JP2007173716A - Dose shift evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize high-precision ion implantation by fully reducing the dose shift caused by outgassing from a resist. <P>SOLUTION: By the dose shift evaluation method, ion implantation is performed for a first test wafer, which has no resist and whose surface is exposed under given conditions with specific ion types to be implanted and prescribed implantation energy and by a specific dose amount (S2). After that, the method includes a first step, wherein electrophysical characteristics of an ion implantation region are measured and the relationship between the dose amount and the electrophysical characteristics is found; a second step wherein ion implantation is performed for a second test wafer, which has resist formed on its surface and has an opening in a part of the resist for exposing its surface under the same conditions of ion types and implantation energy as those of the first step and electrophysical characteristics of the ion implantation region are measured; and a third step (S6) wherein the electrophysical characteristics, which are measured in the second step and the electrophysical characteristics with the same dose amount which are measured in the first step, are compared and the difference between the dose amounts is evaluated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a dose shift evaluation method for evaluating a dose shift amount caused by outgas from a resist in an ion implantation apparatus.

  The ion implantation apparatus is used in an ion implantation process for introducing impurities into a semiconductor wafer. In the ion implantation process, it is required to precisely control the amount of ion implantation into the semiconductor wafer. In general, the ion implantation amount is controlled by a dose controller by measuring the beam current value of an ion beam with a Faraday cup placed behind or adjacent to a semiconductor wafer. In order to precisely control the ion implantation amount, it is required to set an appropriate beam current value and accurately measure the beam current value.

FIG. 6 is a diagram for explaining an outline of conventional ion implantation and its problems.
An oxide film or a nitride film (not shown) is formed on the surface of the silicon wafer 13, and a patterned resist 12 serving as an implantation mask is formed thereon. Then, ions are implanted into the silicon wafer 13 by the acceleration tube 10.
However, in the above conventional technique, by performing ion implantation on the resist 12, outgas (mainly H ₂ gas) 11 is generated from the inside of the resist 12, and the vacuum in the ion implantation apparatus is deteriorated. For this reason, an error occurs in the measured value of the beam current by the Faraday cup 14, and thus the actual ion implantation amount deviates from a desired value. That is, there arises a problem of fluctuation of the ion implantation amount due to vacuum deterioration.

  FIGS. 7A and 7B are diagrams for explaining fluctuations in the amount of ion implantation caused by outgas generated from the resist. In FIG. 7A, the divalent positive ion I1 receives electrons from the outgas 11, and as a result, the valence decreases and becomes the monovalent positive ion I2. In FIG. 7B, the monovalent positive ion I3 is neutral atom I4 as a result of receiving electrons from the outgas 11.

That is, the ion beam that has passed in the vicinity of the semiconductor wafer gets (or is deprived) of charges from the outgas 11 that is generated during ion implantation from the resist partially applied to the semiconductor wafer. The main component of the outgas 11 is H ₂ gas as described above. When ions collide with the outgas 11, the valence is reduced or neutralized to become atoms. In this collision process, the kinetic energy hardly decreases, and atoms are introduced as impurities into the substrate.

  For example, consider the case where ions are neutralized. The ratio of ions depends on the pressure of outgas. For example, assuming that 100 ions have been accelerated, about 90 ions reach the substrate as ions, but about 10 collide with the outgas 11 and charge. Lost and neutralized. Here, although the amount of impurities in the semiconductor wafer 13 is actually 100, it is measured that the Faraday cup 14 has implanted about 90 impurities, and thus corresponds to 10 ions. Ion implantation is continued until the beam current flows.

  Therefore, it becomes an overdose (excess ion implantation amount) state, and the resistance value of the resistor formed by the impurity layer is reduced from a desired value. A similar problem occurs when the valence of the implanted ions decreases. However, the overdose does not always occur, and depending on the implantation conditions (particularly on the high energy side), the electrons are separated from the positive ions, resulting in an underdose (insufficient ion implantation amount) state.

As a countermeasure against this outgas, for example, a method described in Patent Document 1 has been proposed. In the method described in Patent Document 1, outgas from the resist is reduced in advance by pre-baking the resist.
JP-A-10-106967

  However, even if the resist is pre-baked, outgassing is not completely eliminated, and a certain degree of vacuum deterioration cannot be avoided. Therefore, an error may occur in the dose measurement, and it will still be affected by the deterioration of the vacuum.

