JPH0210823A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To reduce the displacement of previously formed pattern size on a semiconductor substrate largely by automatically detecting the optimal set value of the adjustment of a stigma by using returning secondary electrons at the time of beam scanning. CONSTITUTION:Beam scanning is conducted in the X direction or the Y direction under the state of stigma set values (Sx, Sy) at every step by an auto- focussing function, and a best focussing set value Fx(X beam scanning) or Fy(Y beam scanning) where the crest value of a signal waveform acquired by receiving and molding secondary electrons from a reference mark is maximized is detected. The best focussing values Fx and Fy are compared, and the stigma set values (Sx, Sy) at a time when Fx=Fy holds are detected, and transferred to a stigma adjusting section 36. The stigma volume of the stigma adjusting section 36 changes inresponse to the set values (Sx, Sy), and the intensity in the X direction and Y direction of a stigma meter 13 is corrected.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention uses an electron beam lithography system to process a semiconductor substrate (
This relates to a method of manufacturing a semiconductor device in which a pattern is written on a wafer (mainly a wafer) and a mask substrate, etc., and in particular, it involves correction of stigma (also referred to as astigmatism correction) of an electron beam in the step of adjusting the electron optical system of the drawing device before pattern drawing. Used in automatic methods.

(Prior Art) Semiconductor devices are becoming increasingly finer and more dense, and processing dimensions in the submicron or nanometer range are now required. Such fine processing exceeds the performance limits of conventional optical devices, and electron beam lithography devices are now being used.

As an example of such a microfabrication pattern drawing device,
The JBX-5DII (F) type electron beam lithography system (manufactured by JEOL Ltd.) will be discussed below, and the conventional technology will be explained below.

FIG. 3 is a schematic diagram showing the configuration of the electron optical system of the device. In the figure, cathode 1, Wehnelt (weh
ne l 1. Electrons emitted from an electron gun 4 composed of a J electrode 2 and an anode 3 are sent to an alignment coil 1 to a coil.
coil) 5, a small circular hole (aperture) 6, and a beam blanking electrode (beai blanke).
r) The first magnetic field lens 8 that incorporates 7 is used to reduce the cross-over point between beams 1 and 5 (bean + 5 to
pper) A reduced image is formed at position 9. This reduced image-formed electron beam further passes through the alignment coil 10 and enters an intermediate lens (second lens 11 and third lens 12), and the intensities of the second and third lenses are controlled in conjunction to form a second reduced image. The statue is performed. Stigmeter (stiBato)
r, stigmator) 13 is also called an astigmatism correction device, and has the function of correcting astigmatism caused by imperfect rotational symmetry of the magnetic field lens. Reference numeral 14 is a final aperture. ), the fourth lens 16 or the fifth lens 18 is an objective lens, and third reduction imaging is performed. Eight-pole electrostatic deflectors 15 and 17 for beam deflection are installed inside the fourth and fifth objective lenses. electronic detector (backsca)
ttered electron detector
) 19 includes the reflected electrons returned when the work piece 20 is scanned with an electron beam.
It has the function of receiving secondary electrons (hereinafter sometimes simply referred to as secondary electrons).

In the above-mentioned electron optical system, the electrons emitted from the electrons Rq are focused on the wafer using the fourth lens to the fourth lens.
A beam of micrometer or less can be formed (in the case of Gaussian beam method).

When drawing a pattern on a semiconductor substrate (wafer) using this electron beam drawing apparatus, it is necessary to adjust the electron optical system before drawing. For example, since the central part of the electron beam emitted from the electron gun is used, alignment adjustment is required to correct the deviation of the electron beam with respect to the lens axis, or if the electron beam becomes an elliptical spot due to astigmatism, it must be adjusted to a perfect circle. We will carry out stigma adjustments to reduce

Further focus adjustment is required. Currently, focus adjustment is performed by detecting the secondary electrons that return when an electron beam scans a reference mark provided on the substrate stage or wafer of the lithography equipment, and then using the scanner while viewing a monitor image on a CRT. The focus is adjusted manually or automatically using the detection signal.
However, stigma adjustment is mostly done manually by the operator while looking at the monitor image.

