JP2886294B2 - Electron beam exposure method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Regarding an electron beam exposure method in an electron beam exposure apparatus used in an LSI manufacturing process or the like, even if the pattern size is 0.1 μm or less, without reducing the throughput, The purpose of which is to enable high-precision exposure, after measuring the effective height of a mark on a sample by scanning with an electron beam, the resist to be exposed is determined from the effective height of the mark. After correcting the difference in height up to the upper surface by increasing the lens strength, the resist is exposed.

The present invention relates to an electron beam exposure method in an electron beam exposure apparatus used in an LSI manufacturing process or the like.

[Prior Art] FIGS. 2A to 2C are views for explaining a conventional electron beam exposure method.

In the drawing, reference numeral 1 denotes a substrate, 2 denotes a concave focusing mark formed on the substrate 1, and 3 denotes a resist applied on the substrate 1. Conventionally, the mark 2 is scanned by an electron beam 4. For example, after obtaining a reflected electron intensity curve as shown in FIG. 2B, this reflected electron intensity curve is differentiated to obtain a differential curve as shown in FIG. ) The lens intensity was adjusted so that the -P (peak) value was maximized, the focal position at this lens intensity was used as the optimal focal position, and then the resist 3 was exposed.

[Problems to be Solved by the Invention] Here, in the conventional electron beam exposure method, the optimum focus position is determined under the condition that the contrast of the reflected electrons at the edge portion 5 of the mark 2 is maximized. The focused position is the surface 6 of the concave portion of the mark 2.
Instead, it is considered that it is not the surface 7 of the convex portion, but is effectively its intermediate surface 8. That is, in the conventional electron beam exposure method, the focal position of the electron beam 4 cannot be set on the upper surface 3A of the resist 3, which should be the focal position.

However, in general, the height of the unevenness of the mark 2 and the thickness of the resist 3 are each about 1 μm, which indicates that the distance between the intermediate surface 8 and the upper surface 3A of the resist 3, in other words, the effective Height H and upper surface 3A of resist 3
The difference up to 1.5 μm is about 1.5 μm.
The difference of about μm was within the range of the depth of focus of the electron beam exposure apparatus, and did not cause any particular problem.

That is, the depth of focus of the electron beam exposure apparatus is several tens of times deeper than the exposure apparatus using an optical lens such as a stepper when compared with an exposure apparatus using an optical lens. The entire surface of the wafer can be exposed only by focusing on a certain point on the wafer, and focus correction is not required. To be more precise, focusing is performed by deflecting the electron beam, but in terms of focusing on the wafer, it is sufficient to perform focusing once. Of course,
The flatness of the wafer is corrected by an electrostatic chuck, and the flatness and the horizontality are within a range of several μm by applying the upper surface to the horizontal surface. Distortion and displacement caused in the exposure field due to the warpage and undulation of the remaining wafer of several μm must be corrected, but the displacement of the focal position in the height direction was absorbed by the depth of focus.

Of course, as the wafer process is repeated, insulating layers, contact layers, wiring layers, and the like are stacked on the wafer. For this reason, the marks on the wafer are not always present at the same height, and as the wafer process is repeated, the positional deviation between the focus position adjusted by the marks and the upper surface of the resist to be exposed is large. Become. Also, depending on the process, the mark becomes invisible due to the laminated material, or the shape of the mark becomes blunt, so that the shape of the intensity distribution of the reflected electrons deteriorates, or because the laminated material is an insulator, the distribution of the reflected electrons is reduced. It is necessary to dig up the original mark because it becomes difficult to see. In such a case, the positional deviation between the focal position and the upper surface of the resist on the laminated film could be avoided with a sufficient depth of focus.

As described above, an electron beam exposure apparatus has a deeper depth of focus than an exposure apparatus using an optical lens, and conventionally, a focus error caused by a fundamental error of focusing, a height of a mark due to wafer warpage and waviness, and the like. The difference between the position in the vertical direction and the upper surface of the resist to be actually exposed, a focus error caused by stacking various layers, and the like can be avoided with a sufficient depth of focus.