  The present invention has been made in view of such circumstances, and an object of the present invention is to sufficiently reduce the dose shift due to the outgas from the resist and realize more accurate ion implantation.

The above object of the present invention is achieved by the following configuration.
(1) A dose shift amount evaluation method for evaluating a dose shift amount generated by outgas generated from a resist when ion implantation is performed on a wafer having a resist formed on the surface, wherein the wafer surface is exposed without having a resist. After ion implantation is performed on the first test wafer at a predetermined dose with the ion species to be implanted and the implantation energy as predetermined constant conditions, ion implantation of the first test wafer is performed. A first step of measuring a region's electrophysical characteristics to determine a relationship between a dose amount in the first test wafer and the electrophysical characteristics; and a resist is formed on the wafer surface and part of the resist For the second test wafer having an opening exposing the wafer surface, the same ion species and implantation energy as in the first step are used. The electrical physics of the ion-implanted region of the second test wafer is selectively ion-implanted into the wafer surface of the second test wafer exposed from the opening of the resist at a desired dose setting value under the condition of the rugi The second step of measuring the characteristics, the electrophysical characteristics measured in the second step, and the electrophysical characteristics at the same dose determined in the first step are compared to evaluate the dose deviation. A dose shift evaluation method comprising: a third step.

  According to this dose shift evaluation method, a resist having a predetermined film thickness having an opening of a predetermined size is provided on the surface of the second test wafer. Therefore, ions are implanted into an actual product by performing ion implantation. In the same way as when outgas is generated, ions can be implanted into the wafer through the resist opening in an environment where the outgas exists. Ion implantation can be realized easily. Then, the electrophysical characteristics of the ion-implanted region of the second test wafer are measured, and the measurement result is obtained as the electrophysical characteristics acquired in advance using the first test wafer on which no resist is formed. By comparing, it is possible to easily determine how much dose shift occurs at a predetermined dose amount.

(2) The dose shift evaluation method according to (1), wherein the first step uses a plurality of the first test wafers, and a plurality of stages with different dose amounts for the first test wafers. And performing the ion implantation, measuring the electrophysical characteristics of each of the first test wafers after the ion implantation, and obtaining calibration curves of the electrophysical characteristics with respect to various dose setting amounts. A dose shift evaluation method.

  According to this dose shift evaluation method, by using a plurality of first test wafers and performing ion implantation with different dose settings, it is possible to obtain calibration curves of electrophysical characteristics for various dose settings, The evaluation accuracy of dose shift can be improved.

(3) The dose shift evaluation method according to (1) or (2), wherein the electrophysical property is a sheet resistance value.

  According to this dose shift evaluation method, the sheet resistance (surface resistance) can be measured by using a sheet resistance measuring device having four deep needles, and the electrophysical characteristics of the region into which the impurity is introduced can be evaluated.

(4) The dose shift evaluation method according to (1) or (2), wherein the electrophysical characteristics are measured by SIMS (secondary ion mass spectrometry) and the impurity concentration distribution characteristics in the depth direction of the wafer. A dose shift evaluation method characterized by

  According to this dose shift evaluation method, the impurity concentration characteristic of the region into which the impurity is introduced is evaluated with high accuracy by the impurity concentration distribution characteristic in the depth direction of the wafer measured by SIMS (secondary ion mass spectrometry). be able to.

  According to the dose shift evaluation method of the present invention, it is possible to efficiently perform highly accurate dose shift evaluation even with a single wafer ion implantation apparatus. In recent years, in particular, in a high current ion implantation apparatus, a single wafer type apparatus has been used in order to realize ion implantation with higher accuracy. Since the wafer is processed every time, it is difficult to perform ion implantation into the wafer while creating a state of vacuum deterioration due to outgas using a resist, and it is difficult to evaluate the dose shift. According to the present invention, in a single-wafer type ion implantation apparatus, ion implantation under conditions where outgas exists can be easily realized, and a dose shift amount can be evaluated.

Next, a preferred embodiment of a dose shift evaluation method according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing the main configuration of an ion implantation apparatus for implementing the dose shift evaluation method of the present invention. Here, a single-wafer type medium current ion implantation apparatus is used.