FIG. 4 is a diagram showing an example of the reference mark position and its shape. In FIG. 2A, a wafer 23 held by a holder 22 is placed on a wafer placement stage 21. As shown in FIG. Symbols P, Q, R, and S are cross-shaped reference marks provided on the wafer, and symbols M1, M2, and M3.
, M4. M5 is a mesh-like reference mark provided on the stage L, which is made up of connected cross shapes. Figure (1)) shows four scans (solid line) to detect the cross mark (dotted line).
Mo [1), (2), (3), and (4), and the same figure (
C) is a cross-sectional view of the step mark 24 and the dissimilar metal mark 25, respectively. FIG. 5 shows the flow of mark detection signal processing and its processing waveform, and FIG. 6 is a block diagram showing an outline of the mark detection control system including focus adjustment and stigma adjustment.

The reference mark 24 or 25 is scanned with an electron beam, and the returned secondary electrons are received by the electron detector 19 to obtain detection signals A and B. If the reference mark is a step mark, a difference signal output Wl, (A-B) is provided, and if the reference mark is a different metal mark, a sum signal output W2 is provided.

The output obtained by differentiating (A+B) by the differentiating circuit 27 is amplified by the variable gain amplifier 28 to obtain an amplifier output W3 of a desired magnitude. Reference numeral 26 is a changeover switch, SUB for step marks, ADDl for dissimilar metal marks.
11! Switch to I. A part of the amplifier output W3 is input to a monitor 29, a part of which is input to a waveform memory 30 containing A/D conversion, and a part of the output of W3 is input to an absolute value amplifier 31. A part of the absolute value amplifier output W4 is input to the monitor, the other part is input to the waveform forming circuit 32, and the waveform forming output W5 is sent to the monitor and signal processing section 33.

A signal waveform of secondary electrons stored in a waveform memory or processed by a signal processing section is input to the computer 34 .

Autofocus uses this signal waveform, and the computer 34
The focus volume of the focus adjustment section 35 is changed under the control of , the outputs of the detection signals A and B are processed according to the flow shown in FIG. , X-direction scanning and Y-direction scanning, and the average value of both is taken as the best focus. The focus adjustment unit 35 controls the strengths of the second lens 11 and the third lens 12 in conjunction with each other via the computer 34, and functions to align the imaging position of the electron beam on the standard mark.

Taking as an example the case where a fine pattern of 0.2 μm level is formed using the electron beam writing apparatus, focus adjustment and stigma adjustment, which are the main problems in the work before pattern writing, will be explained in more detail. Figure 7 shows each isolated pattern with dimensions of 0.2 μm to 1 μm.
It shows the dimensional margin (focus margin) due to focus shift when patterning S-EX(R) (Toyo Soda) negative electron beam drawing resist.

The horizontal axis indicates the deviation from the best focus, and the unit point is the minimum unit of the focus setting value and corresponds to the strength of the second and third lenses. The vertical axis is the patterned resist dimension (μn).

The circle mark indicates a drawing area of 1600 μm (1600 μTl×16
00μ111) field, - indicates the case of 1100μm front field. From Figure 7, the 0.2μm pattern has a focus shift of about ±50 (points) for a 1600μm front field with a drawing area of ±130 (points) for a 1100μm front field. Although there is dimensional margin,
Even with a field of 1100 μm, there will be a deviation of about ±(100 to 200) (points) due to individual differences among workers. Therefore, secondary electrons are detected by beam scanning,
There is the aforementioned autofocus function that checks the best focus based on the waveform. When this function is executed, it is currently possible to focus within ±60 (points) (3σ) without individual differences.

In the conventional stigma adjustment, independent volume values in the X direction and the Y direction are manually adjusted. FIG. 8(a) shows the dimensional margin due to the stigma adjustment deviation in the X direction, and FIG. 8(b) shows the dimensional margin in the Y direction. In the same figure, the O mark and the * mark are each 1600.
The case of μm0 field and 1100μ1 mouth is shown.
The horizontal axis shows the stigma setting value for best focus as 0.
and indicates the deviation of the stigma setting value from this setting value,
A unit point is the minimum unit of stigma setting value and corresponds to the strength of the stigma meter. The vertical axis is the patterned resist dimension. From the same figure (a), in the X direction, the 1100 μm field is about ±300 (points), and the 1600 μm field is ±200 (points).
There is a dimensional margin due to some degree of stigma adjustment deviation.
Also, from the same figure (b), in the Y direction, there is a dimensional margin of about ±250 (points) for a 7100 μm field and ±100 (points) for a 1600 μm field.

