JPH0724208B2 - Ion implantation uniformity monitor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an ion implantation uniformity monitoring device for monitoring the uniformity of the amount of ions implanted into a wafer in an ion implantation device.

[Conventional technology]

FIG. 5 is a schematic diagram showing an example of an ion implantation apparatus.
The predetermined ion beam 3 extracted from the ion source 2, mass-analyzed, and accelerated is supplied from the X-axis scanning power source 14 to the X-axis scanning voltage.
The X-axis scan electrode 4 supplied with VX scans in the X-axis direction, and the Y-axis scan electrode 6 supplied with the Y-axis scan voltage VY from the Y-axis scan power supply 16 scans in the Y-axis direction. After passing through, the whole surface of the wafer 10 is irradiated with the ions, so that the ions are implanted into the wafer 10. The wafer 10 is held by the detection electrode 12, and the beam current I of the ion beam 3 with which the wafer 10 is irradiated is detected by the detection electrode 12.

FIG. 6 is a diagram showing the signal waveform of each part of FIG. Y
The axis scanning voltage VY is, for example, a triangular wave of about 500 Hz, the X-axis scanning voltage VX is, for example, a triangular wave of about 90 Hz, and the beam current I
Has a waveform close to a rectangular wave of about 1 KHz, for example. The ion beam I ′ is an enlarged view of the portion A of the ion beam I.

In the ion implantation apparatus as described above, distortion may occur in the scanning waveform, the beam amount may not be constant over time, and the uniformity of the ion implantation amount on the wafer 10 may deteriorate. If such abnormalities are left and ion implantation into the wafer 10 is continued, defective products will appear one after another. When the scanning waveform is distorted, the ion beam comes into contact with a structure or the like and secondary electrons are emitted from the structure, and the secondary electrons are absorbed by the scanning electrodes to cause distortion, or the distorted scanning power supply itself causes distortion. There are cases, etc. As a case where the beam amount is not constant, there are cases where the ion source unit has an unstable operation.

Conventionally, the determination of the uniformity of the amount of ion implantation into the wafer 10 has been performed as follows.

(1) Each wafer is commercialized and then tested as a product to make a pass / fail judgment.

(2) When the advance should perform characterization of the ion implantation apparatus, the wafer F sample injection → heat treatment → [rho _S distribution measurement → uniformity calculation of (surface resistance), through a process such as a determination.

(3) As a simple method to confirm the characteristics in advance,
There is also a method in which a sample is injected into a special plastic film and the distribution of the injection is examined by its transmittance for infrared rays.

[Problems to be solved by the invention]

However, the uniformity determining means as described above has the following problems.

(1) In the case of making a determination after commercialization, since a defect is not identified until it is commercialized, all the wafers manufactured by the time it is identified are defective products, which may cause a large loss.

(2) Even in the case of injecting a sample into a wafer, it takes a long time to make a determination, and the production stop time is long.

(3) When a sample is injected into a plastic film, a special material is consumed as a film, and the result for each wafer is unknown.

Therefore, it is an object of the present invention to provide an apparatus capable of determining the uniformity of implantation amount immediately after ion implantation for each actual wafer.

[Means for solving problems]

Referring to FIG. 1, the ion implantation uniformity monitoring apparatus of the present invention comprises a storage means 18 capable of storing a plurality of sample values of a beam current I of an ion beam actually irradiated on a wafer at respective addresses, X-axis scanning voltage VX, Y-axis scanning voltage VY
And sampling means 20 for sampling the beam current I as a set, and addressing means for designating the address of the storage means 18 based on the set of the X-axis scanning compaction VX and the Y-axis scanning voltage VY sampled by the sampling means 20.
22, an arithmetic means 24 for storing the beam current I in the sampled set while accumulating it at an address designated by the address designating means 22 of the storing means 18, and a storing means 18.
And a uniformity determining means 26 for determining the uniformity between the beam currents stored at the respective addresses.

Moreover, the addressing means 22 includes a partitioning means 221 that divides the variation range of the X-axis scanning voltage VX and the Y-axis scanning voltage VY into a plurality of predetermined sections, and the sampled X-axis scanning voltage VX and The discriminating unit 222 discriminates the segment to which the Y-axis scanning voltage VY belongs, and designates the address of the storage unit 18 based on the discriminated segment.

