阅读说明：本技术 光罩热效应的补偿方法 (Method for compensating heat effect of photomask ) 是由 朱至渊 李玉华 黄发彬 林辉 吴长明 姚振海 金乐群 于 2020-12-14 设计创作，主要内容包括：本发明公开了一种光罩热效应的补偿方法,包括步骤：步骤一、将光罩放置在光罩工件台上并收集曝光条件下光罩的温度分布；步骤二、对光罩进行对准并形成光罩对准结果；步骤三、结合光罩的温度分布和光罩对准结果来计算曝光补偿量；步骤四、根据曝光补偿量调整光刻机的曝光参数以补偿光罩热效应；步骤五、进行曝光。本发明能很好的补偿光罩热效应产生的形变对曝光的影响,从而能提高产品的套刻精度；同时不用增加光罩对准标记数量,从而能提高产能。(The invention discloses a compensation method of a photomask heat effect, which comprises the following steps: placing a photomask on a photomask workpiece table and collecting the temperature distribution of the photomask under an exposure condition; step two, aligning the photomask and forming a photomask alignment result; thirdly, calculating exposure compensation amount by combining the temperature distribution of the photomask and the photomask alignment result; adjusting exposure parameters of the photoetching machine according to the exposure compensation amount to compensate the thermal effect of the photomask; and step five, carrying out exposure. The invention can well compensate the influence of the deformation generated by the heat effect of the photomask on the exposure, thereby improving the alignment precision of the product; meanwhile, the number of mask alignment marks is not increased, thereby improving the productivity.)

1. A method for compensating a thermal effect of a photomask is characterized by comprising the following steps:

placing a photomask on a photomask workpiece table and collecting the temperature distribution of the photomask under an exposure condition;

step two, aligning the photomask and forming a photomask alignment result;

calculating exposure compensation quantity by combining the temperature distribution of the photomask and the photomask alignment result;

adjusting exposure parameters of the photoetching machine according to the exposure compensation amount to compensate the thermal effect of the photomask;

and fifthly, carrying out exposure according to the adjusted exposure parameters of the photoetching machine.

2. The method of compensating for thermal effects of a reticle of claim 1, wherein: in the first step, an infrared temperature sensor is used for collecting the temperature distribution of the photomask.

3. The method of compensating for thermal effects of a reticle of claim 2, wherein: the temperature distribution of the reticle is a temperature distribution over an entire extent of the reticle.

4. The method of compensating for thermal effects of a reticle of claim 2, wherein: the infrared temperature sensor is installed between a converging lens of the lithography machine and the back surface of the photomask.

5. The method of compensating for thermal effects of a reticle of claim 4, wherein: the infrared temperature sensor is arranged at the bottom of a converging lens of the photoetching machine.

6. The method of compensating for thermal effects of a reticle of claim 4, wherein: the infrared temperature sensor is installed on the photomask workpiece table.

7. The method of compensating for thermal effects of a reticle of claim 4, wherein: in the first step, obtaining the temperature distribution of the photomask by adopting a photographing mode;

or, in the first step, the temperature distribution of the photomask is obtained by adopting a scanning mode.

8. The method of compensating for thermal effects of a reticle of claim 7, wherein: in the first step, the temperature distribution of the photomask is digitized and converted into a gray scale value.

9. The method of compensating for thermal effects of a reticle of claim 1, wherein: in the first step, the temperature distribution of the photomask is converted into a first deformation distribution of the photomask.

10. The method of compensating for thermal effects of a reticle of claim 9, wherein: the deformation of the photomask comprises X-direction deformation and Y-direction deformation.

11. The method of compensating for thermal effects of a reticle of claim 1, wherein: in the second step, the mask alignment marks adopted by the mask alignment process comprise coaxial alignment marks or image sensor marks.

12. The method of compensating for thermal effects of a reticle of claim 9, wherein: in the second step, the photomask alignment result is a second deformation distribution of the photomask obtained through the photomask alignment mark.

