TWI675180B - Optical detecting device and detecting method for semiconductor device - Google Patents

Abstract

The invention provides an optical detection device for a semiconductor device, which can monitor changes in the size or shape of an opening of an etching hole. The optical detection device of the present invention includes a cavity. The cavity includes a pedestal. A wafer is fixed on the pedestal. The upper surface of the wafer has holes or grooves formed by etching. A reference light source is provided above the wafer for emitting reference light. To the wafer, it also includes a receiver for receiving reference light reflected from the wafer. The angle between the beam of reference light incident on the wafer surface and the wafer plane is less than or equal to 60 degrees, and the receiver is located on the same side of the reference light source; The controller receives and processes the optical signals received by the receiver.

Description

Optical detection device and detection method for semiconductor equipment

The invention relates to the technical field of semiconductor processing, in particular to an optical detection device and a detection method for an etching result.

Plasma processing devices are widely used in semiconductor wafer processing processes. Plasma etching is used to form etched vias or trenches with specific dimensions. These etched holes or trenches need to be very accurate. If there is a deviation in the size structure, the performance of the entire semiconductor device will eventually be reduced or completely scrapped. During the etching process debugging phase, the best process parameters were obtained after a large amount of debugging. Under this optimal process parameter, the required etching hole structure can be obtained, in which the critical dimension and the profile of the sidewall of the etching hole are profiled. It is the reference material for the two most important reactive etching hole structures. During the long-term etching of a large number of wafers by the same etching equipment using the same etching process, the etching results will shift due to various environmental factors such as pollutant deposition, temperature shift, and hardware deformation, and the shift value will reach After a certain degree, the amount of change in key dimensions or sidewall topography reaches a critical value, making the structure formed by etching unable to meet its functional design requirements, and the semiconductor devices on the entire wafer cannot work properly. However, at this stage, the critical size has reached the nanometer level, and 14-45 nm is common. At such a small scale, it is difficult to detect that the critical size of the etched hole on the wafer has a small amount (5-15%). shift. The conventional method is: take out the etched wafer and put it into a large-scale special magnification instrument to check the size or shape of the etched hole. However, these specialized large-scale instruments are not only expensive but also take a long time to test. For a large number of newly produced wafers on the semiconductor production line, it is impossible to test each wafer. Instead, sampling is performed at intervals. The way. Once the sampling test finds that the etching results are outside a reasonable range, the current semiconductor processing is stopped, the current processing process is re-adjusted, or the hardware status of the plasma processing device is detected. A large number of wafers produced within the period from the previous spot check to the current problem need to be re-inspected. These wafers may also have the problem of offset of the etching results, resulting in the entire wafer being scrapped, and the wafer cost after multiple processing steps. Very high, such large quantities of scrap wafers need to be avoided.

Figure 1 shows a conventional optical detection device for semiconductor devices. The optical detection device uses the principle of optical interference to detect the thickness of an etched or deposited film. The optical detection device includes a cavity 100, a cavity including a base 10, and a cavity. The top includes a reference light source 20, which sends an incident light beam A1 to the upper surface of the wafer that completes the processing process at an approximately vertical angle (the angle between the incident light and the wafer plane θ> 80 degrees), and the reflected light beam A2 on the wafer surface is also located at The receiver 31 at the top of the cavity receives the phase change of the thickness of the wafer below by detecting the phase of the waveform formed by the interference of the incident reference light and the reflected light. This optical system cannot be effectively used to monitor the key size and morphology of the etched holes, because the size of the etched holes is already only a few tens of nanometers, and the size of the spot formed by the interference light source of the conventional ordinary visible light can reach the cm level Even if the most expensive laser light source with the smallest wavelength is used, the light spot formed by it is also on the micrometer level. The intensity of the light reflected to the receiver 31 is actually the upward reflection of light from all etched holes / slots within the spot surface of the wafer and the remaining planar areas. Synthesized, no valid information can be detected at all. If the hardware structure shown in Figure 1 is used to detect the size and morphology of the etching structure, the smaller the light spot formed by the light source is, the better, and the light source needs to be able to move accurately horizontally by detecting the difference in reflectance on the wafer surface. To identify the etched structure size. However, neither of the above two conditions can be achieved under the conventional cost and technical conditions.

Therefore, the industry needs to find a new low-cost device and method to quickly and easily identify the size and morphology of the etched structure.