  As shown in the figure, the ion implanter main body 100 includes a gas system 102, an ion source 104, an ion extraction high voltage acceleration system 106, a mass analysis system 108, a post acceleration system 110, a beam focusing system 112, It has a Faraday cup 114, a load lock chamber 118 for placing a target wafer 116 while sucking it, a load / unload mechanism and a cassette station 120.

  The control system for controlling the operation of the ion implanter main body 100 includes a dose controller 130 and a control console (control display panel) 132.

  When the ion implantation is performed on the product wafer 116, the operator sets the ion species, the implantation energy, and the dose amount using the control console (control display panel) 132. When the ion implantation conditions are input in this way, the dose controller 130 performs ion implantation with a standard beam current value based on the dose.

  The Faraday cup 114 is in a position not in contact with the ion beam 6 while the semiconductor wafer 116 is irradiated with the ion beam 6, and moves to a position where the ion beam 6 can be captured as necessary for measurement. In FIG. 1, the Faraday cup 114 is provided in front of the semiconductor wafer 116, but may be provided in the rear or may be provided in the periphery of the semiconductor wafer 116. In the large current ion implantation apparatus, for example, the current value of the ion beam can be measured at a cycle of about 200 msec.

  FIG. 2 is a diagram for explaining the movement of the platen and the measurement of the beam current value by the Faraday cup in the example of the single wafer type high energy ion implantation apparatus of FIG. In FIG. 2, the same parts as those in FIG.

  As indicated by the dotted line in the drawing, the platen 5 that holds the wafer 116 is kept in a horizontal state during conveyance, and is rotated 90 degrees as indicated by an arrow in a vertical state during ion implantation. As a result, the surface of the wafer 116 becomes perpendicular to the ion beam 6 and ion implantation is possible.

  In FIG. 2, the Faraday cup 114 is provided behind the semiconductor wafer 116. When the beam current is measured by the Faraday cup 114, the platen 5 sinks downward as indicated by a thick arrow in the figure, so that the ion beam 6 reaches the Faraday cup 114. Yes. The above configuration is an example, and other configurations may of course be used.

Here, the main procedure of the control method of the ion implantation apparatus of FIG. 1 will be described.
As described above, at the time of ion implantation, an operator inputs conditions such as a dose amount (other ion species, implantation energy, etc.) from a control console (control display panel) 132. The condition includes a result of correcting the standard beam current value using a correction value measured in advance, which will be described in detail later. Then, ion implantation is performed using the corrected beam current value as a target value.

  According to the ion implantation control method of the present embodiment, overdose (or underdose) is generated in order to set an appropriate beam current value with reference to dose shift evaluation information obtained by a dose shift evaluation method described below. Can be sufficiently suppressed. Therefore, the influence of outgas from the resist is suppressed to the minimum, and highly accurate ion implantation that has not been possible in the past becomes possible.

Next, the dose shift evaluation method will be described.
In this embodiment, dose shift evaluation is performed using two types of test wafers to correct the beam current.
FIGS. 3A and 3B are plan views of a wafer for explaining the types of test wafers used for dose shift evaluation of the present invention, and FIG. 3A has a predetermined coverage (aperture ratio). It is a top view of the test wafer with a resist (2nd test wafer), (b) is a top view of the test wafer without a resist (1st test wafer). However, a 100 mm thermal oxide film is formed on the surfaces of both test wafers.

  As shown in FIG. 3A, a resist having a predetermined film thickness is provided on the surface of the first test wafer 115a, and a square opening (lateral size) is provided at the center of the resist. L1 and vertical size L2) are formed. Here, L1 = L2 = 40 mm.

  Since the surface of the second test wafer 115a is provided with a resist having a predetermined thickness and having an opening of a predetermined size, by performing ion implantation, outgas is generated as in the case of ion implantation into an actual product. In an environment where the generated outgas exists, ions can be implanted into the wafer through the opening of the resist. Therefore, even with a single wafer ion implantation apparatus, ion implantation under the condition where outgas exists can be easily realized by a single test wafer.

  FIG. 4 is a diagram illustrating an example of a result of performing ion implantation on the first and first test wafers and obtaining a relationship between a dose amount and a sheet resistance in an ion implantation region of each test wafer.

For the first test wafer 115b (no resist), ions of triple charge As (mass number 75) are used as ion species, and three doses (D1 to D3) are set at an implantation energy of 600 keV. Implantation was performed, and the sheet resistance (surface resistance) in the ion implantation region was examined. The dose amounts D1, D2, and D3 are 4.7 × 10 ¹³ , 5.0 × 10 ¹³ , and 5.3 × 10 ¹³ , respectively.

