A method for estimating the ion beam width at the analysis slit

Abstract

The present invention discloses a method for estimating the width of the ion beam at the analysis slit. The present invention is used in fields related to ion mass analysis, mainly in the field of ion implanters in semiconductor equipment. The resolving power of a mass analyzer mainly depends on the width of the ion beam at the analysis slit and the width of the analysis slit itself. The width of the ion beam itself is not easy to measure directly, but the width of the analysis slit can be controlled, and the resolution of the mass analyzer is mainly determined by the wider of the two widths. By measuring the resolution of the mass analyzer at different analysis slit widths, the present method can obtain different resolutions determined by the ion beam width and the analysis slit width, and then can estimate the width of the ion beam itself at the analysis slit.

Description

Technical Field

[0001] The present invention is used in fields related to ion mass analysis, mainly in the field of ion implanters in semiconductor equipment. Background Art

[0002] Ion implanters are machines used in semiconductor manufacturing to dope substrates. Ion implantation involves bombarding the substrate with ions of the desired type and energy at a specific angle. During the ion implantation process, selecting the desired ions is crucial, and this is primarily dependent on the resolution of the mass analyzer.

[0003] When the ion beam generated by the ion source passes through the mass analyzer, it is affected by the magnetic field, causing ions of different charge-to-mass ratios to move along different trajectories, forming beam spots at different locations. By controlling the mass analyzer's magnetic field, the ion beam that passes through the analysis slit can be precisely the desired ions. The resolving power of a mass analyzer, or resolution M / ΔM, is primarily determined by the width of the beam at the analysis slit and the width of the analysis slit itself. While the width of the analysis slit is generally adjustable, the width of the ion beam at the analysis slit is generally determined by the mass analyzer itself. The ion beam width at the analysis slit also determines the optimal resolution achievable by the mass analyzer.

[0004] The present invention measures the resolution under different analysis slit widths to obtain the resolution under the condition that it is mainly affected by the ion beam width, and estimates the width of the ion beam at the analysis slit. Summary of the Invention

[0005] The present invention is a method for estimating the ion beam width at the analysis slit. In a specific exemplary embodiment, the technology can be implemented as a method for estimating the ion beam width at the analysis slit in an ion implanter system. In an ion implanter, the ion source is a key component for generating plasma, the mass analyzer is a key component for screening desired ions, the analysis slit is a key component for separating ion beams of adjacent masses, and the Faraday cup is a component for detecting the desired ion beam strength. The present invention should at least include an ion source, a mass analyzer, an analysis slit with adjustable width, and a Faraday cup.

[0006] The resolving power of a mass analyzer, or resolution R = M / ΔM (where M is the ion mass), is primarily determined by the width of the ion beam at the analysis slit and the width of the analysis slit itself. When the analysis slit is wide, the resolution is primarily determined by the slit width. When the analysis slit is wide, the resolution is primarily determined by the ion beam width. The relationship between the resolution and the wider of the two is the same:

[0007] R=M / ΔM≈R m / 2w (1)

[0008] where R mis the fixed ion deflection radius of the mass analyzer, and w is the wider of the analysis slit width and the beam width. Based on the above relationship, by comparing the mass analysis system resolution when the analysis slit width is larger than the ion beam width, and when the analysis slit width is smaller than the ion beam width, the relative relationship between the ion beam width and the analysis slit width can be indirectly obtained. Since the analysis slit width is known, an estimate of the ion beam width at the analysis slit can be obtained. The specific method is as follows, optionally including the following steps:

[0009] Step 1: Set the analysis slit width to a fixed width D1 and calculate the resolution R1 of the mass analysis system under this condition.

[0010] Step 2: Adjust the width of the analysis slit from D1 to D2 and calculate the resolution R2 of the mass analysis system under this condition.

[0011] Step 3: Adjust D2 in step 2 to D3, D4...D n , calculate the corresponding resolutions R3, R4...R n ;

[0012] Step 4: Define α as the analysis gap width D i Corresponding to system resolution R i The product of α1, α2, ... α n ;

[0013] Step 5: Compare α1, α2, ... α n , select several larger and closer α i , find its average value α A ;

[0014] Step 6: Compare α1, α2, ... α n , select several lower α i , and its corresponding R i , selected from R i The values should be close. After removing the values with large errors, calculate the remaining R i The average value R A ;

[0015] Step 7: Calculate and compare α A / R A , which is the estimated width of the ion beam at the analysis slit.

[0016] In the above step 5, the selected α i , is when the analysis slit width is larger than the ion beam width. At this time, the resolution of the system is mainly affected by the analysis slit width. A Approximately R m / 2, from which we can get R mIn the above step 6, the selected α i , is when the analysis slit width is smaller than the ion beam width. At this time, the resolution of the system is mainly affected by the ion beam width. According to formula (1), the estimated ion beam width at the analysis slit can be obtained in step seven.

