JP2005236007A - Method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a method of controlling the implanted amount of ions in an ion implanting process by using the sheet resistance of the diffusion layer of the ions implanted into a monitor substrate has been used in a method of manufacturing semiconductor devices as a convenient management method, but such a case that desired accuracy is not obtained occurs due to the condition and state of the ion beam used at ion implanting time and, as a result, the fluctuation of the electric characteristics of an integrated circuit increases and the yield of the semiconductor device drops. <P>SOLUTION: The ion implantation into the monitor substrate is performed after an ion beam used for implanting ions into a semiconductor substrate for product is adjusted. At the time of performing ion implantation into the monitor substrate, the actual implanted amount of ions is controlled to a sheet resistance value that can be measured stably by using a four-point probe in accordance with the thickness of the diffusion layer by changing the actual implanted amount of the ions by only changing the implanting time of the ions. Then the actual implanting time of the ions into the semiconductor device for product is corrected by using a correction factor obtained from measured results. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to an ion implantation process for creating an impurity region in a semiconductor device.

The product characteristics of a semiconductor device are greatly influenced by the electrical characteristics of various semiconductor elements constituting the semiconductor device. The electrical characteristics of the semiconductor element are determined by the impurity concentration of the impurity region constituting the semiconductor element such as a transistor or a resistance element. For example, the impurity concentration for adjusting the threshold voltage of the transistor and the impurity concentration in the resistance element.
In general, an impurity is introduced into a semiconductor substrate by an ion implantation apparatus. However, since the electrical characteristics greatly vary depending on the amount of impurities, that is, the amount of ion implantation by the ion implantation apparatus, in determining the yield of the semiconductor device. Control and management of the amount of ion implantation is extremely important. In particular, control of the ion implantation apparatus is particularly important because the amount of ion implantation by the ion implantation apparatus varies.

explain in detail. In the ion implantation apparatus, the amount of ion beam current that reaches the surface on which the ion beam is implanted is measured, and the amount of ion implantation is controlled by the amount of current and the implantation time. The ion beam current is measured by an ammeter connected to a Faraday cup that captures the ion beam.
Variation factors of the ion implantation apparatus include a change in the neutralization rate of ions accompanying a change in the degree of vacuum in the implantation chamber, a measurement error in the ion beam current measurement system, and the like. Neutralized ions have no electric charge, so current measurement is not possible, but the change in neutralization rate can be measured as a change in vacuum and can be managed independently. Therefore, the main factor of variation is a measurement error of the ion beam current measurement system.
As an error factor of the ion beam current measurement system, it is said that many errors are generated in the process of capturing the ion beam. For example, charging due to dirt on the surface of the Faraday cup, current leakage, and the like can be mentioned.
These error factors are problems in the ion implantation apparatus, and must always be taken into account when manufacturing a semiconductor device using the ion implantation apparatus.

In order to control the ion implantation amount of the ion implantation apparatus, the ion implantation amount into the semiconductor substrate may be examined. Conventionally, various proposals have been made for measuring the amount of impurities (ion implantation amount) introduced into a semiconductor substrate. As a typical method, there is a method of measuring an impurity introduced into a semiconductor substrate as a resistance value.
In this method, an ion-implanted semiconductor substrate is heat-treated to form an impurity diffusion layer, and the sheet resistance of the diffusion layer is measured. From the measured sheet resistance, the amount of ion implantation is known by referring to a reference diagram that has obtained a correlation with the amount of impurities.

There are several methods for measuring sheet resistance, and the most widely used method is the four-probe method. The four probe method will be described with reference to FIG.
FIG. 5 shows an outline of sheet resistance measurement by the four-point probe method. 11 is a semiconductor substrate, 12 is a probe, 13 is a power source, 14 is a voltmeter, 15 is an ammeter, and S is an interval between the probes 12.
Four probes 12 are brought into contact with the semiconductor substrate 11 to be measured at an equal interval S. A power source 13 and an ammeter 15 are connected to the two outer probes 12 to pass a direct current. A voltmeter 14 is connected to the two inner probes 12 to measure the voltage. The resistance value is derived from the values of the ammeter 15 and the voltmeter 14. The sheet resistance measurement by the four-probe method is widely used because the measurement method is simple and does not require large-scale equipment. The average sheet resistance value is given by:

  Many proposals have been made for a method of managing an ion implantation apparatus based on a management value calculated from a measurement result such as an actually measured sheet resistance. For example, there is a process management method in which a monitor substrate using the same semiconductor substrate as a product semiconductor substrate is used, ion implantation is performed on the monitor substrate, sheet resistance is measured, and the result is fed back to a periodic management monitor. (For example, refer to Patent Document 1).