However, when stigma adjustment is performed while looking at a monitor image, there are variations due to individual differences, and the stigma adjustment deviation is approximately ±(300 to 400) (point l-). In addition, it is conceivable that the stigma adjustment deviation will affect the focus adjustment.

(Problems to be Solved by the Invention) The main adjustments of the electron optical system on the drawing surface of an electron beam drawing apparatus are focus adjustment and stigma adjustment.

Regarding focus adjustment, by providing the above-mentioned autofocus function, the adjustment deviation can be kept within an allowable value. However, in the conventional technology, stigma adjustment is handled by manual adjustment. Therefore, adjustment deviations occur due to individual differences among workers, and this deviation affects autofocus adjustment, for example, 0.
．． There is a problem that pattern formation at the 2 μm level causes deviations in finished dimensions, and in the worst case, patterning cannot be performed.

An object of the present invention is to determine the optimal setting value for stigma adjustment using secondary electrons (including reflected electrons) returned during beam scanning, in order to reduce the deviation in finished pattern dimensions due to manual stigma adjustment. An object of the present invention is to provide a method for manufacturing a semiconductor device that can automatically detect the problem and thereby solve the above problem.

[Structure 1 of the Invention (Means for Solving the Problems) The present invention is characterized in that when a circuit pattern is drawn on a semiconductor substrate or the like by an electron beam, stigma correction is automatically performed in the stigma IRMk before drawing. This is a method for manufacturing a semiconductor device.

That is, when scanning the reference mark (FIG. 4) provided on the substrate mounting stage or substrate of the drawing apparatus with an electron beam,
Secondary electrons (backscat) including reflected electrons that return
Jered electron) is received by an electron detector, and the signal waveform of this secondary electron is shaped.
X and Y directions perpendicular to each other on the stage or substrate
Stepwise changing the stigma setting value in one direction or in both the X and Y directions by a predetermined value,
At each step of this stigma setting value, the autofocus adjustment setting value F that maximizes the peak value of the shaped secondary electron signal waveform when the beam scans in the X direction is detected, and similarly in the Y direction. Detect the setting value Fx of the autofocus adjustment value that maximizes the peak value when scanning the beam,
Detect stigma setting values of the same group where Fx=Fy,
This stigma setting value is defined as a stigma correction value. These operations are automatically performed under computer control.

Note that the stigma setting value is determined by two setting values in the X direction and the Y direction. The above-mentioned same set of stigma setting values means that one set of stigma setting values when scanning the beam in the 5X direction and one set of stigma setting values when scanning the beam in the Y direction are the same. Also, if the stigma setting values in the X and Y directions are both undetermined, the stigma setting in both directions, or in one of the X and Y directions (if Iri is specified, the stigma setting value in the other direction is stepped) change into shape.

(Function) If the setting values of the stigma adjustment in the X direction and Y direction are adjusted well, the secondary electron signal waveform will change even if the beam is scanned in the X direction or in the Y direction. It was confirmed from the trial results that the focus adjustment setting values that maximize the peak value are equal, that is, Fx=Fy. The present invention was completed based on this knowledge. If the electron optical system has astigmatism, the beam spot shape on the pattern drawing surface will be elliptical, but if the stigma adjustment settings in the X and Y directions are adjusted sufficiently, the beam spot will become almost a perfect circle. Become. For this reason
It is estimated that the focus adjustment setting value that maximizes the peak value of the secondary electron signal waveform is the same regardless of whether the beam is scanned in the Y direction or the Y direction.

The means of the present invention changes the stigma setting value in a predetermined step width by the method described above under control from a computer, calculates the Fx value and Fx value at each step 5, and sets the stigma as shown in FIG. 2, for example. The intersection point of the curves showing the relationship between the value and the best focus setting value F8 and Fy is found, the stigma setting value at the intersection point is detected, and this setting value is used as the stigma correction value. As a result, the beam spot becomes almost a perfect circle. Furthermore, since the stigma setting value at the intersection point is detected by automatic control of the total M and R, the conventional adjustment deviation due to individual differences is eliminated.

(Example) The present invention will be explained in more detail with reference to Examples below.

