A method for measuring thick film overlay accuracy

Abstract

The application provides a thick film overlay accuracy measurement method, which comprises the following steps: providing a wafer with a prepared front layer overlay mark; preparing a mask which only opens the overlay mark between the current layer and the front layer according to the overlay mark coordinates between the current layer and the front layer; obtaining a plurality of grooves with different depths for exposing the overlay mark of the front layer through photoetching and etching; the depths are respectively represented as H1, H2,..., and Hn; the grooves expose the upper surface of the overlay mark of the front layer through their bottoms; spinning a photoresist layer on the wafer to cover the grooves with different depths; transferring the overlay mark of the current layer to the photoresist layer by using the mask; respectively measuring the overlay accuracy of the overlay mark of the current layer relative to the overlay mark of the front layer in the grooves with different depths to obtain the first, second,..., and nth overlay accuracy values corresponding to H1, H2,..., and Hn; and preparing a relationship curve of H1, H2,..., and Hn and the first, second,..., and nth overlay accuracy values. The method can optimize measurement and find the optimal solution of the etching depth corresponding to the overlay accuracy.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a method for measuring the accuracy of thick film overlay. Background Technology

[0002] In integrated circuit manufacturing, especially in deeper ion-implanted photolithography layers, thicker photoresist is required to prevent ion breakdown from affecting device performance. Due to the thickness of the photoresist, asymmetry in the open area is prone to occur, a phenomenon more pronounced with non-optically amplified photoresists. Poor photoresist pattern symmetry can even affect the measurement accuracy of photolithography overlay, causing measurement distortion, hindering effective online product quality monitoring, and even impacting product yield.

[0003] The mechanism of asymmetry in the open area of ​​non-optical magnifying adhesive is mainly due to the generation of N2 during the reaction of non-optical magnifying adhesive. The generated N2 will squeeze the existing photoresist during the elimination process. When the open area is asymmetrical, the open area of ​​the photoresist will exhibit asymmetry. Solving this asymmetry caused by the design of the patterning device requires a large investment of resources. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for measuring the overlay accuracy of thick film, which solves the problem of inaccurate measurement of overlay accuracy in photolithography due to poor symmetry of photoresist patterns in the prior art.

[0005] To achieve the above and other related objectives, the present invention provides a method for measuring the accuracy of thick film overlay, comprising at least:

[0006] Step 1: Provide a wafer with pre-prepared overlay markings for the previous layer; and prepare a photomask that only displays the overlay markings for the previous layer based on the coordinates of the current layer over the previous layer's overlay markings.

[0007] Step 2: A plurality of trenches of different depths are obtained by photolithography and etching to expose the previous layer overlay mark; the plurality of different depths are respectively represented as H1, H2...Hn; the trenches expose the upper surface of the previous layer overlay mark through their bottoms;

[0008] Step 3: Spin-coat a layer of photoresist onto the wafer to cover the multiple trenches of different depths;

[0009] Step 4: Use the photomask to transfer the overlay mark to the photoresist layer; the overlay mark in the photoresist layer is located within the trench;

[0010] Step 5: Measure the overlay accuracy of the current layer overlay mark relative to the previous layer overlay mark in the multiple trenches of different depths to obtain the 1st, 2nd...nth overlay accuracy values ​​corresponding to H1, H2...Hn;

[0011] Step 6: Create the relationship curves between H1, H2...Hn and the 1st, 2nd...nth set of etching accuracy values; take the depth of the trench corresponding to the minimum value among the 1st, 2nd...nth set of etching accuracy values ​​as the optimal etching depth.

[0012] Preferably, the cross-sectional pattern of the front layer overprinting mark in step one is formed by four rectangles; the four rectangles are arranged in pairs opposite each other and horizontally and vertically; one of the longitudinal cross-sectional patterns of the front layer overprinting mark is a first and a second groove that extend longitudinally and are spaced apart from each other.

