JPS6246057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to alignment in electron beam drawing technology, and more particularly to an improvement in a mark position measuring method using an electron beam.

[Technical background of the invention and its problems]

In electron beam lithography technology, alignment of an electron beam and a sample is well known as registration technology. FIG. 1 is a schematic diagram for explaining the conventional positioning method, and 101
indicates a [100] oriented silicon wafer, and 102 indicates a V-shaped groove (mark) made by anisotropic etching technology. When the mark 102 is scanned with an electron beam and its reflected signal is detected by an electron detector or the like, a reflected electron signal 103 corresponding to the shape of the mark 102 is obtained. Then, the position of the electron beam relative to the mark 102 is measured from this detection signal (reflected electron signal) 103, and registration is performed.

Here, the maximum level point 1 of the detection signal 103 is
The maximum backscattered electron intensity at 04 is I _nax , and the minimum backscattered electron intensity at minimum level point 105 is I _nio
i and the steady reflected electron intensity corresponding to the location 106 where there is no mark 102 _{is Iav} , then the size of the signal portion from the mark 102, that is, the mark signal strength S
is defined as S=I _nax −I _nioi (1). Also, 50 of the above mark signal strength S
[%] Letting the electron beam positions corresponding to the intensities be x ₁ and x ₂ , the center position x ₀ of the mark 102 is given by x ₀ =(x ₁ +x ₂ )/2 (2). Furthermore, it is known that the alignment accuracy Δx during alignment is given by the following equation.

Δx=N/S·D (3) where N is the noise level of the detection signal, and D is the distance between the maximum level point 104 and the minimum level point 105.

Incidentally, in order to manufacture an LSI, steps are required to thermally oxidize the surface of a silicon wafer and to deposit an oxide film, a nitride film, etc. on the silicon wafer. Figure 2 shows a silicon wafer 201
FIG. 3 is a schematic diagram showing a reflected electron signal waveform when a thermal oxide film 207 is formed thereon. In addition, 201,
~, 206 are 101, ~, 10 in Fig. 1, respectively.
Corresponds to 6. The shape of the mark 202 is deformed due to thermal oxidation, and the mark signal strength S decreases as shown in FIG. This is mainly due to the maximum reflected electron intensity I
This is because _nax approaches the steady reflected electron intensity _Iav . For this reason, as the process progresses, the accuracy of mark position measurement decreases, resulting in problems such as a decrease in the accuracy of alignment between the electron beam and the sample. Further, in order to avoid the above-mentioned problem, it is conceivable to form a positioning mark for each process step, but in this case, a plurality of mark forming steps are required, resulting in complication of the process steps.

[Purpose of the invention]

An object of the present invention is to be able to accurately measure the mark position even when an oxide film or the like is formed on the alignment mark, and to prevent a decrease in alignment accuracy as the process progresses. An object of the present invention is to provide a mark position measuring method that can prevent the above problems.

[Summary of the invention]

The present inventors focused on the fact that the maximum backscattered electron intensity I _nax approaches the steady backscattered electron intensity I _av as the process progresses, and the accuracy of mark position measurement decreases due to this. I _nax
It has been found that if the constant backscattered electron intensity I _av and I av are made substantially equal and sufficient mark measurement accuracy is obtained in this state, it is possible to prevent the mark position measurement accuracy from decreasing due to the process steps described above. According to intensive research by the present inventors, by appropriately selecting the Gruhn range R _G of the electron beam, I _nax 〓I
It turned out to be _AV .

The Gruhn range R _G of the electron beam is generally defined by the following equation.

R _G =4.6×10 ⁻⁶ /ρE ^{1 .75} [cm] (4) where ρ is the density of the mark material and E is the energy of the electron beam in keV units. I _nax 〓I _av
Under these conditions, the value of the maximum reflected electron intensity I _nax hardly decreases even after the thermal oxidation process. Therefore,
Even if the process steps progress, the mark position measurement accuracy will hardly decrease.

Figure 3 shows ΔI= when the mark depth is h.
It is a figure which shows the relationship between ( _Inax - _Iav )/S and h/ _RG . Note that in the figure, the ○ mark indicates the case before the process step, and the ● mark indicates the case after the process step. It can be seen from this figure that when h/R _G becomes smaller than 1/6, the respective ΔIs are approximately equal regardless of whether before or after the process step and become smaller than 0.25. In other words, by setting h/R _G <1/6, deterioration of the mark signal before and after the process step is extremely small. Also, h/
When R _G <1/6, I _nax = I _av and the mark signal strength S becomes smaller, but in this case the distance D also becomes smaller, so the decrease in alignment accuracy given by the third equation is Almost no problem.

The present invention focuses on these points and provides a mark position measuring method using an electron beam, in which an electron beam is irradiated onto alignment marks formed on a sample, and the mark position is measured by detecting the reflected electrons. , when the depth or height of the above mark is h, and the Gruhn range of the electron beam within the mark is R _G , set the Gruhn range _RG to a value that satisfies h/ _RG < 1/6. This is the method.