  The sheet resistance values corresponding to the dose amounts D1, D2, and D3 are P1, P2, and P3. And the point (x1-x3) prescribed | regulated by each of D1-D3 and P1-P3 is plotted, and the calibration curve Y is obtained by this. The calibration curve Y is a characteristic line serving as a reference for determining the dose shift amount caused by outgas.

  Subsequently, with respect to the second test wafer (test wafer with resist having an opening) 115a, ions with respect to the first test wafer 115b at a dose amount D2 (a dose amount corresponding to the center point x2). Ion implantation is performed under the same conditions as the implantation conditions.

  At this time, normally, the valence of the ion species is reduced (or neutralized) due to outgassing, resulting in overdose (excess ion implantation amount). Therefore, the sheet resistance value is P4 lower than P2. That is, the point x2 on the calibration curve Y moves to the point Q1 located below the calibration curve Y. However, when electrons are deprived from high-energy ion species, an under dose (insufficient ion implantation) may occur, and the sheet resistance value may become P5. In this case, the point x2 on the calibration curve Y moves to the point Q2 located above the calibration curve Y.

  Here, overdose (excess ion implantation amount) occurs, and the sheet resistance value moves to P4 lower than P2 (that is, the point x2 on the calibration curve Y is positioned below the calibration curve Y). Suppose the case of moving to point Q1). In this case, the difference (D4−D2) between the dose amount D4 and the dose amount D4 in the sheet resistance value P4 is the dose shift amount.

  That is, when a 40 mm × 40 mm opening is provided in a resist with a predetermined film thickness, the dose shift amount in the dose amount D4 is (D2−D4). In order to suppress this dose shift, it is necessary to reduce the beam current value to reduce the ion implantation amount.

  Therefore, a beam current correction value is obtained based on the experimental result of FIG. That is, in the case where an opening of 40 mm × 40 mm is provided in a resist with a predetermined film thickness, when triple charge As (mass number 75) is used as an ion species and the implantation energy is 600 keV, the dose correction value is The beam current value is corrected as “D4-D2”.

  When ion implantation is performed on an actual product by the ion implantation apparatus of FIG. 1, the corrected dose amount is obtained by adding the dose shift amount to the beam current standard value corresponding to the dose amount. Then, ion implantation is performed with a beam current value corresponding to the corrected dose.

  In the above example, the dose resistance was evaluated by measuring the sheet resistance of the ion-implanted region of the second test wafer 115a, but the impurity concentration characteristics (impurity surface concentration, Concentration profile characteristic) may be measured, and the dose shift amount may be evaluated based on the measurement result. In that case, when there is an ion that cannot be accelerated by the outgas and is implanted, the determination can be made with SIMS, so that a more accurate evaluation is possible.

  In this way, by drawing a calibration curve based on the measurement result using the first test wafer and comparing the measurement result of the second test wafer with the calibration curve, how much dose shift is achieved at a predetermined dose amount. It can be easily detected whether it occurs. By accumulating dose shift amount data, dose shift amounts for various dose amounts or under different conditions can be obtained, and highly accurate dose shift evaluation can be performed efficiently.

  For example, the dose shift can be evaluated in relation to the resist coverage by variously changing the resist coverage of the second test wafer 115a. In the semiconductor manufacturing process, resists having various patterns are formed. Since the resist coverage with respect to the entire wafer is known, the second test wafer 115a is manufactured in accordance with the resist coverage of the actual product wafer. By doing so, it becomes possible to accurately grasp in advance the amount of dose shift that will occur in the actual product due to outgassing.

  In addition, the dose shift can be evaluated in relation to the resist film thickness by variously changing the resist film thickness of the second test wafer 115a. In the semiconductor manufacturing process, resists with various film thicknesses are formed. Since the resist film thickness is known, if the second test wafer 115a is manufactured in accordance with the resist film thickness in the actual product wafer. The dose shift amount that will occur in the actual product due to outgassing can be accurately grasped in advance.

FIG. 5 is a flowchart showing the main procedure of the dose shift evaluation method described in this embodiment.
First, a dose is set (S1), and ion implantation is performed on a test wafer without a resist (first test wafer 115b) (S2). When ion implantation is performed a plurality of times while changing the dose amount, and the number of ion implantations sufficient to create a calibration curve is performed, the ion implantation is terminated (S3).