[Description of Prior Art: FIG. 6]
The prior art shown in Patent Document 1 will be described. FIG. 6 is a flowchart showing a conventional management method disclosed in Patent Document 1.
First, a predetermined ion implantation amount of desired ions is implanted into the monitor substrate (S1), and then the sheet resistance of the diffusion layer on the ion-implanted monitor substrate is measured (S2) and input to the periodic management monitor for management. Record (S3) in the figure, determine whether the resistance value is within the standard (S4), calculate a correction coefficient for correcting the ion implantation amount as required (S5), and use this correction coefficient. Then, the amount of ion implantation is corrected and the semiconductor substrate for the product is processed.

The prior art disclosed in Patent Document 1 employs a method in which ion implantation is performed once on a monitor substrate and an ion implantation amount to a semiconductor substrate for products is determined based on the result. The sheet resistance of the monitor board is measured, and this result is input to the periodic management monitor. For this reason, since the state of the change over time of the ion implantation apparatus (for example, charging due to contamination on the surface of the Faraday cup) can be feedback-managed, the ion implantation amount of the ion implantation apparatus can be corrected. That is, there is an advantage that variation due to the ion implantation apparatus can be reduced.

Japanese Patent Laid-Open No. 15-151913 (term 3, FIG. 2)

  Although the conventional technique shown in Patent Document 1 has the advantage that there are few failures in ion implantation and the variation over time of the ion implantation apparatus can be managed, ion implantation on a monitor substrate and ion implantation on a semiconductor substrate for products However, no countermeasures are taken when implemented under different ion implantation conditions.

  Usually, ion implantation on a monitor substrate and ion implantation on a semiconductor substrate for a product are performed under the same ion implantation conditions, but may be performed under different ion implantation conditions. This is the case where the four-probe method is used for measuring the sheet resistance and a region (high resistance region) having a small ion implantation amount and a low impurity concentration is formed in the semiconductor substrate.

As already described, the four-point probe method is a widely used sheet resistance measurement method. The reason why the four-probe method is widely used is that there is an advantage that the cost required for measurement is low in addition to the stable measurement. However, there is a drawback that a high resistance value cannot be measured.
In the four-probe method, the measurement error tends to increase as the impedance between the probes increases, and a sheet resistance exceeding 5 MΩ / cm ² cannot be measured. When the depth of ion implantation is shallower, it is more serious. For example, when an impurity element having a large ion radius is ion-implanted with low energy, the peak of the impurity concentration profile is at or near the surface. In this case, since the cross-sectional area of the diffusion layer is reduced and the resistance is increased, the measurement limit is much smaller than 5 MΩ / cm ² .

  On the other hand, a semiconductor device often requires a low impurity concentration region or a high resistance. Semiconductor devices are necessary for both the element structure and the circuit configuration of the elements. The former is, for example, ion implantation for adjusting the threshold value of a MOS transistor. In this case, it is necessary to form a diffusion layer of a low concentration impurity having a relatively shallow diffusion depth. In the latter case, for example, the reference resistance used for the reference current source of the constant voltage circuit requires a high resistance of several MΩ.

  Measurement of sheet resistance by the four-point probe method is indispensable for its advantages. However, unless the disadvantage is solved, the semiconductor device cannot be used when a low impurity concentration region or a high resistance is required. Therefore, to compensate for this drawback, the amount of ion implantation into the monitor substrate and the amount of ion implantation into the semiconductor substrate for the product are changed, and until the sheet resistance can be measured with the four-probe method on the monitor substrate. A method is generally used in which ion implantation is performed by increasing the ion implantation amount, and the semiconductor device for a product is ion-implanted by extrapolating a normal ion implantation amount from the measured sheet resistance of the monitor substrate.