13. The method of compensating for thermal effects of a reticle of claim 11, wherein: and step three, combining the first deformation distribution and the second deformation distribution to form the overlay deviation formed by the thermal effect of the photomask.

14. The method of compensating for thermal effects of a reticle of claim 13, wherein: the exposure parameters of the photoresist in step four include the position of the mask stage, the position of the wafer stage and the lens manipulator operating parameters.

15. The method of compensating for thermal effects of a reticle of claim 1, wherein: the reticle includes a multi-layer mask.

Technical Field

The present invention relates to a method for manufacturing a semiconductor integrated circuit, and more particularly, to a method for compensating a thermal effect of a photomask (reticle).

Background

FIG. 1 is a schematic diagram of a conventional mask 101; the photomask 101, also called as a photomask and a mask, is made of quartz glass 102 as a substrate, a layer of metal chromium 103(Cr) and a photosensitive resist is coated on the substrate to form a photosensitive material, a designed circuit diagram is exposed on the photosensitive resist through electronic laser equipment, an exposed area is developed, a circuit diagram is formed on the metal chromium 103 to form a photomask similar to an exposed negative, and then the photomask is applied to projection positioning of an integrated circuit, and photoetching is performed on the projected circuit through an integrated circuit photoetching machine.

Besides forming a circuit pattern, the chrome metal 103 of the mask 101 further includes a mask 101 Alignment (RA) mark (mark), and the RA mark is used to align the mask 101. The mask 101 further includes a protection layer 104 formed on the surface of the chrome metal 103 for protecting the circuit pattern.

In photolithography, a reticle 101 is placed on a Reticle Stage (RS) and fixed by a jig 105, and a wafer placed on a Wafer Stage (WS) is exposed to a photoresist on the wafer and a pattern is transferred to the photoresist by irradiating the reticle 101 with a laser 106 and projecting a circuit pattern on the reticle 101 onto the wafer. The photomask 101 is irradiated by laser in the exposure process, the laser and the photomask 101 act on each other, the photomask 101 generates heat after absorbing light, the heat is mainly absorbed by the metal chromium 103, the heat is mainly dissipated by the surface of the photomask 101 in a convection mode as shown by a mark 107, but the heat dissipation rate is limited, the photomask 101 generates thermal expansion finally, the exposure is deviated due to the thermal expansion finally, and the exposure deviation phenomenon formed by the heat generated by the photomask 101 in the exposure process is the thermal effect of the photomask 101. Such mask 101 thermal effects typically result in Barrel-type (Barrel Shaped) Overlay (error) misalignment (error). Generally, the lower the light transmittance of the reticle 101, the more severe the thermal effect of the reticle 101.

The conventional method mainly compensates the thermal effect of the reticle 101 by the deformation obtained by the alignment of the alignment marks of the reticle 101.

However, as shown in fig. 2, it is a layout diagram of a Mask of a first Multi Layer Mask (MLM) product; in fig. 2, the mask of the MLM product is individually marked with a mark 101a, and on the MLM product, for example, for a 2-in-1 MLM product, fig. 2 includes 2 layers of patterns distributed as a first layer pattern 201a and a second layer pattern 201b, the two layers of patterns are separately exposed, that is, each exposure only exposes one layer of pattern, taking the exposure of the first layer pattern 201a as an example, the exposure area corresponding to the first layer pattern 201a on the mask 101a is half of the size (size) of the projected exposure area (shot) of the mask 101 a. Corresponding reticle alignment marks are provided at the edges (borderls) of the reticle 101a, and the reticle alignment mark near the edge of the first layer pattern 201a is denoted by 202a and the reticle alignment mark near the edge of the second layer pattern 201b is denoted by 202b for the convenience of the following analysis.