The electron beam drawing device used in this example is the JBX-5DI [(F) type (manufactured by JEOL Ltd.) described in the prior art section, and the configuration of the electron optical system of the device is shown in Figures 3 to 6. See diagram.

First, the trial results that formed the basis of the present invention will be explained with reference to FIG. First, the stigma setting values in the X and Y directions are set to 0 (offset state! r
3), manually increase or decrease 100 points in steps, and execute the autofocus a function for each step of the stigma setting value. Detect values. The above best focus setting value is determined by scanning the reference mark in the X direction or Y direction with an electron beam and returning the 2
The focus is obtained by automatically performing focus adjustment under computer control so that the peak value of the signal waveform obtained by receiving secondary electrons by an electron detector and shaping the secondary electron signal waveform is maximized. This is the setting value.

In FIG. 2, the Δ marks indicate the best focus setting values Fx and Fy when the electron beam is scanned in the X direction, the mu marks respectively in the Y direction, and the ○ marks indicate the average value of Fx and Fx.

Figures (a) and (b) show the case where the stigma setting value is changed stepwise by 100 points I· in the X and Y directions.

In the following explanation, the stigma setting value in the X direction is represented by Sx, the stigma setting value in the Y direction is represented by Sy, and the staircase width (step width) is represented by ΔSx and ΔSy. Setting value (SX, 5y) =
(nΔSx, nASy), where n-0 to 5 integer, Δ
Sx=ΔS,=100 points and (SX,5y)=
(-rmΔSx.

1ΔSy), however, an integer from m-1 to 5, ΔS x Δ5y-
Represents 100 points. The vertical axis is the best focus setting value Fx in the stigma setting value (S,,S,)
(Δ mark), Fy (mu mark). In the same figure (b), the stigma setting value is (Sx, 5y) = (nΔS,, -n
ASy) and (sx, SV) = (-IIΔS,
, -nASy).
Also, in the same figure (C), when Sx is changed with S, −〇, stigma setting value (8, 5V) = (nΔ5
80) and (sx, 5y) = (IIΔS, , O). In the same figure (d), when Sy is changed with S = 0, (sx, sy ) = (o, nΔS, ) and (S
x, Sy) = (0,-rxΔS,).

In each of Figures 2 (a), (b), and (C), as the stigma setting value (Sx, s,) increases, the difference between FX and Fy increases, and it is clear that there is only one location, namely A. , B
, C intersect at each point.

In the same figure (d), there is no extreme change in FX or Fx with respect to the deviation of the stigma setting value, or the two curves intersect at point D. This phenomenon occurs because when the stigma setting value deviates from the appropriate value, astigmatism occurs, which affects the best focus setting value, and the M1 is deviated from the original best focus setting value (when the beam spot is a perfect circle). , it is determined that such a result will be obtained.

An example of a block diagram of the procedure of the autostigma function using the above trial results is shown in Figure 1.Beam mark detection is performed in advance at the position where the reference mark P on the wafer is expected to be as shown in Figure 4 (a). The position of point P is automatically detected by scanning and stage movement, and the focus is adjusted using the autofocus R function.

Next, in step ■. The operator performs stigma adjustment using one monitor to a certain extent.

The stigma setting values SXO and Syo at this time are (SX,
This is the initial value of Sy).

In step ■. Switch to auto mode using computer processing. As a result, the autofocus and autostigma adjustment functions operate, and the next step automatically proceeds.

In step ■. Stigma settings in X and Y directions (
sx, S,) are changed stepwise by a predetermined value ΔS. That is, 5x=S. ±nΔS, 5y=S, J0±
nΔS, n is an arbitrary transfer value, which is stored in advance in the computer's memory together with ΔS, for example, n = 0.1.
,2. . . . The process changes in a stepwise manner in the order of . Steps ① to ② are repeated until F8Fy is detected. Furthermore, the stigma setting values (sx, sy
) signals are outputted from a total of 3 Wa 34 and transferred to the stigma adjustment unit 36, which sets the intensity of the stigma meter 13 and, therefore, the shape of the beam spot in the X and Y directions via the stigma volume etc. in the adjustment unit 36. (SX
, Sy).