Thus, in order to obtain a low resistance sheet resistance, when performing ion implantation into the monitor substrate under ion implantation conditions different from the ion implantation conditions for ion implantation into an actual product semiconductor device, Changing the ion beam current value is generally used to change the ion implantation amount.
However, when this ion beam current value is changed, the ion density distribution changes, and there is a problem that ion implantation into a semiconductor device for products becomes inaccurate.
For this reason, there is a strong demand for an ion implantation method based on sheet resistance measurement using the four-probe method that is widely used at present, and an ion implantation amount management and control method.

  The problem to be solved by the present invention is that, in the case of ion implantation performed under different ion implantation conditions, ion implantation on a monitor substrate and ion implantation on a semiconductor substrate for a product are performed with high accuracy. It is a point that cannot be controlled.

  In order to solve the above-described problems, the following method is adopted as a method for manufacturing a semiconductor device of the present invention.

A semiconductor having a first ion implantation step for ion implantation into a monitor substrate and a second ion implantation step for ion implantation into a product semiconductor substrate using a monitor substrate having the same substrate as the product semiconductor substrate In the device manufacturing method,
An ion beam adjustment step for adjusting the ion beam of the ion implantation apparatus before the first ion implantation step, a sheet resistance measurement step for measuring the sheet resistance of the monitor substrate after the first ion implantation step, and a sheet resistance measurement A correction coefficient calculation step for determining the implantation time of ion implantation based on the result obtained from the step,
The second ion implantation step is characterized in that the ion implantation amount is controlled by information obtained from the correction coefficient calculation step.

  The ion implantation amount in the first ion implantation step is different from the ion implantation amount in the second ion implantation step.

  The step of measuring the sheet resistance is characterized by a four-probe method.

A feature of the present invention is that a sheet resistance can be stably measured by a four-probe method in a method of manufacturing a semiconductor device relating to a method for controlling the amount of ion implantation into a semiconductor substrate, and the amount of ion implantation into a semiconductor substrate for a product. This can be controlled with high accuracy.
According to the semiconductor device manufacturing method of the present invention, since the ion beam current values of the monitor substrate and the product semiconductor substrate are the same, the effects of charging and current leakage caused by the Faraday cup contamination are accurately reflected. be able to. In addition, since the monitor substrate is processed with an ion beam adjusted to process a semiconductor substrate for products, the current density of the ion beam and the uniformity of the beam scan, that is, errors due to the ion density distribution are faithfully monitored. Since this is reflected on the substrate, there is an effect that high-precision control is possible.

  Therefore, the manufacturing method of the semiconductor device of the present invention can be realized with high accuracy by using an inexpensive monitor substrate by using a low-cost and simple four-short needle method and managing a low ion implantation amount and a low energy ion implantation process. Has no excellent effect.

  Hereinafter, a method for manufacturing a semiconductor device of the present invention will be described with reference to the drawings. In the embodiment of the present invention, an ion implantation process will be described. In the following embodiments of the present invention, a description will be given of an example in which a threshold diffusion layer forming step provided as a semiconductor layer in an element region of a semiconductor substrate is formed using an ion beam scanning ion implantation apparatus. To do.

[Description of control of ion implantation amount of the present invention]
First, the ion implantation process of the present invention will be described with reference to FIG. FIG. 1 is a diagram for explaining a method of manufacturing a semiconductor device according to the present invention. In order to make it easy to understand the relationship between each manufacturing process, it is represented by a flow diagram. FIG. 2 is a correlation diagram between the ion implantation amount and the sheet resistance value. The horizontal axis indicates the sheet resistance value, and the vertical axis indicates the correction coefficient. FIG. 3 is a conceptual diagram of a hybrid scanning ion implantation apparatus capable of implanting a parallel ion beam having mechanical scanning and electrostatic scanning in each axial direction. Further, FIG. 4 is a schematic view of an ion implantation chamber of the ion implantation apparatus.