The thermal effect of the reticle 101a of the MLM product shown in FIG. 2 cannot be calibrated by reticle alignment marks, as described below:

FIG. 3A is a schematic view of the alignment of the mask of the first MLM product of FIG. 2 in the cold state without thermal effect; it can be seen that the area 204a defined by the alignment of the reticle alignment marks 202a and 202b matches the actual exposure area of the first layer pattern 201a, i.e., Image field203a, which results in good alignment.

FIG. 3B is a schematic view of the mask of the first MLM product of FIG. 2 aligned with a thermal effect; it can be seen that the area 204b defined by the alignment of the mask alignment marks 202a and 202b does not match the actual exposure area 203b of the first layer pattern 201a, and the actual exposure area 203b is often larger than the aligned underlying pattern, and there is a non-linear deviation therebetween as indicated by the arrow line 205, so that the registration problem may occur finally. The corresponding deviation in fig. 3B is because the mask 101a only generates heat and thermal expansion in the first layer pattern 201a when only the first layer pattern 201a is exposed, and finally the size of the mask 101a in the area of the first layer pattern 201a is larger than the size of the mask 101a in the area of the second layer pattern 201B, thereby generating the non-linear deviation shown in fig. 3B. Obviously, the effect of thermal effects cannot be eliminated by the alignment of the reticle alignment marks 202a and 202 b.

FIG. 3C is a schematic diagram of alignment when introducing a mask alignment mark around an exposure region pattern to overcome thermal effect deformation of FIG. 3B; as shown in fig. 3C, in order to overcome the alignment problem when the size of the reticle 101a in the area of the first layer pattern 201a is larger than the size of the reticle 101a in the area of the second layer pattern 201B, a reticle alignment mark needs to be introduced around the first layer pattern 201a, that is, a reticle alignment mark corresponding to the mark 202C is added on the basis of the reticle alignment mark 202a, since the reticle alignment marks 202a and 202C are both located in the area of the first layer pattern 201a, they have the same deformation, and thus the area 204C defined by the reticle alignment marks 202a and 202C matches with the actual exposure area 203C, thereby eliminating the problem of fig. 3B.

FIG. 4 is a schematic layout diagram of a conventional second MLM product mask designed according to the alignment marks around the exposure region pattern introduced in FIG. 3C; as can be seen from comparison with FIG. 2, the mask alignment mark 202c is added in FIG. 4.

Although the mask 101b of the second MLM product corresponding to fig. 4 can compensate the thermal effect of the mask well, the number of the mask alignment marks is increased, and the increased number of the mask alignment marks increases the alignment time, which finally affects the throughput.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a compensation method for the heat effect of the photomask, which can well compensate the influence of the deformation generated by the heat effect of the photomask on exposure, thereby improving the overlay precision of products; meanwhile, the number of mask alignment marks is not increased, thereby improving the productivity.

In order to solve the above technical problem, the method for compensating the thermal effect of the photomask provided by the invention comprises the following steps:

the method comprises the following steps of firstly, placing a photomask on a photomask workpiece table and collecting the temperature distribution of the photomask under exposure conditions.

And step two, aligning the photomask and forming a photomask alignment result.

And thirdly, calculating exposure compensation amount by combining the temperature distribution of the photomask and the photomask alignment result.

And step four, adjusting exposure parameters of the photoetching machine according to the exposure compensation amount to compensate the thermal effect of the photomask.

And fifthly, carrying out exposure according to the adjusted exposure parameters of the photoetching machine.

In a further improvement, in the first step, an infrared temperature sensor is used for collecting the temperature distribution of the photomask.

In a further refinement, the temperature profile of the reticle is a temperature profile over an entire extent of the reticle.

In a further refinement, the infrared temperature sensor is mounted between a converging lens of the lithography machine and a back surface of the reticle.

In a further improvement, the infrared temperature sensor is mounted at the bottom of a converging lens of the lithography machine.

In a further refinement, the infrared temperature sensor is mounted on the reticle stage.

The further improvement is that in the first step, a photographing mode is adopted to obtain the temperature distribution of the photomask;

or, in the first step, the temperature distribution of the photomask is obtained by adopting a scanning mode.