[0013] Preferably, the width of the groove in step two is 5 to 300 μm greater than the distance between the first and second grooves.

[0014] Preferably, in step two, the trench exposes the upper surfaces of the first and second trenches through its bottom.

[0015] Preferably, in step two, the etching process is adjusted to obtain the multiple trenches of different depths.

[0016] Preferably, after the photoresist layer in step three covers the multiple trenches of different depths, the lowest point of the photoresist layer is still higher than the upper surface of the multiple trenches of different depths.

[0017] Preferably, in step four, the cross-sectional pattern of the overlay mark within the photoresist layer is formed by four rectangles; the four rectangles are arranged in pairs opposite each other and horizontally and vertically; one of the longitudinal cross-sectional patterns of the overlay mark is a third and fourth groove that extends longitudinally and is spaced apart from each other; the cross-sectional pattern of the overlay mark is overlaid within the cross-sectional pattern of the previous overlay mark.

[0018] As described above, the thick film overlay accuracy measurement method of the present invention has the following beneficial effects: The method of the present invention prepares a photomask that only opens the area of ​​the overlay mark by using the overlay accuracy coordinate value of the current layer relative to the previous layer, thereby obtaining wafers with different trench depths through etching. The deep trench sidewall can effectively prevent the pattern asymmetry caused by the left and right stress asymmetry, thereby optimizing the measurement, measuring the overlay accuracy index of the current layer relative to the previous layer, and finding the optimal solution of the etching depth corresponding to the overlay accuracy. Attached Figure Description

[0019] Figure 1 The diagram shows a longitudinal cross-sectional view of the front layer overprint mark and the current layer overprint mark in this invention.

[0020] Figure 2 This diagram shows the cross-sectional positional relationship between the front layer overlay mark and the current layer overlay mark in this invention.

[0021] Figure 3 The graph shown is a curve showing the relationship between overlay accuracy and groove depth in this invention. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] Please see Figures 1 to 3 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0024] This invention provides a method for measuring the accuracy of thick film overlay, comprising at least:

[0025] Step 1: Provide a wafer with pre-prepared overlay markings for the previous layer; and prepare a photomask that only displays the overlay markings for the previous layer based on the coordinates of the current layer over the previous layer's overlay markings.

[0026] In a further embodiment of the present invention, the cross-sectional pattern of the front overprint mark in step one is formed by four rectangles; the four rectangles are arranged in pairs opposite each other and horizontally and vertically; one of the longitudinal cross-sectional patterns of the front overprint mark is a first and a second groove that extend longitudinally and are spaced apart from each other.

[0027] like Figure 1 As shown, Figure 1 The diagram shows a cross-sectional view of the front layer overlay mark and the current layer overlay mark in this invention. Step one provides a wafer with the front layer overlay mark already prepared; such as... Figure 1 As shown, the front layer structure 01 of the wafer has been etched to form the front layer overlay mark. The first and second trenches (both represented by 03, where the one located to the left of the front layer structure 01 is the first trench and the one located to the right of the front layer structure is the second trench) are the longitudinal cross-sectional patterns of the front layer overlay mark; the first and second trenches extend longitudinally.

[0028] And based on the coordinates of the overlay marks of the current layer to the previous layer, prepare a photomask that only opens the overlay marks of the current layer to the previous layer;

[0029] Further, in step one of this embodiment, the cross-sectional pattern of the front overlay mark is formed by four rectangles; the four rectangles are arranged in pairs opposite each other, horizontally and vertically; one of the longitudinal cross-sectional patterns of the front overlay mark is a first and a second groove that extend longitudinally and are spaced apart from each other. Figure 2 As shown, Figure 2 The diagram shows the cross-sectional positional relationship between the front layer overlay mark and the current layer overlay mark in this invention. In the cross-sectional pattern of the front layer overlay mark, the cross-sectional pattern of the front layer overlay mark B is formed by four rectangles; the four rectangles are arranged in pairs opposite each other, horizontally and vertically.