[Action]

The sampling means 20 samples the X-axis scanning voltage VX, the Y-axis scanning voltage VY during ion implantation into the wafer and the beam current I of the ion beam actually applied to the wafer as a set at regular time intervals. The address designating means 22 designates the address of the storing means 18 based on the sampled set of the X-axis scanning voltage VX and the Y-axis scanning voltage VY. As a result, the address corresponding to the coordinates of the beam on the wafer is designated. The calculation means 24 stores the beam current I while accumulating the beam current I at the address of the storage means 18. As a result, the beam current corresponding to the integrated value of the beam current applied to each coordinate of the wafer is stored in the corresponding address of the storage unit 18. The uniformity determining means 26 determines the uniformity between the beam currents stored at each address.
Thereby, the uniformity of the amount of ion implantation to the wafer is judged.

The addressing means 22 is the partitioning means 221 and the classification discriminating means 2
If equipped with 22, X-axis scanning voltage VX and Y-axis scanning voltage
The scanning area of the ion beam can always be grasped by a fixed number of matrices regardless of the size of the change range of VY.

〔Example〕

FIG. 2 is a block diagram showing an embodiment of the present invention. This embodiment comprises a microcomputer consisting of an input port 34, a CPU 36, a memory 40 and an output port 42 connected together by a bus 38. 5 and 6
The X-axis scanning voltage VX, the Y-axis scanning voltage VY and the beam current I of the ion implantation apparatus shown in the figure are, for example, 0 to ± 15 V (including DC), 0 to ± 15 V, respectively, by appropriate means (not shown).
It is converted into a range of ± 15V (including DC) and 0 to 10V, and is input to the input port 34 via the A / D converters 28, 30, 32. Further, the ion implantation apparatus outputs a beam irradiation signal SW which becomes, for example, at a high level (for example, + 5V) during beam irradiation to the wafer, and at a low level (for example, 0V) otherwise, which is input to the input port 34. . A CRT 46 is connected to the output port 42 via a CRT drive circuit 44, and a buzzer 50 is connected to the output port 42 via a buzzer drive circuit 48.

3A to 3C are flowcharts showing an example of the operation of the embodiment shown in FIG. This example consists of the range matching operation mode shown in FIG. 3A, the data acquisition operation mode shown in FIG. 3B, and the tabulation display operation mode shown in FIG. 3C.

First, the range matching operation mode will be described with reference to FIG. 3A. In this mode, the ion implantation apparatus set under predetermined operating conditions is operated for trial before the wafer is set. Then, a push button (not shown) provided on this monitoring device is pushed, and this is judged in step S1. The minimum value VX of the X-axis scanning voltage VX in step S2
_A is obtained, and the maximum value VX _B of the X-axis scanning voltage VX is obtained in step S3. The following calculation is performed in step S4.

VX _D = (VX _B −VX _A ) / 18 This VX _D means the width of one section obtained by dividing the minimum value VX _A and the maximum value VX _B into 18 equal parts. Then, based on this VX _D , the following calculation is performed in step S5.

VX ¹ m = (VX _A -VX _D ) + (m-1) VX _D VX ² m = VX _A + (m-1) VX _D m = 1 to 20 The above calculation is the minimum value VX _A and the maximum value VX VX before and after _B respectively
It means that _D is added to make a total of 20 sections, VX ¹ m represents the lower limit value of the m-th section, and VX ² m represents the upper limit value of the m-th section.

The above steps S2 to S5 are the processes for the X-axis scanning voltage VX, but the same processes as those for the Y-axis scanning voltage VY are performed in step S6, and the following VY ¹ n and VY ² n are processed.
Ask for.

VY ¹ n = (VY _A −VY _D ) + (n−1) VY _D VY ² m = VY _A + (n−1) VY _D n = 1˜20 Here, VY _A is Y It is the minimum value of the axis scanning voltage VY, VY _B is the maximum value, and VY _D = (VY _B −VY _A ) / 1
8

Next, in step S7, the maximum value of the beam current I is obtained. The beam current I is 0 to 0 as described above in this example.
It is supposed to be input in the range of 10V, and step S
In 8, it is determined whether the maximum value of the beam current I is within the range of 5 to 10 V. If the maximum value of the beam current I is not within this range, the beam current I is within the normal range for uniformity determination. If it is not entered, an excess / deficiency display is made in step S9 and the program ends. If the maximum value of the beam current is within the range, in step S10, (VX ¹ m, VX ² m, VY ¹ n, VY ² n), m = 1 to 2 described above.
0, n = 1 to 20 is stored as a set of data in, for example, the address (m, n) of the memory 40, and the ready display is displayed in step S11. This ends the range matching operation mode. In this example, the beam current Imn, which will be described later, can also be stored in the address (m, n) of the memory 40.