In a further improvement, in the first step, the temperature distribution of the photomask is digitized and converted into a gray scale value.

In a further improvement, the first step further comprises converting the temperature profile of the reticle to a first deformation profile of the reticle.

In a further improvement, the deformation of the mask comprises an X-direction deformation and a Y-direction deformation.

In a further improvement, in the second step, the mask alignment marks used in the mask alignment process include in-line alignment (in-line alignment) marks, which are abbreviated as TIS marks, or image sensor (image sensor) marks, which are abbreviated as PARIS marks.

In a further improvement, in the second step, the reticle alignment result is a second deformation distribution of the reticle obtained through the reticle alignment mark.

In a further improvement, the third step, the first deformation distribution and the second deformation distribution combine to form the overlay deviation formed by the thermal effect of the photomask.

In a further improvement, the exposure parameters of the photoresist in step four include the position of the mask stage, the position of the wafer stage, and lens manipulator (lens manipulator) operation parameters.

In a further refinement, the reticle includes a multi-layer mask.

According to the invention, the step of collecting the temperature distribution of the photomask is added before exposure, the exposure compensation amount for compensating the thermal effect of the photomask can be accurately calculated by combining the photomask alignment result, and then exposure is carried out by using the exposure parameters of the photoetching machine adjusted according to the exposure compensation amount, so that the influence of deformation generated by the thermal effect of the photomask on exposure can be well compensated, and the alignment precision of a product can be improved; meanwhile, the number of mask alignment marks is not increased, thereby improving the productivity.

Drawings

The invention is described in further detail below with reference to the following figures and detailed description:

FIG. 1 is a schematic diagram of a conventional mask;

FIG. 2 is a layout diagram of a photomask of a first conventional MLM product;

FIG. 3A is a schematic view of the alignment of the mask of the first MLM product of FIG. 2 without thermal effects;

FIG. 3B is a schematic view of the alignment of the mask of the first MLM product of FIG. 2 with thermal effect;

FIG. 3C is a schematic diagram of alignment when introducing a mask alignment mark around the exposure region pattern to overcome thermal effect deformation of FIG. 3B;

FIG. 4 is a layout diagram of a reticle for a second prior art MLM product designed based on the alignment marks around the exposure field pattern introduced in FIG. 3C;

FIG. 5 is a flowchart illustrating a method for compensating thermal effects of a mask according to an embodiment of the present invention;

FIG. 6 is a schematic structural diagram of a lithography machine according to an embodiment of the present invention;

FIG. 7 is a diagram of a second arrangement of an infrared temperature sensor in an embodiment of the present invention;

FIG. 8A is a schematic diagram of a photomask layout when a temperature distribution of the photomask is collected in a shot mode according to an embodiment of the present invention;

FIG. 8B is a temperature profile of the collected reticle corresponding to FIG. 8A;

FIG. 9A is a schematic diagram of a reticle layout corresponding to a scan mode for collecting temperature distributions of the reticle in an embodiment of the present invention;

FIG. 9B is a temperature distribution plot of the collected reticle of FIG. 9A;

FIG. 10 is a diagram illustrating deformation of a mask alignment mark during mask alignment according to an embodiment of the present invention;

FIG. 11 is a graph of overlay measurements after exposure without exposure compensation adjustment according to an embodiment of the present invention;

fig. 12 is a diagram of overlay measurement after exposure when exposure compensation amount adjustment according to the embodiment of the present invention is performed.

Detailed Description

FIG. 5 is a flow chart of a method for compensating thermal effect of a mask according to an embodiment of the present invention; FIG. 6 is a schematic structural diagram of a lithography machine according to an embodiment of the present invention; the compensation method for the heat effect of the photomask comprises the following steps:

step one, the reticle 101 is placed on a reticle stage 303 and the temperature distribution of the reticle 101 under exposure conditions is collected.