The invention discloses an optical detection device for a semiconductor device. The optical detection device includes a cavity, the cavity includes a pedestal, a wafer is fixed on the pedestal, and an upper surface of the wafer has holes or grooves formed by etching. A reference light source is disposed above the wafer for emitting reference light to the wafer, and further includes a receiver for receiving reference light reflected from the wafer, wherein the beam of the reference light incident on the surface of the wafer and The included angle of the wafer plane is less than or equal to 60 degrees, the receiver is located on the incident side of the reference light source, and the included angle of the receiver and the wafer plane is 15-50 degrees; a controller receives and processes the receiver received Light signal.

Preferably, the cavity is selected from one of a transmission cavity and a vacuum lock in a semiconductor device.

Preferably, an opening size of the hole or the groove formed by the etching is less than 100 nm.

Preferably, the receiver is located below or on the side of the reference light source.

Preferably, a second receiver is further located on the incident side of the reference light source, and the two receivers are configured to receive light at different angles reflected by holes or slots on the wafer. The controller compares the intensity of the optical signals from the two receivers, and determines that the shape of the opening of the etched hole changes when the optical intensity signals from the two optical receivers change at different ratios.

The present invention further provides a method for optical detection of semiconductor devices. The optical detection device is used for detection. The controller stores a reference optical signal intensity, and the controller compares the intensity of the optical signal received by the receiver with the reference optical signal. The strength determines whether the size of the etched hole or groove is shifted.

Preferably, the method for optical detection of a semiconductor device includes the steps of subtracting a stored background signal strength from a received optical signal strength to obtain a characteristic signal strength, and the background signal strength is a reference of the optical detection device. The intensity of the optical signal received when light hits the non-etched hole area; compare the intensity of the characteristic signal with the intensity of the stored reference optical signal, if the difference between the two is greater than the Setting the threshold value judges that the size of the hole or groove formed by the etching is shifted. The reference optical signal intensity is obtained according to the following steps: irradiate the reference light source to the area without the etched hole on the wafer, and the background signal intensity obtained by the receiver is stored in the controller; irradiate the reference light source to the area with the qualified size etched hole on the wafer. A second optical signal intensity obtained by the receiver; the second optical signal intensity is subtracted from the background signal intensity to obtain a reference optical signal intensity.

100‧‧‧ Cavity

10‧‧‧ base

12‧‧‧ wafer

20‧‧‧Reference light source

22‧‧‧testing area

31‧‧‧ Receiver

91‧‧‧ etched hole

92‧‧‧slot

A1‧‧‧ incident beam

A2‧‧‧Reflected beam

A3‧‧‧ Effective reflected beam

A4‧‧‧Partially reflected beam

B1‧‧‧ lower boundary

B2‧‧‧ upper boundary

D‧‧‧Width

R‧‧‧ reflection zone

R’‧‧‧ reflection zone

θ ‧‧‧ angle

θ 2‧‧‧ angle

FIG. 1 is a schematic diagram of a conventional optical detection device for semiconductor devices.

Fig. 2a is a schematic diagram of an optical detection device for a semiconductor device according to the present invention.

FIG. 2b is a schematic diagram of a light incident reflection line of the optical detection device of the present invention shown in FIG. 2a and an enlarged view of a surface of a light spot covering area.

3a and 3b are enlarged cross-sectional views of a light spot covering area as shown in FIG. 2b.

FIG. 4 is a schematic diagram of a second embodiment of an optical detection device for a semiconductor device according to the present invention.

The specific embodiments of the present invention are further described below with reference to Figures 2 to 4 of the drawings.

The invention discloses an optical detection device for a semiconductor device, which is used to detect the size and morphology of an etching structure such as a hole or a groove formed by etching. Semiconductor equipment includes multiple chambers, commonly including vacuum locks (load locks), transfer chambers for wafer transfer, and processing chambers for plasma etching. These chambers or other devices that can hold wafers can be installed with the present invention Optical detection device. As shown in FIG. 2 a, the present invention includes a cavity 100 including a susceptor 10 on which a wafer is fixed, and the etched wafer 12 is fixed on the susceptor 10. A reference light source 20 is disposed on one side of the cavity, and emits a high-intensity incident light beam A1 toward the wafer surface. The incident light beam A1 is reflected by the wafer surface to form a reflected light beam A2 that is emitted away from the wafer. The included angle θ of the plane is less than or equal to 60 degrees, and preferably less than 30 degrees. The incident light beam A1 generated from the reference light source 20 is incident from the incident side of the substrate and reaches the detection area 22 on the substrate. After reflected by the upper surface of the detection area of the substrate, a reflected light beam A2 enters the reflection side of the substrate. A receiver 31 is located on the same side near the reference light source 20, that is, the incident side between the reference light source 20 and the detection area 22 above the substrate. The receiver 31 is not used to receive the reflected light beam A2 emitted from a distance, but to receive the incident light beam. A1 reflects the effective reflected light beam A3 entering the incident side in the detection area of the wafer surface.