In FIG. 1, 1 to 9 are steps for performing ion implantation. After the step 2 for performing ion beam adjustment, there is a first ion implantation step 4, and after the step 5 for measuring sheet resistance, there is a correction coefficient calculation step 7 for determining the implantation time of ion implantation, followed by the second ion implantation step. There is an injection step 8.
In FIG. 3, 41 is an ion generating part, 42 is an extraction electrode, 43 is a mass analyzing part, 44 is an ion accelerating part, 45a and 45b are magnetic lenses, 46 is an electrode, 47 is a collimating electromagnet, 48 is an ion implantation chamber. It is. In FIG. 4, 48 is an ion implantation chamber, 51 is an ion beam, 61 and 61a and 62 are Faraday cups, 61b is a retracted position, 63 is an ammeter, 64 is a Faraday switching unit, and 71 is a substrate. The substrate 71 indicates a monitor substrate or a product semiconductor substrate. 4A is a top view of the ion implantation chamber 48 in the ion beam traveling direction, FIG. 4B is a front view of the ion implantation chamber 48 in the ion beam traveling direction, and FIG. It is a side view of a beam traveling direction. 3 and 4 are given the same reference numerals. 1 to 4 will be described with reference to each other.

First, an actual process ion implantation condition setting step 1 for setting ion implantation conditions for a product will be described.
The ion implantation conditions are set so that the uniformity on the substrate is good and the ion beam current value is high in productivity at a desired ion implantation amount and acceleration voltage. Here, in order to adjust the threshold value of a P-type field effect transistor, monovalent ions of B (boron) are implanted into an 8-inch substrate with an implantation amount of 2.0E12 atoms / cm ² and an acceleration voltage of 5 keV. Perform the settings to be performed.

Next, an ion beam adjustment process 2 for performing ion beam adjustment will be described. Based on the above settings, a desired ion beam is generated by an ion implantation apparatus in which a high vacuum is maintained from the ion generation unit to the implantation chamber. Here, BF3 (boron trifluoride) gas is introduced into the ion generation unit 41 in the ion implantation apparatus, thermionic electrons are generated from the electrodes in the ion generation unit to be ionized, and ions are extracted using the negatively charged extraction electrode 42. Then, only the monovalent ion of B (boron) is extracted by the mass analyzing unit 43, and further accelerated to 5 keV by the ion accelerating unit 44 using an electromagnet to generate a directional ion beam. The ion beam passes through magnetic field lenses 45a and 45b that form the ion beam in a desired beam diameter in each axial direction and an electrode 46 that periodically deflects the ion beam to become an ion beam 51 that performs scanning at a constant period.
After that, the collimating electromagnet 47 is used for collimation so that the ion beam implantation angle does not change at each scanning position, and the collimating electromagnet 47 is adjusted so that the scanning speed is equalized. To reach.

  Adjustment of the ion beam in the ion implantation chamber 48 will be described in detail with reference to FIG. FIG. 4 is a view showing the ion implantation chamber 48 divided into a front surface, an upper surface, and a side surface as viewed from the traveling direction of the ion beam 51. As shown in FIG. 4, a Faraday cup 61 a is disposed in a portion corresponding to the substrate 71 in the ion implantation chamber 48, the ion beam is captured by the Faraday cup 61 a, and the current value of the captured ion beam is measured by the ammeter 63. To do. The gas flow rate, thermoelectrons, etc. in the ion generator 41 shown in FIG. 3 are adjusted so that this ion beam current becomes a set value, and a desired current value, here 20 μA, is obtained.

Next, the actual process implantation time setting step 3 for determining the actual process ion implantation time will be described. Based on the obtained ion beam current value, an implantation time is calculated such that a desired implantation amount, 2.0E12 atoms / cm ² is obtained. The implantation time is derived from the following ion implantation equation. Here, the injection area to be scanned is 625 cm ² , and an injection time of 10 seconds is derived.