In an embodiment of the present invention, a structure diagram of the optical mask 101 is shown in fig. 1, where the optical mask 101 includes a substrate formed of quartz glass 102, and a graphic structure of metal chromium 103 formed on the quartz glass 102, where the graphic structure includes a circuit pattern and an optical mask alignment mark; a protective layer 104 for protecting the circuit pattern is also formed on the surface on which the chromium metal 103 is formed.

As shown in fig. 6, the light 106 enters a condensing Lens (Condenser Lens)302 by reflection through a light blocking structure 301, and the light blocking structure 301 usually adopts a REMA light blocking structure, and the light blocking structure realizes the beam shape setting. The condenser lens 302 irradiates the light 106 onto the reticle 101 placed on the reticle stage 303, and the reticle stage 303 fixes the reticle 101 by the jig 105. During exposure, after the light 106 irradiates the mask 101, a diffraction image of the pattern structure on the mask 101 is projected onto the wafer 306 through the projection lens 304. A wafer 306 is placed on the wafer stage 305.

Preferably, the mask 101 includes a multi-layer mask, i.e., a mask corresponding to the MLM product.

In the embodiment of the present invention, the temperature distribution of the mask 101 is collected by using an infrared temperature sensor 307.

The temperature distribution of the reticle 101 is a temperature distribution over the entire area of the reticle 101.

The infrared temperature sensor 307 is mounted between the converging lens of the lithography machine and the back of the reticle 101. In fig. 6, the infrared temperature sensor 307 is mounted at the bottom of the converging lens 302 of the lithography machine. Can also be: the infrared temperature sensor 307 is mounted on the reticle stage 303; fig. 7 is a diagram showing a second arrangement structure of the infrared temperature sensor 307 in the embodiment of the present invention; in fig. 7, which shows a top view of the reticle stage 303, it can be seen that the clamp 105 is of a ring configuration and the infrared temperature sensor 307 is mounted on the clamp 105 of the reticle stage 303.

In the embodiment of the present invention, the temperature distribution of the mask 101 is obtained by using a photographing mode. FIG. 8A is a schematic diagram of a reticle layout corresponding to a temperature distribution of the reticle collected in a photo mode according to an embodiment of the present invention; in fig. 8A, taking the MLM product as an example, which is a two-in-one mask 101a including two layers of patterns, i.e., the mask 101a shown in fig. 2, in the first step, the entire mask 101a including the first layer of patterns 201a and the second layer of patterns 201B is subjected to the temperature-specific collection and the collected temperature distribution map of the entire mask 101a corresponding to fig. 8B is formed. It can be seen that the temperature distribution 401a of the first layer pattern 201a and the temperature distribution 401b of the second layer pattern 201b are not the same.

Can also be: the temperature distribution of the reticle 101 is obtained in a scanning mode. Fig. 9A is a schematic diagram of a reticle layout corresponding to a scanning mode for collecting temperature distribution of the reticle according to an embodiment of the present invention; unlike fig. 8A, fig. 9A collects the temperature distribution by scanning along the dashed arrow line 402; fig. 9B is a temperature distribution diagram of the collected reticle corresponding to fig. 9A, and it can be seen that the temperature distribution 401a1 of the first layer pattern 201a and the temperature distribution 401B1 of the second layer pattern 201B are not the same.

In an embodiment of the present invention, the method further includes digitizing and converting the temperature distribution of the reticle 101 into a gray scale value, and then converting the temperature distribution of the reticle 101 into the first deformation distribution of the reticle 101. The deformation of the reticle 101 includes an X-direction deformation and a Y-direction deformation.

Taking X-direction deformation as an example, the following formula can be used: Δ L ═ α_m*L₀Calculating the deformation quantity of the delta t;

wherein, Δ L is a deformation amount; alpha is alpha_mIs the coefficient of expansion; l is₀Is an initial length; Δ t is the temperature difference between before and after.

And step two, aligning the photomask 101 and forming an alignment result of the photomask 101.