In step 2, the autofocus function scans the beam in the X or Y direction with the stigma setting values (sx, SV) for each step, and the signal waveform obtained by receiving and shaping the secondary electrons from the reference mark. The best focus setting value Fx (X-direction beam scanning) or Fy (Y-direction beam scanning) that maximizes the peak value of is detected.

In step ■. Compare the best focus values Fx and Fx, and if they are equal, proceed to step (2), if they are different, return to step (2), and repeat steps (2), (2), and (2) until Fx=Fy.

In step (3), the stigma setting values (sx, Sy) when F'',=Fx are detected and transferred to the stigma adjustment section 36.

In step ■. The stigma volume of the stigma adjustment unit 36 changes in accordance with this set value (Sx, S,), and corrects the strength of the stigma meter in the X and Y directions.

The general procedure for auto-stigma adjustment has been described above. Regarding stigma adjustment, as shown in Figure 8, the margin of the stigma setting value from a dimensional perspective is
00) points, whereas in the conventional technology, there was a deviation of 300 to 400 points due to individual differences among workers. However, by performing auto-stigma adjustment using this procedure, it was possible to correct the deviation in stigma adjustment with an accuracy of within ±100 points.

[Effects of the Invention] As detailed above, in the present invention, an auto-stigma adjustment function that can automatically detect the optimal setting value for stigma adjustment using secondary electrons returned during beam scanning is provided in the electron beam. Since the present invention is provided in a drawing apparatus, deviations in dimensions of finished patterns on semiconductor substrates caused by conventional manual stigma adjustment can be significantly reduced, making it possible to provide a method for manufacturing a semiconductor device that solves the above-mentioned problems.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a procedure overview of the auto-stigma adjustment function in the present invention, Fig. 2 is a diagram showing trial results that are the basis of the present invention, and Fig. 3 is an example of the present invention and a conventional example. Fig. 4 is a diagram showing an example of the reference mark position and its shape, Fig. 5 is a diagram showing mark signal processing and its processing waveform, and Fig. 6 is a schematic diagram of the electron optical system of the electron beam writing device used in FIG. 7 is a block diagram showing an outline of a mark detection control system including focus adjustment and stigma adjustment, FIG. 7 is a diagram showing a dimensional margin due to focus deviation, and FIG. 8 is a diagram showing a dimensional margin due to stigma adjustment deviation. 1... L, R, cathode, 2... Wehnelt electrode, 3... anode, 4 electron gun, 5.10...
・Alignment coil, 6, 14...small circular hole, 7
...Beam blanking electrode, 8, 11, 12, 1
6゜18...1st. Second. Third. 4th. fifth lens,
9... Beam stopper, 13... Stigmeter, 16.17... Second. first beam deflection plate, 19
...electronic detector, 20...work piece, 21...
Wafer aW stage, 23... Wafer, 29
...Monitor, 35...Focus A Advisory Department, 36
...Stigma adjustment unit, P, Q, R, S...Reference mark on the board, M, or M! l...Reference mark on stage, Wl or W5...Secondary electronic signal output. Procedure figure '/be J-, r' ←
-Yabe Kanshu Destruction (Ship [entering] Figure Figure (1)) To 7th Be L - Evening Waveform Formation (W5 -L''- -Shi''- Figure ( 2) Figure

Claims (1)

[Scope of Claims] 1. Among the operations for adjusting the electron optical system of an electron beam lithography device before drawing a pattern on a semiconductor substrate using the lithography device,
When performing stigma adjustment to make the electron beam narrowed down by the lens system into a perfect circle, the electron beam is scanned over a reference mark provided on the substrate mounting stage or substrate of the lithography device, and the reflected light is reflected back. Using a method of receiving secondary electrons including electrons by an electron detector and shaping the signal waveform of the secondary electrons during scanning,
The stigma setting value in the direction or any one of these directions is changed stepwise by a predetermined value, and for each step value of the stigma setting, the above 2 when the beam is scanned in the X direction.
Detecting a focus adjustment setting value F_x that maximizes the peak value of the secondary electron signal waveform and a focus adjustment setting value F_y that maximizes the peak value of the secondary electron signal waveform when scanning the beam in the Y direction, respectively; A method for manufacturing a semiconductor device, comprising: detecting the same set of stigma setting values in which focus adjustment setting values F_x and F_y are equal; and automatically performing stigma correction using the stigma setting values as correction values.