However, when exposing a very fine pattern of 0.1 μm or less, which is required this time, there is a problem that a difference in resolution depending on the location of the wafer and a deterioration in resolution due to several layers of wafer processes are observed. In particular, the deterioration of the resolution due to the lamination of the wafer processes is the focus shift in the direction in which the lens strength must be strengthened, and furthermore, the warpage and undulation of the wafer also defocus in the direction in which the lens strength must be increased. In this case, there is a problem that the resolution is further deteriorated. That is, 0.1
When exposing a pattern of μm or less, there is a problem that the above-described focus error cannot be tolerated with a sufficient depth of focus.

This point will be described in more detail. For example, when it is assumed that a pattern tolerance (error) up to 1/5 of the pattern size L is allowed in the sum of both sides of the pattern, the depth of focus Z depends on the incidence of the electron beam. If the angle is α, then 2 × (± Z) × tan α ≦ L × 1/5. Here, if the half angle of incidence α is 8 × 10 ⁻³ rad, then Z ≦ + L × 12.5, and the depth of focus Z is allowed only up to 12.5 times the pattern size. For example, if the pattern size is 0.
For a 1 μm pattern, even with an electron beam exposure apparatus, only a focus error of ± 1.25 μm or less is allowed.

Here, for example, if a field emission type electron gun that can obtain a high-brightness electron beam is used, the aperture can be further narrowed, and the depth of focus can be further increased. However, such a field emission type electron gun cannot perform exposure using a variable rectangular beam or exposure using a block mask (stencil mask). There has been a problem that it is impossible to follow the increase in the total number of patterns and the throughput is extremely reduced.

In view of the above, the present invention has a pattern size of 0.1 μm.
An object of the present invention is to provide an electron beam exposure method capable of performing high-precision exposure even for a fine pattern of m or less without lowering the throughput.

[Means for Solving the Problems] According to the electron beam exposure method of the present invention, an electron beam is scanned to measure an effective height of a mark on a sample, and then the target is exposed from the effective height of the mark. After correcting the difference in height up to the upper surface of the resist by increasing the lens strength, the resist is exposed. The correction value for increasing the lens strength can be given, for example, as an offset of the dynamic focus correction coil.

[Operation] In the present invention, after the effective height of the mark is measured by scanning with an electron beam, the difference between the effective height of the mark and the upper surface of the resist to be exposed is determined by the lens strength. After the correction by strengthening, the resist is exposed, so that the focus position of the electron beam is adjusted to the upper surface of the resist. Therefore, even when the pattern size is 0.1 μm or less, there is no need to use a field emission type electron gun to increase the depth of focus. Therefore, according to the present invention, even when the pattern size is 0.1 μm or less, exposure using a variable rectangular beam or exposure using a block mask is performed, without lowering the throughput, and with high accuracy. Exposure can be performed.

Embodiment An embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is a view for explaining, in particular, a case where focusing is performed in an electron beam exposure method according to one embodiment of the present invention, in which 10 is a substrate, and 11 is formed on a substrate 10. A concave focusing mark, 12 is an insulating layer, 13 is a wiring metal layer, 14 is an insulating layer, 15 is a planarizing metal layer, and 16 is a resist. That is, the insulating layer 12, the wiring metal layer 13, the insulating layer
14, a case where a planarizing metal layer 15 and a resist 16 are stacked. The insulating layer 12, the wiring metal layer 13, the insulating layer 14, the planarizing metal layer 15, and the resist 16 each have a thickness of 1 μm.
m, and in this embodiment,
The thickness of each layer is stored as focus correction data.

Here, FIG. 1A shows a case where a focusing mark 17 by the insulating layer 14 is formed above the original focusing mark 11.

In this case, first, the electron beam 18 is scanned in the order of A → B → C in the drawing as in the prior art, and the effective height HA of the focusing mark 17 is measured. In this case, this
HA is 0.5 μm. Here, a film thickness of 1 μm is formed on the insulating layer 14.
Since a flat metal layer 15 and a resist 16 having a thickness of 1 μm are formed, the effective height of the focusing mark 17 is increased.
The difference in height between HA and the upper surface 16A of the resist 16 is 2.5 μm.

Therefore, in this embodiment, from such data, the intensity of the focus correction lens is increased, and the focus position of the electron beam 18 is raised by 2.5 μm above the effective height HA of the focus mark 17. To Here, the focal position of the electron beam 18 can be made to coincide with the upper surface 16A of the resist 16.