FIG. 4 is a diagram conceptually showing a certain area of the memory 40. The address m corresponds to the X axis of the beam surface, and the address n
Corresponds to the Y axis of the beam surface, and the circle in the figure corresponds to the mask 8 shown in FIG. 5, and it can be considered that the wafer 10 is in this circle. Then, for example, at the address (1,1), the data (▲ VX ¹ ₁ ▼, ▲ VX ² ₁ ▼, ▲ VY
_{^{1 1 ▼, ▲ VY 2 1}} ▼, I 11) is stored. However, this drawing is merely a conceptual one, and the memory 40 does not necessarily have to be arranged in a matrix.

The reason why the changing range of the X-axis scanning voltage VX and the Y-axis scanning voltage VY is equally divided into a plurality of predetermined sections, which is 18 in this example, is as follows. That is, in the ion implanter, when the acceleration voltage of the ion beam is changed, the change range of the X-axis scanning voltage VX and the Y-axis scanning voltage VY is also changed in order to maintain the size of the predetermined beam scanning region. ing. In such a case, as described above, the X-axis scanning voltage VX
And the Y-axis scanning voltage VY are equally divided, it is possible to always grasp a predetermined beam scanning region with a fixed number (for example, 18 × 18) of the matrix regardless of the size of the changing range. This has the advantage that the memory 40 can be used efficiently. In addition, as described above, the data is stored in 20 after dividing into 18 equal parts even when the range of change in the X-axis scanning voltage VX and the Y-axis scanning voltage VY is slightly larger than that in the range matching during actual ion implantation. This is to secure a place.

When the range matching operation mode ends, the program will
Proceed to the data acquisition operation mode shown. First, in step S21, the beam current Imn in the memory 40 is set to zero. In step 22, it is determined whether the beam irradiation signal SW is at high level. The high level means that the wafer is irradiated with the beam, and the process proceeds to step S23. In step S23, it is determined whether or not a clock signal is given from a clock signal generator (not shown) in this monitoring device. The cycle of this clock signal is, for example, 200 μS. If there is a clock signal, step S24
X-axis scan voltage VX is sampled at step S2
In step 5, the Y-axis scanning voltage VY is sampled, and step S
At 26, the beam current I is sampled. That is, the X-axis scanning voltage VX, the Y-axis scanning voltage VY, and the beam current I are sampled as a set with one clock signal. Step
In S27, the sampled X-axis scanning voltage VX was stored in the memory 40 in the range matching operation mode described above.
By comparing with VX ¹ m and VX ² m, X-axis scanning voltage VX
Discriminate (determine) the category m to which the belongs. Similarly, in step S28, the section n to which the sampled Y-axis scanning voltage VY belongs is discriminated (determined). Based on the classification (m, n) discriminated in this way, in step S29, the memory that should store the beam current I sampled as a set
Specify 40 addresses (m, n). In step S30, the beam current Imn stored at the address (m, n)
The beam current I is added to (initially 0 as described above), and the result is stored as a new beam current Imn in the address (m, n). That is, the beam current I is stored while being integrated at the address (m, n). When this is completed, the program returns to step S22, and if beam irradiation is in progress, the program proceeds to step S23 and the X-axis scanning voltage VX, the Y-axis scanning voltage VY and the beam current I are sampled again with the next clock signal. By repeating the above, the beam current at each time is accumulated in the corresponding address of the memory 40 in response to the change in the X-axis scanning voltage VX and the Y-axis scanning voltage VY, that is, in response to the ion beam scanning. .

That is, referring again to FIG. 4, the integrated value of the ion implantation amount at each point on the XY coordinates of the target (or wafer) is stored as the integrated value of the beam current at the address corresponding to each point. Therefore, it is possible to judge the uniformity of the ion implantation amount to the wafer by judging the uniformity of the beam current Imn (m = 1 to 20, n = 1 to 20) stored in each address of the memory 40. You can This judgment is made in the following tabulation display operation mode. That is, in step S22, when the beam irradiation signal SW becomes low level, it means the end of beam irradiation, and the program proceeds to the tabulation display operation mode of FIG. 3C.