[0030] Step 2: A plurality of trenches of different depths are obtained by photolithography and etching to expose the previous layer overlay mark; the plurality of different depths are respectively represented as H1, H2...Hn; the trenches expose the upper surface of the previous layer overlay mark through their bottoms;

[0031] In a further embodiment of the present invention, the width of the groove in step two is 5 to 300 μm greater than the distance between the first and second grooves.

[0032] Furthermore, in step two of this embodiment, the trench exposes the upper surfaces of the first and second trenches through its bottom.

[0033] Furthermore, in step two of this embodiment, the multiple trenches of different depths are obtained by adjusting the etching process.

[0034] like Figure 1 As shown, in step two, multiple trenches of different depths are obtained through photolithography and etching to expose the previous overlay mark; the multiple different depths are respectively represented as H1, H2...Hn; in the trench with depth represented as Hn in 1 (representing the depth of any one of the trenches), the previous overlay mark (the upper surface of the first and second trenches 03) is exposed, and the trench exposes the upper surface of the previous overlay mark through its bottom; in step two of this embodiment, the width of the trench is 5 to 300 μm larger than the distance between the first and second trenches. That is, as... Figure 1 In the longitudinal cross-sectional structure, the overlay marks of the previous layer (first and second trenches 03) fall into the trenches. That is, based on the overlay accuracy coordinates of the current layer relative to the previous layer, a photomask is prepared that only opens at the overlay marks, while other positions are covered by photoresist. The range of photoresist opening depends on the size of the overlay accuracy marks, generally 5 to 300 μm larger than the overlay marks. In step two of this embodiment, the trenches expose the upper surfaces of the first and second trenches through their bottoms. In step two of this embodiment, the multiple trenches of different depths are obtained by adjusting the etching program.

[0035] Step 3: Spin-coat a layer of photoresist onto the wafer to cover the multiple trenches of different depths;

[0036] Furthermore, in step three of this embodiment, after the photoresist layer covers the multiple trenches of different depths, the lowest point of the photoresist layer is still higher than the upper surface of the multiple trenches of different depths. For example... Figure 1 As shown, after covering, the lowest point of the photoresist layer is still higher than the upper surface of the multiple trenches of different depths.

[0037] Step 4: Use the photomask to transfer the overlay mark to the photoresist layer; the overlay mark in the photoresist layer is located within the trench;

[0038] In a further embodiment of the present invention, the cross-sectional pattern of the overlay mark in the photoresist layer in step four is formed by four rectangles; the four rectangles are arranged in pairs opposite each other and horizontally and vertically; one of the longitudinal cross-sectional patterns of the overlay mark is a third and fourth groove that extends longitudinally and is spaced apart from each other; the cross-sectional pattern of the overlay mark is overlaid in the cross-sectional pattern of the previous overlay mark.

[0039] In step four, the photomask is used to transfer the overlay markings to the photoresist layer; the overlay markings in the photoresist layer are located within the trenches. That is, the photomask contains the overlay markings, which are transferred to the photoresist layer 04 after exposure and development, forming the overlay markings (including the third and fourth trenches). Figure 2 As shown, in step four, the cross-sectional pattern of the overlay mark within the photoresist layer is formed by four rectangles; these four rectangles are arranged in pairs opposite each other, horizontally and vertically; one of the longitudinal cross-sectional patterns of the overlay mark A is a third and fourth trench extending longitudinally and spaced apart from each other (e.g., Figure 1 The third and fourth trenches are represented by 02, where the one located to the left of the photoresist layer is the third trench, and the one to the right is the fourth trench; the cross-sectional pattern of the overlay mark of the current layer is overlaid in the cross-sectional pattern of the overlay mark of the previous layer (e.g., Figure 2 (As shown).