  Next, ion implantation is performed on the test wafer with resist (second test wafer 115a) under predetermined conditions (S4), and the relationship between the dose amount and, for example, the sheet resistance value is plotted for each test wafer. To do. Next, a deviation amount between the sheet resistance value and the calibration curve in the test wafer with resist is obtained (S5), and the beam current value is corrected based on the deviation amount (dose shift amount) (S6).

  As described above, according to the dose shift evaluation method of the present invention, even in a single wafer type apparatus, the dose shift amount due to outgas can be easily and efficiently known, and the evaluation result can be applied to the product. By reflecting it in the ion implantation, more accurate ion implantation is realized.

  As described above, according to the present invention, it is possible to efficiently perform highly accurate dose shift evaluation, and the second product according to the resist coverage and the resist film thickness on the actual product wafer. If a test wafer is manufactured, it becomes possible to accurately grasp in advance the amount of dose shift that will occur in an actual product due to outgassing.

It is a block diagram which shows the main structures of the ion implantation apparatus which implements the dose shift evaluation method of this invention. It is a figure for demonstrating the movement of the platen in the single-wafer | sheet-fed high energy ion implantation apparatus of FIG. 1, and the measurement of the beam current value by a Faraday cup. (A), (b) is a figure for demonstrating the kind of test wafer used for dose shift evaluation of this invention, (a) is a test wafer with a resist which has a predetermined coverage (aperture ratio). A plan view of the (second test wafer), (b) is a plan view of a test wafer without resist (first test wafer). It is a figure which shows an example of the result of having implemented ion implantation to the 1st and 2nd test wafer, and having calculated | required the relationship between the dose amount and the sheet resistance in the ion implantation area | region of each test wafer. It is a flowchart which shows the main procedures of the dose shift evaluation method demonstrated in this embodiment. It is a figure for demonstrating the outline | summary of the conventional ion implantation, and its problem. (A), (b) is a figure for demonstrating the fluctuation | variation of the ion implantation amount resulting from the outgas generated from a resist, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Ion implantation apparatus main body 102 Gas system 104 Ion source 106 Ion extraction high voltage acceleration system 108 Mass spectrometry system 110 Later stage acceleration system 112 Beam converging system 114 Faraday cup 115a Second test wafer 115b First test wafer 116 Target wafer 118 Load lock chamber 120 Load / unload mechanism and cassette station 130 Dose controller 132 Control console (control display panel)

Claims (4)

A dose shift amount evaluation method for evaluating a dose shift amount generated by outgas generated from a resist when ion implantation is performed on a wafer having a resist formed on a surface thereof,
With respect to the first test wafer having the wafer surface exposed without having a resist, ion implantation is performed on the first test wafer with a predetermined dose with the ion species to be implanted and the implantation energy as predetermined constant conditions. A first step of measuring an electrophysical property of an ion implantation region of the first test wafer to obtain a relationship between a dose amount in the first test wafer and the electrophysical property;
For a second test wafer having a resist formed on the wafer surface and having an opening exposing the wafer surface to a part of the resist, a desired dose is obtained under the same ion species and implantation energy conditions as in the first step. A second ion beam is selectively ion-implanted into the wafer surface of the second test wafer exposed from the resist opening at a quantity setting value, and the electrophysical characteristics of the ion-implanted region of the second test wafer are measured. Steps,
A third step of evaluating the deviation of the dose amount by comparing the electrophysical property measured in the second step with the electrophysical property at the same dose amount obtained in the first step. Characteristic dose shift evaluation method. A dose shift evaluation method according to claim 1,
The first step uses a plurality of the first test wafers, sets the dose amount of each of the first test wafers at a plurality of different stages, performs the ion implantation, A dose shift evaluation method comprising: measuring the electrophysical characteristics of each of the first test wafers to obtain a calibration curve of the electrophysical characteristics for various dose setting amounts. A dose shift evaluation method according to claim 1 or claim 2, wherein
A dose shift evaluation method, wherein the electrophysical property is a sheet resistance value. A dose shift evaluation method according to claim 1 or claim 2, wherein
The dose shift evaluation method, wherein the electrophysical characteristic is an impurity concentration distribution characteristic in a depth direction of the wafer measured by SIMS (secondary ion mass spectrometry).

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