[0017] As can be seen from the above description, the present invention needs to record the resolution of the mass analysis system at different analysis slit widths, and then obtain an estimate of the ion beam width. The resolution of the mass analysis system can be obtained by the following method, which optionally includes the following steps:

[0018] Step 1: The ion source generates a stable ion beam and sets the analysis slit to a fixed width;

[0019] Step 2: Adjust the mass analyzer current to I1 so that the Faraday cup detects the beam of the desired ions;

[0020] Step 3: Adjust the mass analyzer current from I1 to I0 so that the Faraday cup cannot detect the ion beam current;

[0021] Step 4: Adjust the mass analyzer current from I1 to I2 so that the Faraday cup cannot detect the ion beam current;

[0022] Step 5: Adjust the mass analyzer current from I0 to I2, and record the mass analyzer current value and the ion beam current value detected by the Faraday cup when the mass analyzer current changes;

[0023] Step 6. From the recorded data, find the maximum value of the ion beam current detected by the Faraday cup I MAX , and the corresponding mass analyzer current I3;

[0024] Step 7: From the recorded data, find half of the maximum value of the ion beam current detected by the Faraday cup. MAX / 2, and the corresponding two current values I4 and I5 of the mass analyzer (I4<I5);

[0025] Step 8. Calculate I3 / 2(I5-I4), which is the resolution of the current system.

[0026] The principle of the above method to obtain the resolution of the mass analysis system is that the resolution is defined by the ion mass M, and

[0027] Mv 2 / 2=E·q (2)

[0028] M·v 2 / R m =B·q·v (3)

[0029] From (2) and (3), we can get

[0030] M=q(B·R m ) 2 / 2E (4)

[0031] Differentiate (4) to get

[0032] dM=q·R m 2 ·B·dB / E (5)

[0033] Dividing (4) and (5) yields

[0034] M / dM=B / 2dB (6)

[0035] When M is much larger than ΔM, M / ΔM can be regarded as M / dM, and the magnetic field strength B is proportional to the mass analyzer current to a certain extent, then

[0036] M / ΔM=I / 2ΔI (7)

[0037] M is the ion mass corresponding to the analyzer current when the Faraday beam current reaches its maximum value, and ΔM is the full width at half maximum. Equation (7) shows that the resolution of the mass analysis system can be obtained from the analyzer current corresponding to the ion beam peak and the analyzer current width corresponding to the full width at half maximum.

[0038] The present invention has the following advantages: the present invention only requires an ion source, a mass analyzer, an analysis slit with adjustable width, and a Faraday cup to estimate the width of the ion beam at the analysis slit, without adding any additional hardware facilities; the ion deflection radius R inherent in the mass analyzer is m If the ion deflection radius R is unknown, this method can also be used to obtain the ion deflection radius R. m ; Since the analysis slit width is adjustable, the ion beam width at the analysis slit determines the highest resolution that the mass analysis system can achieve. By estimating the ion beam width through this method, the highest resolution that the mass analysis system can achieve can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to help more fully understand the content disclosed by the present invention, reference is now made to the accompanying drawings. These drawings should not be understood as limiting the content disclosed by the present invention, but are only used for exemplary explanation.

[0040] Figure 1 Schematic diagram of the quality analysis system

[0041] Figure 2 Faraday cup beam current change trend diagram DETAILED DESCRIPTION

[0042] The content disclosed in the present invention discloses a method for estimating the width of the ion beam at the analysis slit. To introduce the present invention in more detail, an example is now introduced with reference to the accompanying drawings.

[0043] Figure 1 This is a simplified diagram of a mass analysis system. In one specific example, an ion source 101 generates a stable plasma, which is extracted to form a particle beam 102 containing desired ions. After the particle beam is processed by a mass analyzer 103, an ion beam 104 formed by the desired ions is screened out and converges at an analysis slit 105. The analysis slit 105 separates the desired ion beam from ion beams of similar mass, and then the ion beam 104 is detected by a Faraday cup 106.

[0044] First, the width of the analysis slit 105 is set to 10 mm. When the beam is in good condition, this width is generally larger than the ion beam width at the analysis slit. Then, the current I1 of the mass analyzer 103 is adjusted to 98.5 A so that the desired ion beam 104 is detected by the Faraday cup 106.

[0045] Then adjust the current of the analyzer 103 up and down to 97.5A and 99A, so that the Faraday cup 106 cannot detect the ion beam current. Under normal circumstances, it is sufficient to make the beam current detected by the Faraday cup 106 less than 1 / 2 of the maximum value.

[0046] The analyzer 103 current was slowly adjusted from 97.5 A to 99 A with a step size of 0.02 A. Each time the current was adjusted, the analyzer current and the corresponding beam current detected by the Faraday 106 were recorded.

[0047] Figure 2 For the Faraday cup beam current variation trend diagram, find the maximum value of the beam current detected by the Faraday cup I MAX , is 7.89mA, the corresponding analyzer current I3 is 98.37A, and the Faraday cup beam current is I MAX The analyzer current range of / 2, I4-I5, is 97.96A-98.99A.