〔Effect of the invention〕

According to the present invention, even if an oxide film or the like is formed on the mark, the mark position measurement accuracy does not deteriorate, so that alignment can be performed with high precision even as the process progresses. Further, since the alignment accuracy does not deteriorate even as the process progresses, complicated operations such as forming alignment marks for each process are unnecessary.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to illustrated embodiments. In this example, the first
Using a V-shaped groove similar to the one shown in the figure, h/R _G was set to 1/10. The reflected electron signal waveform at this time is I _nax =I _av as shown in FIG. 4, and there is no shoulder peak that existed in FIG. 1. In addition, 401,~,4 in the figure
05 correspond to 101, . . . , 105 in FIG. 1, respectively.

Next, after going through a process step of forming a thermal oxide film etc. on the wafer provided with the above mark, the mark position was measured again to align the electron beam and the wafer. At this time, the reflected electron signal waveform is almost unchanged from that shown in FIG. 4, as shown in FIG. 5, and the deterioration of the reflected electron signal is extremely small.
This is because the shoulder peak of the mark portion in the backscattered electron signal is eliminated by setting I _nax =I _av in advance. In addition, 501, ~, in FIG.
505 corresponds to 401 to 405 in FIG. 4,
507 indicates an oxide film.

Therefore, it is possible to accurately measure the mark position even after the process steps have been completed, and thereby it is possible to prevent the positioning accuracy from decreasing as the process steps progress. In addition, since positioning can be performed with high precision even after the process has passed, complicated steps such as forming a new mark for each process are unnecessary, and the present invention is extremely useful in electron beam drawing technology.

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the mark is not limited to a V-shaped groove, but may be a convex shape. In this case, conventionally, by setting h/R _G <1/6 for a backscattered electron signal with a large peak at the shoulder corresponding to the mark edge as shown in FIG. 6a, the peak at the shoulder corresponding to the mark edge as shown in FIG. It can be made small, and the contribution to the mark position measurement error can be made small as in the previous embodiment. Further, when the mark is a groove, if the depth is shallower than 1 [μm], the groove will be filled in during a process such as coating with an oxide film, making it impossible to obtain a good reflected electron signal. Therefore, the depth of the groove must normally be made deeper than 1 [μm]. The same applies when the mark is a convex portion, and the height of the convex portion needs to be higher than 1 [μm].

Furthermore, when a multilayer film as shown in FIG. 7 is used, the Gruhn range R _G is defined as R _G =R ₁ +R ₂ +...+R _n-1 +R' _n . Here, R ₁ to R _n-1 is the thickness from the first layer to the m-1th layer, and R _n ' is the range of electrons in the m-th layer. However, R _n ' is determined by the following formula.

E ₁ = E-(ρ ₁・R ₁ /4.6×10 ⁻⁶ ) ^1/1 . ⁷⁵ E ₂ = E − (ρ ₂・R ₂ /4.6×10 ⁻⁶ ) ^1/1 . ⁷⁵ 〓 〓 E _n-1 =E _n-2 −(ρ _n-1・R _n-1 /4.6×10
⁻⁶ ) ^{1/ 1.75} ∴R _n ′=4.6×10 ⁻⁶ /ρ _n E _n-1 ^{1. 75However} , R _n ′<R _n . Here, ρ ₁ ,...
ρ _n is the density of each layer.

[Brief explanation of the drawing]

Figures 1 and 2 are for explaining conventional examples, respectively. Figure 1 is a schematic diagram showing the alignment mark and the corresponding reflected electron signal waveform, and Figure 2 is the mark after the process step. FIG. 3 is a schematic diagram showing the waveform of the reflected electron signal, and FIG. 3 is for explaining the outline of the present invention. FIG. 4 is a characteristic diagram showing the relationship between (I _nax −I _av )/S and h/ _RG . and FIG. 5 are for explaining one embodiment of the present invention, respectively. FIG. 4 is a schematic diagram showing the alignment mark and the corresponding reflected electron signal waveform, and FIG. 5 is a schematic diagram showing the mark after the process step. FIGS. 6A and 6B are schematic diagrams showing a reflected signal waveform, FIGS. 6A and 6B are schematic diagrams for explaining a modification, and FIG. 7 is a schematic cross-sectional diagram showing a multilayer film structure. 101,201,401,501...Silicon wafer, 102,202,402,502...
Mark, 103, 203, 403, 503... Backscattered electron signal, 104, 204, 404, 504...
...Maximum level point, 207,507...Oxide film.

Claims (1)

[Claims] 1. A mark position measuring method using an electron beam, in which an electron beam is irradiated onto a positioning mark formed on a sample, and the mark position is measured by detecting the reflected electrons. When the depth or height is h and the Groen range of the electron beam within the mark is R _G , an electron beam characterized in that the Groen range R _G is set so that h/R _G <1/6 is used. Mark position measurement method.