. Wherein:

[0019] Figure 1 This is a schematic flowchart of the ion implantation method according to an embodiment of this application;

[0020] Figure 2 This is a schematic diagram of the ion implanter according to an embodiment of this application;

[0021] Figure 3 This is a schematic diagram showing the results of testing the metal contamination content using the ion implantation method of this application. Detailed Implementation

[0022] The following description provides specific application scenarios and requirements for this application, intended to enable those skilled in the art to make and use the content of this application. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.

[0023] An ion implanter is the equipment used in the ion implantation process for semiconductor chips. To prevent metal contamination introduced by the ion acceleration system, a thick layer of carbon is wrapped around the inner layers of the entire ion beam system (including the inner walls of the mass spectrometer's analytical magnetic field, the scanning system, the focusing system, and the filtering system). However, the carbon protective layer's effect on preventing metal contamination is limited to reducing metal ions generated by sputtering. It has no significant effect on metal doped ions generated by ion source dissociation. Metal ions with a mass-to-charge ratio similar to the selected implanted ions will still be implanted into the final wafer, causing metal contamination and forming recombination centers of minority carriers in the wafer. This leads to dark current and causes white pixel defects in CIS chips.

[0024] In the most advanced image sensor chip manufacturing processes, arsenic ions are used as the ion source for implanting the N-type region of photodiodes in ion implantation. To obtain a high-energy arsenic ion beam, arsenic ions with a valence of +3 are often used for acceleration. However, the mass-to-charge ratio of +3 arsenic ions is close to that of +2 titanium ions, +2 iron ions, +2 chromium ions, and +4 molybdenum ions. In particular, the ion source of ion implanters is usually made of molybdenum metal, leading to severe molybdenum contamination of the wafer. Currently, the common approach is to change the ion source cavity material (from molybdenum metal to tungsten metal) to reduce the degree of molybdenum metal contamination. However, tungsten metal itself is expensive, and boron ion beam implantation may introduce tungsten fluoride, contaminating the final wafer.

[0025] Based on this, the present application provides an ion implantation method that can reduce the metal contamination content of wafers, and is applicable to both molybdenum metal ion sources and tungsten metal ion sources.

[0026] refer to Figure 1The ion implantation method in this application embodiment uses an ion implanter to implant arsenic ions into a wafer, and includes the following steps:

[0027] Step S1: An arsenic ion beam is generated by the ion source of the ion implanter. The arsenic ion beam includes a variety of doped ions with different mass-to-charge ratios. The doped ions with different mass-to-charge ratios have different trajectories when moving in a magnetic field.

[0028] Step S2: The mass analyzer of the ion implanter is used to screen out doped ions that meet the standard by mass-to-charge ratio. The doped ions that meet the standard include at least arsenic ions with a +2 valence.

[0029] Step S3: The standard-compliant doped ions are implanted into the wafer through the implantation system of the ion implanter, wherein the implantation content of +2 valence arsenic ions accounts for more than 99% of the total implantation content of doped ions.

[0030] Combination Figure 1 and Figure 2 The ion source 1 of the ion implanter uses arsenic ions for wafer ion implantation, for example, to form the N-type region of a photodiode. The ion source 1 of the ion implanter can generate an arsenic ion beam. The arsenic ion beam includes various doped ions with different mass-to-charge ratios, and these doped ions have different trajectories when moving in a magnetic field. The ion source 1 of the ion implanter can be a molybdenum metal ion source or a tungsten metal ion source. When using existing ion implantation methods, the use of a molybdenum metal ion source introduces molybdenum metal contamination. While a tungsten metal ion source can reduce the degree of molybdenum metal contamination, it introduces tungsten fluoride contamination. The ion implantation method of this application embodiment can significantly reduce the metal contamination content even when using a molybdenum metal ion source or a tungsten metal ion source. The ion source gas of this application embodiment may include arsine.

[0031] After generating the arsenic ion beam, it is accelerated using an accelerating electrode 2. Then, the mass analyzer 3 of the ion implanter filters out dopant ions that meet the standard based on their mass-to-charge ratio, allowing these compliant dopant ions to proceed to the next system. In actual operation, the mass analyzer 3 of the ion implanter distinguishes the trajectories of dopant ions with different mass-to-charge ratios in the magnetic field, thereby filtering out dopant ions that meet the standard. In this embodiment, the dopant ions that meet the standard include at least arsenic ions with a +2 valence. In some embodiments, in addition to the +2 valence arsenic ions, the dopant ions that meet the standard may also include other dopant ions with a mass-to-charge ratio between 34.5 and 40.5.

[0032] Table 1 shows the types of ions that may cause wafer metal contamination and their relative atomic masses. Existing technologies typically select +3 valence arsenic ions as implantation ions. Considering the accuracy of the mass analyzer 3 during actual ion implantation, metal ions within the target ion mass-to-charge ratio range of ±3 have a very high probability of being implanted into the final wafer. Among them, Ti... 2+ Cr 2 + V 2+ Fe 2+ Mo 4+ The mass-to-charge ratios of these five metal ions are all around 25 and are similar to those of As. 3+ The mass-to-charge ratios of these five metal ions are close, so all of them could potentially pass through mass analyzer 3 and enter the wafer, causing metal contamination. However, the mass-to-charge ratio of +2 valence arsenic ions is 37.5, therefore using +2 valence arsenic ions as the arsenic ion beam source can effectively remove the contaminants from Ti. 2+ Cr 2+ V 2+ Fe 2+ Mo 4+ These five metal ions are filtered in the mass analyzer, and this method can also effectively filter out Mo. 3+ Mo 2+ Metal doped ions.