[0040] Step 5: Measure the overlay accuracy of the current layer overlay mark relative to the previous layer overlay mark in the multiple trenches of different depths to obtain the 1st, 2nd...nth overlay accuracy values ​​corresponding to H1, H2...Hn;

[0041] Step Six: Create a relationship curve between the H1, H2…Hn and the 1st, 2nd…nth etching accuracy values; take the depth of the trench corresponding to the minimum value among the 1st, 2nd…nth etching accuracy values ​​as the optimal etching depth. Figure 3 As shown, Figure 3 The graph shows the relationship between overlay accuracy and groove depth in this invention. Experimental verification shows that the optimal groove depth value is obtained when the overlay accuracy is minimized.

[0042] In subsequent growth processes, using this optimal value as the etching depth of the trench can optimize the measurement of overlay accuracy.

[0043] In summary, the method of this invention prepares a photomask that only opens the area at the overlay mark by using the overlay accuracy coordinates of the current layer relative to the previous layer. This allows for the etching of wafers with different trench depths. The deep trench sidewalls effectively prevent pattern asymmetry caused by left-right stress asymmetry, thereby optimizing measurement. By measuring the overlay accuracy index of the current layer relative to the previous layer, the optimal solution for the etching depth corresponding to the overlay accuracy can be found. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0044] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for measuring the accuracy of thick film overlay, characterized in that, At least including: Step 1: Provide a wafer with pre-prepared overlay markings for the previous layer; and prepare a photomask that only displays the overlay markings for the previous layer based on the coordinates of the current layer over the previous layer's overlay markings. Step 2: A plurality of trenches of different depths are obtained by photolithography and etching to expose the previous layer overlay mark; the plurality of different depths are respectively represented as H1, H2...Hn; the trenches expose the upper surface of the previous layer overlay mark through their bottoms; Step 3: Spin-coat a layer of photoresist onto the wafer to cover the multiple trenches of different depths; Step 4: Use the photomask to transfer the overlay mark to the photoresist layer; the overlay mark in the photoresist layer is located within the trench; Step 5: Measure the overlay accuracy of the current layer overlay mark relative to the previous layer overlay mark in the multiple trenches of different depths to obtain the 1st, 2nd...nth overlay accuracy values ​​corresponding to H1, H2...Hn; Step 6: Create the relationship curves between H1, H2...Hn and the 1st, 2nd...nth set of etching accuracy values; take the depth of the trench corresponding to the minimum value among the 1st, 2nd...nth set of etching accuracy values ​​as the optimal etching depth.

2. The method for measuring the accuracy of thick film overlay according to claim 1, characterized in that: The cross-sectional pattern of the front layer overprinting mark in step one is formed by four rectangles; the four rectangles are arranged in pairs opposite each other and horizontally and vertically; one of the longitudinal cross-sectional patterns of the front layer overprinting mark is a first groove and a second groove that extend longitudinally and are spaced apart from each other.

3. The method for measuring the accuracy of thick film overlay according to claim 2, characterized in that: The width of the groove in step two is 5 to 300 μm greater than the distance between the first groove and the second groove.

4. The method for measuring the accuracy of thick film overlay according to claim 2, characterized in that: In step two, the trench exposes the upper surfaces of the first trench and the second trench through its bottom.

5. The method for measuring the accuracy of thick film overlay according to claim 1, characterized in that: In step two, the etching process is adjusted to obtain the multiple trenches of different depths.

6. The method for measuring the accuracy of thick film overlay according to claim 1, characterized in that: After the photoresist layer in step three covers the multiple trenches of different depths, the lowest point of the photoresist layer is still higher than the upper surface of the multiple trenches of different depths.

7. The method for measuring the accuracy of thick film overlay according to claim 1, characterized in that: In step four, the cross-sectional pattern of the overlay mark within the photoresist layer is formed by four rectangles; these four rectangles are arranged in pairs facing each other and horizontally and vertically; one of the longitudinal cross-sectional patterns of the overlay mark is a third groove and a fourth groove that extend longitudinally and are spaced apart from each other; the cross-sectional pattern of the overlay mark is overlaid within the cross-sectional pattern of the previous overlay mark.

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