In step S41, the following equation is calculated for the coordinate value m, n of each address.

m = 1 to 20, n = 1 to 20 In step S42, if the value of r for each address is larger than the value of R initially set, the beam current Im
n is replaced with 0 in step S43. This means that, with reference to FIG. 4, the beam current outside the mask having the radius R indicated by a circle is replaced with 0 and is not the object of the uniformity judgment. Then, in step S44, 0
The average value of the beam current Imn other than is calculated according to the following equation.

Here, x is the number of beam current values replaced with 0.

In step S45, the beam current Imn at each address is replaced with the error Emn from the average value according to the following equation.

In step S46, the standard deviation σ of each error Emn is calculated according to the following equation.

In step S47, the obtained standard deviation σ is compared with the set value, and if it is larger than the set value, the buzzer 50 is driven and an alarm is issued in step S48. On the other hand, in step S49, the map of each error Emn, the average value of the beam current and the standard deviation σ are displayed on the CRT 46, and the program ends.

In the above, the standard deviation σ exceeding the set value means that there is a large variation in the integrated value of the beam current between each point on the wafer, in other words, the ion implantation amount of the wafer. Means poor uniformity. Therefore, immediately after the ion implantation into one wafer, the uniformity of the implantation amount into that wafer is immediately judged and displayed.

〔The invention's effect〕

As described above, according to the present invention, the actual wafer 1
Immediately after the ion implantation for each wafer, it is possible to accurately determine the uniformity of the implantation amount within the wafer surface by using the beam current of the ion beam actually irradiated to the wafer.
Therefore, even if an abnormality occurs in the ion implantation device and the uniformity of the implantation amount deteriorates, it can be immediately judged and dealt with, and loss such as defective product can be minimized. .

Further, since it is not necessary to use a consumable item such as a sample wafer or a special plastic film, it is economical, and it is also possible to constantly monitor it in the actual production scene.

In addition, in order to make a fine determination of the injection amount uniformity,
Since it suffices to increase the number of samplings and the number of addresses in the sampling means, the address designating means and the storage means, it is possible to easily cope with this.

Moreover, since the addressing means is provided with the segmenting means and the segmenting means as described above, the X-axis scan electrode pressure and Y
It is possible to always grasp the scanning region of the ion beam with a fixed number of matrices regardless of the magnitude of the change range of the axial scanning voltage. That is, the same storage means can be used regardless of the change range of both scanning voltages, and the required storage area is constant, so that the storage area of the storage means can be used efficiently.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of the present invention. Figure 2 shows
It is a block diagram which shows one Example of this invention. Figure 3A ~
FIG. 3C is a flowchart showing an example of the operation of the embodiment shown in FIG. FIG. 4 is a diagram conceptually showing a certain area of the memory. FIG. 5 is a schematic diagram showing an example of an ion implantation apparatus. FIG. 6 is a diagram showing the signal waveform of each part of FIG. 18 ... storage means, 20 ... sampling means, 22 ... address designating means, 24 ... arithmetic means, 26 ... uniformity determining means, 221 ... partitioning means, 222 ... classification discriminating means, VX ...
X-axis scanning voltage, VY ... Y-axis scanning voltage, I ... beam current

Claims (1)

[Claims] 1. An accelerated ion beam is scanned in the X-axis direction and the Y-axis direction using an X-axis scan electrode to which an X-axis scan voltage is applied and a Y-axis scan electrode to which a Y-axis scan voltage is applied. While being used in an ion implantation apparatus that irradiates a wafer, the uniformity of the amount of ion implantation into the wafer is monitored based on the X-axis scanning voltage and the Y-axis scanning voltage and the beam current of the ion beam that is actually irradiated to the wafer. An apparatus, comprising: storage means capable of storing a plurality of sample values of the beam current at respective addresses; sampling means for sampling the X-axis scanning voltage, Y-axis scanning voltage and beam current as a group; Addressing means for designating an address of the storage means based on the sampled set of the X-axis scanning voltage and the Y-axis scanning voltage, and the address of the storage means Uniformity judgment for judging the uniformity between the beam currents stored in the respective addresses of the storage means and the calculation means for accumulating the beam currents in the sampled set at the address designated by the designating means The addressing means further comprises: partitioning means for dividing the change range of the X-axis scanning voltage and the Y-axis scanning voltage into a plurality of predetermined sections, and the sampled X-axis scanning voltage. And a section discriminating means for discriminating the sections to which the Y-axis scanning voltage belongs and for designating the address of the storage means based on the discriminated sections.