As shown in Figure 2b, the incident light forms a light spot on the wafer as the detection area 22 to cover the detection area on the substrate. The smaller the diameter of the light spot, the more accurate the detection, but it is not necessary to achieve the required nanotechnology. The spot size of meters, micrometers and even millimeters can also effectively detect the size and morphology of the etched structure in the range of the spot. The lower part of FIG. 2b is an enlarged view of the spot area on the upper surface of the wafer. The spot coverage area includes a large number of etched holes 91 or grooves 92 formed by etching. As shown in Figure 3a, an enlarged cross-section of the wafer is shown in the area covered by the light spot. If the incident light beam A1 is irradiated on a planar area without etching holes / slots on the wafer, most of the light will be reflected to the reflection side away from the light source 20. , And finally reached the side wall of the cavity after multiple refraction weakened so that it cannot be observed. The included angle θ 2 between the receiver 31 and the wafer plane may be the same or different from the incident angle θ of the reference light source. Part of the incident light beam A1 is also irradiated on the side walls of the openings of the plurality of etching holes 91 and is reflected back to the incident side in the direction of the incident light source to form an effective reflected light beam A3. The effective reflected light beam A3 is received by a receiver 31 disposed near the reference light source 20. Since the incident light beam A1 is incident at a large angle with respect to the wafer plane, only the light beams between the lower boundary line B1 and the upper boundary line B2 as shown in Fig. 3a will be reflected back to the light source direction, and the other is at the lower boundary line. The light on the left side of B1 will be reflected by the flat area around the opening to the right side away from the light source, and the same light that hits the right side of the upper boundary line B2 area will also be reflected away from the light source. Only a part of the area on the right side wall of the top opening of the etching hole will effectively reflect the light beam A3 in the direction of the light source, and this area can be used as the return reflection region R of the incident light beam A1. Of course, there is also a part of the reflected light beam A4 incident on the return reflection area R. It will be reflected down into the depth of the etching hole. After multiple reflections, it will be absorbed by the sidewall material and will not be received by the receiver 31 above. These lights do not affect Judgement of final etched hole size and topographical deviation. Under the premise that the incident energy and incident angle of the incident beam A1 are fixed, the ratio of the reflected beam A2, the effective reflected beam A3, and the partially reflected beam A4 is fixed, and the intensity of the effective reflected beam A3 received by the receiver 31 and the above-mentioned return reflection The area of the area R is proportional to the area of the retro-reflective area R, which is proportional to the width D of the etching hole opening. When the width D of the etching hole opening becomes larger, the retro-reflection between the lower boundary line B1 and the upper boundary line B2 The area of the area R also increases accordingly, and vice versa. Therefore, by detecting the change in the intensity of the light received by the receiver 31, the change in the opening width D can be calculated, so that the size deviation of the etching opening can be detected, and the plasma processing parameters or hardware failures can be adjusted in time to avoid further changes. Big losses occur.