FIG. 1B shows that the insulating layer 14 at the portion of the focus mark 17 is removed, and the focus mark by the wiring metal layer 13 is placed above the original focus mark 11.
19 shows the case where it is formed.

In this case, first, the effective height HB of the focusing mark 19 is measured by scanning the electron beam 18 as shown in FIG. In this case, this
HB is 0.5 μm. Here, an insulating layer 14 having a thickness of 1 μm, a flattening metal layer 15 having a thickness of 1 μm, and a resist 16 having a thickness of 1 μm are formed on the wiring metal layer 13. Target height HB and upper surface 16 of resist 16
The difference in height from A is 3.5 μm.

Therefore, in this embodiment, from such data, the intensity of the focus correction lens is increased, and the focus position of the electron beam 18 is set higher than the effective height HB of the focus mark 19.
Raise by 3.5 μm. Here, the focal position of the electron beam 18 can be made to coincide with the upper surface 16A of the resist 16.

FIG. 1C shows the original focusing mark.
This shows the case where 11 is dug out.

In this case, first, the effective height HC of the focusing mark 11 is measured by scanning the electron beam 18 as shown in FIG. In this case, this
HC is 0.5 μm. Here, mark 11 for focusing
Is formed on a substrate 10 on which an insulating layer 1 having a thickness of 1 μm is formed.
2, 1 μm thick wiring metal layer 13, 1 μm thick insulating layer 1
4. Since the flat metal layer 15 having a thickness of 1 μm and the resist 16 having a thickness of 1 μm are formed, the focusing mark 11 is formed.
Of the effective height HC of the resist 16 and the height of the upper surface 16A of the resist 16 is 5.5 μm.

Therefore, in the present embodiment, from such data, the intensity of the focus correcting lens is increased, and the focal position of the electron beam 18 is raised above the effective height HC of the focusing mark 11.
Raise it by 5.5 μm. Here, the focal position of the electron beam 18 can be made to coincide with the upper surface 16A of the resist 16.

Thus, in this embodiment, the electron beam
Since the focal position of 18 can be made coincident with the upper surface 16A of the resist 16, even when the pattern size is 0.1 μm or less, the depth of focus is not increased by using a field emission type electron gun.

Therefore, according to the present embodiment, the pattern size is 0.
Even in the case of 1 μm or less, exposure using a variable rectangular beam or exposure using a block mask is performed, and high-precision exposure can be performed without lowering the throughput.

[Effects of the Invention] As described above, according to the present invention, after measuring the effective height of a mark by scanning an electron beam, the height from the effective height of the mark to the upper surface of the resist to be exposed is measured. After correcting the difference in height by increasing the lens strength, the resist is exposed, so that the focus position of the electron beam can be adjusted to the top surface of the resist, and the pattern size is 0.1 μm or less. However, since the depth of focus is not increased by using a field emission type electron gun, even when the pattern size is 0.1 μm or less, exposure using a variable rectangular beam or exposure using a block mask can be performed. As a result, high-precision exposure can be performed without lowering the throughput.

[Brief description of the drawings]

1A to 1C are diagrams for explaining, in particular, a case of performing focusing in an electron beam exposure method according to an embodiment of the present invention, and FIGS. 2A to 2C are diagrams for explaining a conventional electron beam exposure method. FIG. 11, 17, 19: Focusing mark 16: Resist 18: Electron beam

Continuation of front page (56) References JP-A-3-46220 (JP, A) JP-A-61-34936 (JP, A) JP-A-62-76620 (JP, A) JP-A-60-95845 (JP) , A) JP-A-61-34935 (JP, A) JP-A-63-217627 (JP, A) JP-A-62-100677 (JP, U) (58) Fields investigated (Int. Cl. ⁶ , DB (Name) H01L 21/027

Claims (2)

(57) [Claims] 1. A step of measuring an intermediate height of a concave focusing mark on a sample by scanning an electron beam, and a height of an intermediate portion of the depth of the focusing mark. A step of correcting the difference in height from the top surface of the resist to be exposed to light by increasing the lens strength to perform exposure on the resist. 2. The electron beam exposure method according to claim 1, wherein a correction value for increasing the lens strength is provided as an offset of a dynamic focus correction coil.