[0033] Table 1. Types of ions that may cause wafer metal contamination and their relative atomic masses.

[0034]

[0035]

[0036] After selecting dopant ions that meet the criteria, the dopant ions are accelerated by the accelerator of the ion implanter, and the acceleration method is radio frequency linear acceleration. In this embodiment, the accelerator includes at least eight radio frequency acceleration units 4, and each radio frequency acceleration unit 4 is used to accelerate the dopant ions that meet the criteria. Figure 2 Nine radio frequency (RF) acceleration units 4 are shown. The structure of each RF acceleration unit 4 can be any existing structure capable of accelerating doped ions. In this embodiment, each RF acceleration unit 4 includes a quadrupole focusing electrode 41 and an RF acceleration electrode 42. The input power of each RF acceleration unit 4 is not less than 2 kW. Therefore, the energy during implantation of +2 valence arsenic ions is 100 keV to 5000 keV. The implanted ion energy in this embodiment is relatively high, enabling deep implantation of the wafer.

[0037] Subsequently, the standard-compliant doped ions are implanted into the wafer through the implantation system 5 of the ion implanter. The structure of the implantation system 5 can be any existing implantation structure, as long as it can achieve ion implantation. The implantation method of this embodiment can make the implanted content of +2 valence arsenic ions account for more than 99% of the total implanted doped ions, significantly reducing the metal contamination content of the wafer.

[0038] The ion implantation method of this application embodiment was tested as follows.

[0039] On a high-energy ion implanter using radio frequency linear acceleration, an ion beam with arsenic as the ion type and an energy of 2000 keV was tuned. Arsenic ions with a mass-to-charge ratio (M / q) of 37.5 with a +2 valence were selected and implanted into wafer A.

[0040] Take wafer B and, on a high-energy ion implanter using radio frequency linear acceleration, tune an ion beam of arsenic with an energy of 2000 keV. Use the ion implanter to select +3 valence arsenic ions with a mass-to-charge ratio (M / q) of 25 and implant them into wafer B.

[0041] The metal impurity content of wafers A and B was measured using inductively coupled plasma mass spectrometry (ICP-MS) to obtain the metal contents of titanium, iron, and molybdenum. Figure 3 As shown, when arsenic ion beams with +2 valence and +3 valence are implanted into the wafer, the content of metal impurities introduced by the +2 valence ion beam is significantly reduced.

[0042] In summary, after reading this application, those skilled in the art will understand that the foregoing application content is presented by way of example only and is not restrictive. Although not explicitly stated herein, those skilled in the art will understand that this application is intended to encompass various reasonable changes, improvements, and modifications to the embodiments. These changes, improvements, and modifications are all within the spirit and scope of the exemplary embodiments of this application.

[0043] The terms “comprising,” “including,” “including,” or “comprise” as used in this application document indicate the presence of the described features, wholes, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or groups thereof.

[0044] Furthermore, this application specification describes exemplary embodiments by referring to idealized exemplary cross-sectional views and / or plan views and / or perspective views. Therefore, differences from the illustrated shapes are foreseeable due to factors such as manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but should include deviations in shape caused, for example, by manufacturing processes. For instance, etched areas shown as rectangular typically have circular or curved features. Therefore, the regions shown in the figures are substantially schematic, and their shapes are not intended to illustrate the actual shape of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

Claims

1. An ion implantation method, comprising implanting arsenic ions into a wafer using an ion implanter, and used to reduce the metal contamination content of the wafer, characterized in that, include: An arsenic ion beam is generated by the ion source of the ion implanter. The arsenic ion beam comprises various doped ions with different mass-to-charge ratios. These doped ions with different mass-to-charge ratios exhibit different trajectories during their movement in a magnetic field. The doped ions with different mass-to-charge ratios include arsenic ions with a +2 valence and Ti ions. 2+ Cr 2+ V 2+ Fe 2+ Mo 4+ ; The mass analyzer of the ion implanter screens out doped ions that meet the standard by mass-to-charge ratio. The doped ions that meet the standard are doped ions with a mass-to-charge ratio between 34.5 and 40.5, and include at least arsenic ions with a +2 valence. The standard-compliant doped ions are implanted into the wafer using the implantation system of the ion implanter, wherein the implantation content of +2 valence arsenic ions accounts for more than 99% of the total implantation content of doped ions.

2. The ion implantation method according to claim 1, characterized in that, The mass analyzer of the ion implanter distinguishes the trajectories of doped ions with different mass-to-charge ratios in the magnetic field, thereby screening out doped ions that meet the standards.

3. The ion implantation method according to claim 1, characterized in that, The ion source is a molybdenum metal ion source or a tungsten metal ion source.

4. The ion implantation method according to claim 1, characterized in that, The ion source gas includes arsine.

5. The ion implantation method according to claim 1, characterized in that, Before implanting the standard-compliant impurity ions into the wafer, the ion implantation method further includes: accelerating the standard-compliant doped ions using the accelerator of the ion implanter, wherein the acceleration method is radio frequency linear acceleration.

6. The ion implantation method according to claim 5, characterized in that, The accelerator includes at least eight radio frequency acceleration units, and each radio frequency acceleration unit is used to accelerate the standard-compliant doped ions.

7. The ion implantation method according to claim 6, characterized in that, The input power of the radio frequency acceleration unit is not less than 2kW.

8. The ion implantation method according to claim 1, characterized in that, The energy for implanting the +2 valence arsenic ions is 100 keV to 5000 keV.

9. The ion implantation method according to claim 1, characterized in that, Arsenic ions are implanted into the wafer to form the N-type region of the photodiode.

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