Fig. 3b is similar to the embodiment shown in Fig. 3a, the main difference is that the position and angle of the receiver 31 are different. In Fig. 3b, the angle θ 2 between the receiver 31 and the substrate plane is smaller than the incident light and the substrate. The included angle θ changes the area of the effective reflected light beam A3 received by the receiver 31. As shown in FIG. 3B, the upper boundary line B2 and the lower boundary line B1 of the light that can be reflected to the receiver 31 change. Compared to the lower boundary line B1 and the upper boundary line B2 in FIG. 3a, the angle between the upper boundary line B2 in FIG. 3b and the upper surface of the substrate is also reduced to θ 2, but the lower boundary line B1 is blocked by the side wall of the etching hole. Inclined upward, so the included angle will be larger than θ 2, and the area of the corresponding final return reflection region R ′ will also be smaller than the area of R in FIG. 3a. Therefore, the lower the position of the receiver is, the smaller the included angle θ 2 between the effective reflected light beam A3 and the substrate plane is, and the weaker the effective reflected light beam A3 that can be received correspondingly. When the received effective reflected light beam A3 is too small, it is difficult to identify the optical interference signal and the effective reflected signal, so θ 2 cannot be too small. Conversely, when the angle θ 2 between the receiver and the substrate surface becomes larger, the area of the return reflection region R ′ will also become larger, and more reflected light will enter the receiver, but more light will also be reflected from the upper surface of the substrate into the receiver. Device 31, so as the effective signal increases, the interference light also increases, so θ 2 is not as large as possible. The setting of θ 2 must be within a reasonable range to ensure an effective reflected beam A3 of sufficient intensity, while reducing various interference lights. Entry into the receiver 31 creates interference. The angle range of θ 2 is preferably 15-45 degrees, and the most effective range is 20-40 degrees, which can detect the effective reflected beam A3 and reduce the interference light reception.

The conventional technology detects all reflected or scattered light reflected from the detection area. In order to reduce noise and receive optical signals as much as possible, the incident angle is basically perpendicular to the substrate or incident on the substrate surface at a large angle. The receiver also receives the overall reflection signal of the etched hole and the flat area in the spot range. Since the area of the flat area on the wafer surface is much larger than the area of the etched hole, and the reflectivity of the flat area is larger than the area of the etched hole, the receiver receives The intensity of the optical signal basically reflects only the condition of the flat area in the spot area below, and the optical signal representing the etched hole cannot be effectively separated. The optical detection device provided by the present invention can separate the signal irradiated to the planar area in the light spot and the signal irradiated to the opening of the etching hole by a special structure design. The receiver arranged on the same side of the reference light source, that is, the incident side, can only be selected. After receiving the signal irradiated to the etching hole opening and returning to the reflection area R, the optical signal representing the width data of the etching hole opening was successfully obtained. The angle set by the receiver is also in the optimal range (20-40 degrees), which can effectively detect the effective reflected light from the opening of the etching hole and reduce the interference light reception.

In actual operation, the receiver 31 can not only receive the reflected light from the return reflection region R of a large number of etched holes in the spot area below, but also receive a small amount of reflected light from the planar area of the wafer surface and the opening of the side wall of the cavity 100 or The window illuminates the background light entering the cavity. In order to reduce these background noises, the present invention proposes a method for detecting the size of an etching hole. After debugging the plasma etching process to obtain the optimal etching morphology, the optical detection proposed by the present invention is performed. The device is set on a wafer with an etched structure, and the reference light source is selectively irradiated to the area of the wafer surface without etched holes / grooves. These areas are only flat areas, and most of the incident light beam will be reflected away from the light source, so the intensity of the optical signal that the receiver can receive at this time represents the intensity of the background signal that will interfere with the detection of the present invention. The intensity is stored in the controller as the background signal intensity. When large-scale production is subsequently officially started, the light beam output from the reference light source 20 in the optical detection device of the present invention is irradiated to an area with an etched structure. At this time, the signal received by the receiver 31 is transmitted to the controller, and the controller sends the signal. The intensity of the received signal is subtracted from the intensity of the background signal stored in the controller, and the intensity of the reflected light from the etching hole opening back to the reflection area R is the characteristic optical signal intensity. By continuously monitoring this optical intensity signal, you can monitor Whether the size of the etched hole has been shifted during the processing of different wafers under the same process.

Since the present invention monitors the average intensity of reflected light from all etched holes / slots in the spot area, the spot size reaching millimeters or even centimeters will not have a great impact on the detection result, as long as the number of etched holes in the selected spot area Not too little can get enough reflected light intensity. Therefore, the present invention has very low requirements on the light source, and basically has no strict requirements on the light source, as long as the brightness is sufficient to be received by the receiver. At the same time, the receiver only needs to detect the light intensity in a small range in functional design, which is also a common requirement in the industry. Related parts are also very common and do not need special design. The controller only needs simple storage and does not require complicated program calculations. Therefore, the optical detection device of the present invention has the advantages of low cost, simple structure, and convenient installation. It does not require complicated and precise optical systems, and can be installed in a large amount in various plasma processing equipment. In the cavity, a preliminary inspection is performed in time for each wafer that has been subjected to plasma etching. Once a data deviation is found, it is immediately corrected to avoid greater losses.