  After that, the connection of the ammeter is switched by the Faraday switching unit 64, and the ion beam current is measured also by the Faraday cup 62 arranged at the scanning end, and the current ratio with the Faraday cup 61a in the substrate region is acquired. At the time of actual implantation, the Faraday cup 61a for measuring the ion beam current in the actual implantation region is moved from the ion beam flow path to the retreat position 61b, and the ion beam reaches the substrate position. For the implantation, only the Faraday cup 62 at the scanning end is used, and ion implantation is performed based on the acquired ratio.

  However, even in the processes so far, variations in the ion beam current at each scanning position in the substrate region occur as variations in the amount of ion implantation in the substrate 71. In addition, current leakage in the path to the ammeter 63 such as insulation failure of each Faraday cup and charging of the Faraday cup surface may occur as errors in ion current measurement, which may cause fluctuations in the actual ion implantation amount. .

Further, in the case of a scanning ion implantation apparatus that indirectly measures the ion beam current injected into the substrate 71, there is an error that cannot be generated by the mechanism that directly measures the ion beam current on the substrate 71 that has been used in the past. appear.
This will be described in detail with reference to FIG. In recent years, the structure of the semiconductor substrate support part has become complicated due to demands such as multi-directional injection into the semiconductor substrate, and it has become difficult to connect an ion beam ammeter to the support part, and the ion beam current injected into the semiconductor substrate cannot be directly measured. Therefore, the indirect ion beam current measurement method as described above is adopted.
With such a configuration, in the Faraday cup 61, when there are variations in beam current values between the ion beam scanning positions in the substrate 71 and around the substrate 71, the ion beam current value measured by the Faraday cup 61 is Causes a problem that ions are implanted into the substrate 71 with different ion beam current values. This is also the case when the current density changes between the positions of the substrate 71 and the Faraday cup 61. Since such an event changes every time an ion beam is formed, if the ion implantation into the monitor substrate and the ion implantation into the semiconductor substrate for the product are not performed continuously, an implantation error cannot be detected. .

  The present invention has been made to solve this error factor, and the steps shown below are more characteristic.

A first ion implantation step 4 in which the implantation time is adjusted and ions are implanted into the monitor substrate will be described. Using an N-type silicon substrate having a resistivity of 10 Ω · cm as a monitor substrate, the uniformity of implantation and the actual ion implantation amount are confirmed. In order to obtain a concentration that provides a sheet resistance that can be stably measured by the four-probe method by arranging a monitor substrate in the ion implantation chamber 48 (position of the substrate 71) of the ion implantation apparatus, the ion implantation amount is 4.0E13 atoms. In order to obtain / cm ² , ion implantation is performed by increasing the implantation time obtained in the actual treatment implantation time setting step 3 by 200 times to 200 seconds. At this time, the ion beam is not adjusted.

The sheet resistance measurement process 5 for measuring the sheet resistance will be described. The monitor substrate subjected to ion implantation is immediately subjected to a heat treatment at 1050 degrees Celsius for 10 seconds by a rapid heating apparatus (not shown) to recover a damaged layer by ion implantation and activate B (boron). Is formed. Further, the sheet resistance value of the diffusion layer is measured by a four probe method using a four probe resistance measuring device (not shown). Here, a sheet resistance value of 1.2 kΩ / cm ² was obtained under the above conditions.

  Next, the standard determination process 6 will be described. The sheet resistance value of the monitor substrate is compared with the control value of the control chart that has previously obtained a correlation with the electrical characteristics, and determines whether or not ion implantation can be performed. At this time, if the sheet resistance value deviates from the control value, the ion implantation is stopped and an implanter maintenance process 9 which is a maintenance process of the ion implantation apparatus is performed. If the uniformity in the monitor substrate deviates from the management value even if the sheet resistance is within the management value, the process returns to the ion beam adjustment step 2 to readjust the scanning speed with reference to the resistance value distribution.

A correction coefficient calculation step 7 related to ion implantation and a second ion implantation step 8 for performing actual ion implantation processing at the implantation time after correction will be described.
In the determination in the standard determination step 6, when the sheet resistance value is within the control value, a correction coefficient is derived from the correlation diagram between the ion implantation amount acquired in advance and the sheet resistance value shown in FIG. Then, actual ion implantation processing is performed on the product semiconductor substrate during the corrected implantation time.