[0048] As explained above, the resolution of the current system can be calculated using I3, I4, and I5. Therefore, when the analysis slit width is 10 mm, the resolution of the mass analysis system is I3 / 2(I5-I4)=48.

[0049] The analysis slit width is set to 9mm, 8mm, 7mm...1mm in sequence, and the above method of calculating the resolution of the mass analysis system is repeated to obtain the resolution of the analysis system under each analysis slit width, and the product α of the analysis slit width D and the resolution R is calculated.

[0050] At 10mm, the resolution is 48, α = 480;

[0051] At 9mm, the resolution is 53, α = 477;

[0052] At 8mm, the resolution is 60, α = 480;

[0053] At 7mm, the resolution is 68, α = 476;

[0054] At 6mm, the resolution is 79, α = 474;

[0055] At 5mm, the resolution is 98, α = 490;

[0056] At 4mm, the resolution is 123, α = 492;

[0057] At 3mm, the resolution is 141, α = 423;

[0058] At 2 mm, the resolution is 136, α = 272;

[0059] The resolution is 136 at 1mm, α=136.

[0060] Analyzing the above data, we can see that when the analysis slit width D>=4mm, the α value is large and close. At this time, the analysis slit width is larger than the ion beam width at the analysis slit, and the resolution is mainly affected by the analysis slit width. Calculate the average value of α when D>4mm A =481.3.

[0061] When D < 4 mm, the α value is small and the resolution is close. At this time, the width of the analysis slit is smaller than the width of the ion beam at the analysis slit. The resolution is mainly affected by the width of the ion beam at the analysis slit. Find the average value R of the resolution R when D < 4 mm. A =137.7.

[0062] As explained in the previous article, α A With R A The estimated width of the ion beam at the analysis slit is about α A / R A =3.5mm.

[0063] In this example, the ion beam width at the analysis slit is approximately 3.5 mm.

[0064] It should be noted that this example is only for introducing the present invention, not for limiting the present invention. Practitioners in related fields can clearly understand the implementation method of this patent through this patent. Minor changes based on this example will not affect the implementation of the method of this patent.

Claims

1. A method for estimating the width of an ion beam at an analysis slit, comprising at least an ion source, a mass analyzer, an analysis slit with adjustable width, and a Faraday cup, wherein: The following steps are involved: Step 1: Set the analysis slit width to a fixed width D1 and calculate the resolution R1 of the mass analysis system under this condition. Step 2: Adjust the width of the analysis slit from D1 to D2 and calculate the resolution R2 of the mass analysis system under this condition. Step 3: Adjust D2 in step 2 to D3, D4...D n , calculate the corresponding resolutions R3, R4...R n ; Step 4: Define α i The width of the analysis gap D i Corresponding to system resolution R i The product of α1, α2, ... α n , where i=1, 2, ..., n; Step 5: Compare α1, α2, ... α n , select several larger and closer α i , find its average value α A ; Step 6: Compare α1, α2, ... α n , select several lower α i , and its corresponding R i , selected from R i The values should be close. After removing the values with large errors, calculate the remaining R i The average value R A ; Step 7: Calculate and compare α A / R A , which is the estimated width of the ion beam at the analysis slit; The analysis gap width is D i The resolution R of the mass analysis system i The calculation formula is I3 / [2(I5-I4)]; I3 is the width of the analysis gap D i The maximum value of the ion beam current IMAX detected at this time corresponds to the mass analyzer current, and I5 is the analysis slit width D i The maximum mass analyzer current corresponding to half of the maximum value of the ion beam current detected at this time is IMAX / 2, and I4 is the analysis slit width D i A smaller mass analyzer current corresponding to half the maximum value of the detected ion beam current IMAX / 2.

2. The method according to claim 1, characterized in that The method for calculating the resolution of a mass analyzer system consists of the following steps: Step 1: The ion source generates a stable ion beam and sets the analysis slit to a fixed width; Step 2: Adjust the mass analyzer current to I1 so that the Faraday cup detects the beam of the desired ions; Step 3: Adjust the mass analyzer current from I1 to I0 so that the Faraday cup cannot detect the ion beam current; Step 4: Adjust the mass analyzer current from I1 to I2 so that the Faraday cup cannot detect the ion beam current; Step 5: Adjust the mass analyzer current from I0 to I2, and record the mass analyzer current value and the ion beam current value detected by the Faraday cup when the mass analyzer current changes; Step 6. From the recorded data, find the maximum value of the ion beam current detected by the Faraday cup I MAX , and the corresponding mass analyzer current I3; Step 7. From the recorded data, find half of the maximum value of the ion beam current detected by the Faraday cup. MAX / 2, and the corresponding two current values of the mass analyzer I4 and I5, where I4<I5; Step 8. Calculate I3 / [2(I5-I4)], which is the resolution of the current system.

3. According to the method of claim 1 or 2, the mass analysis system can be implemented as a partial subsystem of an ion implanter system.

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