FIG. 10 is a schematic diagram illustrating deformation of a mask alignment mark during mask alignment according to an embodiment of the present invention; in fig. 10, the mask 101a shown in fig. 2 is used as an example, and the mask alignment marks 202a and 202b used in the alignment process of the mask 101 include coaxial alignment marks or image sensor marks.

The reticle 101 alignment result is a second deformation distribution of the reticle 101 obtained by the reticle alignment mark. As shown in fig. 10, after the thermal expansion of the reticle 101a, the reticle alignment marks 202a and 202b also expand, and as shown by the arrows corresponding to the reticle alignment marks 202a and 202b, each arrow shows the expansion direction and magnitude of the corresponding reticle alignment mark. It can be seen that the deformation of the reticle alignment mark 202a corresponding to the edge of the first layer pattern 201a is relatively large, and the deformation of the reticle alignment mark 202b corresponding to the edge of the second layer pattern 201b is relatively small. Because the deformation of the reticle alignment marks 202a and 202b is non-linear and non-uniform, compensating for thermal effect bias cannot be accomplished by deformation of the reticle alignment marks 202a and 202b alone.

And step three, calculating exposure compensation amount by combining the temperature distribution of the photomask 101 and the alignment result of the photomask 101.

In an embodiment of the invention, the first deformation distribution and the second deformation distribution combine to form an overlay deviation formed by a thermal effect of the photomask.

FIG. 11 is a diagram of overlay measurement after exposure without adjustment of exposure compensation according to the embodiment of the present invention; that is, when adjustment of the exposure compensation amount according to the embodiment of the present invention is not considered, an overlay deviation generated by a thermal effect finally occurs, and fig. 11 shows a point to be aligned corresponding to the mark 502, but due to the thermal effect of the mask, when the point 502 is considered to be aligned by using the existing alignment method, a point formed during actual exposure is a point corresponding to the mark 501, a deviation between the points 501 and 502 is a registration deviation between the two points, and the registration deviation can be measured after exposure on the wafer 306, that is, a deviation between the point 502 corresponding to the previous layer pattern and the point 501 corresponding to the current layer pattern formed by exposure is measured. It can be seen that the existing methods are subject to large deviations.

In the embodiment of the invention, information of the photomask 101 and the infrared temperature sensor 307 can be acquired by using different shot sizes and combining different exposure energy operations, and shot internal distribution is acquired through overlay measurement.

And step four, adjusting exposure parameters of the photoetching machine according to the exposure compensation amount to compensate the thermal effect of the photomask.

In the embodiment of the present invention, the exposure parameters of the photoresist include the position of the mask stage 303, the position of the wafer stage, and the operating parameters of the lens manipulator. The lens operator operating parameters control the position of the projection lens 304 and allow the magnification to be adjusted.

And fifthly, carrying out exposure according to the adjusted exposure parameters of the photoetching machine.

As shown in fig. 12, the overlay measurement chart after exposure when the exposure compensation amount is adjusted according to the embodiment of the present invention is shown, and as compared with fig. 11, the two layer patterns corresponding to the point 601 in fig. 12 can be well registered, and the situation that the deviation between the points 501 and 502 in fig. 11 is large does not occur.

According to the embodiment of the invention, the step of collecting the temperature distribution of the photomask 101 is added before exposure, the exposure compensation amount for compensating the thermal effect of the photomask can be accurately calculated by combining the alignment result of the photomask 101, and then exposure is carried out by using the exposure parameters of the photoetching machine adjusted according to the exposure compensation amount, so that the influence of deformation generated by the thermal effect of the photomask on exposure can be well compensated, and the alignment precision of a product can be improved; meanwhile, the number of mask alignment marks is not increased, thereby improving the productivity.

The present invention has been described in detail with reference to the specific embodiments, but these should not be construed as limitations of the present invention. Many variations and modifications may be made by one of ordinary skill in the art without departing from the principles of the present invention, which should also be considered as within the scope of the present invention.