  As is apparent from the above description, the semiconductor device manufacturing method of the present invention performs the process using the monitor substrate in the above-described steps, thereby making it possible to perform the ion beam current at the ion beam scanning position, which was unclear in the prior art. It is now possible to accurately grasp variations caused by the device such as variations in current and minute current leaks, correct them, and feed them back to the ion implantation of the product semiconductor substrate. For this reason, variation in threshold values of the transistors is suppressed, defects in the semiconductor elements due to variation in threshold values are remarkably reduced, and yield of the semiconductor device can be improved.

A characteristic part of the method for manufacturing a semiconductor device according to the present invention is that a sheet current is measured by processing a monitor substrate after adjusting a beam current value and scanning uniformity in ion implantation. Without changing, the product is processed by correcting the ion implantation time to control the ion implantation amount. By adopting such a manufacturing method, variations caused by the ion implantation apparatus can be offset, and an unprecedented high-precision control of the ion implantation amount has become possible.

  In addition, in order to improve productivity, the yield can be predicted in advance during the manufacturing process of the semiconductor device even if the sheet resistance is confirmed at the same time as or after the ion implantation process to determine whether the product is acceptable or not.

The present invention relates to a method for manufacturing a semiconductor device including a low impurity region in which sheet resistance is measured using a four-probe method. Since the semiconductor device manufacturing method of the present invention can be manufactured at low cost, it can be used for manufacturing a semiconductor device mounted on a mass-produced electronic device.
In recent years, portable electronic devices and small information devices are required to have low power consumption, and as a countermeasure, the threshold voltage of MOS transistors constituting a semiconductor device is being lowered. The method for manufacturing a semiconductor device of the present invention can also be employed for manufacturing these semiconductor devices.

It is a figure which shows the manufacturing method of the semiconductor device of this invention. It is a reference diagram of the correction coefficient in the manufacturing method of the semiconductor device of the present invention. It is a system conceptual diagram of an ion beam scanning ion implantation apparatus. It is the schematic of the ion implantation chamber of an ion implantation apparatus. It is a figure explaining a four-point probe measuring method. It is a flowchart which shows the management method of the ion implantation apparatus in a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Actual process ion implantation condition setting process 2 Ion beam adjustment process 3 Actual process implantation time setting process 4 First ion implantation process 5 Sheet resistance measurement process 6 Standard determination process 7 Correction coefficient calculation process 8 Second ion implantation process 9 Implanter Maintenance Process 11 Semiconductor Substrate 12 Probe 13 DC Power Supply 14 Voltmeter 15 Ammeter 41 Ion Generator 42 Extraction Electrode 43 Mass Analyzer 44 Accelerator 45a Magnetic Lens 45b Magnetic Lens 46 Deflection Electrode 47 Parallel Electromagnet 48 Ion Implantation Chamber 51 Scanning ion beam 61 Faraday cup 61a in ion implantation region Faraday cup 61b in ion implantation region on ion beam flow path Faraday cup 62 in ion implantation region in retraction position for ion implantation Faraday cup 63 in scanning end Ammeter 64 Faraday switching unit 71 board

Claims (3)

Using a monitor substrate having the same substrate as the product semiconductor substrate, a first ion implantation step for ion implantation into the monitor substrate and a second ion implantation step for ion implantation into the product semiconductor substrate are included. In a method for manufacturing a semiconductor device,
An ion beam adjustment step for adjusting the ion beam of the ion implantation apparatus before the first ion implantation step, a sheet resistance measurement step for measuring the sheet resistance of the monitor substrate after the first ion implantation step, and A correction coefficient calculation step for determining the implantation time of ion implantation based on the result obtained from the sheet resistance measurement step,
In the second ion implantation step, the ion implantation amount is controlled based on information obtained from the correction coefficient calculation step.   2. The method of manufacturing a semiconductor device according to claim 1, wherein an ion implantation amount in the first ion implantation step and an ion implantation amount in the second ion implantation step are different. The method of manufacturing a semiconductor device according to claim 1, wherein the step of measuring the sheet resistance is performed by a four-probe method.

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