The present invention uses the receiver 31 to detect the light signal intensity of the retro-reflective reflection region R to calculate the corresponding etched hole opening width D. However, when the opening shape of the etched hole 91 changes, such as the retro-reflective reflection in FIG. 3 When the outline of the area R becomes a right angle instead of an inclined curve, the opening width D remains the same. If it remains unchanged, the intensity of the optical signal received by the receiver 31 will also change significantly, and a misjudgment will occur at this time. In order to comprehensively detect the shape of the opening of the etching hole and the width of the opening, the present invention provides a second embodiment as shown in FIG. 4. The second embodiment is basically the same as the first embodiment, except that an additional receiver 33 is provided, and the receivers 33 and 31 are arranged up and down. In the long-term etching process, if the etching topography is shifted, the intensity and direction of the reflected light in different parts of the retroreflective reflection region R will change. The optical signals received by the receivers 33 and 31 in different positions will also change, and the changes between the two are not the same. For example, the light received by 31 will increase, but the receiver 33 will decrease. If the signal strength of the two receivers increases or decreases at the same proportion, it means that the shape of the opening of the etching hole is basically unchanged, and the change of the signal strength comes from the change of the width D of the opening. By comparing and judging the signal strength of two or more receivers, it is possible to comprehensively analyze whether the etched hole has undergone a change in topography or a change in opening width.

Although the content of the present invention has been described in detail through the above-mentioned preferred embodiments, it should be recognized that the above description should not be considered as limiting the present invention. Various modifications and substitutions of the present invention will become apparent to those skilled in the art to which the present invention pertains after reading the foregoing. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (6)

An optical detection device for a semiconductor device. The optical detection device includes a cavity selected from one of a transmission cavity and a vacuum lock in the semiconductor device. The cavity includes a base on which the base is fixed A wafer with holes or grooves formed on the upper surface of the wafer, a reference light source for emitting reference light to the wafer is disposed above the wafer, and further includes a first receiver, wherein the reference light source is incident on the wafer The angle between the light beam on the wafer surface and the wafer plane is less than or equal to 60 degrees, the first receiver is located on the incident side of the reference light source, and the angle between the first receiver and the wafer plane is 15-50 degrees; It further includes a second receiver located on the incident side of the reference light source, the second receiver and the first receiver are in different positions, and the two receivers are used to receive different angles of reflection of holes or grooves on the wafer Light; the first receiver is used to receive the reflected light reflected from the hole or the groove on the wafer into the incident side, wherein the opening size of the hole or groove formed by the etching is less than 100nm, and a reference optical signal intensity is stored The controller compares the intensity of the optical signal received by the receiver with the intensity of the reference optical signal to determine whether the size of the hole or the groove is offset. The optical detection device for semiconductor equipment as described in item 1 of the patent application scope, wherein the first receiver is located under or on the side of the reference light source. A method for optical inspection of semiconductor equipment, using an optical inspection device as described in item 1 of the patent application scope, wherein the controller stores the reference optical signal strength, and the controller compares the The optical signal strength and the reference optical signal strength determine whether the size of the etched hole or groove is shifted. As described in Item 3 of the patent application scope, the method for optical inspection of semiconductor devices includes the following steps: subtracting the stored background signal strength from the received optical signal strength to obtain a characteristic signal strength, the background signal strength is The optical detection device refers to the intensity of the optical signal received when the light irradiates the area without the etching hole; and compares the characteristic signal intensity with the stored reference optical signal intensity, and if the difference between the two is greater than a preset threshold, it is judged that the etching is formed The size of the hole or slot is offset. The method for optical inspection of semiconductor devices as described in item 3 of the patent application scope, wherein the reference optical signal intensity is obtained according to the following steps: irradiating the reference light source to the area of the wafer without etching holes, the background obtained by the receiver The signal strength is stored in the controller; the reference light source is irradiated to the area of the wafer with an etched hole of acceptable size, the receiver obtains the second optical signal strength; and the second optical signal strength is subtracted from the background signal strength The reference optical signal strength. A method for optical inspection of semiconductor equipment, using an optical inspection device as described in item 1 of the patent application scope, the controller compares the optical signal strength from the two receivers, the controller from the two receivers When the intensity of the optical signal changes in different proportions, it is determined that the opening shape of the etched hole changes.